Maverick_IX

I am currently runnning a GM performance 350 HO (330hp) crate motor with the stock 305 throttle body, 65 lb injectors, stock fuel pressure, PROM tuning(runs rich & surging idle), and a GM perfromance TBI Vortec manifold. I know that the stock throttle body is not enough to get the 330HP potential from this motor.

I am considering a 50mm(750cfm) throttle body, fuel pressure regulator, and larger injectors(if needed).

What will I need to accomplish this?
...50mm throttle body
...if so is it necessary to bore the manifold as well?
...what size injectors?
...how mauch psi fuel pressure?
...will I have to get a new pump or use full pressure on stock pump?
...any PROM advice would also be welcome.


maverick_ix@yahoo.com

BMmonteSS

You need to do a search for Jprevost, he's running your exact motor. You deffinately want the 50mm TB, which does require that you bore the intake. I think JP is running 65 lb/hr injectors at around 28 psi....you'll have to confirm that. As you can see thats pretty high, so bigger injectors would help. Your best bet is to pick up a GM 454 TB off of ebay or at the local wrecking yard, you'll get your injectors and TB in one shot. You'll deffinately NEED a new pump, the stocker barely fed your 305.

As for tuning, get the basics fixed first, and things will go much smoother. Keep in mind vortecs don't need much timing. Get a WB if you can afford it, you'll save so much time it isn't even funny.

Maverick_IX

91 Camaro RS TBI 305...I recently sawpped a GM performance 350 HO (330hp) crate motor with the stock 305 throttle body, 65 lb injectors, stock fuel pressure, PROM tuning(runs rich & surging idle), and a GM perfromance TBI Vortec manifold. I know that the stock throttle body is not enough to get the 330HP potential from this motor.


FIRST OF ALL, WHAT LIMITS THIS MOTOR TO 330 HP????
...OR CAN MORE BE ACHIEVED WITH A TBI, EXHAUST????


I am considering a 50mm(750cfm) throttle body, fuel pressure regulator, and larger injectors(if needed).

What will I need to accomplish this?
...50mm throttle body
...if so is it necessary to bore the manifold as well?
...what size injectors?
...how mauch psi fuel pressure?
...will I have to get a new pump or use full pressure on stock pump?
...any PROM advice would also be welcome.

five7kid

iTrader: (14)

Moving from Engine Swap to TBI.

z71stroker

if you use the "search" button, you should find the majority of everything you need to know, alot of people have done this swap.

DM91RS

Check out JPrevost............he's running what you have

Gunny Highway

iTrader: (1)

You'll need atleast a Walbro 190 fuel pump to flow enough PSI, some go with the 255 one. When I went to a 50mm throttle body I also had my Edelbrock TBI Manifold also bored out to 50mm. It just doesn't make a lot of sense to have those smaller bores blocking the air flow to me. I'm no engineer, but it just doesn't seem like a good way to take advantage of the bigger throttle body. On my 350 I'm still running 55# injectors although I'm still sitting on my 65# in the garage. I tried to run the thing initially with 85#, but getting it to idle good was more of a PIA than it was worth. After doing some tuning on my motor my biggest hinderance seems to be airflow, not fuel flow. Until it's obvious through my datalogging that fuel flow is stopping me, I'm going to stick with the 55#.

And if you're still using stock exhaust manifold stuff on your motor, get rid of it ASAP. That stuff doesn't even deserve to be recycled.

swerve-driver

1) Yes.
2) The 65's should suffice
3) The 26-28 values mentioned by BM should, at a minimum, put you in the ball park.
4) I ran mine with the stock fuel pump- it worked fine. Your situation may differ.
5) Prom Adivce: Get your current setup running correctly (idle, crusie and WOT) before further complicating things with a larger TBI. Who is doing your tuning? What tools are you using to tune your current setup?
With my old 350Vortec setup, the tuning was such that the idle was barely noticable, I logged no error codes, all emissions were working, fuel economy and performance were both very good. (13.8 @100mph). The things I learned while perfecting that setup allowed me to tune and run my current 383 with 2" TBI with little trouble.
Understanding and nailing down the tuning aspect is key for any setup.

