LT4 Convesion ... ??

[95z28]

i was reading about this in school today ... just wondering if any one has done it or knows of some one who has. just wondering what the end results were and things like that cuz it didnt realy specify.

[TSS23]

I was thinking of doing it to my TA but i don't know if it works out good i found heads and a throttle body etc to do it.

[Injuneer]

GM Performance Parts sells the "LT4 Conversion kit".... and you can get it through Summit or any of the discount GM parts dealers. Cost is about $2,200-2,400. The package includes complete LT4 heads with larger sodium filled valves, and intake (about 15% flow improvement, and a nice red powder coat on the intake), the LT4 HOT cam with GM's version of the Crane Gold 1.6 roller rockers, and a bunch of gaskets and other parts.

Pace PArts LT4 Conversion Kit listing

GMPP claims this conversion is good for 425 flywheelHP. That is a bit misleading, since the dyno test that produced those results, run by MORE Performance back in the '90's used a number of upgraded parts that are not included in the "kit".... the most significant of which was a $3,000+ aftermarket engine management computer (and they conveniently forgot to mention that fact).

For the 425HP level, you also need:
-long tube headers
-52mm throttle body
-28# injectors (marginal)
-aftermarket tuning.

Whether the "kit" is a good deal is open to debate..... maybe 1/2 the people feel you get all the parts you need in a nice neat package, components that are proven to work together. The other 1/2 figure you could take your stock LT1 heads, get them ported, and pick a cam equal to, or a little more aggressive than the HOT cam, and end up with a little more power for a little less $$$$.

I like the idea of the LT4 heads. Although they are only a 15% flow improvement over the LT1 heads, the LT4 heads respond VERY well to aftermarket porting and polishing, with flow numbers approaching the 300CFM level.

I've used the LT4 heads/intake as the basis for my stroker, and it makes a nice 500HP package. And the red intake looks good....

[N20LT4Bird]

I've got the conversion and figure im making around the 400 HP mark w/o spray. But, like engineer said, you've got to do some more than just bolt on a set of heads and an intake.

[fastTa]

Like mentioned above, some people might feel that you could port your stock LT1 heads & intake, and use a more aggresive cam, but the LT4 heads/intake combination can be ultimately made to out perform the LT1 combination.

[crazilyconfused]

Gee......I'm wondering, if tuning, long tubes and a 52mm TB are good to make the LT4 setup produce what it's supposed to, then i'm starting to wonder what mine is gonna produce. I'm building a 383 stroker LT1 4bolt main, using the lt4 hotcam setup, but with 11:1 compression, 40lb injectors, lt4 intake/heads port matched to the arizona s&m monoblade TB with 1350cfm. Anyone wanna speculate?

[fastTa]

Originally posted by crazilyconfused
Gee......I'm wondering, if tuning, long tubes and a 52mm TB are good to make the LT4 setup produce what it's supposed to, then i'm starting to wonder what mine is gonna produce. I'm building a 383 stroker LT1 4bolt main, using the lt4 hotcam setup, but with 11:1 compression, 40lb injectors, lt4 intake/heads port matched to the arizona s&m monoblade TB with 1350cfm. Anyone wanna speculate?

Speculate is about all we could do. There are too many variables such as cam, extent & type of porting, tuning, head flow #'s, etc. that come into play. Give us some specifics and we will make an educated guess.

I was going to use the monoblade myself but heard many stories of idle and tuning problems with it. Let us know how it works out.

Will this motor be n/a?

[Injuneer]

Originally posted by crazilyconfused
Gee......I'm wondering, if tuning, long tubes and a 52mm TB are good to make the LT4 setup produce what it's supposed to, then i'm starting to wonder what mine is gonna produce. I'm building a 383 stroker LT1 4bolt main, using the lt4 hotcam setup, but with 11:1 compression, 40lb injectors, lt4 intake/heads port matched to the arizona s&m monoblade TB with 1350cfm. Anyone wanna speculate?

I think you may have a mismatch on parts......

The LT4 HOTcam is going to "disappear" in that 383. Way too small. I have a very mild 230/242 114LSA cam, and its..... well, "very mild". A stroker needs a bigger cam.

I would also question the need for the Monoblade. Unless your heads have huge flow numbers, and you are using a truely wild cam, you aren't going to see that kind of air flow.... well, actually you wouldn't ever see that kind of air flow on a 383. When doing the dyno tuning on my setup, we found that the engine reached peak airflow at only 77% blade opening on the 58mm TB. Opening the blades further did not increase air flow. In effect, the air needs of my engine could have been easilly met by a 52mm TB. A friend of mine was running 1,125flywheelHP on a 383 LT1 with Vortech S/C at about 20# boost. He used a 58mm BBK.

I don't think you will see big HP numbers with that kind of mismatch. If you think about it, if all you are doing on the heads/intake is port matching, and you are using the HOTcam, the only HP gain you will see would probably be proportional to the small increase in dsiplacement. The 10% extra displacement might gain you 10% more HP, assuming the "port match" picks up 10% more airflow to support the displacement increase. 425 x 1.1 = about 470HP.

[crazilyconfused]

Yeah my motor will be n/a, i think that if you match increased air flow to more fuel, and use a high octane with higher compression it will in turn increase the power produced, but i may be wrong. The more i think about the cam though, the more i think you are right, it may be to small.

[Injuneer]

The engine can only use as much air as it can flow. Just putting a 1,350 CFM TB on an otherwise mild engine will not increase air flow in any way. You need a complete "air supply machine".... and that would include a cold air intake of adequate diameter, a good MAF, a larger TB, very well ported heads and intake... not just "port matched". And, no matter how well the heads/intake flow, the air will not flow into the engine unless there is enough lift and duration on the cam. For a healthy 383, you need heads that flow well to at least 0.600" lift on the valves, a cam that will provide at least 0.550" lift, and maybe more like 0.600" lift. And the 218/228 0.525/0.525 of the HOTcam isn't enough.

A 383ci engine, turning 7,000rpm, and reaching 100% volumetric efficiency (not likely) will pull 775 CFM air flow. Restrict any part of the intake track, and volumetric efficiency drops.... you might only see 90%.

Same goes with the fuel side.... just putting 40#/HR injectors on an engine doesn't mean it makes more power. The fuel can only be added at a rate commensurate with the air flow. 40# injectors would support 600HP, but you need the air flow before you add the fuel.

[fastTa]

Originally posted by crazilyconfused
Yeah my motor will be n/a, i think that if you match increased air flow to more fuel, and use a high octane with higher compression it will in turn increase the power produced, but i may be wrong. The more i think about the cam though, the more i think you are right, it may be to small.

crazily confused I am not sure of your goals for this motor or how it will be used (street or dedicated drag motor) but just to further Injuneer's point we had a 233/239 - .569/.577 cam with stage 3 ported LT4 heads/intake on 383 cubes with only a 52mm TB that put 447hp to the tire. Given the fact that it was dynoed with a 4L60E and stock 10 bolt that is approx 535 flywheel hp.

So until you get pretty serious, a 52mm TB flowing at approx 770 - 790 cfm should satisfy your needs.