Hi

I am new to corvettes and new to lt1 and other engines. I am wondering how big of a cam can a stock lt1 handle, I haven't pulled the engine out and don't know what differs from a 350 chevy to an lt1. I would like to upgrade cam to biggest I can respectively to still be able to get it to run well, I am wanting to upgrade cam, fuel injectors, possibly put a bottle on it and if need be buy new heads however I hope to do most of it still fairly stock yet retain about 500-600 hp at the crank. I do not want to modify the car to be a drag car just a weekend toy with a little more power when I want to play. My vette is a 92 lt1 completely stock. Any help is very much appreciated.

Thanks,
Justin

 

Welcome to the C4 world !

As for how big a cam you can run - the answer is "it depends". Your 1992 LT1 uses a "speed density" EFI system - meaning there is no Mass Air Flow sensor, and the computer figures out how much fuel to inject based purely on the tables stored in the PCM (Powertrain Control Module). You can modify the tables in the PCM, but you don't do it like newer models where you can program through the OBDII port. On a 1992 - you have to open up the computer, physically remove the PROM, wipe out the old programming (typically by exposing the PROM to a strong UV light), and reprogram it with a PROM burner. Without the ability to reprogram the PCM - you are limited to a more or less stock cam.

You can check out places like PCMforless, they can do the reprogram - but you need to know what to tell them to do - so it's typically a matter of telling them what you've modified, and they will take a guess at what you need - then you need to datalog, and see where you are with that tune - and then figure out what you need to do to go further. Not exactly a "real time" process.

There are people running cams with 236 degrees duration in LT1 based motors - but even with a decent tune - it's not going to idle below 1,000 RPM, and it's not going to have much bottom end torque.

I will also say that the 1992's came with pretty small injectors - even with minor mods - you get to the point where the duty cycle is over 85% very easily - and that's the upper limit for most injectors - so plan on going to bigger injectors - which (you guessed it) will require a PCM reprogram - the good news is that if it's just a bigger injector being done - they people who reprogram the PCM can do that very accurately (injector size is one of the variables in the base map).

Since you're very new to the LT1 world - one MAJOR piece of advise. NEVER NEVER EVER wash the engine. The LT1 uses an Optispark distributor that is mounted behind the water pump. Water and optisparks don't get along well, and if they get wet - they frequently die, and they are not fun or cheap to replace. Do a search on "optispark" on this forum and you will see many many issues with the optispark distributor.

The LT1 is considered a Gen II Small Block Chevy. It uses something called reverse flow cooling that keeps the cylinder heads cooler, thus allowing higher compression with less detonation risk. The Gen II blocks do not interchange with Gen 1 blocks and neither do the heads (at least without a lot of machine work). The LT1 heads flow quite well for a factory head, which allows the LT1 to make 300 HP , and 300 ft lb of torque from about 1,800 RPM to about 5,800 RPM. In the day - it was definitely a state-of-the-art engine. You can find some power by going with long tube headers - much more than that and you're going to be running into the need to change a lot of components to get more power. Once the exhaust flows decently - you don't have any more single bottlenecks that hurt performance.

 

Your post is confusing you state your "new to lt1 and other engines." I don't think building a engine is in the works for you just yet.

If your goals are 500-600HP at the crank. You NEED to do a full build. 383 or 396. Forged rods, pistons, possibly crank. Reworked factory or aftermarket heads, injectors, cam, etc, etc...Bring money like at least 4K or more.

IMHO, if you plan on playing with that much power, you need to think about how to stop the car and make the driveline take the power so it is reliable. I would start there first and leave the engine build to last. Auto or manual, you have a TON of weak points at those power levels.

If your serious I suggest you buy and read these two books. Do a quick amazon search for these titles.

How to Rebuild Small-Block Chevy Lt1/Lt4 Engines

How to Build Max Performance Chevy LT1/LT4 Engines

Speed, Reliability, Cheap-Pick Two

Your not going to build 500-600HP and keep it "fairly" stock. You can with Nitrous. You'll get about 5 hits and turn the pistons sideways in the block however....

 

you do not need to rebuild a perfectly fine working bottom end to forged components.

im running 520 rwhp, supercharged on a stock bottom end with no problems on a 93 lt1

heck its probably making more power than that.

one of the things to remember is that the corvette is a 'light' car. its not like its a truck pulling a trailer up a hill at wot. the durability demands of the crank and stuff arent in the same league.

you can get around the chip issue by plugging in a moates ostrich into the chip socket. the other end of the moates has a usb cable attachment you can hook to laptop and use tunerpro or tunercat to tune the car.

though i recommend getting in touch with alvin@pcmforless for a base tune and learning to modify it yourself from there.

you will need to do some datalogging (must buy a cable and log thru aldl cable) and datamaster software which is the best.

also helps to have a wideband o2 sensor. you can data reference its signal using the analog 0 to 5v in place of the a/c pressure sensor and convert it to afr so its referenced alongside everything else (rpm, map, spark advance, etc)

 

All the guys have made valid points. Now you can sift through the info and decide what you think is right. Now it's my turn. There's a fairly big difference between 500 and 600 hp N/A. Dizwiz may be making 520 rwhp but that is probably at 5500 rpm and I don't know how he uses his car. How fast do you need to spin a 350 to make 600hp N/A???? I have seen it done, but "fairly stock" is out the window in my opinion.. If the bottom end held together, you still need, cylinder heads, fuel injectors, fuel pump, exhaust, cam, lifters, and tuning. It's not fairly stock anymore. Have fun and good luck!

 

I must rephrase that first title. I'm new to corvette engines not engines in general, however I have not done much research on what exactly an lt1 is vs a chevy sb 350 so I figured I'd ask the experts"you guys" thanks a lot for all the info I'm already loving the car only had her for 3 weeks and my intentions are to paint it give it some power and weekend drive her. Actually truth be told I never even looked at owning a corvette and my brother talked me into test driving this one, one test drive for 15 minutes and I bought the car on the spot, lol It's like no other feeling. The moates ostrich is pretty fascinating so I'm gonna look into what I want to do with the build. I'll stay in touch and once again thankyou very much for your help

 

Yeah, no disrespect Dizwiz but this is likely true.

The stock connecting rods will NOT handle high RPMS much over 6K and the HP levels your talking about. I might buy the stock crank working and MAYBE the pistons but the rods NO F-en way. Unless you baby the car.

Your motor would NOT last in my use and how I drive. Auto-x/track use and lots of it. Sustained RPM's and cornering. My engine is stock because Cheap and Reliable.

 

The LT1 and 350 SB are very similar. Bottom end is interchangeable with the SB 350 other than the block. Heads and block are unique because of reverse flow cooling. Heads are similar design to the Vortec heads. Intake on a LT1 is good to about 500hp.

Basically the 2nd Gen LT1 is a enhanced 350 SB.

 

With a lot of power, the LT1s rod bolts will be the first to go. Many F-body guys swap the stockers for ARP and have the rods resized. Throw in new bearings and rings and they are good to go. Forged doesn't come into play unless boost is involved.

Give this guy a call: http://elliottsportworks.com/

He just ported my AFR's and did a knockout job. Many LT1 guys use him and come back with great #s. Depending on your set-up, you can be running mid 11s on the stock bottom end with the LE2.