Best-
S-D

liquidh8

I have a similar setup. Vortec motor, like the 330, but with more compression and more cam. just picked up a bbc throttlebody, 90pph injectors, using a 4bbl gmpp intake with tb adapter. I have to fix my laptop before I can tune some more. But it runs good, a little rich @idle and down low, but good up top. I started with a 454 bin with a 700r4 and 3,73's, and I am tuning from there.

Ronny

iTrader: (1)

the walbro is a good unit. i suspect a TPI pump might save you some $$. i have used it past 2 years. i have 80 lb injectors at 17.5 lbs and running lean at WOT 13.5/1. need to bump up the FP to accomodate A/F but the idle will suffer(moreso).

ShiftyCapone

iTrader: (7)

Threads have been merged.

Maverick_IX

This is what I'm now considering doing:

1) An edelbrock (electric in-tank) fuel pump from summit 220pph-110psi ($100)

2) A bored out stock throttle body w/ ultimate mods, 50mm bore, new blades/rebuilt kit(~750cfm)
...this kit come with a AFRP(vaccuum compensated), throttle body spacer, injector spacer, and hardware($400)

3) Boring GM manifold out to 50mm ($65)

Install everything, boost the fuel pressure(keeping 65lb/hr injectors), finish tuning.

Maverick_IX

Sorry about the double post.

From what I hear Jprevost is the man I need to see, I tried PM but no response.

Anyone who has done some tuning for this type of application I would be very greatful if you could help me out, the experts at a GM Performance Cetified Dealership who have been doing the datalogging and PROM burning have ran into a few roadblocks.

I know it sounds like asking for a shortcut, but the frustration is getting to me...I would still like to love thirdgen's when this is completed.

Ronny

iTrader: (1)

VAFPR can be tuned but may not be for novice. changing FP may confuse the ECU. especially autocross on-off throttle. not sure why anone would want to use it unless they exhaust the limits of a big block injector. i do not have enough inj today as 13.5/1 WOT at 17.5 lbs. i believe VAFPR is used marine applications with a 7.4L. maybe it has a TBI auto application as well but i doubt it..

Maverick_IX

I have heard from many people who have used a VAFPR that it may be easier to tune because of the need for higher fuel pressure at WOT cause a rich condition and motor surging at idle. According to these certain advocates, this allows the idle to be tuned more closely because the fuel pressure would be much lower than just bumping the overall pressure by a regular AFPR.

BMmonteSS

Very few engines actually have a dynamic range that is too great for the ECM (when properly tuned) to handle. By dynamic range, I mean that your PW is too short at idle and too long at WOT. I'll say for 90% of motors you won't run into this. It's only when your really pushing things that this will become a problem. Like I and others mentioned, from our experience you'll need lots of FP to feed your beast at WOT. Crank that FP up to 28 PSI and start tuning, or have your guys start tuning.

I'm very surprised there is a dealership that is doing your tuning. They actually burning you a prom?...cool. We can offer tuning help if we know whats going on, you'll have to find out what the road blocks are before we can figure out how to fix them.

The 330HP rating that your crate motor has, was rated with headers, carb intake and carb, all tuned to perfection. Your making way less than that right now. There is a good thread where one of the truck guys had a stock and 454 TB flowed. The stock TB flowed around 550 CFM and the BB unit flowed near 775 CFM. So with a BB TB and proper tuning and free flowing exhaust you should be able to make 330 HP.

Maverick_IX

Yeah, the PROM burning is being done a a GM Certified Pefromance Parts Dealer...

Yes, they sell cars but they get a lot of business because of the huge amounts of Performance Parts they have in stock.

I walked through one warehouse where they had literally hundereds of crate motors included some of the 572's and 3 of the limited edition $25,000+ ZL1 motors.

The problems they have run into a mostly at idle it seems that the tuned well at W.O.T. but the car surges and idles rough, smells rich (haven't pulled any plugs but I'm sure it is), and won't stay running at all sometimes.

