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Old 07-26-2003, 11:35 AM
elukas elukas is offline
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Question A few changes to 540 hp carcraft buildup... what kind of hp loss? guesstimates please

First time poster here. Just finished browsing through all 304 pages of the archives in the last 2 weeks. Whew!!!

Ok, on to the question.

I'm tentatively following this Carcraft buildup of a 383:

There's a dynograph, etc to take a look at and a parts list.

I say tentatively because certain things are going to be different until next spring. All internals, heads ($$$OUCH$$$), cam go along with the article though.

The only differences until next spring are a 600 cfm edelbrock carb, no 2 inch spacer, and the smaller diameter primaries.

The article says the spacer was worth 8.5 hp, and believe it or not my dyno 2000 program says I won't lose much power at all until 6000 rpms with the 600 cfm carb. We'll see about that, but anyway that's not my question.

They don't detail what size header, open pipes, mufflers, they used in the test, but my guesses were probably 1 3/4 pipe and open headers.

Now what I plan to do is use 1 5/8 primaries with open headers via electric cutout (FUN). Anyone want to estimate how much power I will lose by using the small primaries?

My guesstimate is that it will chop off around 50 hp off the top end.

But in the dyno2000 trial program I've got, I modeled it and get this with a 600 cfm carb and small primary tubes OPEN, it says this puppy will still churn out 540 hp at 6,000 rpms.

What does the program assume is a small primary tube? 1 5/8 or 1 3/4? That's where I'm a little lost, can't seem to find that info anywhere.

So what do all you hot rodders think? Small primaries, 600 cfm carb, will it really not lose much power below 6000 rpms?

Thanks in advance,


P.S. When looking at the models, feel bad for me... I can't turn that 6,500 that would turn this 383 into a 560+ hp bad *** (with small primaries open and a 600 cfm carb, mwuhahahah). Stupid budget.

In case anyone's wondering about why I don't go with a 3 inch exhaust instead of the electric cutouts....

I already have an exhaust system in place. Dual running to the back. Was built to support the original olds 350.

And it's....

2 1/4"!!!!!

The cost of the cutouts is much less (with a higher fun factor) than redoing an entire 3 inch exhaust system.


Chevy 383
4.030 bore
3.750 stroke
9.5 comperession
single plane victor jr intake manifold

lobe center angle 110
intake duration 248
intake lift at valve .525
intake centerline 110
exhaust duration 248
exhaust lift at valve .525

.200 129
.300 195
.400 240
.500 260
.550 262
.600 262

.200 108
.300 156
.400 178
.500 190
.550 192
.600 194

head size 2.02 intake, 1.6 exhaust

Last edited by elukas; 07-26-2003 at 01:05 PM.
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