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Old 05-28-2003, 10:24 PM
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Post new 383 very sad dyno please help

hi, although this post could be long i will try to make it short. first the specs, 90 6speed corvette,350 5.7 stroked to a 383. new crank, rods,pistons 30 over,bearings,double roller timing chain,cam with .503 intake 510. exhaust lift, center force duel friction clutch. now for the top end factory 58cc heads 3angle valve job with bronze guides and stiffer springs. stock intake (big spider looking runners intake and plenum. after market ram air breather,stock fuel set up injectors ect.msd 6a box.hedman long tube headers with borla cats. stock rear end gears.(after market computer chip befor i bought the car). now for the dyno only 267hp with 376trq.the car came from the factory 245hp. i need advise bad on new intake and or heads. what ever i can do to get the hp up around at least 350. please no nitrus or blower. thanks a million trillion for pointing me in that direction. at this point i feel iv wasted 6 grand on the motor. thanks.

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Old 05-29-2003, 01:40 AM
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The stock TPI intake runners were designed for a 305. They are too narrow to flow enough air for a decent 350, much less a 383. Your heads are the same as the ZZ4 (355hp). They should be adequate. Be sure your chip is matched to your final combination.

[ May 29, 2003: Message edited by: jimfulco ]</p>
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Old 05-29-2003, 01:42 AM
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was it a real dyno or desktop?if its desktop dont pay any attention to it,i've seen them be way off.i dont know a lot about efi, but no-one uses it in their hot rods, me included.carburators seem to produce more hp.i dont know what valves you have but 58cc chamber seems slight for a 350.i guess i am agreeing with you , heads and intake.mike
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Old 05-29-2003, 02:02 AM
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More than likely the chip you are using is the problem. My brother-in-law had six custom chips made for his modified 350 and all were duds. He went to no computer, Holley carb and intake and Mallory ignition. Problems solved and runs great.
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Old 05-29-2003, 05:26 AM
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check the chip first as without the right programming it will always fall flat, then check out intakes as that will be cheaper to replace than the heads

try this site, they have a number of items for optimising your engine (the MAF trick box says it's specifically for high horse/stroked 84-2002 corvette):
<a href="http://www.fasttoys.net/8498ybodyinduc.html" target="_blank">84-2002 CORVETTE INDUCTION PARTS</a>

did you do most of the work yourself? a good workshop should have known all this.

your cylinder heads should support a lot more horse power than that, going aftermarket would add even more though

[ May 29, 2003: Message edited by: andybird ]</p>
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Old 05-29-2003, 09:21 AM
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My advice in the simplest form. Go and see an expert. They can help you.

I'm no expert, but I can help you. However, you will have to see a TPI expert to get your EPROM dialed in.

To ANYONE who says that a carb is the way to go, do not listen to them. There would be about four reasons for someone to say such: they can not afford EFI; they are racing in a class that does not allow EFI; they are ignorant about EFI... Okay, make that about three.

DO NOT take the fuel injection off of your VETTE. You would regrett that forever. The TPI system can get you 400hp at the rear wheels.

Here's what general motors engineers did. They wanted to make a torquey 5.7L engine. They used a tube-style intake runners as they could easily change the diameter and the length. They went with a longer tube as the extra length will increase torque. Same thing with the small diameter, this will promote velocity and good cylinder filling to aid in low-speed power. Now, when they found a diameter and length they liked for a certain RPM they called it "tuned", and thus the name tuned port injection.

The runners are small on a stock TPI set-up and are not adequate for your engine. Here is the first order of busines...

Oh, post your cam duration. This could be a lot of your problem if you have too much. What is it? What is your compression?

The first order of business is to fix the air intake. This will net you gains. There is a company called SLP that sells new runners. Their runners are cast. The SLP runners are larger, shorter, and siamesed. You will have to remove your runners and upper plenum. Use the gasket in the new runners to port-match your upper intake. If you don't feel comfortable take it to a shop. They will siamese the two intake ports. You will have one large oval where you now have to medium holes next to each other. You can find pictures of this on the 'net. You should also get a 58mm throttlebody and have the front of your plenum opened up to accomodate the 58mm throttle body as it will be larger.

