I've personally seen a 6 speed Comp T/A put down 370 rwp with the lt4 package. That was through SLP shorties and a borla exhaust.

 

That kit included Heads which may or may not have already been worked over. Perhaps they are not stock LT4 heads.... I also agree that they are talking flywheel HP

 

I have seen a stock headed LT4 Hot Cam and LTs six speed car put down 348rwhp. So add some heads to that and I can see getting some were close to that at the fly wheel.

 

I think all these "articles" and HP claims at Pace and now apparently at Summit, relate back to a dyno test that was done by More Performance. That was done at least 3 years ago, but I saw a reprint of it in Pontiac Enthusiast about 6 months ago. More got 429HP on the engine dyno. What they failed to tell people about in the magazine article was the little "extras", like a complete exhaust system, a $3,500 MoTeC engine management computer, and apparently a few other tweeks that went well beyond simply testing an "LT4 conversion kit"......

 

I pulled 320ish untuned with the LT4 heads/HOT cam/intake, stock PCM other than basic idle and small low RPM timing changes. This was also thru the A4 and ST3500, now if you take that 320 and use a 15% drive train loss, what does that come to? About 425? Is the A4 more or less than 15%? Some one else will have to come up with that but I do agree that 425 from this conversion is possible and with the stock PCM. I did not touch the PE tables so it was RICH!!!!

I later went back and tuned some and picked up 20HP from leaning the mixture out and it is still rich. and I picked up a bunch of TQ down low but this was thru a TH350/3600 stall....

Why does this 425 statement cause so much problems? It is possible and there is nothing magical about my car, as a matter of fact it is a POS when comparing other cars....

 

I plan on gettting the LT4 convershion my self. I understand that it will be on the expensive side but I dont care. I personally think that LT4 heads, intake are better then the LT1 heads and intake. I belive you can get LT4 heads to flow better then ported LT1 heads and the higher rise on the LT4 intake is just plane better then that of the LT1 intake. IMO of course.

 

i might be wrong but the LT4 engine has a different cam. Close but slightly different

 

The topic is the "LT4 conversion" kit, which includes the LT4 HOT cam.

 

OK. My whole point of starting this thread was to find out where the extra 95 HP came from. If it was rated at 330HP from the factory, a little low I agree, but it's still no 425!!!! Do the conversions head flow better? Is the intake better? I know the cam is slightly larger than the factory LT4 cam. Why does this kit claim so much power?

 

The Lt4 was rated at 330 hp from the factory. This was somewhat low so as not to eclipse the consumer interest in the new LS1 (actually a lot of the drawing board ideas for the LS1 that didn't make it into the final cut were incorporated into the LT4, but that's a different story). The LT4's actual output in a C4 Grand Sport was *really* around 350-360 hp. That leaves 65-75 fwhp to be picked up by the hotcam, translating to about 50-60 on the ground. Which is not out of the realm of reason when you consider that there are LT1 guys with a fairly stock setup putting more than 300 hp to the ground with just the hotcam and maybe cai and headers.

Oh, and the heads, intake, etc should be the exact same ones as on the stock LT4. I think the setup just greatly benefits from a slightly lumpier cam since the heads can flow a bunch more stock than unported LT1 heads.

 

rwhp?


and to think -
i went through all this trouble of building a 383 with a redical cam

 

No, not 425 rwhp , silly. In the whole post above I talk about fwhp. The LT4 conversion makes around 425 fwhp (as the Summit ad states), but probly 330-350 rwhp conservatively depending on the transmission and bolt on stuff. With a very conservative deduction of 20 percent for driveline, (425fwhp x .20 = 85fwhp. 425fwhp - 85fwhp = 340rwhp, right about where it should be).

Now your 383 Strokemonster could no doubt make 425 rwhp (and take out some LS1's while at it ).

 

Did the LT4 hot cam ever actually come in a car from the factory?

The only reason I ask is that in my class, I can update/backdate with any 4th gen fbody. I'm just looking to the mostest for the leastest if you know what I mean! If it didn't I'd have to go with the stock LT4 cam.