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Auto-Trend Repairs and Service Information Forums -> Corvette -> LT4 Vs. LT1
Post Info TOPIC: LT4 Vs. LT1
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$y$Op

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LT4 Vs. LT1
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I have done an extensive write up on our private forum for the LT1 Vs. LT4
and the LT4 VS. The GM Performance LT4 Conversion Kit.

Here are some photos to knaw on.

-- Edited by Administrator at 18:01, 2007-12-08

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$y$Op

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The diffrences between the LT4 Grand Sport and GM's LT4 Conversion Kit
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The GM LT4 Engine got its start in 1996 with the Chevrolet Corvette. The most popular LT4 "Grand Sport" Corvette was the one painted blue with a thick center comp. stripe. This engine was rated at some 340 horsepower from the factory and had a red intake manifold part #12550630 which is now No Longer Available thru GM. The badge on the intake throttle body read "Grand Sport" and the LT4 engine found in the Grand Sport Corvette had a .477 lift camshaft with bigger LT4 heads. You can see more details about the LT4 heads our other thread.

Later GM Performance rolled out with a kit that was basiclly a bunch of parts pulled from the shelf and made into what is now known as the LT4 Conversion kit. It retailed for some 2800-3200 USD and bosted even more horsepower than that of the Grand Sport LT4! The power output was rated for this conversion kit at 420 HP. The great thing about this all in one kit is that you could put it on any LT4 and get serious horsepower gains. The kit included the special "Red" LT4 intake part # 12550631, LT4 heads, GM Perfromance HOT Camshaft @ .525 lift, 1.6 Aluminum full roller rocker arms, and a complete gasket kit. Once the Grand Sport intake manifold became NLA this kit followed.

-- Edited by Administrator at 13:36, 2008-03-30

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$y$Op

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RE: LT4 Vs. LT1
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The main thing that makes the LT4 engine are the Heads, Camshaft and Roller Rockers. The manifold I would say flows similar to stock but with a diffrent port hight. I will go into more detail on the private forum.



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$y$Op

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RE: The diffrences between the LT4 Grand Sport and GM's LT4 Conversion Kit
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The part numbers for the LT4 intake manifold seem to bring much debate in many other forums. For this reason we have done some extensive research to nail down the truth about the LT4. Thanks to many customers whom have paid for us to gather this information you can now read on better inform yourself about the LT4.

Part Numbers at a glance-

LT4 Grand Sport - 12550630
LT4 Conversion   - 12550631
LT1 Stock           - 10108630



-- Edited by Administrator at 07:48, 2008-01-22

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$y$Op

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GM Performance LT4 Conversion kit PART NUMBERS
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These are the part numbers to make up the new GM Performance LT4 conversion kit. They have now dis-contenued the kit that includes the Red LT4 intake manifold, however you can still buy the kit less the intake.

DESCRIPTION: LT1 to LT4 Conversion Kit without LT4 intake manifold
This conversion kit DOES NOT include the GM LT4 intake manifold, due to the GM LT4 intake manifold as been discontinued by GM. An aftermarket LT4 intake manifold will need to be purchased from an aftermarket source for this kit to be a complete LT1 to LT4 conversion, see an aftermarket vendor for a LT4 intake manifold.
A bolt on LT4 performance upgrade for your LT1. The LT4 conversion kit includes parts needed to change the top end of the LT1 to LT4 specs. Conversion kit includes:


2 Cylinder Heads P/N 12363287

1 GM Performance Parts LT4 Hot Cam P/N 24502586

1 1.6:1 Aluminum Roller Rocker Arm kit P/N 12370839

2 Head Gaskets P/N 12551488

2 Intake Gaskets P/N 12367777

1 Front Timing Cover Gasket P/N 10128293

1 Water Pump Seal P/N 10217886

1 Front Crankshaft Seal P/N 10128316

1 Oil Pan Gasket P/N 10108676

2 Valve Cover Gaskets P/N 10108625

2 Exhaust Gaskets P/N 12552470


Also includes: 1 Distributor Seal(1995-1997 cars) P/N 12552428, and 1 Distributor Seal (1992-1994 cars) P/N 10128317, but only one of these is used depending on application.


Not included in the kit, but recommended is the "Extreme Duty LT1/LT4" timing chain kit P/N 12370835.

Also not included and required is the LT4 intake manifold, must be purchased from an aftermarket source.