I have read this is due to a rich-lean alternating state due to imporoper tuning with the large overlap in the cam.

I don't think they are using a wibe band O2 (which I might suggest), and I am hoping a boost in fuel pressure will allow easier tuning.

I have introduced these forums to the man leading the tuning, but they are busy people and I think I might understand more at this point.

BMmonteSS

The funny thing is, if they didn't learn about Prom burning from here, they learned it from DIY mailing list, which most of those guys are still around here. Unless they have some mucho proprietary GM software this is the place for DIY GM prom burning info.

If they got enough fuel at WOT, you don't need to increase the FP. I HIGHLY doubt that they did though, Jprevost has your exact motor, and had to run in the high 20's to get enough fuel. Also if they aren't using a WB O2 sensor, there is no real way they can tune WOT.

The idle problems you speak of are common with big cams and combo's that are far from stock. The thing is your cam isn't a monster. It should be pretty easy to tune. They'll definitely have to mess with some of the proportional controls to get it smoothed out, but it shouldn't be a problem for anyone who is experienced with prom tuning.

I hate to be stickler, but are you absolutely sure they are physically burning you a chip, not just trying stock or aftermarket off the shelf chips? I find it hard to believe that a GM affiliated dealership is burning chips for the sole reason that it's not exactly PC. In theory the DIY guys are hackers that reverse engineered the GM code, and by reselling it you could possible get yourself into copyright infringement. In reality GM has much bigger fish to fry, but I doubt they would let one of their "own" do it. I could be wrong, and I will gladly apologize if I am.

Maverick_IX

Yes, they are physically buring a PROM in fact they aren't even using an EPROM as far as I know because they burnt up the original and replaced it with an identical stock. I don't think GM is going to keep much of an eye on this sort of thing. As far as it being PC... this is Nebraska and everything is a little "different" here. As far as where they learned, I'm not sure. Not even sure what software they are running.

You are absolutley right about needed more fuel pressure at WOT, which is why I am going to purchase the Edlebrock pump (mentioned above).

Right now it has a stock throttle body, so they probably had enough psi to tune the amount of air it let in.

Despite, the fact the the stock intake won't allow for 330hp it runs really consistant...EXCEPT AT IDLE/STARTUP where it experiences all the problems of the cam overlap problem... I know it's not a monster but it seems like the alternating lean/rich condition experienced with larger cams is exactly the problem.

Hopefully they are using a WBO2, if not for any other reason than the fact that they charged me to replace the O2 sensor when they started tuning during the swap.

BMmonteSS

Sorry to keep posting without giving the other guys a chance.....I'm bored

The cam that comes in the HO crate motor is actually very tame, it can be tuned for a smooth idle. The rich/lean surge your seeing is the stock programing chasing it's tail trying to get to stoich. With a bigger than stock cam and an enine that is much more sluggish at idle you need to reduce your Prop gains, and increase your Prop duration at idle. These settings need "fiddled" with to find the sweetspot of your new motor. This is all DIY prom speak for what you actually change when you tune.

The wide band O2 sensor we speak of is a tuning aid that is used independently of your stock ECM. It gives an actual AFR instead of simply switching over .45 volts at 14.7 to 1 like your stock NB sensor does. The reason why your car runs better once warmed up is that it starts paying attention to the NB O2 sensor once your in closed loop. GM ecm's have a good bit of self learning built in, the problem lies in that once you go WOT the ECM ignores the corrections and goes off of whats programed into your chip, if it's not correct your in big do-do. Open loop is a great way to see if your tune is spot on or not. We DIY prom tuners will disable closed loop just to see how well our tune is without the help of the self learning feature, some of us even leave our ecm's like this to run an AFR other than the 14.7 that the stock ecm tries so hard to maintain.

