Question: Rebuilt my LT1 and need answers. please

[EmsFather]

I just finished putting a lot of money into my 93 LT1. I went with an LT4 Hot Cam Kit, including heads, 58mm TB as opposed to stock 52mm, 32 Lb. injectors instead of 24 lb. injectors, Edelbrock LT4 intake, Hooker shorties, Borla cat back exhausts and a K&N air filter and a new chip burned for the motor. It feels fatser than the old LT1 but not where I thought it would be. I was told that after the break in period and when the chip and motor work out any problems, I will feel a big difference. I was given all sorts of final crank HP numbers, ranging from 430-475. GM performance people rate the LT4 Hotcam kit with heads at 425 crank horse. The car feel very strong but will it get stronger? Thank you in advance for any answers. I appreciate it.

Bob

 

[dogfish246]

Well, I it is said that the stock LT1 is stronger after it gets broken in! Where most cars loose HP after driving the car a while, the Vette actually runs stronger!

 

[So Bay Vetter]

Where, exactly,do you feel it's lacking? Out of the hole? torque on the pull? top end?

 

[Hib Halverson]

When you say "heads" what head are you talking about and did you do any additional work to them before installation?

 

[EmsFather]

When you say "heads" what head are you talking about and did you do any additional work to them before installation?

I am using LT4 Hot Cam heads, which are, for lack of a better description, an upgrade from the standard LT4 heads. I chose not to do any work with them because I felt the HP numbers I was promised were right were I wanted to be, not any higher. As I drove it more today and approached 300 miles on the motor, it started to come to life quite a bit. It felt a lot stronger today. It is starting to put a smile on my face. I hope it just gets better.

Bob

 

[Hib Halverson]

Forgive my ignorance but I've never heard of "LT4 Hot Cam" heads. I'm familiar with the OE LT4 head...are these "Hot Cam" heads a GM part or are they some head porters modification of a production LT4 Head?

Also, if you're having doubts about the engine's performance, I'd put 1000 miles on it, change the oil then take it to a chassis dyno. That will tell you if the engine is performing up to the builder's promises.

 

[EmsFather]

Forgive my ignorance but I've never heard of "LT4 Hot Cam" heads. I'm familiar with the OE LT4 head...are these "Hot Cam" heads a GM part or are they some head porters modification of a production LT4 Head?

Also, if you're having doubts about the engine's performance, I'd put 1000 miles on it, change the oil then take it to a chassis dyno. That will tell you if the engine is performing up to the builder's promises.

GM Performance sells, for around $2,750, a package that includes the heads, cam and all the goodies associated with the cam. The heads are a notch or two above the original LT4 heads.

 

[Kid_Again]

I only see LT4 cylinder head PN 12363287 on the GM PP website. They are the stock LT4 heads. Do you have a PN?

 

[EmsFather]

I only see LT4 cylinder head PN 12363287 on the GM PP website. They are the stock LT4 heads. Do you have a PN?

These are the specs on the stock LT4 heads and beneath that are the upgraded LT4 heads for the Hot Cam kit:

Cylinder heads: Aluminum, with 185cc intake port volume
Combustion chambers: 54.4cc
Valves: 1.94 intake/1.50 exhaust
Valve spring pressure: 100 lbs.
Rocker arms:1.5:1 adjustable, self-aligning, stamped steel
Camshaft: Roller
Lift: .447 intake/.459 exhaust
Duration: 202� intake/208� exhaust@.050-inch
Intake manifold: Aluminum, matched runners
Torsional Damper: Dual mass


Heads:
LT4 Aluminum Cylinder Head Assembly Aluminum performance head Can only be used on 1992-newer LT1 and LT4 engines Completely assembled with 2 00"/1 55" valves 195cc intake port 54 4cc combustion chamber No heat riser

Hot Cam specs & Dyno w/o above heads.
http://paceperformance.com/ProductImages/manufacturer/gm/internalimages/ZZ4HotCam.pdf

 

[Hib Halverson]

I hate to rain on the parade here but, I have the 2008 GMPP catalog open on my desk and there is no "package" of an "enhanced" LT4 head and LT4 Hot Cam sold by GM Performance parts.

