supercharged87

I saw an LT4 conversion kit and was wondering if its worth it. They claim 425 horsepower out of it, but it says you would have to do computer modifications, but to what extent? Would a power programer be enough? Does anyone know anything about this kit and what else I'd need to get it running in the car? I would also think the fuel system would have to get upgraded also. Thanks in advance for any info. given.

1994TransAm

waste of time


port your heads, grab a cam and some rockers and a gasket set and you'll save 1000$

lloyd elloit heads, xe 230/236 ca,, and some crane gold race rockers

you'll be any stock lt4 car, infact they are really like 320 hp if anything not 425

HM Murdock

LT4 conversion kit is rated 425 flywheel horsepower. Hotcam, LT's, and 1.6's are generally good for about 320 rear wheel HP on their own. Add the LT4 heads, and it is higher. If you only get 320, I'd complain. You can also always sell the cam out of the kit and go with a better cam.

Of course, the reason I bought the kit is to give myself brand new heads and, for down the road, LT4 cores. Ported LT4's are generally the best LT series head, and will outflow equally ported LT1's, due to the runner design. I sold the hotcam, personally, and went with the CC306.

FacelessZ

LT4 heads can only handle a mild porting if you stick with your stock engine size...considering the raised runners the ported LT4 heads will run better on bigger engines...

btw I know a guy selling a BRAND NEW LT4 head for $250...the conversion is not worth the $$$ for what you get...

JMHO

HM Murdock

I've seen LT4 castings get over 300... Plus, I am not a stock engine size. 361CI isn't stock...

FacelessZ

Then more power to ya!

The stock LT4 flows MUCH better than a stock LT1 head. Stock LT1's flow about 215/150 and have about a 170 cc intake runner. After porting, they will be flow about 265 cfm with a 195 cc intake port or 275 cfm with a 205 cc intake runner. A 350 cubic inch motor turning 6200 would be fine with a 195 cc port. Anything larger and the car will not accelerate as well and will make less HP. The 205 cc intake port is best for 6800 RPM 350's that do not need as much low end torque or ANY 383 cubic inch motor. These extra cubic inches will eat up runner volume and allow a larger runner volume to be used.

To take advantage of the LT4 castings you need to open them up to a 210 cc port or better and this is too large for most build ups. You can get 290 cfm (or more) from them but the LARGE runner volume makes them suited for a LARGE motor. So I suppose this will work great in your case...

supercharged87

Thanks for the responses. I just seen it in Summit and thought it looked pretty cool. I probably won't get it, I have stock bottom end and I plan on keeping that way. But out of curiosity HM Murdock, what exactly did you have to do the computer to run this kit? Also I see you have SVO 30lb injectors, did you have to recalibrate the mass air and computer for them or is that just a Ford thing? Also what is the stock size injector on the LT1?

HM Murdock

I'm aware of that. I am not sticking with this stroke, I am going for a 401ci engine, once built up. 3.875 stroke and 4.060 bore.

BTW, are you saying that a ported LT4 can't make more power on a stock or moslty stock bore LT1? I have seen 2 400+rwhp 355's with ported LT4's and a 230/236 and 415 with a CC306. But hey, that's just a couple friends of mine... Granted, all of them have built fuel systems, as well, injectors, walbro pump, etc.

Supercharged, it was able to run under the stock programming, but got about 4 miles per gallon, literally. All I have had to do to nail a 12.7:1 A/F is some tuning to the fueling tables and timing courtesy of TunerCAT, and more than some help from Brian @ pcmforless.

HM Murdock

Oh, and stock injector size is 24 lbs/hr.

supercharged87

Thanks, I was really wondering because I have a set of 24lb SVO injectors just sitting in my garage with only about 250 miles on them, I thought it might be an improvement, but I guess not.