LT4 LT1 to LT4 Conversion

[92ghost]

Looking through one of the corvette magazines I noticed the LT1 to LT4 upgrade kit for around $2300 from Summit. It says "The kit will give you a proven 425+ HP" . On top of that it says all I need are computer engine management mods and a fuel rail from a 94 - 95 model.

So for about $3000 and throw in some labor cost, I have Z06 HP!!! Sounds to good to be true.

Heck, I'd think even the LT4 guys would be jumpin on this let alone all LT1 owners...
What's wrong with this picture?

List of Items:
LT4 cylinder heads with valves and springs
Red aluminum LT4 intake manifold
GM PErformance Parts' HOT cam with 1.6:1 ratio Bow Tie roller rockers
All necessary gaskets.

Wayne

 

[vader86]

It only gives 425hp if you put full headers on

You also dont really need the LT4 heads and manifold, porting your own would be cheaper and actually perform better.

 

[6 Shooter]

I'll agree with the cheaper part . . .

 

[firedawg]

What would you port the heads/manifold to?

 

[Tuna]

I bought the LT4 upgrade kit from GMPartsDirect.com and can't complain.

It comes with the LT4 heads and intake, the LT4 Hot Cam, 1.6 roller rockers and all the gaskets. I also bought the latest version of the OptiSpark and the timing cover to go with it. It was installed on my 92 with the 92 fuel rails - the 94-96 fuel rails are not needed as the 92 works just fine.

I bought a chip from FastChips.com in Tulsa, OK to make the cam work right.

With less than 500 miles on the motor after installing fresh rings and bearings, it cranked out 324+ lbs-ft of torque and 306+ RWHP - that is a big improvement over a stock LT1. Since them I've added Corsa exhaust but haven't been back to the dyno. This is with stock exhaust manifolds and cats. If I added the long tube headers to the setup, 425 at the crank wouldn't be too far off.

Having your heads and intake ported, installing the Hot Cam and 1.6 rockers will do just as well and may be cheaper - I can't say. However, I love the looks of that red intake under the hood on my reverse grand sport.

 

[92ghost]

Tuna. Did you install the kit yourself or have someone else do it. Also, was the price about the same for the parts when you purchased from GM PartsDirect compared to the 2300 I'm seeing from Summit?

 

[firedawg]

Ghost, I found the part tuna was talking about it was about $2100 Here it is

GMPartsDirect LT-1 to LT-4 Kit

 

[vader86]

Ported LT1 heads outflow stock LT4 heads by quite a fair margin.

 

[firedawg]

Ported LT1 heads outflow stock LT4 heads by quite a fair margin.

So how much should the LT1 heads be ported to achieve this?

 

[Tuna]

Tuna. Did you install the kit yourself or have someone else do it. Also, was the price about the same for the parts when you purchased from GM PartsDirect compared to the 2300 I'm seeing from Summit?

Glad you ask - no. I have a really good service department at my local Chevy dealer that loves to do this kind of work and they did it. They overhauled the lower end and installed the LT4 upgrade stuff and did it right the first time - I don't think I could have done that. They also installed a new oil pump, water pump and did the OptiSpark upgrade.

The gmpartdirect kit is $2100 as noted. One nice thing about their website is that they provide information about other componets that may add to the project. BTW, I took the parts list to my local dealers parts department and after they pulled all the prices, they told me to order them from GMPartsDirect as they could not match the price - and that was with my club discount.

One thing to add - the 92 valve covers will not work with the 1.6 rockers - they're too short. I bought GM performance catalog valve covers (black with red letters) for mine. The black valve covers from the 93-96 will work but you would have to cut the oil dripper tabs out.

Later,

 

[vader86]

So how much should the LT1 heads be ported to achieve this?

Not that much difference in LT1 and LT4 heads, but I dont have the specs on this computer.

Contact GTP, probably one of the best, for a port job.

 

[92ghost]

Tuna. You mentioned needing new (taller) valve covers. I noticed a bracket that huggs the front/top of the drivers side valve cover. There may be a gap of 1/4 inch and that is all. I don't think anything taller than 1/4 inch will fit. Did you have any problems aligning the brackets, or rather did the mechanic do anything noticeable?

