whitedevilTA

iTrader: (8)

Well, my brother and I have played with this car trying to get it to run where it should for so long now and were at a loss. It's a VERY healthy 350 and it just runs way too slow for what it is. We've made jet changes, played with timing, swapped PV's, and nothing seems to help it. The plugs are a nice brownish tan color and overall the car runs really good and has awesome driveability but it's just not fast. At WOT, it runs smooth but just doesn't pull like it's supposed to. I'm looking for ANY advice to get it to where it should be.....whether a possible vacuum leak can cause it to have no power or something!! Any advice on things to check is appreciated.

Combo is...

71 350 shortblock w/ 10.7:1 comp
procomp 210CC 2.02/1.6 aluminum heads
1.5 roller rockers
howards .488/.510 lift, 234/244 duration cam
edelbrock performer RPM air gap intake
Holley 750 cfm mech secondary carb
Re-curved dist with 31* full timing all in by 3100 rpm

We have played with the timing from 29* to 36* with little to no change in performance, went from 79 secondary jets to 83's with no improvement in acceleration, and found that the fuel pressure was at 3 PSI so we cranked the reg to 4.5 and it made no difference. We are at a complete loss and I know for a fact that an engine of this build should be able to trap around at least the 112-115 mph range.

Car is a T56 trans car with 4.10 gears as well.

UnstableAviator

My first thought is timing. Set your advance to about 38 degrees, see if that wakes it up any. 31 us just way too slow for any small block chevy ice worked on.

sofakingdom

iTrader: (1)

There's the majority of your problem, right there.

Doesn't matter who you bought that cam from; could have got it this way http://www.summitracing.com/parts/SUM-1107/ for cheeeeeper (and cost less too), or this way http://www.summitracing.com/parts/EDL-7102/ for ALOT more. Ignore the "advertised" durations, they're measured at different lifts, anywhere from .000" to .006"; they're all the same cam you have, which is, a generically copied generic copy of a copied copy of a generic copy of a generic cam from 40 years ago. GUARANTEED, not a race winner.

So, time to pick a less inadequate cam.

First off: what makes you think you have 10.7:1 compression?

Next: what exhaust?

I definitely agree about the timing; 31° is too little for gasoline. Gasoline requires about 36° almost no matter what else about the motor. Then if you're running vac adv, it should be IN ADDITION TO that, for a finished product of about 50 - 52° at high RPMs.

Also, check for the REALLY simple stuff; like, have someone sit in the driver's seat and floor the throttle, and check to be sure it's opening all the way.

whitedevilTA

iTrader: (8)

Sofa,

It's a stock 71 bottom end with 58cc heads which should bring the compression right around 10.7:1. The engine stock with 76cc heads was 8.5:1 with standard felpro blue head gaskets.

As far as exhaust, it has hooker longtubes with the bigger primaries into a catless Y pipe and a hooker aero chamber exhaust. Car with the old combo has gone low 12's so the exhaust shouldn't be very restrictive.

We have checked for WOT activation via the pedal before but will check again to be sure since it's been a while.

As far as the cam, we bought it from skip white performance and they use it in an almost identicle crate engine they offer with less compression that is advertised at 415 HP. I would assume it makes decent power judging by that, and it definately sounds on the bigger side with the car idling.

EDIT: Just looked at the links you posted for the cams. One is on a 114 LSA, one is a 112, and ours is a 110. I'm not a cam expert but would the LSA change the performance at all? All I know is that with a higher LSA, it's more compatible with FI most of the time.

sofakingdom

iTrader: (1)

The LSA changes the spread betwen the peak torque and peak RPM, and affects idle slightly.

