MikkoT

I am planning to rebuild my corvette C4 -92 LT1 engine.
First I thought that I use original parts but I need to renew crankshaft,
few connecting rod and pistons so I think that now it is so easy use 383 stroker kit.
Does anyone know how 383 stroker kit works with original ecm without tuning?

96 lt-4

Unless you put a stock cam in it it will need to be tuned.

It may run "ok" with a small cam put I wouldn't guess with the tune if I spent that much money on a stroker.

Kevova

The extra 34 ci is going to require some tuning, regardless of cam. Possibly larger injector and adjusting fuel pressure may prevent ecm tune, but I think ecm will need some tweaking.

aklim

My 383 with 36pph injectors SUCKED. Blew out black smoke and hardly made it up the trailer and that was with a 74219 cam. Why are you spending all the money and being that afraid of a dyno tune? Making the cam and head work around the stock EPROM just to avoid a dyno tune is kinda dumb, IMO. All you did was spend money and hamstring yourself.

Vett1990

My 383 works very well however, if you want all the benifits of the extra CI you will also need to keep in mind air flow and fuel flow. The engine can support more air flow, will your heads flow enough air? Your engine will support more fuel burn, will your injector flow enough fuel? The ECM will need a re-tune to get everything back in balance for optium performance and to avoid a lean or rich condition.

To get my 383 working well there is no longer anything stock on my 383, my stroker kit led to (new headers, TB, injectors, intake, heads and several dyno tunes.

BrianCunningham

Running my supercharged 383 with a healthy cam and AFR with the stock ECM

Obviously it was tuned

bjankuski

If you are just increasing the displacement but using the stock heads, cam, intake, and exhaust I believe you will be fine with the stock chip. I would try it and adjust as needed.

aklim

MAYBE but what would the point be? Spend money on a 383 just to choke it with the exhaust manifolds and stock heads and cam? All to save a few hundred bucks that you won't need to spend until the next major iteration? I have honest doubts it will work. The Superram Intake and Tri-Y headers on my 91 F-body already made it NOT ideal on the stock chip. IF it runs on the stock chip with just a 383, it might run but not well which once again defeats the purpose of the 383. Unless I am misunderstanding something.

five7kid

'92 being a speed density system, I don't think it'll be happy with the extra cubes without a tune.

Tom400CFI

More low end tq and more fun to drive. If he has to buy a crank/rods anyway, he can add cubes in the process and more fun. May not pick up 1hp, but it will certainly gain low end punch.

I went from a 305 to a 400 CID on a stock ECM/tune. I made it work with injector sizing and it ran GOOD; factory-like idle, wicked throttle response and low end tq, 24 mpg hwy...it "met the criteria". Actually it exceeded my expectations by a lot. So it CAN be done and there are definitely reasons/rewards for it -especially if you keep the cam stock-ish.

Is it the BEST way? No, it's not the best way. Can it be "good enough" and reward the effort? It sure can.

Purple92

Bottom line - Your 1992 has a Speed density based EFI system. So - at any RPM / throttle condition - the amount of fuel injected is calculated not by the actual airflow into the engine - but by what is programmed into the tables. So - if you increased displacement by 33 cid - or about 9.4% - so you are going to be about 9.4% lean. While the car will probably run - it won't run well, and at any reasonable power output level - you risk burning a piston or worse.

If you are going to increase displacement more than about 2% - you have two choices - either get the PROM in the ECM reprogrammed for the extra displacement, or get a set of fuel injectors that flow about 9.4% more than the stock injectors. (I believe the 1992's had 19 Lb/hour injectors - so you would want to get 21 Lb/hour injectors - which I don't believe are available....) So - I would strongly suggest that going with the reprogrammed ECM. Check out companies like PCMforless - where you send them your PROM, and they reflash it for you. The displacement increase is a VERY simple thing to do a reflash for.

IF you go the reflash route - I strongly recommend you consider making a few other changes in the OEM programming... I would change (lower) cooling fan on temps, and depending on where you live, and the risk of theft - I would think about eliminating the VATS system.

bjankuski

The car will run fine with 10% additional displacement if that is the only change you are going to make. The stock 1992 injectors are 24 lbs and the computer will adjust the BLM to compensate for the additional fuel required. This adjustment is also applied to the WOT fuel settings so it will not run lean at WOT. I do suggest scanning the car to see what the BLM fuel trims are and if they are significantly out of spec then get a chip burned.

If the only change being made to this car is the increased displacement the changes from the stock tune will be very minimal.

MikkoT

Thanks for all replies.

This operation started to get interested.

What kind of camshaft you would recommend for my car? Camshaft should be better than original, but not too radical.

I will be using original cylinder heads and 383 Scat strouker kit. What kind of pistons +18...-18cc you would recommend?
Car is for street use and needs to get through car inspection. I try to get about 400hp for the engine.

Some details:

- cylinder bore 4.030 in
- stock chamber size 54 cc
- deck height 0.027 in(?)
- Head gasket crush thickness 0.050 in



(ps. I don´t let it be without tune...)

five7kid

Since you're increasing the displacement, you'll have to increase the compressed volume to maintain stock compression ratio. There are on-line compression ratio calculators you can use to play around with various piston dish volumes to figure out what that should be.

It shouldn't take too much cam to get to 400 HP. Get with a cam or LT1 specialist outfit to help with the choice.

steven mack

GM hot cam will do the trick.

BrianCunningham

Make sure the cam clears the rods

aklim

400 is a little bit low. For a 383, I'd like to see the thing hit more than 450. High 400s or low 500s since we are talking about an LT1

five7kid

There are different ways of measuring HP.

The most common bench-racing method uses the unrealistic "gross flywheel HP", which is on an engine dyno with no accessories being powered by the engine, whatever air intake and exhaust they want to use, regardless of what it'll have when in the car. Since the numbers produced this way are always the biggest, it is the method used for crate engines.

You'll also hear "rear wheel HP", which is commonly quoted because the chassis dyno is the easiest method. You would think it would be the most useful because it's measuring what's actually getting to the wheels - except chassis dynos vary wildly from brand-to-brand, and can even vary run-to-run on the same dyno. Chassis dynos should only be considered a tuning aid, but you'll still hear people bragging about what their car put down on the chassis dyno.

The factory uses "net flywheel HP", which is on an engine dyno, but the accessories (alternator, water pump) are being powered by the engine, and the air intake and full exhaust are installed as they are in the car. It is the most consistent and realistic (although powertrain loses aren't accounted for).

So, if you compare the new output to the factory-rated 300 NFWHP, 400 is a pretty impressive number.

On the other hand, if the goal is 400 GFWHP, then the stock engine isn't all that far to start with.

If 400 RWHP is the goal, you'll probably need more than an LT4 Hot Cam.

Tom400CFI

^Well said^

And, I'll add that since most are inertia dynos, they can vary wildly car to car, same dyno due to drive train weight; My LS2 (400hp) C6 put down 360 at the wheels. On the same dyno, our LS6 CTS-V put down 338 to the wheels. Both SAE 400 net hp engines. Why the diff? Caddy has a ~45 lb flywheel, a HEAVY drive shaft, 14" heavy rear rotors, and heavy wheels and 6 lug hubs. It all adds up to quite a lot more mass for an engine to accelerate.

aklim

So maybe the best is to say "I have 200 RWHP as measured on a brand X dyno" so we can know what is going on? I mean, measuring without accessories is kinda of a "beer drinking number" as is net flywheel since we both know that you cannot drive that, for want of a better term "lack of a vehicle". Just a thought.