SA68SS

Hi All. I am looking at a 93 Z28 in Cali which has C.A.R.B. compliant headers on it. I am wondering if this set MUST go, considering the work involved.
Car produces 399 hp at rear wheels at the moment. I am not chasing horsepower, but wondering how much of a plug this set of headers is....

Engine -
4 bolt LT1 Corvette block bored .030 over
383 stroker, Cola forged crank
Callies forged rods (could be Childs and Albert - engine builder cant recall)
J&E forged pistons
AFR 195 heads
Stock Optispark distributor
Ported LT! plenum, larger injectors

McLeod dual clutch
Stock T56 transmission
Mini tubbed rear
Currie Ford 9 " carrier with Strange posi 4.30 and Strange forged axles
Strange lightweight center
Corvette ZR1 wheels - 335 rear and 275 fronts
Hoop roll bar with rears and spreaders (Not full cage)

Considering the current hp figures, and the fact I will not be racing this car, is the header worth replacing with something like 1 3/4 inch primaries?
Seems like enough car for me for daily driver, just don't want to be choking it

This is my first experience with a LT1 engine. Or a fuel injected car. Am I leaving cheap horsepower in the bucket ?

Z28Freak86

If i understand correctly, you're saying that you're wondering what kind of gain you will see if you were to switch to a non-carb compliant header set, and is it worth it? It depends on what set you have on now. Some carb compliant sets aren't too bad in terms of restricting exhaust, it just depends on what kind you have. The primary's on most are the same (again, depends on the set), but with your current motor you could see about 10-15 horsepower at the rear with a good set of long tubes. What size is the headers primarys now, and is it a shorty or midlength now? Futhermore, what kind of cat back system do you have, aftermarket or stock? Do you have the original cat or a high flow cat? There is a lot of restrictions in a exhaust system, so it depends if everything else has been taken care of. Anytime you go to long tubes you will see a gain, mostly with but the gain you will see will depend on what is already on the car compared to what you would go with.

The long tubes will help a bit more with your exhaust velocity and pulse, but will not have much effect unless the rest of the exhaust has been opened up. Im assuming that it is considering your at 399 rwhp, so i will make a complete guess at the gains... i would predict from shorties to long - maybe 13 horsepower. From mid-length to long, maybe 8. (complete guess, but it wont be anything crazy).

Are they a plug, not necessarily, the long tubes are just more efficient with evacuating/suctioning out the exhaust gas. More efficient= more power.

SA68SS

Thanks Z28Freak86, that is the info and advice I was looking for. The car runs just fine now, and even 15-20 hp is not worth it to me to do the change to new headers right now.
Not sure what size or type are fitted currently, only that they are CARB compliant. The exhaust has a stock catalytic converter, but the owner has a 'bypass' pipe section to replace it for track days.
The car no longer passes smog. I will assume it is not a stock exhaust system. But I am not going to start changing headers right now, for 15 hp.

Thanks for the reply

Injuneer

Read his post closely..... it depends. I had a set of JBA CARB-legal 1-5/8" step headers, and they choked my bolt-on LT1 at high RPM. Can't imagine what they would have done to a 460HP 383. Difference could be more than 13HP, but you've given us little info to go by.

If it's got a CARB-EO plate on one of the primaries, it should have the manufacturer's name on it.

SA68SS

Fair enough. The car is in California, I am in Michigan. The car was built for the builders brother, about 10 years ago, and it was built to make power, handle well enough for track duty, and still pass smog testing. Recently it has failed smog testing. The owner has fiddled with two catalytic converters, and some other ignition system to try to make smog testing. It did not pass, and the optispark was reinstalled.
The builder has done work for me before, and I believe he is genuine in his suggestions to improve the car.
His suggestions include new headers with 1 3/4 - 1 7/8 primaries, and eliminate the catalytic converter(s). He suggested removing the FI system and going with a Victor Jr and a Holley HP950 carb.
From my limited knowledge and research I am happy the 93 speed/density and batch fire fuel injection is reliable enough to retain. The benefits outweigh the cost of changing out the system, especially since the power level in this car is more than any car I have had before.
The headers seem to be a good item to change out, but I don't really want to get stuck in California working on a car that is probably going to be more than enough for me right now, in current trim. If the gains were 50-75 horses it might be worth it, but it is a case of me not knowing enough about the LT1 engines, and "if it aint broke, don't fix it" mentality.
I apologize but I get to over-thinking decisions sometimes, especially when it comes to 'hot engines'
I probably should have just posted a "Do you think this is a good reliable car"
It has been raced for 10 years, and to me it is proof it is a stout engine, and also a warning that it may be about to break. No one can answer that.
I just need to make my mind up and go get it, and quit bothering folks here.

