I was flipping through the summit racing catalogue the other night and i saw in the 'new products' section the LT1 to LT4 converson kit.....its for $2,289.00 and it says 'this kit will give you a proven 425+ HP', but i read on an LT4 website the other day that the LT4 came with like 330HP.....Just wanted to find out what sorta power i'd be getting. Also, how would this effect my gas milage? I'd love to do this cause it would get me right about to the power i'm looking for, isnt TOO expensive, and i havnt seen many LT4 thirdgens :-P
Just wanted to get opinions on this.....

 

<-- LT4 Thirdgen

I didn't buy the kit, I got the Hotcam first then got the heads and intake at a later date. I've heard 425 is not unreasonable for the swap but it takes a real good tune to get to that.

The difference between the factory LT4's and the conversion is the Hotcam. Big difference between it and the factory cam. And let me put it in perspective:

Heads: $1299
Intake: $220
Hotcam:$175
1.6 RR's: $190 (?)
Heavy duty timing set: $80
Good dyno tune: $150-300

There's your LT4. Screw that package from Summit. You can usually find stuff for cheaper too if you look around. The heads/intake/cam prices listed are fromScoggin-Dickey. You can also get all of the parts from your GM dealership, they can order GM Performance Parts just as easily as Scoggin-Dickey. The heads I was actually able to get a little cheaper from the dealership.

Let me know if you've got any questions.

 

Well I have never done that swap before, so I honestly cannot comment on the power output. However, 2300 of your money is a lot for just heads, intake, and cam. Plus you have to get your computer recalibrated once you change everything (added expense.....at the bottom of that add btw) You could nab the heads and intake for next to nothing used....and get the LT4 cam and 1.6 roller rockers just about anywhere....it'd be cheaper to do it that way instead of buying the whole kit. I think the aluminum Fast Burn heads actually flow better than the LT4 heads
and they are cheaper....might want to think of those instead. I don't think the conversion puts out that much power as advertised, not with just bolting on those parts anyways. Maybe with a **** load of tuning and some other stuff (i.e. exhaust, pulleys, etc.) it could.....but like I said...dunno for sure. I would love to know if someone has used this and what power they are seeing as well.
LC

 

okay, so the kit isnt the best way to go. What about gas mileage?
Are there better, less expensive ways to get more power than that? I'd like to know all my options. Thanks in advance

 

The kit may not be the best way to go because you can find better deals out there, but the LT4 conversion parts make great power, I've been real impressed with how well its performed. But beware, once you start modding for power, it doesn't stop, you just want to keep going farther and farther .

Gas mileage is great even with it running pretty rich. I'm getting about 18 around town, usually 25 on the highway.

Oh yeah, and Fast Burn heads won't work on the LT1.


An option I'm considering is getting my LT1 heads fully ported, GM847 cam, 58 mm TB, and a good dyno tune, should definitely put me over 400 hp at the wheels.

I'll be able to post numbers this crhistmas because I will be getting my car dyno'd and tuned. Then once and for all we'll be able to see just how much the LT4 conversion puts out. I guarantee its at least 350 RWHP. I've run with cars that have had similar or higher power levels and run predictably compared to them.

 

Okay, well that seems pretty cool.

How much would a Vortech supercharger add on top of that? Not for like all at once, but eventually i'd like to add a supercharger?
What sorta quarter mile times/speeds would i be looking at?

 

well the problem is that there is no kit made for this swap. You'd have to piece together and basically combine an L98 and LT1 blower package. not sure how that would work.

As far as 1/4 times, right now I'm running a best of 13.1@109.5 with a 2.0 60'. The Hotcam is definitely a top end cam, it pulls like no other in the second half of the 1/4, doesn't seem to have the lowend like I would have expected. The main problem with mine is I think its running pretty freakin rich with this mail order tune, once I get it dyno tuned and get it all running right, I've got the trap speeds for mid 12's, its just a matter of getting my launch down.

The supercharger would easily add 100 hp over the conversion kit, but you would want to switch cams, the Hotcam is not a real blower friendly cam. Depending on what amount of boost you ran and all that stuff, you could get a lot of power from a 'charger.


*edit* Keep in mind, I'm also running pretty small headers through a stock GM rear section exhaust. If I got some 1 3/4" headers and a full 3" exhaust I could probably pick up another 10-20 hp. that would definitely drop me into the 12's, just a matter of time and money.