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5.7 lt1 vs 5.7 lt4

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Old 01-10-2018, 02:28 PM   #1  
LT1 Man
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Default 5.7 lt1 vs 5.7 lt4

I know the C4 Corvette's LT-4 Engine is a Hopped-up LT-1 with 30 more Horsepower, but are there any other differences?
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Old 01-10-2018, 03:03 PM   #2  
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In 96 LT1 only available with automatic and LT4 only available with 6-speed.

I believe in the engine, the intake, cam and possibly heads were changed to get the 30 more horsepower.
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Old 01-10-2018, 03:44 PM   #3  
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In addition to more power, the higher rev limit of the LT4 allows it to take advantage of each gear through a broader rpm range over the LT1.
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Old 01-10-2018, 04:40 PM   #4  
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Originally Posted by LT1 Man View Post
I know the C4 Corvette's LT-4 Engine is a Hopped-up LT-1 with 30 more Horsepower, but are there any other differences?
In reality the LT4 made a LOT more than 30 HP. If you ever drive a LT1 and an LT4 back to back you can absolutely feel the difference in just regular driving and spirited driving.... they are night and day. What GM ended up doing is 'protecting' the millions they invested into the LS engine that was to debut the next year because they only invested something like 100 grand into the LT4 updates and it produced as much, if not more, power.

As for what was changed.... most everything.
Heads, head gaskets, rockers, springs, cam, crankshaft, knock sensor, pistons, rings, injectors, valves, intake manifold, timing chain, front torsional damper, rear crank seal, main bearing caps, cam sprocket, crank sprocket.... I probably missed some items. Bottom line is anyone who says they upgraded their LT1 to an LT4 has no idea what they are talking about because it would require a full rebuild bottom up.
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Old 01-10-2018, 04:41 PM   #5  
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Old 01-10-2018, 05:20 PM   #6  
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Quote:
Originally Posted by bjankuski View Post
Good information there that details the differences.

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Originally Posted by vetteLT193 View Post
In reality the LT4 made a LOT more than 30 HP. If you ever drive a LT1 and an LT4 back to back you can absolutely feel the difference in just regular driving and spirited driving.... they are night and day. What GM ended up doing is 'protecting' the millions they invested into the LS engine that was to debut the next year because they only invested something like 100 grand into the LT4 updates and it produced as much, if not more, power.

As for what was changed.... most everything.
Heads, head gaskets, rockers, springs, cam, crankshaft, knock sensor, pistons, rings, injectors, valves, intake manifold, timing chain, front torsional damper, rear crank seal, main bearing caps, cam sprocket, crank sprocket.... I probably missed some items. Bottom line is anyone who says they upgraded their LT1 to an LT4 has no idea what they are talking about because it would require a full rebuild bottom up.


I have a '95 LT1 6M and a '96 LT4 6M and I do drive them back to back. There is a difference even at normal rpms.

When you look at all the changes, it is hard to think they only made 30hp more. The '95 LT4 Grand Sport prototype at the corvette museum says it has 350 hp. I suspect that may be the real number.
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Old 01-10-2018, 06:41 PM   #7  
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on of the best parts (or lack thereof) of an LT4, is that LT4's have no EGR; the LT4 camshaft has sufficient valve overlap to make an EGR system unnecessary. Oh, that and the fact that every LT1 wants to grow up and be an LT4

Last edited by mtwoolford; 01-10-2018 at 06:42 PM.
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Old 01-10-2018, 06:47 PM   #8  
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I agree. I had a 96 Collecttor Edition 6 speed with the LT4. It was an amazing difference over the LT1. That was one of the best Corvettes I’ve owned.
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Old 01-10-2018, 06:49 PM   #9  
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Quote:
Originally Posted by mtwoolford View Post
on of the best parts (or lack thereof) of an LT4, is that LT4's have no EGR; the LT4 camshaft has sufficient valve overlap to make an EGR system unnecessary. Oh, that and the fact that every LT1 wants to grow up and be an LT4
That's why they came out with the Hot Cam Kit

(Yes, I understand that there is more to the LT4 than just a cam and 1.6 roller rockers)
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Old 01-10-2018, 09:32 PM   #10  
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Quote:
Originally Posted by vetteLT193 View Post
In reality the LT4 made a LOT more than 30 HP. If you ever drive a LT1 and an LT4 back to back you can absolutely feel the difference in just regular driving and spirited driving.... they are night and day. What GM ended up doing is 'protecting' the millions they invested into the LS engine that was to debut the next year because they only invested something like 100 grand into the LT4 updates and it produced as much, if not more, power.

As for what was changed.... most everything.
Heads, head gaskets, rockers, springs, cam, crankshaft, knock sensor, pistons, rings, injectors, valves, intake manifold, timing chain, front torsional damper, rear crank seal, main bearing caps, cam sprocket, crank sprocket.... I probably missed some items. Bottom line is anyone who says they upgraded their LT1 to an LT4 has no idea what they are talking about because it would require a full rebuild bottom up.
I think itís really about 30hp...what youíre feeling is power /torqueunder the curve. Itís significant....peak hp only tells a small story. The legends of 380hp lt4s are crap.
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Old 01-11-2018, 02:03 PM   #11  
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Quote:
Originally Posted by QCVette View Post
Good information there that details the differences.





