I have a 83Z...see sig.....9.0:1 compression I believe. Can I supercharge it?? Or should I have rebuilt the engine with a 8.0:1 compression to do this?

I have a budget of about 3,000 bucks. I'd like to run high 12's on pump gas ....possible??? Any suggestions? I will eventually throw a stroked 350 in it, so I'd like the blower to pretty much match. Nitrous is NOT out of the question either.

 

It's a carbed car, with a mild cam (see sig). What brand has a kit for my car?? I looked around a little, but I see very little listed for a 83 car, especially with a carb.

Speaking of carbs...what mods do you think I'll need to do to make it work with a blower? Is my cam compatible? How about my A/C...do I have to lose it for a blower?

I do want all the parts I throw into this 305 to be compatible with a 350 I plan to build after I recover from the cost of the blower. And I will keep it carbed also. BTW...I would also assume I would have to ditch my CCC computer also..

Any Supercharger guru's, please help!! I'm serious about this. I'd just like to get the right parts and info together before I do this!! - Thanks guys/gals

 

Vortech makes a centrifugal charger for carbs, so does procharger. You have to set up the carb for blow through, which I have never done. Whipple makes a roots type where the carb sits on top. Just have to fatten up the secondaries and some other things. Haven't ever done that either. Holley makes all kinds of blowers. Roots blower is the cheapest way to go I believe, but compromises hood clearance. I'm no guru, but maybe this will point you in the right direction.

 

check out car craft, and hotrod of this month. i like using centrifugal superchargers, and you can get the carbs set pre-set for blow through. check out ATI as well.

 

Thanks for the replies. I would like to get a roots type, but I'm not sure I could fit it under a 2 1/2 inch cowl hood though, and I don't care for the 4inch cowl. Too funky lookin IMO.

Plus I'll have to research to find out if I can keep my A/C or not.

Maybe I could cut out the hood??

ATOMonkey, I'll check out the centrifugal blowers too. If I could find one that allows me to fit under my stock fiberglass hood, that in essance, saves me from buying a new hood.



nitrobreth, I subscribe to CC, I guess I didn't get that issue yet.



What do you think about the other things, like if my cam is blower compatible, and do I have to ditch the computer.

I'm a serious novice when it comes to a decent combo that will work with what I have. Also, what does setting a carb for "blow-thru" mean. I assume that's because the vacuum would be lower than a N/A car????

I have a VIN "7" engine. Hyperetic (misspelled) pistons, stock crank cut .003 undersize bearings.

Like I mentioned earlier, I have a budget of 3500 bucks TOTAL, and I'd like a good combo that works together. I was considering Nitrous, but I want the power full-time.

Thanks for tips fellas....keep em comin' !!!

 

Most roots blowers come with a low profile manifold to fit it under the hood. Holley Powercharger. Good for about 100 ponies semi low profile. $2000 out of Jegs ~ $1500 out of Summit. Make sure whatever you get comes with everything you need. You can also buy straight from holley.com.

As far as blow through setups go what they are trying to accomplish is keeping the fuel in the carb instead of blowing it out. The bowls are at atm press and the venturies are at positive press so no fuel comes out. One way around is to use a carb bonnet which encloses the whole carb. The other way involves nitro fill bowls and increased fuel pressure I believe. Not real sure about that.

 

Yeah, I've checked out Holley's website. The 144 is what I am checking out. I want to keep the car street-freindly. I'll give them a call and see what they think I need.

BTW...these are my cam specs:
* Advertised duration: 270 intake/276 exhaust
* Duration at .050 in. cam lift: 210 intake/216 exhaust
* Gross valve lift: .440 in. intake/.454 in. exhaust
* Lobe separation: 114 degrees
* RPM range: 2,000 to 5,000
* Good mid and top end torque and horsepower.
* Axle ratios of 3.73 or numerically higher required
* Auto or 5-speed manual
* Must use adjustable fuel pressure regulator

I barely broke the cam in, and I'd hate to change it out already, unless I have to. Maybe they could answer that too.

I'll also need to get at least a 2 1/4" cowl hood also. Of course the carb doesn't come with the kit either, and the "Supercharger series carbs" look d*mn expensive to me!

The way it's looking, I'll end up breaking my budget. I guess the paint job will have to wait.

If anyone has any more info on this.....fell free to chime in!

 

The cam has too much duration, but on a blown engine it doesn't hurt as much as on a turbo engine. The 114 lobe separation helps too. Get 1.6 rockers and springs to match, because the lift isn't high enough. Install the cam 6 or 7 degrees advanced and that will help too.

 

Generally, a bonnet fits over the top of a carb just like the air cleaner did, the alternative is a box which the carb mounts inside.