These are the basic components that make up the LT4 engine and performance please note other parts may be required to properly install these parts on your non-LT4 engine.


1993-1994 ignitions are different than 1995-newer LT1's and may require changing to the newer ingnition system.

Please check with a certified installer before performing this conversion.

Additional parts may be required.


The LT4 intake manifold will need to be purchased from an aftermarket source.



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Stellar007


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I dont know that the new Edelbrock air gap manifold would flow as much as the original LT4. It seems that the portion that they hollowed out to make it an "Air Gap" would take away from the volume of air the box can store/intake. Thats just my thoughts. Anyone out there using the Edelbrock air gap? If so what do you think?

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Anonymous

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RE: LT4 Vs. LT1
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Do the LT4 heads come stock on all Corvettes or just the LT4?

What other vehicles may have the LT4 heads?

I am looking for an LT4 Conversion kit but GM performance no longer sells the intake manifold. My LT1 started pounding last week so I am going to do it right the first time! wink



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$y$Op

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LT4 heads come on the LT4 engines only. Same with the red intake.

You can still buy the LT4 conversion kit but they no longer sell the intake manifolds. It kind of makes you wonder if the heads are not far behind! I mean if they run out of intakes, they must be getting close to running out of the heads. I should stock up but the price is still WAY up there.

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$y$Op

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Also read this write up about the LT1 and LT4 intake manifolds. It sheads some more light on the subject.

http://autotrend.activeboard.com/index.spark?forumID=91042&p=3&topicID=14783164

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SELLC


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Whatever you do be careful about information you get on www.ls1tech.com we have found this forum to be very poor with regards to keeping factual information on hand. Just the other day someone there tried telling us that an LT4 intake manifold will work on LT1 heads. For the record this is NOT TRUE.



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Big Angry Hillbilly


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An LT4 conversion for the most part, is a waste of money.

You can make factory aluminum LT1 castings flow MUCH better.

The LT4 Hot cam is a DECENT cam, but driveability and the powerband SUCKS.

The valvesprings on the LT4 heads in the conversion kit are barely enough spring to maintain constant follower to camshaft contact at high RPM's.

I know a guy with a stock shortblock LT1 car, with worked LT1 alum heads and an aftermarket cam, in a 4400LB car, that runs 11.90's. This is with a JUNKYARD SHORTBLOCK and LT1 heads.

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SELLC


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I agree, the springs that come in the LT4 heads arent worth a damn. I do however dis-agree with what you are saying about the heads. Without spending a lot of time you would be hard pressed to make LT1 heads outfolw the LT4 heads. Then agian if you spent that kind of time on the LT4 heads, the LT1 heads would not hold a candle to them.

Just look at the cutaway's for both the heads. You can see they were made to allow more airflow.

I agree that more than enough power can be had from a properly built LT1, however do all that to an LT4 and you better watch out.

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Big Angry Hillbilly


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The main benefit of the LT1 over the LT4 is the powerband is drastically lowered, so you don't have to beat the piss outta the engine to make power.

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SELLC


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That sounds like moderation Hillbilly...

Are you turning a new leaf or something?

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chandler330


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 https://depositphotos.com/vector/vector-2018-12-07-sitemap-2286.xml

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SELLC


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What are these?

.xml?

Not so sure these links above are safe to click on... wish Rastus was still here, he loved clicking on this sort of thing.



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Rastus


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SELLC wrote:

What are these?

.xml?

Not so sure these links above are safe to click on... wish Rastus was still here, he loved clicking on this sort of thing.

 

LOL !

To answer the questions prior about the head comparison, there's really no straight answer, unless you have a vacuum device with instrumentation to measure flow...

The variables to flow are / will be port to valve size ratio, followed by determining at what lift of the valve, offers the best flow.

Intake manifolds for EFI are best sourced that have bell intake runners ( of equal length ) for each cylinder, whilst feeding-off a common plenum-chamber, that can have single or multiple throttle-plates.

The above set-up is a 50 / 50 blend of IR ( independent runner ) & plenum-chamber designs.

Full IR systems will have their own throttle plate per cylinder, & enhance low-end get-up-&-go dramatically, since each cylinder isn't fighting the other for close proximity to the throttle-plate in a plenum-design. And equal volumetric efficiency is experienced for each cylinder. Top-end power is enhanced too.



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