In fact, the above list doesn't even correctly describe the LT4 head.

The LT4 head has 195cc intake port volumes, larger intake valves and uses an aluminum 1.6:1 roller rocker.

My guess is the engine in question has stock LT1 castings and an LT4 Hot Cam. That along with the other mods listed in the first post have me of the opinion that the 430-475 hp is a bit optimistic. I'm going to guess 375-425 hp SAE at the flywheel and that's provided the injector sizing is correct and the ECM's cal is right.

The easiest thing to do is run that pup on a chassis dyno. If you do that, post the numbers, here.

 

[EmsFather]

I hate to rain on the parade here but, I have the 2008 GMPP catalog open on my desk and there is no "package" of an "enhanced" LT4 head and LT4 Hot Cam sold by GM Performance parts.

In fact, the above list doesn't even correctly describe the LT4 head.

The LT4 head has 195cc intake port volumes, larger intake valves and uses an aluminum 1.6:1 roller rocker.

My guess is the engine in question has stock LT1 castings and an LT4 Hot Cam. That along with the other mods listed in the first post have me of the opinion that the 430-475 hp is a bit optimistic. I'm going to guess 375-425 hp SAE at the flywheel and that's provided the injector sizing is correct and the ECM's cal is right.

The easiest thing to do is run that pup on a chassis dyno. If you do that, post the numbers, here.

The LT4 has smaller intake valves. 184cc. I can't find the rest of the info but I do know about the intake valves being 11 cc smaller than the heads for the hot cam. Check please, if you do not mind, what the stock LT4 Heads have again. You are right though. The best way to find out is by putting it up on the dyno and getting answers. Like the song says though,...Feelin' Stronger Every Day".

 

[Tuna]

A few years ago, I did the LT4 + Hot cam conversion on my 92 but without the extra mods you have done - i.e.: LT4 heads and Hot Cam only then CORSA exhaust. I used the stock 48 mm TB and 24# injectors.

I got 330 HP at the rear wheels afterward on a dyno using a fastchips.com chip. Had I upgraded the TB and injectors, I would have expected around 350 at the rear wheels. Never got around to doing that however.

Seat of the pants feel for performance increases is never right, the dyno is the only way to really see what you have done (or 1/4 miles times). Years ago, I changed chips and installed a ram air system on my Grand National and it felt slower but ran 1/2 second faster 1/4 mile times.

 

[EmsFather]

A few years ago, I did the LT4 + Hot cam conversion on my 92 but without the extra mods you have done - i.e.: LT4 heads and Hot Cam only then CORSA exhaust. I used the stock 48 mm TB and 24# injectors.

I got 330 HP at the rear wheels afterward on a dyno using a fastchips.com chip. Had I upgraded the TB and injectors, I would have expected around 350 at the rear wheels. Never got around to doing that however.

Seat of the pants feel for performance increases is never right, the dyno is the only way to really see what you have done (or 1/4 miles times). Years ago, I changed chips and installed a ram air system on my Grand National and it felt slower but ran 1/2 second faster 1/4 mile times.

Whatever I felt on Wednesday, when I first took it home, is nothng like I felt last night. The car, now with over 400 miles on the engine, sprung to life. I took it on this one road and when I stepped into it on Wednesday night,felt a little more powerful than before. Last night, on the same road, I actually had to let off the gas because of the difference. Now when you step on the gas it lurches forward and is not nearly as civil. It is now paying off the dividends I was promised. Maybe there is something to be said about a brand new chip having to synch with the motor. It is great no matter what caused it to meet my expectations. Thanks to all for advice and support.