If all else is equal, a narrower LCA typically idles worse (narrow LCA = late exh opening = when the exh opens there's more pressure left over in the cyl = exh flows backwards into the intake which contaminates the incoming charge = lope), has higher peak torque (later exh opening = pressure keeps doing work longer toward the end of the power stroke), higher peak HP and a lower peak HP RPM; a wider LCA typically idles smoother, has lower torque and lower peak HP, but the peak HP is moved up in RPM and the curve is flatter. Area under the curve is typically about the same, so if you could do a run from 0 RPM to 7000 or whatever, you'd get overall about the same total output. Narrower LCA will make a car faster on the track, IFF the gearing is set up to keep the RPMs always between peak torque and peak RPM; wider LCA tends to be better for the more variable conditions on the street. The better idle characteristics is what makes EFI happier with the wide LCA.

In the case of that particular archaic obsolete cam, the primary problem is just severely outdated lobe designs. The LSA will produce variations in the details but has a relatively minor effect on the overall result.

If the bottom end is "stock" from 71, it has 12cc dish, .025" nominal (usuallly it's a little more than that) of deck clearance, .016" steel shim head gaskets because the FelPro blue ones hadn't been invented yet (came out in about 77 or so IIRC), and the stock CR was in fact about 8.4:1. Later when they switched to the red Victorcore ones, in about 73 or so, the CR on that motor dropped to about 8.3:1.

That stock bottom end except with 58cc heads and .039" FelPro blue head gaskets is right about 9.7:1.

If the bottom end has been rebuilt with "stock replacement" pistons, with the same dish, then it has about a 99.999999% chance of having .020" more deck clearance than stock (pistons are farther "down in the hole" at TDC). With that combo — .030" over, 12cc dish, .045" clearance, .039" gasket, 58cc heads — the CR is about 9.3:1.

That would be another reason for poor performance... the CR is WAY low for what that cam requires to have any hope of working even halfway right. Just an all-around mis-matched combo.

pancherj

I would still be looking at the valve train geometry, springs, etc. Are the cam lobes starting to go already? The compression probably is low...but you can still make power at that compression, just not with that cam. I would call bullet, Chris Straub or another custom cam company. The Lunati Voodoo cams were designed by a real famous guy also and I know several people that have used them. You need someone to get a cam that will work with your compression. I think you will be looking at a really tight LSA (106 or so), 230 duration @.050 and as much lift as you can squeeze in there. Another thing you could check is the cranking compression (dry and with oil in the cylinders). Perhaps the ring seal is marginal. Also, the low fuel pressure is not good, but probably not your problem. 6.5psi at idle and a small drop at WOT is what you want.

whitedevilTA

iTrader: (8)

Sofa,

I honestly have no idea on the history of the bottom end. It came out of my uncles 67 camaro but was not the original engine and he nor us did the rebuild so thats a mystery. The pistons appeared to be stock looking with the slightly higher ridge around the outside perimeter and the valve reliefs. It runs good and doesn't puff smoke out the exhaust so we didn't touch it. The odd thing is that skip white performance uses the identicle cam in thier crate engine 350 with 9.5:1 comp and advertise it as 415 HP as I said before. Same heads and intake as well. Whether thats a stretch or not I don't know, but skip white is a large company.

As for the cam, it does seem like an old design but the way this car runs I can't imagine it makes any more than 300 RWHP and that is just terrible!

Pancherj,

I don't think the cam is rounding lobes. The valvetrain is quiet and we broke it in the proper way with the ZZ-whatever additive in the oil. Just did an oil change as well and the oil was clean. As for cranking compression, thats a mystery and I really don't want to go buy a compression tester at the moment just to check, but I guess it's def a possibility. I'm really trying to help my bro out on this but he is ready to give up and sell the car unfortunately. Hopefully we make some progress soon. I think we'll try at least bumping timing to around 36 degrees with the bigger sec jets and see if it makes a difference from before.

UnderCover89TBI

iTrader: (25)

so it traps at 105 and runs a 13.1-13.5 or so? That doesnt seem that bad to me for the combo. your 60' are like 2.4 or something right?

Bullydawg

iTrader: (7)

My Formula ran a 13.1 at 105 with the old engine. Cut a 1.8 60ft too...