Maverick_IX

They aren't using 14.7/1 AFR so they must have disabled the closed loop. As far as running better, it sounds like they were very confident in there tuning at higher rpms just not with the idle, hopefully they know what they are doing. You make it sound like a piece of cake, and they couldn't get it down. I have learned a huge amount of DIY PROM "in theory" from these forums, but have never done any burning myself. I need to just organize everything into a manual kind of like what is in the DIY PROM forum and say "this is what I have learned, what I want you to do, get it done"

In the next month or so I'll be installing the fuel pump, throttle body, AFPR, and send it back for tuning

I am also considering having them do 3.73s w/ a posi unit while they have it there.. depending on $$$ flow and if that requires tuning.

swerve-driver

What is the name of this GM dealer? If they can offer chip tuning at a good price, without reprisal from the EPA etc... I think there would be more than a few people on the boards interested in that option.

Also wondering what the experts at this dealership thought of your next steps (listed below) while they are held up by the current tuning roadblocks?


"This is what I'm now considering doing:

1) An edelbrock (electric in-tank) fuel pump from summit 220pph-110psi ($100)

2) A bored out stock throttle body w/ ultimate mods, 50mm bore, new blades/rebuilt kit(~750cfm)
...this kit come with a AFRP(vaccuum compensated), throttle body spacer, injector spacer, and hardware($400)

3) Boring GM manifold out to 50mm ($65)

Install everything, boost the fuel pressure(keeping 65lb/hr injectors), finish tuning."


Are the experts in favor of making these changes and then trying to tune around the additional roadblocks that will arise? Or are the experts interested in getting the current setup running correctly first, then moving to the larger components mentioned in your to do list above?

Just curious.

S-D

Maverick_IX

When I stated experts I should have wrote "experts" (no offense to them, I appreciate all the work they have done thus far), but I feel if there are really experts in this field they are here on the thirdgen forums.

Like we were talking about before I think they probably learned through mailing lists and online forums. As far as the dealerships name, they know who they are and they probably are using this forum now, so if they get to the point of advertising I'll have to leave it to them...

My advice... listen to the EXPERTS here and learn what you can

Doing it yourself proves more rewarding and educational and in my case, it would have been less frustrating.

I think they would prefer getting the current setup down first, but it is more of a timing issue...As much money and parts have gone into the camaro it is essentially a daily driver.

Fast355

iTrader: (2)

Not to brag, but with that engine a larger TBI is not manditory to reach the full 330 HP potential. My old 355 made 279 RWHP with the stock sized TBI with Ultimate TBI mods and a factory TBI intake. That engine was using 454 90 lb/hr injectors @ 20 PSI.

My current 305 has turned 300 RWHP @ 6,000 with a 454 TBI. I am using 32 PSI fuel pressure under WOT and 22 @ IDLE (through a VAFPR) and using 68 lb/hr 9C1 350 injectors to get 12.8:1 A/F mixture.

You can get an engine to run with a smaller injector and more pulsewidth, but it won't rev very high. The stock calibration is often static at 4,500-5,000 rpm on most vehicles that I have messed with. My old 2.8 TBI GMC Jimmy 1988 went static, started popping, and fell on its face at 4,200 on the stock calibration with headers, exhaust, and intake mods (thanks to BLM correction adding pulsewidth). Some 305 injectors at 15 psi and some chip changes, then the engine would pull all the way to 6,500 RPM.

Maverick_IX

Your current setup sounds quite similar to what I am planning on.
454 TBI = 50mm Bore
65lb/hr injectors=68lb/hr injectors
Average fuel pressure 27 psi=28 psi

...Did you have any problems tuning for the VAFPR? (someone mentioned it causes problems)

...Where did your 9C1 350 injectors come from ...those are the model from a police interceptor caprice, right?

Fast355

iTrader: (2)

I needed the VAFPR to stay out of Async at idle and to clean up the emissions standards I have to meet, STILL. The VAFPR can give problems with tuning. Most noticeable you have a super lumpy VE table, but with WINALDL you can get it sorted out, just takes more time than usual. My biggest issue was getting the transitions right, IF I floored it the fuel pressure would rise and give a BLM of 108 for a split second. You basically end up lying to the ECM to get the desired fuel right. Just things like that, not really a performance issue, but just something you don't like to feel in the SOTP.