When using a bonnet the whole inside of the carb sees boost pressure, including the bowls, the 3 problems you run into are:
- you must boost reference the pump/regulator, ex: if the pump is only producing 5psi, and you've got 6psi boost the carb will see a pressure differential of -1psi, so the boost will force the fuel out of the carb. What you want is a setup that has the correct pressure NA and increases pressure 1:1 with boost pressure
- many carbs use brass floats. In a blow through app the boost pressure could crush the hollow brass float and then the float would sink, causing rich running
- The boosters are above the throttle shafts, and some boost inevitably escapes out othe throttle shaft bushings, this can be dangerous since if you leave it like that you've got perfectly metered air/fuel being forced out into the engine bay. If you don't have something attached to both sides of the throttle shafts you can usually cut one side short and cap the hole in the casting, the traditional solution for the other side is to drill the carb for an air seal.

Using a box fixes the throttle shaft problem, but creates a new on in that every linkage and fuel line has to pass through the side of the box and needs to be sealed. Tuning also becomes an issue since you have to take this thing apart every time you need to change something. Vortech just released a box that all the mags are jumping all over that comes with a pass through linkage and fuel lines but I've heard that it's priced over $700.

The advantages with blow through over draw through is that most people believe that it is easier to tune right, you don’t end up with any funky oil/vacuum problems with centrifugal blowers and turbos (when the throttle blades close on a draw through the blower sees a big vacuum which can suck oil past the seals), and you don’t have to worry about the coatings and bearings in the blower being effected by the gas.

 

I don’t get it, that cam is too big for what? As far as I’m concerned it’s almost perfect except that it has a little too little exhaust duration for a traditional SBC head with a power adder. I wouldn’t mess with it, and I don’t think that you’ll gain much by changing it even to a custom cam.

If you go with a positive displacement (roots type) don’t even consider advancing it, the blower will make all the low end you’ll want. I’m not sure that I’d consider it with a centrifugal blower either…

 

Thanx for the info. I think I may be a little confused however. (no pun intended).

I kinda understand why you would want to have a positive air seal around the carb throttle shaft, but is it a different type of seal I would need to install? I thought that they had to seal air normally even on a N/A motor, so you wouldn't have a vacuum leak???

About the floats and fuel pressure - makes sense to me...I have to have more gas pressure than intake pressure to feed fuel into the engine.

How do I "Boost/reference" my fuel pump?? I don't have a regulator. Is this an additional part I'll need?


So, please correct me if I misunderstood your post - What I'm gathering overall, is if I use a centrifugal blower, or any type of blower which pumps air into the carb airhorn, I'll need a "Blow-thru" carb, correct???

Likewise, If I decide on a Roots type blower (which I'm leaning towards due to cost) , I could use a "Draw thru" carb???

Warned you guys...I'm a rookie at this. Trying to learn.
So my existing cam seems OK? That's one good thing then. Should I get the 1.6:1 rockers?

Again , thanks.....

 

Well, yes and no, they do try to seal the air, but if you check, most with any miles on it will have some leakage. You don’t want to try any kind of mechanical seal because it would be prone to causing binding on the throttle shaft… a bad thing…

What I mean is that you drill a passage that intersects with the throttle shaft at one end, with the other end being either in the air horn above the boosters or on the outside of the carb, where you mount a fitting that you can run a hose to from some location between the boosters and the compressor. This way you’re forcing clean compressed air into the bearing area which is what will escape instead of air/fuel.


Easiest way is to use a regulator modified so that that you can run a line from the intake or other pressurized area to the backside (the side that the gas is not on, the one with the spring) of the regulator. That way the boost pressure is added to the diaphragm spring pressure and you will always have a fuel pressure that is spring pressure + boost pressure. With the exception of really low boost with a HP mechanical pump, you’ll have to use an electric pump to make this work.

I’ve got a bigger problem with your wording there then what you actually said:
First, blowthru or drawthru, they ‘re the same carb, though tuned differently, the terminology is just based on what you’re doing with the carb, whether you’re blowing thru it or drawing through it with the blower.

