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I am currently in a deal to buy a 96 MT LT4 Corvette. From what I see on line, you tube and other sources of information the LT4 engine rated at 330 HP might be way under rated. For many reasons GM might have under rated the LT4 engine because "C5 LS1" coming out the next year. I have heard that dead stock LT4 engines did dyno's to rear wheels with as much as 310 to 320 HP. That would put flywheel HP to at least 360 HP. Can anyone verify this for me. Just very curious ...
I can’t verify stock numbers but with a hot cam, stainless works long tubes, and corsa exhaust mine did right at 360 to the wheels. So with a little subtraction that sounds about right.
DKPJ79, thanks for the info and reply. Your rear wheel HP figure is what I had on my stock 2002 Z06. That car pulled 355 HP to the rear wheels stock. After cam, hedders etc. it pulled 415 to the rear wheels. This is not going to stop me from buying the C4 I was just curious as it seems GM did under rate the HP on LT4.
Thanks for your response sir and have a safe and enjoyable holiday weekend.
There are many sources that say the LT4 was under rated, but I have never found anything that proves it.
My opinion is that it should have been rated at 350 hp. That is based on the '95 prototype grand sport. It was rated at 350 hp per the sign in the corvette museum.
If you look at all the changes between the LT4 and LT1 it is hard to believe all of them were only worth 30 hp like the ratings show.
I have a '96 LT4 and it is stronger than my '95 LT1. It is very close to my lightly modded LS1 C5. So I tend to think it is more than the 330 hp rating and more like 350-360 hp.
There are many sources that say the LT4 was under rated, but I have never found anything that proves it.
My opinion is that it should have been rated at 350 hp. That is based on the '95 prototype grand sport. It was rated at 350 hp per the sign in the corvette museum.
If you look at all the changes between the LT4 and LT1 it is hard to believe all of them were only worth 30 hp like the ratings show.
I have a '96 LT4 and it is stronger than my '95 LT1. It is very close to my lightly modded LS1 C5. So I tend to think it is more than the 330 hp rating and more like 350-360 hp.
If you find proof, let us know.
Good luck.
I've never been able to swallow that all of the performance tweaks that were included in the LT4 versus the LT1 could have only been good for 30 HP. And, having owned one of each didn't change my mind about that.
Maybe someday someone will do a complete tear-down to verify originality and condition of an LT4, and put it on an engine dyno to lay this long-standing question to rest once and for all.
If it did 330 and was marketed as that it for sure made 330 somewhere. I doubt it was very underrated but I'm sure it was rated under less than optimal conditions. SAE certified wasn't a thing to the best of my knowledge so whatever it was done on it was probably done to make sure it would always hit that number minimum.
Case in point I believe the ls7 gained 5 hp or so being rated on the new SAE system and I think the northstar gained or lost 10. I don't remember. But it's probably about right honestly. The numbers down the track seem similar and it's on par with LS1 cars more or less given all the different characteristics of the two engines and chassis I would say it isn't underrated by much.
I've never been able to swallow that all of the performance tweaks that were included in the LT4 versus the LT1 could have only been good for 30 HP. And, having owned one of each didn't change my mind about that.
Maybe someday someone will do a complete tear-down to verify originality and condition of an LT4, and put it on an engine dyno to lay this long-standing question to rest once and for all.
Live well,
SJW
Hi SJW, Like you and others I can't be sure about the true HP rating 330, 340, 350 ? Was just curious as I mentioned. Either way it wont stop me from buying a beautiful C4 that my friend owns. Hope we can complete the sale next week sometime. I do thank all who replied and maybe someone will chime in with proof either way.
Over the years, I have noticed the stock LT4 rwhp dyno numbers tend to be about 300. LT1 manual cars tend to be about 260rwhp, so maybe the LT4's were a little under rated by around 10hp, but not significant, and it doesn't really matter except for bragging. The HP that get to the ground is all that matters.