The 9C1 injectors actually came from a 1992 G20 van 350 but are identical to the 9C1 ones. The one that I got the old 355 from. To the best of my knowledge, they were stock equipment on that van. Be careful if you go that route and check to make sure the Part # and color code match as some came with standard 350 injectors too. You can get brand new GP sorenson 68 lb/hr injectors or get them through TurboCity. Occasionally some will pop up on Ebay too.

dimented24x7

iTrader: (2)

GM, in the later iterations of TBI, had an interesting alterative to help aid with the dynamic issue of the fuel injectors. They force async mode at high loads/RPMs to increase teh ammount of firing time available by reducing the number of fires to 80 times a seccond. The guys here who where running low 13's and 12's with the PCMs where likely using this stratagy by default. This could offer a good alternative to the VAFPR as youd be able to run slightly lower fuel pressures. Obviously there are restrictions like it probably wont work well on engines that rev past 5k and you also wouldnt want to run right on the ragged edge AFR wise while in async.

Ronny

iTrader: (1)

Boy i wish i had more time this summer to tune. seems something always going awry. i fried my WB sensor last week. left in on for 3 days.

anyway. back to the VAFPR. i believe it is used on MAF systems. i know nil as far as tuning them just the basics of NA tuning. now it would appear it may be easier to tune a MAF system. seems it is somewhat self correcting(?) as far as A/F ratio. could that be compared to a carb that also meters fuel based upon air flow past a jet? with our speed density system it appears a lot of trial and error in getting tune corrrect. i believe the VAFPR allows proper A/F in PE with eight smaller injectors yet allows proper A/F at idle. i am sure GM engineers spent some time sorting this all out back then. that was my problem with CL operation. again 80 lbs at 17.5 FP. the NB 02 was "chasing its tail" as was stated earlier. add to that the IAC preventing stall and opening up just added to the erratic pulsing idle. WB02 was all over the place. add to this the chalenging calibration for AE with changing FP. tuning is difficult enough on some cammed engines. adding a VAFPR would seem to make it double fold. OBTW i am running OL and my idle no longer has the surging and this AM(40 deg F) was 14.5/1. rock solid. i am gonna burn a chip CL and revist my BLM's as occasionally it hits a cell that is a bit rich or a bit lean.

dimented24x7

iTrader: (2)

Vac ref'd regulators are used on some of the port fuel systems to compensate for the vacuum in the manifold. The vacuum at the tip of the injector is like adding up to 10 psi of fuel pressure, so the regulator provides compensation for this.

BMmonteSS

Bingo, Like Dimented said on a port injected setup the vacume referenced regulator keeps the amount of fuel that comes out of the injector constant for any given PW. By using a VAFPR on a tbi setup, you just threw a wrench into getting X amount of fuel for Y PW. This isn't a big deal for part throttle tuning because you can simply scew with the VE table to compensate. Where you run into problems is with AE. You get so much PW for a given delta in TPS or MAP. With an VAFPR in the mix AE for 25% throttle might return x amount of fuel, or may return Y depending on what the vacume is at the time. In my mind this would be very difficult to tune for in all situations.

The "fix" for this is to have your base BPW vacume compensated, that way all fueling calculations that the ECM does is based off of a corrected value. Rbob incorporates this into his U-tbi code.

Clear as mud?

Ronny

iTrader: (1)

Quote: The "fix" for this is to have your base BPW vacume compensated

our fuel tables do have a MAP correction for any given RPM. right?

does not a change in MAP not reduce the BPW for us? or is that the issue causing a problem for us TBI's. then the 02 is also changing BLM's as a result of the FP increasing for that single event. maybe i need to hook up my VAFPR and see what happens just for kicks. sorry to highjack but this is always interesting topic.

so how would port fueling systems be different?

BMmonteSS

PW= Pulse Width, how long the injector is held open.

BPW= base pulse width, with TBI this is your cylinder size and injector size all rolled up into one. If you change your FP you change the effective size of the injectors, which means you really should change your BPW since pretty all fueling calcs start with this, hence the word "base".

