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elukas 07-26-2003 11:35 AM

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

elukas 07-26-2003 01:04 PM

Any guesses... remote, educated, uneducated, off by a mile, off the top of your head, or anywhere in between are appreciated. Thanks!

lluciano77 07-26-2003 01:29 PM

I couldn't give you any estimates on the output of it, but that 600 CFMs just doesn't sound right. Unless you are just looking to roast the tires, I think that carb is going to be a little small, and it might have a little bit too lean of an idle circuit. I would get a larger used carb on Ebay. They are pretty cheap and if you don't think the bigger one made any difference, you can always sell it back to someone on Ebay, or keep it in case you add something else to your engine later that will require it.

elukas 07-26-2003 02:43 PM

Thanks for your response, Luciano.

Yeah, I know the 600 cfm sounds too small to me too. I will definitely be stepping up to a larger carb in the future if not right away.

I was just surprised at the modeling program I have showing only a very small difference in hp below high rpms.


roys63 07-26-2003 03:50 PM

That is a HP series Holley a bit different than the street carb, just a thought to ponder.

elukas 07-26-2003 08:13 PM

I know, Roy, but thanks for reminding me. I'll ponder that, along with this primary dealie some more.

5-7heaven 07-27-2003 02:03 AM

:cool: howziit guy!

JMO, you'll lose more than 50 HP engine size at 6000rpm,but not just because of the 1 5/8" pipes. the 383 might peak below that rpm.

from 1500-6000rpm, your engine will need 665cfm or more, and that single plane manifold will not perform its optimum as an rpm intake(or similar), especially with a teeny 600 carb on a street car.

my choice: 700cfm carb/edelbrock rpm intake(or equivalent)/1.75" headers/2.5" FULL exhaust system.

on DDD2000, the single-plane intake will show an advantage over the dual-plane, with any carb size from 390-850cfm. in reality, it would be a disappointing mismatch for a street-strip.

2wld4u 07-28-2003 04:54 AM

I think to get the rated 540+ hp youll need 1 3/4 header's, along with a HP carb, (which can be substituted with a proform main body)

elukas 07-28-2003 07:09 AM

Thanks, 5-7 heaven and 2wild4u.

I hope it does peak below 6,000, because it won't ever see the high side of that number!

And just to clarify, with the pipes CLOSED and the current 2.25" dual exhaust, I expect a much, much larger hp loss, which until I redo the entire thing, I'm willing to live with, so long as I can open those cutouts at the click of a switch.

And bigger carb, definitely in the plans for the future.

This is a street-strip car so your intake mismatch comment hits me where it hurts:)

Everyone seems to tell me a different story. I try to listen to all of them. Every drag racer has a different preference. And every dyno operator. And every article writer and every magazine. What is the answer?

I've personally only had dual planes in the past, but I think I'm going to try the victor jr. for a while and if it's really too much of a hassle for the street, I'll switch over. The main reason is I'm hesitant to mess with any of the major specs like that. (Not that they know everything, it's just nice to have a real dynograph I can work from). The smaller carb and lack of spacer is a very temporary thing, so I don't really consider those permanent changes. All in all, the change in primaries was the only real change I was considering making and I'm still thinking that over.


5-7heaven 07-28-2003 02:43 PM

:cool: JMO, since this is a strip/strip car, i'd experiment with single-plane AND dual-plane manifolds, different-size carbs, headers,etc.

methinks you should try lots of parts out, and see for yourself. that's why modifying hotrods/street-strip cars is an expensive hobby.

trial and error.:pain:

Super Streeter 07-28-2003 09:07 PM

First off,a real 540 hp is a tall order out of a 383 or even 406 on the street.Westech's dyno is a bit optimistic,so figure that you are looking at that engine being a real world 500 hp combo.The combo of a small carb and dual plane is a disaster.The split plenum of the dual plane needs more carb then a single plane,a lot more.In reality,that engine combo needs to spin 6500 rpm of even a bit more to make an honest 500 hp.I would want at least 800 cfm on that combo,even maybe a 950 hp carb.that combo should work best with at least 4000 stall and 4.56 or more gears.It isnt a very streetable combo for everyday use.I would run it with a gasket matched Victor JR or Strip Dominator,and an out of the box 850 double pumper with the correct jetting.I would also run at least 1 3/4 primary pipes and 3" exhaust.Good luck.

elukas 07-29-2003 08:07 PM


JMO, since this is a strip/strip car, i'd experiment with single-plane AND dual-plane manifolds, different-size carbs, headers,etc
Can do. And thanks for reminding me that nothing has to be set in stone, 5-7 heaven.


modifying hotrods/street-strip cars is an expensive hobby.
It is?

Oh crap.

And Super Streeter, thanks for the heads up on Westech's dyno. I'd never heard that before but it's good to know. And a real world 500 hp combo will make me smile from ear to ear so that's ok. I'm just looking for a street car that makes me grin and makes em spin. Strip wise just looking for mid 12s with the potential to go farther when I want to.

Please more comments from all you lurkers. Not that I haven't already gotten a good amount of feedback from these cool cats.


5-7heaven 07-30-2003 12:27 AM

:mwink: if you've conquered your traction/hookup issues, you're WAY past 12-second timeslips.:D

FWIW, i'm also using MAXIMUM OVERKILL(blown big-block), to reach 12.00 times. just doing it differently, and more mildly(RV cam/junk heads/2-600cfm carbs/2.69 rear gears..and a 6-71 supercharger.:mwink:

elukas 07-30-2003 12:06 PM


if you've conquered your traction/hookup issues, you're WAY past 12-second timeslips.
Haha, We'll see.

As for 12s, I was talking shifting a 3 speed 400 at 5500 rpms, with the miniscule torque converter I have now, and 3.08 gears.

Looking at different options for torque converters right now. I wanted to retrofit my 400 tranny with a switch pitch conversion and torque converter but the company's web site doesn't seem to be up any more.

A lot needs to be beefed up before I can try leaving the line at anything above 2000 rpms more than a few times.


FWIW, i'm also using MAXIMUM OVERKILL(blown big-block), to reach 12.00 times. just doing it differently, and more mildly(RV cam/junk heads/2-600cfm carbs/2.69 rear gears..and a 6-71 supercharger.
Maximum overkill is fun. That sounds like an interesting buildup. What are you putting it in?


5-7heaven 07-31-2003 12:35 PM

:cool: an old '56 chevy truck, daily driver. should run on 92 octane, idle like a stocker, except for that "defective pulley" noise(blower whine!)

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