Let me say that that is almost true. In both cases you’ll have the carb flowing the same amount of fuel, but tuned to do it under the conditions that it sees dependant on the location that it is used in. The reason I’m saying ‘almost true’ is that although they’ll be setup to flow the same amount of fuel, you may not be able to use the same carb because you’ll need a carb that flows the total amount of air being used by the engine in a draw thru app where you’ll only need a carb that will flow the amount that the engine would use NA in a blow threw app since the compressor is forcing the extra air thru it. At 10 psi, this could be a 1.8x difference which could be a problem if NA the engine runs fine with a 750cfm carb, since in a draw thru setup you’re looking for 1350 cfm (either really expensive or 2 carbs)

My second problem with your statement is that a roots type blower does not have to be a draw thru setup, for an example check out the setup that my brother and I built that I posted some pictures and a description of in this thread His car is injected but I’m sure that you could imagine how this setup could be made to work with a carb as a blow thru. BTW, this is a total low buck setup, I’d guess that there is less then $500 in that blower setup, including the blower, but we did build everything…

I like your cam. You’ll usually gain something with 1.6 rockers but I can think of 2 reasons not to:
- I don’t know what heads you’re running, but you’ll have .484” lift with them, and you may run into valve spring issues or retainer/valve stem seal interference with that much lift on a lot of stock SBC heads
- Many stockfish SBC heads hit port stall in the .450” range, and once you go higher then the lift at which you get port stall you often will LOOSE flow.
So the choice of if you’ll get more flow out of 1.6rr’s is up to whether your heads are up to it.

 

Thanks for taking time out for the help 83 Crossfire TA. I did word the "drawthru" and "blowthru" question wrong. I realize they are the same carb, set up different ways. I should have just asked you- Do I have to do any modifications to my carb(s), if I use a regular "Roots" type blower where the carbs are mounted on top. This would be close to the way the carbs operate out of the box, for a N/A car right? By saying that, I mean "drawthru". I have read on other sites also that I will have to get a bigger carb to flow more CFM with a blower. I should'nt need to drill bleed passages either ...right?

I know this is asking a lot perhaps, but let me cut to the chase, instead of asking a little at a time here.



...I have a newly rebuilt 83 305HO, 9.0:1 compression, hyperetic pistons. Cam specs in previous post. I am still running the stock intake, E4ME rochester 4bbl, and still CCC (computer) controlled. Also has a NWC T-5 with a 3.73:1 one legger rear gears.

Stock HO single exhaust with 4 bolt monolythic convertor. I will be upgrading to headers and high flow cat with this project.

This engine is all stock except for the cam, and runs strong. I beleive it is very simular to what your car originally came with Mark..., of couse your intake was different.

It's never been dyno'd, but by SOTP I'd say around 200 HP. I'm looking to add additional 150 HP, and maintain my stock redline at 5500 RPM. I want to keep it streetable, and will drive the car occasionally.

The big question....if you owned this car, and wanted to supercharge it with a roots type blower....which "kit" would you get for it, and what is involved. i.e.....carb(s), fuel, etc. ???

Thanks for all the info so far, 83 Crossfire TA, ATOMonkey and nitrobreth. :hail:

- Jeff

 

To be blunt, you’re asking the wrong person. I usually avoid carbs in a performance application since there is always some bit of vagueness in what the carb is actually doing and what it would do if you made a specific change, especially if you have very large air flows or fuel flows. At times it is difficult to get FI to do what you want it to, but it always reacts consistently since it doesn’t rely on air passing through the TB to create the signal that controls fuel flow. I’m much less intimidated with programming or even tricking a stock ecm then changing jets/metering rods, though I know how to do both. If I put a setup together and slapped a carb on it I’m sure I could get it running right, but I’m not sure that I could predict what I would see before I saw it.

One thing along these lines that I have noticed lately is that almost everyone is recommending carbs with adjustable bleeds for blown apps now, specifically the newer ones in the Demon line.

Yep, I’m familiar with the ’83 305, 3 of the 3rd gens that I’ve done the most work on were all ‘83’s, one was an LU5 (mine), and the other 2 were an LG4 and an L69. As far as I could tell the Lu5 and the L69 are identical with different intakes.

That being said unless your hypereutectic pistons have significantly different valve reliefs/dish or you’re running a much thicker gasket you probably have more then 9:1 compression. If that is the case I’d say skip the supercharger since it could be as high as the high 9’s.

OK, now you’re starting to sound like my little brother when we started on supercharging his car. Essentially, you’re asking what would I do if I was to do something that I wouldn’t do… (did that make sense?).

OK, how about what I would do, first?

If you’re looking for 3-400hp I’d skip the blower. I don’t feel it’s worth the hassle/cost at that power level.

I’d get rid of the crap heads (I’m assuming that you’ve still go the stock ones since there is no mention of others), and since it is hard to justify spending $$$ on heads for a 305 (since if you build a 350 later you’ve made everything smaller then what the 350 would be happiest with to work with the 305’s small bore), I’d pick a set of vortec heads. I’d build the thing up 2 different ways depending on one of 2 situations: “I’ll be happy with being able to beat up on LS1’s” or “I really eventually want a blower”

In the case of “happy”: get the heads milled/run thinner gaskets to get the compression to about what you’ve got now (vortecs have 63-64cc chambers, where your stock heads have about 58). Use either a performer rpm or victor jr vortec style intake, keep the stock carb/distributor.