What is your car running?

sofakingdom

iTrader: (1)

Not to be mean; but if there's ANY ONE company that makes ... ummm,,, ... ,,, optimistic ..... claims on the Internet these days, that'd be the one.

Which is not the same as saying they're lying; only, that they probably built about a hundred short blocks, using every trick they knew; and some one of them, when some ...... ,,,, ..... ummm,,, ... ,,, enthusiastic ..... correction factors were applied to the dyno readings, was able to round upwards to that #.

Which is also not the same thing as saying, "put these heads on any short block that happened to come in some car you bought, and slide in this cam, and YOU will make this #".

If you had good quality pistons, with ZERO deck clearance; the BEST POSSIBLE machine work (which things like deck clearance would be among); PERFECT valve train geometry; a PERFECT exhaust; PERFECT air; then maybe, JUST MAYBE, you might make the same numbers.

Out here in the real world, with some random short block from who knows where in who knows what condition beyond "it works OK", maybe not so much.

IMO your #s are not far from where they should be. Maybe a bit better than some others get with the same .... stuff.... .

So you've got an OK set of heads, not the best maybe, but OK, for sure, at the price especially; now all you need is a decent short block and a cam MATCHED TO the heads, and you'll be flyin.

UnderCover89TBI

iTrader: (25)

that's what im saying I mean it sounds normal to me too. But im wondering if its a 105 @13.5 which equates to wheel spin/bad 60 or if its more like bullydogs which I think is very good for the combo.

whitedevilTA

iTrader: (8)

Never had it to the track but we race often and we have been pretty even with a stock 370Z and a freind who traps 107 mph in the 1/4 in his G8 GT put about 2 cars on us every race and we ran 4 times. That to me says this car is only trapping 104 to 105. The G8 is VERY consecutive in the way it runs at the track so it's a good comparison.

And sofa,

IDK, I know the heads are not the best out there but even still I would think an engine like this.....EVEN at 9.5:1 or so should be around a 109-110 mph trap. For comparison, the old combo with a 9:1 350, trick flow heads, XR288 cam, vic jr manifold, and the same carb went 12.1 @ 114 mph. And that setup had no compression, and the same carb. I've built a few motors.....but this just upsets me. I know guys who are running GREAT times on unported procomp heads so that shouldn't be an issue. So the cam may suck, but 104 mph trap is slow for what we have into this set up I think. A 350 TPI would trap 104 with full bolt ons and they have a crap cam and crap heads.

skinny z

Have you done a compression test? The results will help you zero in what your static compression REALLY is.

UnderCover89TBI

iTrader: (25)

I dont think racing on the street and saying it should be this or that is enough to say what it is. You need to do actual track testing. IMO.

LS4GXP

iTrader: (2)

Also agree that you need to bump fuel up, 6.5 or 7 PSI for carb, not 3.5!

2 car lengths is more then 3 mph I trapped 103 in my grand prix gxp and raced a stock cobra that trapped 109-110 and he had 2.5 car lengths on me.

If you plan on trapping 115-117 with that setup I think you have high hopes. Am hoping to trap around 117 with a 11:1 383, AFR heads, 232/234 .570 lift hydraulic cam, 750 Q series Quickfuel carb, ultra pro magnum 1.52 rockers, full msd, air gap, yatta yatta

I agree with others, take it to the track and see what it actually does, worst case, if your timing is almost dead on like you said, take it to a dyno, maybe you only need to play with it alittle, which wont cost too much time and will keep the price down.

Good luck!

whitedevilTA

iTrader: (8)

I know the track gives you real numbers, but I have been in the car/ racing scene long enough that I am positive the car won't trap over 105 mph. We have raced a ton of our freinds that have gotten track numbers and the way the car stacks up to them, thats just what it is I'm sure.