I have a '95 LT1 6M and a '96 LT4 6M and I do drive them back to back. There is a difference even at normal rpms.

When you look at all the changes, it is hard to think they only made 30hp more. The '95 LT4 Grand Sport prototype at the corvette museum says it has 350 hp. I suspect that may be the real number.

Should I buy an LT-1 or an LT-4? The 300 HP LT-1 is enough for me, but I might want the extra horsepower. I doubt that might happen, though because the LT-4 is a very rare car.
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Old 01-11-2018, 02:05 PM   #12  
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[QUOTE=LT1 Man;1596356982]Should I buy an LT-1 or an LT-4? The 300 HP LT-1 is enough for me, but I might want the extra horsepower. I doubt that might happen, though because the LT-4 is a very rare car.

Oh yeah, And that's a really nice Admiral Blue C4 Vette you got there!
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Old 01-11-2018, 02:27 PM   #13  
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Quote:
Originally Posted by SurfnSun View Post
I think itís really about 30hp...what youíre feeling is power /torqueunder the curve. Itís significant....peak hp only tells a small story. The legends of 380hp lt4s are crap.
Most made around 350 HP. The upper end mostly stock was 380 and I have never seen or heard of one dyno at 330. I think the low water mark was in the mid 340's.

Back in the day there was a website that had all the LT4 dyno runs they could scrape up with all mods done or no mods at all. If I remember right it was on the collector edition registry site which is long gone now but had some info on it that was awesome.
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Old 01-11-2018, 02:30 PM   #14  
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[QUOTE=LT1 Man;1596356998]
Quote:
Originally Posted by LT1 Man View Post
Should I buy an LT-1 or an LT-4? The 300 HP LT-1 is enough for me, but I might want the extra horsepower. I doubt that might happen, though because the LT-4 is a very rare car.

Oh yeah, And that's a really nice Admiral Blue C4 Vette you got there!
If you donít HAVE to have an LT4, buy based on condition. If you want an LT4 your options may be more limited but nice ones are out there too. Generally with C4s newer is better and condition may matter more than miles.
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Old 01-11-2018, 03:33 PM   #15  
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Its been generally accepted here for years that the LT4 had 350 crank HP, based on a lot of dyno results of stock LT4 cars, and was rated lower because the LS1 was about to come out with less than that.
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Old 01-11-2018, 03:46 PM   #16  
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Quote:
Originally Posted by vetteLT193 View Post
Most made around 350 HP. The upper end mostly stock was 380 and I have never seen or heard of one dyno at 330. I think the low water mark was in the mid 340's.

Back in the day there was a website that had all the LT4 dyno runs they could scrape up with all mods done or no mods at all. If I remember right it was on the collector edition registry site which is long gone now but had some info on it that was awesome.
There were ZERO 380hp LT4s...I can promise you that. Its laughable to think GM would under rate a motor by 50hp. Ive heard the rumors and even if someone showed be a dyno, Id scream faulty operator. Ive seen enough dyno scams to know it happens.

I had an LT4 for almost 5 year. It basically ran with most early LS1 C5s to 100, the later LS1s pulled me...it was a win some lose some scenario. Was there maybe 10hp on the rating table? yes...more than that? Pipe dream.
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Old 01-11-2018, 03:50 PM   #17  
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Quote:
Originally Posted by vader86 View Post
Its been generally accepted here for years that the LT4 had 350 crank HP, based on a lot of dyno results of stock LT4 cars, and was rated lower because the LS1 was about to come out with less than that.
People around here also ascribe crazy drivetrain loss percentages to boost the crank number.

Last edited by SurfnSun; 01-11-2018 at 03:52 PM.
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Old 01-11-2018, 04:42 PM   #18  
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EVERY LT4 i watched dyno back in the day was 290’s-300’s. I seen 1 ringer do 310.
If you strapped them down to an engine to SAE specs they would all be 340-350 i promise you.
LOL there was NEVER a 380 HP 96 LT4 ‘stock’.
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Old 01-11-2018, 04:44 PM   #19  
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What do LT4's typically trap?
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Old 01-11-2018, 07:48 PM   #20  
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What do LT4's typically trap?
Worth a grain of salt, I remember these times from some old mags:

1990 ZR-1 :110 mph
1993 ZR-1 : 111 mph
1992 LT1:102 mph
1996 LT4:105 mph
LS1 C5:109 mph
LS1 Camaro SS: 107 mph
2003 C5 Z06: 117 mph


From these times, it runs right in line with SurfnSun saying at the 100 mph mark, the LT4 fell behind the LS1. I agree with SurfnSun that the LT4s were underrated but the real output at the crank couldn't have been more than 350. For the tricks they folded into it and all the little details, that sounds about right. Only dyno I saw of one shows 298 hp at the rear wheels, which is great when considering that's just about what an LT1 makes at the crank. That C5 Z06 time was a stocker from "Corvette" magazine when they put it up against a 911 Turbo with 500+ horses. Turbo dusted it in the quarter but the stock Z06 time always stuck with me as amazing for it was for the time.

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