In the case of “I really eventually want a blower”: keep the heads like they come, they’ll lower your compression about a point which will be more blower friendly. Get a victor jr vortec style intake and you’ll eventually have to run a mechanical secondary carb/vacuum advance distributor (disabling your stock computer). Be warned, this setup will make almost the power and run similar times as the above one, but will feel like a dog off the line because your compression will not match your intake/cam/heads. (my brother built up the 302 in his LTD for the blower with a big cam, big heads… and compression in the low 8’s, and until the blower went on the car didn’t really spin its wheels or launch hard even with a 3200 converter but ran in the 12’s in the ¼).

With either setup I’d install headers (my choice would be headman long tubes if you’re willing to give up ground clearance or ¾ length if not, both rock and will really wake up this combination), 3” intermediate pipe and a good muffler. You might have to swap in a bigger cam to get to where you want to be, but I’d bet that you’d be fine with what you’ve got.

BTW, that T5 will blow, and so will the rear.

If you really need to go with a blower now, what would I do? Well, I’d build something like what we did on my brother’s car but with a blow through carb setup. Get rid of the computer and run a double mechanical secondary carb and single plane intake (you don’t want to mess with dual pain intakes and a blower, it can be done but you’ll never get good fuel distribution unless you’re an **** retentive porting wizard). Actually, if it was my car I’d use the money saved building my own blower setup to convert it to efi, I can’t imagine that a carb will be particularly happy with the pressure waves that a roots causes.

If you want something more bolt on look at the small holley and similar roots blowers, they’ll give you that power increase, but I really doubt that one would fit under the stock hood.

Otherwise, a decent, carb style electric fuel pump capable of up to about 15psi and a matching FPR that would accept a vacuum/boost signal (don’t really have a pick, I made the adjustable fpr that is on my ’83, ’87, truck and my brother’s car). Same headers/exhaust (any of these setups will suck without a good exhaust, I like those headers, I’m a fan of dynomax race magnum mufflers, and if you run a cat chuck the stock one and get either 1 large single or run dual cats (that’s what I did on my ’83). You’re pretty safe with Carsound…

BTW, that T5 will blow, and so will the rear.

 

All this time, I was thinking I had 9.0:1 compression!!!!!

After you said that, I started really thinking about it and, you're absolutley right!! My compression is 9.5:1!!!!! I shoud've known, since I installed the d**m pistons myself! This puts me in somewhat of a "crossroads" now.

Too high of a compression for a blower....HMMMMMMM.......

Well, it runs strong as is...and I can't see tearing into this again to change pistons. Wow!...I never thought I'd say this, but if I had an LG4, I would'nt have this problem, because it's compression is lower and a blower would work great!

BTW, no disrespect intended for you LG4 guys..


I would do that but, the vortecs are 305 specific.......I eventually plan to build a blown 383, and shouldn't need vortec heads for it. I was just hoping I could get some serious performance out of my 305 in the meantime.

Again, the vortec head dilemma.

It's funny you should say that...see, my brother bought a 2001 Firebird (or T/A), with a 350 LS1 6 speed, and it's a SWEET car, but I drove it for the first time, and I can honestly say I was a little disapointed with it's low end torque. No offense to you LS1 guys, but it really reminded me of my 4.6 F**d T-bird with the "Modular" engine. Not much off the line, but when you wind it out...it hauls!!

Thanks for all the help Mark. You have given me sound advice, and what I have decided to do is get headers for my 305 and get the bodywork and paint finished on the car. It's in serious need of interior from a newer car also. I'm hoping to run into a wrecked 90 or newer F-body with good interior to swap out the cr*p I have now. That'll probably set me back at least 3,000 when that's said and done.....Then it's 383 time!!

You said that TWICE...and I cringed both times I read it. And you're right again...those are weak links. Hopefully the rear will hold, but I agree, the T-5 will eat itself eventually.

Again, thanks for the advice, and I'd like to tap your wealth of knowledge on '83 models in the future if you don't mind. - Jeff

 

Um, what makes you say that? Vortech heads were designed for 350ci C/K trucks. The reason that I like them is that in stock form they flow better the almost all the available aftermarket heads for up to 2x the cost and still use 1.94/1.50 valves which will work in on the 305, and they aren't that far behind some of the $$$ heads like the AFR's... They can fairly cheaply be modified to keep up with the AFR's, and either way they'd work fine on the 383.

Hey, I think the T-5 is the only thing that you could possibly have in a 3rd gen that is actually weaker then the 10 bolt, and I've broken the 6 sets of 10 bolt gears and one axle in the last 5 years...