Chimera96

OP

as mentioned going from CARB shorty headers to long tubes will not gain "huge" HP. yeah there will be a gain but for the $ 15 +/- HP gain...

given the car has seen years of racing, might want to ask for a leak down test of the motor. That would show if the motor is still in good shape regarding rings/valves. would not show bearing condition but good oil pressure is a reference of bearing condition

SA68SS

Yes, I agree on the dollars to hp gain. Car is in the shop tomorrow for inspection and can do a leak down test.
Spoke with the owner today, and he is not a racer, it is more like a few track days with his friends (bmw's and Porsche crowd) so it is looking better as far as wear and tear.
He said he has Edelbrock shorties on it, and thinks they are 1 5/8 primaries, so that is not too bad really. 3 inch exhaust system with Flowmaster chambered muffler(s) He has a test pipe to replace the cat, and that can come off too.
Edelbrock hardened Optispark - not sure exactly what that is, but apparently it is an upgrade.
AFR heads so he does not know if the EGR is there either.
It apparently does have a smog pump.

anyway, I now own it. Just got to go to California and get it. Paperwork then a long drive to Michigan.

Thanks to all for replies.

Chimera96

sounds like a cool ride. Yeah here is Calif. smog is a PIA and Edelbrock is one of very few CARB headers...

I have a 383 with the Edelbrock shortys (smog) and they are 1 5/8 primaries

SA68SS

Hey thanks Chimera96. It really is a pity that some folks in Government just cant resist being the fun police. For all the actual good it does, I honestly think it is just a certain type of person who loves to make up rules to deter folks from having the type of fun that our 'overlords' don't want us to.
It is worse in other places, believe me. But that does not make you CA folks "lucky" either.

So, I am excited to get this car, it is the most powerful and modern engine I have ever had. Can you tell me what sort of characteristics a 383 has? Fast revving, high revving? Good torque?
Any tips for this engine and car?

Chimera96

The LT1 is just like any other SBC that is .030 overbore with a stroker crank making it 383 CI. It will have more TQ and HP over a identical 350 CI build.

Your cam will dictate how high a RPM the motor needs to spin to make max power. I have a small cam in mine (smog) so I don't shift much higher than 6200. It makes tons of TQ down low which for DD it is great.

As long as your ride is mechanically sound and the tune is right it will be a very solid fun car to drive. Road trip back will be cool.

If it is the McLeod Street Twin clutch, that is a VERY good clutch.

LT1 has Optispark (distributor) behind it's water pump. This makes it vulnerable to coolant exposure from weeping WP. Didn't see in you build list a EWP which is what I and others swap to. You can check for weeping WP (drips on the floor will be a clue) by looking up under the front of the engine between WP & Opti, if there is drips...you should replace WP, remove opti and remove cap/rotor and clean if coolant is inside. MSD makes a good replacement cap/rotor kit. use lock-tite on the rotor screws

SA68SS

Well, news today. It has a brand new billet optispark. Could be Edelbrock according to the owner, although I did not know Edelbrock made the opti. It has the stack water pump, no leaks at this point. I know he changed out the ignition to MSD some time back but did not get the result he wanted so that's why he went back to the opti.

It does have the fancy McLeod twin clutch.

Custom cam ground by Cam Motion in Baton Rouge to McClenon's specs. He saysit was funny that the LT4 hot cam from Cam Motion came out a few months later, with almost identical specs, just a little smaller across the board......so I think this will be a fairly hot cam.

Comes with a number of chips. I was wondering how you all determine your tunes and how many you have? Do you have a DD chip, and a performance chip? Do folks really change them out a lot?
All new to me.

The builder is keen to put a new intake and a carb on this engine, but I would like to run the EFI and see how I like it before I go down that path. Seems to me the 93 is a fairly simple system and quite reliable.

Thanks for your input