Desktop Dyno Help Please

Hey guys, I have built a 383 cu. inch sbc to be installed in a 1974 corvette coupe with a manual transmission. The major components are:
1978 4 bolt block bored 4.030"
Scat 4340 forged 3.75" crank
Carrillo forged 6" rods Carr bolts
Probe SRS -12.8 cc dished pistons 9.8:1 compression
AFR 195 Eliminator cylinder heads
Comp Cams hyd roller cam 230/236 duration .510/.520 lift
Comp Cams 1.6 roller rockers
Edelbrock rpm performer intake
Holley 4150 carb 750 cfm
Using 1 5/8" dyno headers this engine make 479 ft/lb @ 4400 and 468 hp @ 5800.
What effect will running 1 7/8" primaries into a 4" collector headers have on these results. Also I don't think the RPM intake will fit under my stock L82 hood. Can you see what the results would be with a Wiend low rise single plane Stealth intake.
Thanks for you help

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Originally Posted by Rgtrough

Hey guys, I have built a 383 cu. inch sbc to be installed in a 1974 corvette coupe with a manual transmission. The major components are:
1978 4 bolt block bored 4.030"
Scat 4340 forged 3.75" crank
Carrillo forged 6" rods Carr bolts
AFR 195 Eliminator cylinder heads
Comp Cams hyd roller cam 230/236 duration .510/.520 lift
Comp Cams 1.6 roller rockers
Edelbrock rpm performer intake
Holley 4150 carb 750 cfm
Using 1 5/8" dyno headers this engine make 479 ft/lb @ 4400 and 468 hp @ 5800.
What effect will running 1 7/8" primaries into a 4" collector headers have on these results. Also I don't think the RPM intake will fit under my stock L82 hood. Can you see what the results would be with a Wiend low rise single plane Stealth intake.
Thanks for you help

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You're a little mixed up on your manifolds. The Stealth is a dual-plane hi-rise. Here's the rundown on Weiand intakes....
#8120 Action Plus...low rise dual plane, height front 3.50", height rear 4.50", idle to 5500. (Same manifold as Edelbrock Performer).
#8150 Stealth....high rise dual plane, height front 4.19", height rear 5.27", 1500 to 6700. (Same manifold as Edelbrock Performer RPM).

It is my opinion that if you use a single plane intake, you're going to shoot yourself in the foot. Every dyno test I have assembled has shown more hp and torque from idle to 6000 with a dual-plane, high-rise intake. Over 6000, a single-plane intake makes more power and that's great for a circle track car. It just doesn't work too well on a street driver where the motor is operated under 6000 for 99.9% of the time.

Changing from a high-rise to a low-rise dual plane has shown to drop 40-60 hp on the dyno. Going to larger primaries on the headers will drop torque at lower rpm's, but you'll pick up a little power at the top.

List your static compression ratio and I'll run it up on the DynoSim.

Hey Tech, I hoped that you would see this post. I am not sure of the part number for the Wiend intake that I have but it is a single plane and it definitly is a low rise. I edited my post to include the pistons and cr. They are Probe SRS with a -12.8cc dish producing 9.8:1 compression. I thought that the low rise single plane would wreck the great torque numbers and if I have to replace/modify the hood I will. It's the headers I am most curious about. The Hooker 4 into 1 Corvette specific sidepipe system is about $1800.00 so I want to be sure they will perform before I buy them.
Thanks for your interest

1 5/8 headers, low-rise single-plane intake, cam installed straight up.....

RPM HP TQ
2000 141 371
2500 183 385
3000 229 401
3500 290 435
4000 348 457
4500 398 464
5000 437 459
5500 464 443
6000 475 416
6500 468 378

1 3/4 headers, low-rise single-plane intake, cam installed straight up....

2000 143 374
2500 185 389
3000 232 406
3500 293 439
4000 351 461
4500 401 468
5000 442 465
5500 472 450
6000 486 426
6500 483 390
Apparently, the motor likes these bigger tubes.....

1 3/4 headers, high-rise dual-plane intake (RPM), cam installed straight up....

2000 143 375
2500 181 380
3000 233 408
3500 300 450
4000 365 480
4500 423 494
5000 471 495
5500 502 479
6000 513 449
6500 504 407
It seems to like this manifold also....gained 38 hp and 31 ft/lbs torque over the baseline....

1 3/4 headers, high-rise dual-plane intake, cam advanced 2 degrees. Takes away a little power at the top, but adds torque where you can use it....

2000 144 379
2500 182 383
3000 236 413
3500 303 455
4000 366 480
4500 426 500
5000 472 496
5500 498 475
6000 506 443
6500 490 396
This combo reaches a peak volumetric efficiency of 102.1% @ 5000 rpm's. This makes your 383 think it's a 391. :D

Hey Tech, thanks for the work. I thought that the big pipes might put me close to the 500 hp mark. And even though I know it is just a number and torque is much more important, making 500 horses will be really satisfying.
Thanks for the effort.