Your right your VE table is layed out by RPM and vacume, and you can simply change it to compensate for the changing fuel pressure. The problem is that your AE or pump shot does not use this table, it uses the BPW and either your change in TPS or Change in MAP to calculate your actual PW for AE.

What Rbob did was added a table that compensated the BPW via the MAP sensor, thus negating the need to compensate for the VAFPR in the VE curve and providing your AE with a correct BPW.

Still mud?

dimented24x7

iTrader: (2)

I wrote something similar, but never got to use it. The only caveat is that the lag filtering used for the BPW adjustments has to match the response of the VAFPR or they will be out of sync. when the vacuum is changing. This could be difficult to pick out when you have other things like AE going on at the same time. Probably tuning so you have a base line first before hooking up the VAFPR and tuning for that would be the way to go.

DM91RS

swerve-driver

I must not have made myself clear.

I'm tired of hearing about the nebulous "THEY" and nameless "GM Certified Dealerships".

Put a name on "THEY" and this mystery dealership.

And I sure as heck am not soliciting your advice on who to listen to (or anything else, for that matter). I have listened and learned from the people on these boards for sometime now. That is why I can do this: https://www.thirdgen.org/techbb2/sho...hreadid=307640

Essence: Put up or go away.

S-D

Maverick_IX

First of all, I don't mind that the thread has been "hijacked" as one post said. It's still headed in a very helpful direction.

However, I do find it rather annoying that a thread that was created to help people through a very popular engine swap has been turned in the direction of personal demands such as these

...While some of us (swerve-driver) were busy making such demands and claims about our own personal abilities and refusal to take friendly advice, the real point might have been missed...

...I agree with you that if a dealership was producing results for a reasonable price that it would be a very attractive offer and would deserve the interest of thirdgener's. By offering my -ever-so-inadequite advice I was attempting to stress the point that, so far, they have done a poor job and are not an acceptable option. If the results were different I would be singing a different tune.

Either way, I respect your opinions, so be sure to respect mine. These forums are meant to be educational and helpful. So, since your posts have proven neither educational nor helpful and your are already an expert, refrain from using these boards as a way to make youself feel special.

Essence: help out or go away

swerve-driver

I already helped out- way back when (see above).
I believe there is useful information in my original post.

The thing that got my attention though, is that the conversation always moves away from the mystery dealership, the question never gets answered. That is the hitch. Me, personally, I always tell the truth straight up. I'm too dumb and lazy to keep different versions of a given story straight and too laid back to resist when someone asks.

Also, please know- I'm too old to want to make myself feel special (and, I am no expert, you are too kind. See the likes of RBob, Grumpy, Traxion, etc... if its experts you're after). Just trying to find out who the GM dealer is or if they exist. Just a simple question that still hasn't been answered. There may even be others wondering the same thing.

Anywho, it is now a moot point. Poeple will make their own judgements.

Good luck with your project- you will find no better wealth of knowledge than right here on TGO.

Cheers-
S-D

Tobias05

nice to see the 350HO get some love on the boards these days

Personally w/ my HO i'd love to throw in an xe274 k-kit, work the vortecs over, and throw on a HSR

good luck bro with the tuning.

w/ love from the HO family
Tobias

Maverick_IX

I got a hold of the man doing the PROM burning, I discussed a lot of the ideas I had and the conclusions I had come to after posting this thread...

Everything has been pretty much agreed on

The question arose about a 50mm throttle body and manifold bore...

He says, "the stock throttle body and fuel pressure are sufficient up to 4,000rpms, the larger throttle body is only needed to make more power over that"

Isn't this motor pulling enough air, even at lower rpms, that a stock 42mm throttle body is choking the motor and restricting performance???

Ronny

iTrader: (1)

you can determine that by dataloggings and looking for 95-100 MAP under high loads(WOT)... going to too large a TB will create drivability issues(especially TBI). only go to larger TB if you are not getting above. run the smaller TB and swap it later on if need be. there are postings as to what diff configuerations of venturi size will produce - carb vs TBI and the like

dimented24x7

iTrader: (2)

Id go with a 2" TBI with the 350. The stock one is equivelent to 500 CFM at 1.5 in Hg according to test data thats been posted. The larger 2" one is somewhere around 650-680 at 1.5 in Hg.

