Langadorf

I finally got the Vette out to the dyno (Speedworks in Lewisville, TX).
Pulled a best of 353 RWHP and 381 FT-LBS. While I think this is good,
I was hoping for closer to 400 RWHP with my setup. My setup is as follows:

383 LT1 (new style) w/ 11.7:1 compression
750 Holley DP
LT1 dual-plane intake
LT1 heads flowing 270i/200e w/ 2.2/1.6 valves
CC306 cam (230i/244e on a 112 LSA w/ lift of .544/.576)
hooker headers w/ no cats and dual flowmasters

I was able to get the timing up to 31 degrees without any detonation and the AFR was at 12.5 for the entire pull.

Do you think my dual-plane intake is the bottleneck? On all 3 pulls
the power died off at 5700 RPM. If this is it, I'll probably get a
Victor Jr. converted for an LT1 and see how it does.

Could there be anything else hindering me? I was planning on running
race gas and adding a couple more degrees of timing, but the guys at
the shop convinced me I wouldn't see more than a 5-10 HP increase.
Do you agree?

Thanks for any ideas.

Jvette73

When you say the power died off at 5700rpm do you mean that was the rpm for the peak HP reading? Or do you mean that the engine would not rev above 5700rpm?

Langadorf

5700 RPM was the peak HP RPM. After that the HP curve died off quickly.

Jvette73

Yur dyno #'s are not bad i think. Heres a question for you, was the camshaft degreed when it was installed. If so what was the final position? im not sure of the possible limiting factor of your particular intake manifold. But position of the cam in relation to the crank can have and effect on peak HP rpm. Retarding the cam will raise the rpm at which peak HP is produced. with a setup like yours it may give a higher peak reading but it doesnt nessisarily mean it will improve the overall performance of the car. At what rpm did you expect to reach Peak HP and what is yur redline?

427Hotrod

It makes pretty decent power, but like you. I hate it when they nose over too fast. It's much more fun if they hang on for awhile.

I assume you have at least 2.5" pipes under it? They will carry you well past the 425 rwhp range usually. The Flowmasters shouldn't be hurting on this combo either.

Are the valvesprings in good shape and the right ones for the cam?

What size headers? I would seriously be considering 1 3/4" ones for a 383 deal.

750 cfm carb should be fine.

I think you could easily use more intake. Thats a nice piece, but it was best on 302's. 327's and just barely on 350's. A 383 is pushing it. You might throw a 1-2" spacer on it and see if it helps, but I figure you need much more plenum/runner volume.

Those are some pretty good chambers on an LT-1 head. It probably doesn't need a lot of timing,especially with your compression. I think you could have used a tighter LSA on a 383 unless you were really pushing for a smooth idle with that size cam. That would help breathing some. But detonation might sneak in there too with that high of a static compression.

You might pick up a little if you leaned it some more, but once again, you have to watch detonation.

I think you're airflow limited. You might retard cam a few degrees ( Of course I really think a larger cam would be best!)and definitely install a bigger intake and see what happens.


JIM




[Modified by 427Hotrod, 11:32 PM 8/3/2003]

The Money Pit

My 406 nose dived at just over 5000 with the XE-274 cam,and when I replaced it with the XE-284 and 1.60 rockers it'll pull clean to 6500.
Your 230 degree cam isn't all that big for a 383.