This is the first area to fix. You will certainly notice gains, but nothing compared to having the right programming. The stock EPROM will never cut it. Take your car to a professional- Ed Wright for example. Take it to him and he can help you out. I have the name of a guy that programmed some 400+ dyno hp vortec TPI engines. I can get this name for you if you must have it.

Your intake manifold is also a concern, but should be addressed after the runners are purchased and everything is port matched. Get a better TPI base. Your base doesn't flow that well. You will net gains here too. These mods will help you near your hp goal.

You are running full length headers and a good exhaust right?

If you don't have enough compression that can be hurting your performance too.

I can't believe no one told you this before you had your engine built. These mods are a must to get good numbers from a TPI system.

Search around for cheaper runners if you want. They don't have to be SLP. You just want a better horsepower design than what you have now.

If you shop can get your airfuel right, be prepared to replace your 15 year old fuel injectors. You will potentially need larger injectors.

This will get you closer/beyond the power you want.

If you are still not happy have your L98 heads ported. This will set you back ALOT ($1000), but will also certainly give you gains in terms of horsepower. Then, you have to have a new chip burnt too.

Post any more questions.
Ben T.
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Old 05-29-2003, 10:01 AM
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"To ANYONE who says that a carb is the way to go, do not listen to them. There would be about four reasons for someone to say such: they can not afford EFI; they are racing in a class that does not allow EFI; they are ignorant about EFI... Okay, make that about three."

All I have to say is this:

I can fix a carburetion issue in my OWN garage, with a screwdriver and a vacuum gauge. None of that chip programming nonsense.

You could say just as easily that anyone who's ever dis'ed an 8-weber setup for being "too difficult to maintain" just didn't have the brawn or dedication or proper research in order to optimize it for maximum power.

EFI is great when it works right. But especially, in my case, for midyear Corvettes, as EFI was implemented in the 80's models, namely "crossfire injection" or more commonly known as "misfire injection", it's a royal P.I.T.A. - I'll take an easily modified carburetor over a more expensive, more fuel efficient EFI setup ANY day.

Now in the case of the 1990 vette, EFI may be the way to go just because of clearance issues related to how low that hood sits. I'm no expert on the C4's so I really have no idea.

best of luck, steve.
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Old 05-29-2003, 10:18 AM
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Talking

I'm not trying to offend anyone. I'm just saying how it is.

I'm ignorant and don't have the money. I know about the theory and what it takes to make TPI work, but I don't know how to burn a chip. Having AutoTap and PROM burning equipment would fall back into-not having the money for it. I don't currently have money for it right now.

You nailed why I was saying that EFI was superior. I don't think you meant to do it though. You don't have to adjust idle mixtures screws or float levels on an EFI vehicle.

Hands down EFI is the way to go- I'll say it again. I had the Holley Commander 950 multiport fuel injection picked out for my vortec headed motor, but I can not afford it at this time. I'm going to keep my carb. It will always be second best to the efi in everyway but one... The carb is much cheaper.

When I said you might be ignorant about EFI... it appears that you and I both fit that statement. If my car has a lean idle and a low-speed stumble... where would I start with EFI? I'd have to learn as to not be ignorant. If you weren't ignorant about EFI then you could just fix it yourself in your own garage. That would be why you'd make that statement... just because you don't know how to fix it. Now, don't go getting all upset. I'm using the the word "ignorant" in it's denotative meaning- not educated.

No one is being attacked here. Relax. I'm one of those people who is not running EFI. I fit my description. I can't afford it, and without having an EFI system and without ever learning- I don't know how to tune the programming.

EFI is superior. The early GM stuff wasn't that great, but most aftermarket systems and TPI are great for street machines.

Ben T.
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Old 05-29-2003, 11:22 AM
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Your dyno results of 267HP. is that at the back wheel. Because that's how dyno machines measure HP...at the rear wheels. If that's the case, then add at least 50Hp to get your engine HP total.

Compare that to a stock 350.

If it's desktop Dyno then that's a different story.