 

[Tuna]

Tuna. You mentioned needing new (taller) valve covers. I noticed a bracket that huggs the front/top of the drivers side valve cover. There may be a gap of 1/4 inch and that is all. I don't think anything taller than 1/4 inch will fit. Did you have any problems aligning the brackets, or rather did the mechanic do anything noticeable?

You are correct. On the 92, the bracket that supports the A/C and alternator is different than the one used on the 93-96. I forgot to mention that since I had replaced my original covers with the black ones years ago. Part of the process was to replace that bracket with the newer one that curves up higher. The newer bracket clears the valve covers that I bought also - but just barely.

That's the bracket on the left.

 

[Tuna]

Not that much difference in LT1 and LT4 heads, but I dont have the specs on this computer.

Check out http://www.grandsportregistry.com/lt1vslt4.htm#HEADS for a nice article and pictures on the LT4 head.
Port volumn up 25cc 195 vs 170
Flow up 240CFM vs 212CFM
intake port is taller - reason for new, red intake

 

[92ghost]

Tuna,
Kudo's for the pics. The valve covers, intake and injector covers look sharp. My original intent was to just gather information but I'm really starting to think about this mod.


Vader86,
You have some good input as well going with porting the heads and intake. What's a ball park figure for this work along with new springs, valves (I,E) 1.6 RR's etc. I'm thinking about $1200 - $1500 for the works...

 

[vader86]

You have some good input as well going with porting the heads and intake. What's a ball park figure for this work along with new springs, valves (I,E) 1.6 RR's etc. I'm thinking about $1200 - $1500 for the works...

$1000-1500 is the usual price for a CNC job and reassembly. Depends on who you find to do it.

 

[92ghost]

Firedawg, Thanks for the web site. I think I'll be doing some shopping at GMPartsDirect. Definetly the cheapest around.

 

[RonS95]

I have a 95 LT1 other than the conversion kit what else would I have to change?

 

[92ghost]

From what I can gather, you wont need anything. Your 95 LT1, I think, already has the taller valve covers and the correct AC bracket. My 92 has shorter covers and shorter bracket so I would have to replace them due to the larger Roller Rocker arms that come with the kit. You already have the correct fuel rails and I think your 24lb injectors will work too. Others may have a different opinion by saying you will need to go to a higher rate injector. Maybe 28LB. Tuna mentioned adding the LT4 timing chain kit which is a more stout timing chain and gear set.

Wayne

 

[Tuna]

I have a 95 LT1 other than the conversion kit what else would I have to change?

Any LT1 car conversion to the LT4 + Hot Cam kit should consider a computer reprogram.

Your 95 already has the latest fuel rails, valve covers and OptiSpark. The conversion would be straight forward with the gmpartsdirect kit but to get maximum benefit from it, you would want to have your car dyno tuned - i.e.: computer reprogrammed.

In my old 92, I included the latest OptiSpark which required the late LT4/LT1 timing cover and the HD timing chain kit. I had already upgraded the valve covers but didn't want to cut the oil drippers off so I opted for the GM Performance catalog valve covers that did clear the new 1.6 rockers. These really look nice but they are taller and wider than the standard black covers used on the 93-96 so there were a couple of extra tweaks required for brackets to fit and clear. My choice here.

Then to get the most out of the LT4 Hot Cam, you need to upgrade the exhaust.

Initially, after the installation of the LT4 upgrade kit, I ran the car with the stock chip - for 2 days. It ran okay but didn't idle ever well. I had ordered a chip from Fast Chips but did not install it at first. After installing the new chip (OBDII computer cars will need a reprogramming done rather than a chip change), the idle was set higher and much better.

With the Fast Chips chip and LT4 upgrade installed, and only 450 miles on the rebuild, I had it dyno'ed - it cranked out 306+HP at the rear wheels and 324+ lbs-ft of torgue. This was through the stock 92 LT1 exhaust with the stock 24# injectors and stock 48MM throttle body.

Since then, I've changed to CORSA exhaust but I haven't been back to the dyno - too damn cold!.

If you're thinking of doing this upgrade or considering changing cams to some like the LT4 Hot Cam or better to your LT1, don't forget to include a computer program change or a new chip.