Maverick_IX

I understand that more air means more potential as long as you add enough fuel, but, what he was says is that with the vortec heads on a GM 350c.i. H.O. the most air the engine could pull at 5500rpm(red-line) is around 500cfm. He is saying that anything over that is a waste unless you are going to turn 6000+rpms(which I'm not) and could kill mileage or lean out.

Fast355

iTrader: (2)

64cc is the chamber size of the heads and really has nothing to do with the flow of the heads, other than if the chamber is so small it shrouds the valves. The stock vortec heads flow in the area of 240 CFM @ 28 in/h20 pressure drop on the intake. Using the 2 HP per CFM rule that means you could make 480 HP out of vortecs. I have seen several engine builds make over 400 FWHP using unported vortecs. You really aren't going to get too much vacuum under an Ultimate TBI moded factory TBI. Maybe worth 5-10 RWHP with your engine, but you have to decide if it is worth the headaches it can cause.

The problems Ronny speaks of are the changes needed in AE, VE tables, etc. It is best to get the engine running right, then come back and swap to the larger TBI. Plus with the larger TBI it is harder to modulate power as the engine becomes more aggressive in reaction to less throttle movement. I scared myself on the first rainday I had my 454 TBI on mine after almost spinning out. (Its a VAN). Went to pull out, gave it a little gas, the engine pulled much harder than it usually would at that pedal position, and the rear-end slid out. It also decreased my city fuel mileage with the bigger throttle blades. I also had to go to the wrecking yard and find a cruise servo for a 454 TBI truck. My stock cruise control had trouble maintaining speed. It would end up going from 70-85+ on hills. The vacuum apply and bleed orifices are sized differently on the 454 truck due to the 454 which makes it better able to control a more powerful engine.

Ronny

iTrader: (1)

kill mileage? lean out? i think it is possible to run rich with proper FP and inj size at any rpm/load. dont think that is an issue as the ECU controls A/F at stoich. the issue with too big is at low rpms the atomization in compromised and the AE routines are more difficult to optimize. knowing all that you may need 2.00 TB's BUT it will mean more chalanging to tune day one especially if inexperienced w/o WB help. get to know datalogging. it will be your friend.

Maverick_IX

It will only lean out if there is not enough fuel pressure or large enough injectors to match the TB's air flow at higher rpms. The computer can try to correct but if the fuel is not there, these ECMs won't hold the air back.

JPrevost

So fix the fuel problem and be ready for the air!
Simple formula; Walbro non-TBI fuel pump at least 190lph + adjustable FPR = plenty of fuel for a 330HO. I'd start with at the very least #65 injectors and run fuel pressure around 20psi. Set the bpw constant somewhere between 100-110 and tune the VE tables.
#65 injectors (2 of them) is only #130 of fuel. Divide by 8 and you've got about #16.5 injectors for your v8. Even the wimpy 305 TPI's got #19 . If you want to make horsepower you need fuel and TBI is FREQUENTLY fuel starved. 8 #24 injectors is about what you would run if you had port injection on this motor and that equates to needing #96 TBI injectors.

Maverick_IX

What the machanic is saying is that unless I am going to rev past 5000rpm, I don't need any more air than the stock throttle body can supply, the motor only needs more beyond 5000rpm. And without a larger throttle body(more air) 65lb/hr at 14 psi is enough to feed the air/fuel ratio. (haven't had any lean problem as of yet)

It sounds like he knows what he is saying. Truth is the high HP#'s are above 5000rpm but he's saying the motor red-lines at 5500 anyway.

Is that what you'd say?