Greg.
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Old 05-29-2003, 10:16 PM
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thanks for all the help. learned something from every one.i relize the we have a breathing problem here. i dont even think that the ram air is able to work like it should. oh yea musle truck, the duration of the cam is at .050 224/230 at .006 276/281.naw it wasnt a desk top dyno. as for the experts i did all the work my self except the machine work on the block and heads. they put the crank and stuff in the block. i already new what stroker kit to buy, the only other thing that i asked for was that they put the biggest cam in there and keep it streetable. headers,ram air,msd came later. yall know it took me 3 days to learn how to drive the car again after i put the headers on. big difference. any how what do yall think about some kind of super ram type of intake setup? thanks again.
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Old 05-30-2003, 01:13 AM
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I would also suggest checking your valve spring installed height, and open height, and check your coil bind specs. What was your final compression ratio? Do you have a scanner? What is the timing advance when you load the engine? If it is pinging the PCM will retard the timing. Check the fuel trim and injector pulse width. Are you running a colder T-stat? What's the actual coolant temp @ operating temperature?
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Old 05-30-2003, 08:41 AM
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I think the SuperRam is a waste of money considering you can modify what you have now to make good power for way short than what the ram cost. You're running alot of cam. For the extra money you'd have spent on the ram -spend that on headwork or better heads. Your heads are not the optimal choice for your engine. Have someone professionally port them or get some better flowing aftermarket heads and you'll be well on your way to 450 crank hp. That will certainly get your goal of rwhp. Don't give up on your car. You have all of the hard stuff done.

Change those intake parts I told you about earlier and they see how much more you'll have to learn to drive differently. :-) That will really wake your car up. That would be the best bang for your buck as for right now.

I'd modify the intake you have. Then, either get some pro programming or go the head work and then get some good quality programming.

Ben T.
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Old 05-30-2003, 09:26 AM
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You may want to go with a smaller cam. I looked into fuel injection for my ride and Arizona Speed and Marine claims the usually a just better then stock cam is all fuel injection will support. Just a thought. By the way keep the fuel injection.
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Old 05-30-2003, 11:44 AM
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Make sure you throughly discuss if you have too much cam before you remove it. You'll want to talk to whomever you choose to burn your chips about this.

I would be hesitant about pulling the cam out. The ECM that uses speed density (that's the one you are using I think) can be programmed to support a good bit of duration. Many people have to wind up going from the earlier MAF TPI to your style of MAP TPI to support more cam. You already have this, and your cam can probably be made to work.

Yes, this cam is big, but that is not what THE major problem is. Fix your induction problems and go from there.

Ben T.
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Old 05-30-2003, 06:14 PM
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Steve, hang in there with your TPI. Once you get it, right, you will never look back. As far as a ram air system, go with what you can get in your limited space. Ram air does a few things for you of which the best is it gets you outside air that is much cooler than engine compartment air. This equates to more dense air; then you can get up to 2 in Hg pressure which now starts to make for lots more air available to the air valve at cruise speeds. This is worth at least 1.5 MPG and increased cruise performance. You probably will not see any increase performance at low speeds, other than from running cooler air. Ram Air Box makes a great after market system, but unfortunately, you can not use their box with your stock Vette hood. They make the ram air boxes for NASCAR truck series that use snorkle size for restricting air flow, vice restrictor plates. If you click on my Avtar, you can see one of their Ram Air Boxes with a 4" snorkle showing. There is another one on the other side. According to RAB techies, the two 4" tubes flow 800CFM. By the way this is a 383 with Edelbrock Pro Flo EFI, ETEC 200 heads with 2.02 intake valves, 10.2-1 compression and a milder cam than yours.(Edlebrock computer uses manifold vacuum and inlet air temp to compute mass air flow, so it does not like big cams and poor vacuum). The chip requirements for this computer is more driven by the cam specs than anything else you do to the motor!! Some other things you may want to look at, since you have not mentioned it, is your injectors and pressure regulator. For your 383, you need 29#/hr injectors and you will need about 45 psi regulated pressure. I still do not know the source of your TPI system, if it is from a 305, they came with 24#/ hr injectors (too small) and about 40 PSI pressure (too low) and the tubes are too small. You can invest in an adjustable regulator and do some tuning by increasing the pressure a small amount. This means you can stuff more fuel in for each njector event (you did not change the duration of the injector signal)

Again, hang in there. You will love it when it all comes together.

Trees
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