Dynos are really only useful for before and after, or 2 cars back to back.
The LT4 was basically a super light cam and heads engine. I'd have a hard time believing 60hp over an lt1.
If you research the engine a little further than just Horsepower? You'll find like most people, the engine was built better, and stronger, not for more horsepower, but the engine had to be warranted for 3 years 36k miles and therefore had to withstand the higher RPM band. If you think GM just popped some heads and a mild cam in the engine? you'd be wrong. Alot of components in the engine were beefed up, Look for yourself.
From: SCMR Rat Pack'r Charter Member..Great Bend KS
Years ago, a friend took his 6 months-old C5 (LS1, rated at 345hp, manual transmission, bone stock) to a local (San Diego) dyno shop for a couple of pulls. I took my LT4, also bone stock. We ran them both that morning.
His LS1 came out at 314 RWHP average. Mine came out at 311 RWHP.
If the LS1 factory rating was accurate, then the LT4 made about 340 CSHP.
Figuring 10% losses for driveline friction, this would come out pretty close.
I've heard claims that some stock LT4's made up to 380 CSHP. I doubt that factory engines vary in output more than about 3-4 horsepower, and I'm not buying anything NEAR 350 hp for the LT4, let alone 380. That's just wishful thinking.
The "4" was the awesomnest LT small block, but it was still an LT.
If you research the engine a little further than just Horsepower? You'll find like most people, the engine was built better, and stronger, not for more horsepower, but the engine had to be warranted for 3 years 36k miles and therefore had to withstand the higher RPM band. If you think GM just popped some heads and a mild cam in the engine? you'd be wrong. Alot of components in the engine were beefed up, Look for yourself.
Sure, they were built stronger. But in terms of power adding stuff... It's pretty much just light heads and cam work. They also could spin for like another 500rpm or so?
I could see 340 to 350 crank hp on the lt4. But based on all the gains made by a hot cam or having lt4 heads ported, they didn't go extreme on it. So 360 to 380 crank? No way.
One of the most overlooked and key differences between the two is the 4 has 195cc intake ports. LT1 has 170cc intake ports. So even if you upgrade an LT1 to hot cam you will still be missing that intake runner size.
When i researched the car i wanted, what drew me to the LT4 car wasn't the horsepower rating, I just thought the engine driven normally, with an occasionally high spirited run through the gears, would stand up better, simply because the car was designed that way. Plus i figured the price i paid would probably be recouped if i decided to sell it later in life. As mentioned in another thread it is a base car, but the price is what i could afford, for a second car to have fun with.
The cars been in my garage for months now, and every time i pull it out i look for any type of fluids, or drips, amazingly there aren't any. the cars sealed up amazingly well for sitting for 25 yrs. starts quick and easy, runs great, everything works, air blows cold, heat blows hot, I like it.
I am currently in a deal to buy a 96 MT LT4 Corvette. From what I see on line, you tube and other sources of information the LT4 engine rated at 330 HP might be way under rated. For many reasons GM might have under rated the LT4 engine because "C5 LS1" coming out the next year. I have heard that dead stock LT4 engines did dyno's to rear wheels with as much as 310 to 320 HP. That would put flywheel HP to at least 360 HP. Can anyone verify this for me. Just very curious ...
Generally been accepted that the LT4 was underrated from the factory because of the LS1.
Back when there were a lot of stock LT4s on the forum, about 15-20 years ago when I joined, most were putting down those 300-310rw numbers, so yes it was underrated by 10-20 HP at the crank.
The 1971 LS6 and the 1996 LT4 produced nearly identical performance figures and the LS6 net horsepower was rated at 325. So maybe the LT4 was overrated.
Somewhere around here, I have an copy of the CandD issue that tested the '96 Grand Sport. It reported a top speed of 169 and explains that it is rpm-limited. I.e. it will reach that speed at redline in fifth gear. It won't reach that speed in sixth.
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C4 1996 LT4 HP question
