LT4 LT1->LT4 conversion=425+hp?!?

[kevin-design]

I only just bought my vette and now I'm pipedreaming about upgrades.... I had been eyeing some supercharging setups until I came across a conversion kit at summit racing:
http://store.summitracing.com/partdetail.asp?part=NAL-GMP3287-1

It claims that with the kit installed, you can make over 425hp. That's pretty impressive to me... just about what I could expect from supercharging. Then if I went totally insane later on, I could super charge the 'LT4'. I'm a little skeptical about the whole deal and would be interested to hear some opinions. Also, if the heads and intake they provide are the stock LT4 components, then I might be better off snagging a set off ebay or elsewhere online and then just adding the cam/rockers later. I see this move shaving as much as $1k of the cost of the kit.

I guess I would need to get a custom chip for this new setup, I'm surprised they don't list a recommendation as it seems mighty important to have your computer optimized for this specific setup.

Are heads/intake the only real difference between LT1's and LT4's?

Thanks for any info!
-Kevin

 

[TerryD]

I've heard some rumors about crank failures after the head/cam swap. I know that cranks in LT 4's are forged vs cast so be aware.
Terry

 

[UB2 SLOW]

I have the kit and there are a couple of things to consider. The kit does not come complete. Your computer will have to have some custom programming. The kit said you needed a 58mm TB, but that is too big, go with a 52mm. You will have to change your crank just just like Terry said. You will also have to go with the extreme duty timing chain, due to the higher RPMs that the LT4 uses. You should change your Opti spark and water pump. The kit does not come with 8mm wires, but that is a good thing to swap also. The compression will be higher, which is bad for superchargers. Plus you have all the odds and ends. When you are done it will cost you a couple grand more than what the kit cost. The numbers are pretty damn good though. I have a 96 auto and I needed to upgrade the tranny when I did mine. My numbers where 255rwp and 260rwtq with a 1/4 mile of 13.3 @101 stock. After my numbers are 340rwhp and 320rwtq with a 1/4 mile of 12.5@111. I was spininng in first gear with the 12.5.

 

[kevin-design]

>>The numbers are pretty damn good though.

They ARE good, but they're not a 125+ increase as advertised (my LT1 is rated@ 300hp) at least not at the wheels. Sounds to me like its a bit more of a project than I'd anticipated- but still woth considering. I still have the same question about whether it is stock LT4 parts that they are selling with the kit. If so, I could get those parts a lot cheaper elsewhere and then just buy the cam and rockers and have an identical kit.

Where did you get your chip reprogrammed? Does it need to be programmed custom per engine, or is there a chip program that is appropriate to this specific kit? Changing the crank will be a pretty big job/expense as well. Would I need to do that on any power upgrade of this level? Lucky for me, I am upgrading the clutch this week as the originall finally burned out. i expect that my 6 speed will handle the change. Anyway, thanks for the info- keep it coming!
-Kevin

 

[vader86]

No point in paying that much money for a conversion, and it wont give 425hp.

Id do a LT4 Hotcam or cc306, have the stock heads ported and matched to the manifold, add some headers and you should be at the 375rwhp range or better (better with the 306 that is)

you dont need a new crank, youve got to work hard to actually break a crank

what you would need is different springs than the ones which come with the standard LT4 hotcam kit, because they arent stout enough (lt1 uses different valves than lt4), but the 1.6rr would be good.