JPrevost

I'd be pissed to have something as simple as a fuel delivery issue keep me from revving to the engine's safe rev limit.
You might only be making 10-20 more hp by going all the way up to 5500 but you don't "hang out" at a high RPM all the way down the 1/4 or during acceleration. After a 1-2 shift the RPM's will drop like a rock provided you aren't running some loose goose torque converter that stalls around peak hp . What this drop does is pull your engine into a lower RPM where it's making less hp than it would if it dropped to a higher RPM. The jist of it is this; why not crank up the fuel pressure and get it tuned with the increased fuel pressure. Why NOT? Are you afraid it'll blow up, injectors will fail?
As for air flow, I personally wouldn't look at a TB size and say "that's holding me back x hp". A stock TBI can flow enough air for 1000hp! It's all about pumping losses, the larger the TBI the lower the pressure drop (and lower velocity). I guess what I'm trying to say is the TBI's air flow isn't a hp number and then that's it, it's more of a restriction that will show up at high air flow rates. At 330hp I'd go with a 2" bore TBI so as not to have a large pressure drop at high RPM's but if I weren't into racing I'd keep the stocker for up to 350hp. After that the hp being held back by the smaller TBI starts to be "felt" in the seat of the pants where the engine just flat lines.
So what's it going to be? Oh, and don't do the increased fuel OR the increased TBI size, it's either both or nothing because they're linked. If $ is tight, just stick with what the mechanic is saying and when funds become avail or you find a great deal on ebay upgrade the 2 at the same time.

Fast355

iTrader: (2)

All I can say is that several of us have the same or nearly the same engine as you. You should listen to us. 14 PSI even with 65 lb/hr injectors is not enough fuel. You will go static over about 4,000. More fuel is needed. I tuned a 355 with ported 305 HO heads and a Mellings MTC1 cam that made roughly 300 HP. It needed 18 PSI with 65 lb/hr injectors to run to 5,300 rpm. At 18 PSI it went static at 5,500 RPM and I was only making 300 HP @ 4,500 or so. 5,300 was all the cam had in it! My old 279 RWHP 355 liked 454 80 lb/hr injectors at 15 PSI to make its power and not go lean. Go by our information. You will NOT regret our advice if you seek to get the power you desire from your engine.

I have been helping a man over on Chevytalk.com that has a 350 Vortec with a very similar cam in his 89 Chevy Truck. Brian @ TBIchips.com had him running the stock injectors @ 12 PSI. That is enough fuel for maybe 250 FWHP. He had idle issues as well as lower than expected power @ higher reves. I gave him the Part Number for the GM VAFPR to put his fuel pressure to 20 PSI at WOT and bring it down slightly at idle (had too much fuel at idle). That has helped tame his truck alot and give him the ESTIMATED fuel flow for 310 HP. Then he needs a chip with the VAFPR taken into consideration. I am a fan of the VAFPR while others are not. The above 355 of mine was using a VAFPR before I even touched the chip. Power went up on my engine by over 20 RWHP and the idle went to being nearly dead smooth from a rich blubering mess. Then the chip work brought it back to perfect.

To get the 300 RWHP my current engine makes, I have to run 68 lb/hr injectors at 32 PSI!!!!! Then the VAFPR drops it to 20 PSI for a cleaner idle by allowing the pulsewidth to be lengthened on the injectors.

JP- my HP numbers were just from experience after swapping to a 454 TBI on three different engines. My old 355 saw a 5 RWHP gain above 4,500 rpm with the larger TBI, my stock cammed 312 saw about 5 RWHP at the same RPM, my current L82 cammed beast of a 312 saw about 10 RWHP at 6,000 with the larger TBI.

Maverick_IX

So what would you suggest?

I don't plan on revving the motor over 5,500rpms, and want to get as much out of it as I can.

Isn't a stock fuel pump good for up to 18psi?

If I kept everything
----->65lb/hr injectors, stock TB, stock fuel pump
Bumped fuel pressure to 18psi (if it is capable) couldn't I get the max HP up to the 5,500rpm mark without going static.

I understand the concept of the larger throttle body & higher pressure fuel pump to make more HP, but truth is if it isn't going to help unless I rev to 6,000rpm than (to me) it isn't worth the time and money right now.