Def not expecting 115 to 117, but around 110 would be nice! It just doesn't pull top end like I would imagine. I do want to get on a dyno but it's my brothers car so he will have to decide on that one. Hopefully he makes the right choice and goes for it!

skinny z

I take it that you HAVEN'T done a compression test. If you find that you have only 150 psi cranking pressure, THAT'S your problem. A simple test really and one that will give you something concrete to work with. Everything is just speculation at this point, as you can tell by the replies.
An average street engine should have at least 180 psi. A strong street/strip engine should be in the 200 psi range. Beyond that becomes race engine territory.
As an example, my 353 has 190 psi cranking pressure, a true and measured 10:1 static compression, 8.0:1 dynamic compression ratio. In a 3700 lb car, it traps at 107 mph.

UnderCover89TBI

iTrader: (25)

Man I need to do a compression test on mine. Since I changed the heads to smaller combustion chamber I wanan see where i am at.

GSRacing

I have a 86 t top car with h mca a very healthy 355 aluminum headed motor and 373 gears that traps 113 you need to take into account also your tire size and really should go to the track and give it a hit my compression in my motor is only 10.1 :1 with patriot heads

mr305

iTrader: (1)

I built a similar set up with procomp 190cc and a comp cam 290hr-12 .510"/.540" 112 LSA with about a 9.1:1 CR and 34* of total timing that car trapped 110/111 mph and its a fully loaded Firebird.... like others have stated previously the cam is one of your problems and to run 210cc's you need alot more compression than what you have....

Sonix

iTrader: (1)

210cc intake ports are HUGE. I'd want to see a larger cam, preferably a roller, or at least a solid flat tappet for that. Your powerband is going to be fairly high up there, and relatively narrow with that combo of parts (ie lazy cam).

A compression test (screwed into your spark plug hole and crank over the engine) isn't going to tell you what your static compression ratio is. Too many factors effect that. If I were you, i'd pull a cylinder head, and do some measurements on the short block. Only then can you realistically know your CR. I agree with Sofa, it's likely lower than you think it is, which likely means you don't have enough compression to support that big cam, and not enough cam (or compression) to support those heads. 105Mph isn't bad for a 350 that isn't perfectly matched together. You have some decent parts there (namely the big ticket items), so a bit of detail work checking compression, and a better cam will likely go a long ways in waking that combo up to see its full potential.

3.5psi may be enough, as long as you're not out-running it on a run, you should be fine.

skinny z

Actually a compression test is one of THE most effective ways of determing the potential of an engine. You can in fact determine what the static compression is from a compression test provided you have the other requisite information.
Anyone that's built an engine and hasn't done a simple test like that is removing a huge piece of data from the equation. Especially one like the op who is speculating and doesn't really have any hard data to go by.
While I don't dismiss what you suggest with taking the engine apart and getting actual numbers, one can certainly getting a pretty clear picture of what's going on without doing much more than taking out the spark plugs.
Like I said, if the compression pressure is only 150 psi, what would YOU think?

Big Dog Chevy

Dude just do a compression test to see where you are and bump that timing up to 36-38 deg. Get a hold of wide band O2 sensor to check your ARF at WOT and I BET you find your problem. It's not that hard and you have been getting some great advice from the guys on here just try it.

Sonix

iTrader: (1)

Personally? 150 psi on a moderate compression engine with a 233/244 cam sounds in the ballpark. I have never heard anyone claim with any shred of accuracy that they could tell me the SCR or even the DCR based on a compression test. Do you have a calculator, or an excel spreadsheet, or can you explain the calculations?