Bob

 

[EmsFather]

Well it seems I got a lot of really great information here and I can't thank those who helped me enough. I think after all the advice I received, I found the culprit that keeps the car from achieving it's peak power. Whomever owned the car before me put some Hypertech chip in the car. When the chip was burned for the new mods, the chip was burned for the stock PROM, not a hypertech. According to what I think I know now, the Hypertech, which piggybacks the new chip, is hurting the entire motor. I was told to do one of two things. Either get a brand new chip that will run without the stock PROM or replace the Hypertech with the stock PROM since that is what the chip builder was basing his burn around anyway. Once I get the computer chip correct, whenever that happens, the car should be a serious little street machine. Right now it has great low end power but it does not feel like it has that same power throughout.

 

[EmsFather]

Well it seems I got a lot of really great information here and I can't thank those who helped me enough. I think after all the advice I received, I found the culprit that keeps the car from achieving it's peak power. Whomever owned the car before me put some Hypertech chip in the car. When the chip was burned for the new mods, the chip was burned for the stock PROM, not a hypertech. According to what I think I know now, the Hypertech, which piggybacks the new chip, is hurting the entire motor. I was told to do one of two things. Either get a brand new chip that will run without the stock PROM or replace the Hypertech with the stock PROM since that is what the chip builder was basing his burn around anyway. Once I get the computer chip correct, whenever that happens, the car should be a serious little street machine. Right now it has great low end power but it does not feel like it has that same power throughout.

I got the correct PROM even though it was discontinued by GM. I put it in the car and finally the car makes power from low to high RPM. It is a wild little small block. Ironically I blew a header gasket Friday so even though it feels great, it doesn't sound as sweet as should. Thanks all.!

Bob

 

[Schrade]

I'd get my hands on a hardwire interface for your laptop, and some scan software (the free versions first), and see what kind of numbers are passin' through the burn / log data.

Then get a version that lets you 'write' to the PCM, and do a real tune. It won't be easy, unless the parts that you bought were a complete package, and there are reference/baseline numbers to start with.

Otherwise, you'll have to use the stock LT1 numbers that the FSM gives, and go from there...

In the meantime, go to a speed shop, and get a log printout NOW, and call the parts supplier that you got the parts from, and get a copy to them for feedback.

 

[Hib Halverson]

There are no "free" scan test software applications that support 82-93 engine controls. In fact, there are only a few scan test apps you can buy that support an ECM that old. The best of them is TTS Datamaster from TTS Specialties.

You cannot "write" to the calibration software in a 93 ECM. 93s use a "chip" and the hardware and software necessary to change the programming in the chip, while avaiable to DIYs, is expensive.

Your choices here are:
1) Buy the equipment and "burn" your own chip--I'd not advise that unless a) you're rich and b) you've got experience tunning on a chassis dyno.
2) Buy an aftermarket calibration designed for a modified LT1
3) Hire a tuner to custom-tune a chip for your engine using a chassis dyno.

 

[EmsFather]

There are no "free" scan test software applications that support 82-93 engine controls. In fact, there are only a few scan test apps you can buy that support an ECM that old. The best of them is TTS Datamaster from TTS Specialties.

You cannot "write" to the calibration software in a 93 ECM. 93s use a "chip" and the hardware and software necessary to change the programming in the chip, while avaiable to DIYs, is expensive.

Your choices here are:
1) Buy the equipment and "burn" your own chip--I'd not advise that unless a) you're rich and b) you've got experience tunning on a chassis dyno.
2) Buy an aftermarket calibration designed for a modified LT1
3) Hire a tuner to custom-tune a chip for your engine using a chassis dyno.

I believe that I did the second option when I sent out the specs on the car about 6 weeks ago. The place I got it from took every new spec of the engine and with all of that, burned the chip that now sits with the stock PROM. The sheet I had my friend / mechanic turn in, was a very thorough sheet, filled with all the new and old specs on the car, from the top of the motor to the rear end, which was a 3:45. When they pulled the Hypertech chip out and put back in the stock PROm, the car came to life in a big way. It now pulls through all the way through.

 

[Hib Halverson]

Sounds like the new cal you got is pretty close.

 

[Schrade]

Sounds like the shop already did what I was suggesting (except for burning a new chip)...

Otherwise, you'll have to use the stock LT1 numbers that the FSM gives, and go from there...