We can practice on my engine, working backwards. Specs attached in sig. Tell me what my compression test should show? I think I did one when I first got the engine running, so I can dig up those numbers).

skinny z

150 psi is terrible. That would be a smog engine from the 70's. Too little static compression for the duration of cam used.
I'll go through my notes and dig up a compression ratio calculator via compression testing.
You'll need to know that atmospheric pressure on the day you do the test. Possibly air density values too but I'm not sure of that one at the moment.
Do you have the advertised duration numbers for the cam you use? I can do a dynamic compression ratio calculation too. I would also need the ICL and LCA. Perhaps you could use a static compression ratio boost too.
For the record, it works for my engine.

skinny z

Give me: compression ratio, rod length, stroke, advertised intake duration (and whether the cam is installed straight up, advanced or retarded), altitude, and air temperature.
From that I can give the theoretical (zero loss due to cylinder blow-by, etc) cranking pressure.
If you prefer, give me all of the above, leave out the compression ratio (which you MUST calculate from hard data, no assumptions like piston below deck value or head gasket diameter and thickness) and supply your cranking pressure. I'll work out your static compression ratio.
It's just math and numbers don't lie.

Big Dog Chevy

We can practice on my engine, working backwards. Specs attached in sig. Tell me what my compression test should show? I think I did one when I first got the engine running, so I can dig up those numbers).




Well without all the data I need here's my ballpark:

Static CR - 10.23
Dynamic CR - 8.0-8.1
Crank PSI - 185-190


Like I said just my ballpark. There are calcs that can get you the info but you must enter the correct data in return.

Big Dog Chevy

Skinny Z said it perfectly it's just math not black magic.

Sonix

iTrader: (1)

Hey Skinny;

I'm using the Z-25 cam, with 1.6 roller tip rockers and .020" lash. Cam is straight up. Cam details are here:
http://www.iskycams.com/timingchart...._number=201025

Altitude is 4000'
Temperature is ~85*F
Rods are 5.7"
Well, my compression ratio is calculated from hard data, which I measured, such as piston below deck distance, head gasket size, etc. These were measured to the best of my ability, +/- .002" or thereabouts (depending on what it is).

I think you hit the nail on the head with "theoretical". We can calculate "theoretical" static CR based on a cranking pressure, but there are too many wild cards for *me personally* to have any faith in that type of calculation. Just my personal opinion. I'm fairly sure 190psi is pretty optimistic for my engine. I recall it being less, and I chalked that up to large cam syndrome. I'll see if I wrote it down tonight.

Personally i'd feel much more comfortable measuring these things myself. On the upside, when you take off the cylinder heads to measure your CR, you'll also find out what makes up that number. Whether it be piston dish size, head gasket thickness, or head chamber size - all make up the overall static CR - but they lend other traits right? ie, a 10:1 motor with good quench vs a 9.5:1 with poor quench eh? etc etc.

skinny z

Seems to be very close. My 10:1 SCR (measured) gets me 190 psi. 8.1 DCR with a 276 advertised intake installed slightly advanced.
The same shortblock with a smaller cam (closer to 268 advertised intake) yielded a 205 psi cranking pressure. While that combination didn't have nearly the legs my current set up has (100 mph trap speed vs 107 mph), it still had lots a low engine speed torque and excellent mileage.

skinny z

And I agree 100%.

Using your cam spec (278 advertised intake installed straight up), 3.48" stroke, 5.7" rod, 4000' altitude and 84F temps, you cranking pressure should fall in the 165 psi range ASSUMING a 10:1 static compression ratio. (You left out that value so I made the assumption).
It's a safe bet that if your cranking pressure is higher, then one of the input values is off. Perhaps you have more than 10:1. And vice-versa.

With a little more info, you could work out your DCR to see how your SCR relates to your cam choice.( Something you've probably already done I would guess)

All I'm getting at here is that whitedevilTA can do a little easy/cheap investigating to see where he stands at the moment. Although I have to say, it certainly has provoked a lot of conversation.

skinny z

Checked your sig Sonix.
DCR around 8.1:1 (assuming a 6cc valve relief in your Speed Pro piston and a 4.1" head gasket diameter (typical).
Sound about right?

Sonix

iTrader: (1)

Yea, SCR should be 10.3, and DCR of 8.1 sounds about right.
I calculated it 4 years ago when I built the engine.

skinny z

How about your cranking pressure? 165 psi give or take?

Fast355

iTrader: (2)

Don't just toss the timing at 36-38*, start out with 30-32* and creep up 1* at a time. Fastburn chambers do not need nearly as much timing to run well.

I run my 9.6:1 Hemi on 93 octane and it makes the most power at 26.5-28* of timing. Only likes 28* above 5,500 rpm. Makes power until 6,800 rpm and pulls 5,000 lbs of un-aerodynamic Ram to 97-98 mph trap speeds, with a 1.9x 60'. So not all engines need 36-38* of timing.

GSRacing

my setup is running at about 35* and is 60fting 1.64 on pump gas lol

whitedevilTA

iTrader: (8)

To be honest with you guys, we weren't looking to put a ton of money into this engine because the car is possibly getting an LS1 transplant over the winter. We only built it because the engine that came in the car blew unexpectedly so we were forced to build this one to get it back up and running. If it comes down to having to swap cams and do this and that to get it running faster, then we'll just deal with it how it is. I just thought it seemed slow for the combo but a lot of people are saying the cam is killing it so I'll agree with you all on that aspect. The heads are said to be 210cc from procomp but honestly, I'm sure they don't perform or flow like a trick flow or AFR equivalent so the numbers are a little of a stretch I think from procomp. Like I said, the engine is smooth and doesn't miss or have any hesitations which leads me to believe it's running close to how it should. No smoke out the tailpipes on WOT or anything. Were just going to accept that it is what it is and hopefully we can get a nasty little LSx built for it over the winter since thats the ticket for easy performance and drivability these days.

Honestly also, I hate carbs and so does my brother. We bought the car carbed so we kept it carbed but the amount of minor adjustments needed on them and overall knowledge you need to dial them in is something we don't have and just don't want to become pro's on. They make great power and some people get them to run excellent, but I am an FI guy as is my brother and we have no freinds or shops in the area that know anything about how to get a carb running good. We've gone into this blind and have learned a ton....mainly from the boards here....but FI is just so much easier and more popular these days.

Anyways, I appreciate all the help and replies from everyone! This board is always my number one place to start for info.

ownor

iTrader: (5)

I think the property in question for the heads wouldn't be the port volume, but rather the flow they give you for the rather big port, for illustration imagine how a 195cc AFR would flow the same or even better as a ProComp 210cc, (and that with a higher port velocity).
I'm with other posters that suggested the need for more actual measurements rather than assumptions, at least if you wanna squeeze out everything there is to be had, or if you wanna find the culprit. DCR could be changed by cam or SCR, but i wouldn't say that either is a POS, it just may be mismatched
Good luck with the LSX build anyways! I think that's a great way to go if you can shell out the cash to do it right.

Big Dog Chevy

I run my 9.6:1 Hemi on 93 octane and it makes the most power at 26.5-28* of timing. Only likes 28* above 5,500 rpm. Makes power until 6,800 rpm and pulls 5,000 lbs of un-aerodynamic Ram to 97-98 mph trap speeds, with a 1.9x 60'. So not all engines need 36-38* of timing.[/quote]

Yeah that's a hemi, as long as the motor is not pinging or running into detonation then I would add more timing. They could do it 1* at a time if they want but they have a very basic motor that is not putting out what it should. If there is nothing wrong with it mechanically then it's just a matter of Air, Fuel and Spark tunning. Shouldn't be that hard.

paul_huryk

I think part of the problem is combination of parts and the the other factor is the tuning.

The tuning part is easy - timing is easy and a good way to tune the A/F ratio is with an A/F gauge.

Like others have said, the heads are huge and are going to penalize you with a TQ deficit (maybe on a 406 the heads would be awesome, but not a 350). I think the other part of the combination is the cam - from the specs it looks like a hydraulic flat tappet cam that will not have enough lift to really fill up those smallish cylinders. A roller will give you more lift than a flat tappet cam can.