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Minimum Cross Sectional Area: Question

General engine tech -- Drag Racing to Circle Track

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skinny z
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Minimum Cross Sectional Area: Question

Post by skinny z » Tue Feb 04, 2020 4:15 pm

I've been poking around here asking a few questions and going back through old threads trying to gain traction for a potential project.
I'm at a point where I have to decide whether my proposed CID and peak HP RPM target are reachable with the parts I have.
While I had a cam spec'd (courtesy of Mike Jones and in a round about way, DV ) now I'm beginning to think that the heads simply won't support my goals.
For feeding this discussion the specs would be as follows:
383 SBC.
Aftermarket Vortec casting with modest port work and bench flowed ~ 260 cfm at .500-.550 lift.
Dual plane intake (RPM Air Gap)
1 5/8" headers.
Looking to make peak HP ~ 6000 RPM (or less)
Cam specs fell into the 230-240 range with LSAs 106-108.
From a quick question asked here at ST, I've reverse calculated (perhaps crudely) what my current MCA might be and that is about 1.80 sq. ins. (The current engine with the heads in question is assembled and I'd like it to stay that way until I'm ready for the shortblock swap so measurements aren't possible).
More calculations predict a max peak HP RPM less than 5500.
I'm aware there's more to it than just the raw numbers (as one build I'm following uses the smaller head to its advantages namely higher velocity).
The question is then, how far off the mark would this be from the actual result?
And for purposes of this discussion let's limit this to a dyno engine and we're looking for best torque with an RPM ceiling as mentioned.

mt-engines
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Re: Minimum Cross Sectional Area: Question

Post by mt-engines » Tue Feb 04, 2020 5:18 pm

1.9 -2" is about where id size it for that, basic tow truck combo.

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Stan Weiss
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Re: Minimum Cross Sectional Area: Question

Post by Stan Weiss » Tue Feb 04, 2020 6:45 pm

Kevin,
What VE are you looking for and what velocity do you want?

Stan

PS Did you get my last link / download to work?
ab-383-csa-6000.gif
You do not have the required permissions to view the files attached to this post.
Stan Weiss / World Wide Enterprises
Offering Performance Software Since 1987
Do you use engine simulation software that uses cylinder head flow files?
We have a package of more than 3025 DFW or FLW Files

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Re: Minimum Cross Sectional Area: Question

Post by RevTheory » Tue Feb 04, 2020 6:57 pm

mt-engines wrote:
Tue Feb 04, 2020 5:18 pm
1.9 -2" is about where id size it for that, basic tow truck combo.
I don't know if I'd consider that a tow truck combo but I'm with you in ~1.95 probably closer to 2.00" being about right for a 6,000 rpm 383, assuming it slows enough to make the turn without stacking up.

digger
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Re: Minimum Cross Sectional Area: Question

Post by digger » Tue Feb 04, 2020 7:51 pm

what is the Hp target?

skinny z
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Re: Minimum Cross Sectional Area: Question

Post by skinny z » Tue Feb 04, 2020 9:50 pm

mt-engines wrote:
Tue Feb 04, 2020 5:18 pm
1.9 -2" is about where id size it for that, basic tow truck combo.
RevTheory wrote:
Tue Feb 04, 2020 6:57 pm
I don't know if I'd consider that a tow truck combo but I'm with you in ~1.95 probably closer to 2.00" being about right for a 6,000 rpm 383, assuming it slows enough to make the turn without stacking up.
Yeah. I'm seeing that the heads are definitely on the small side for a 6000 RPM 383. That said, I could lower my peak HP RPM and still get satisfying results I would think. Maybe target peak around 5500 with a 5700 RPM shift.
Interestingly, it has been compared to a tow truck.
digger wrote:
Tue Feb 04, 2020 7:51 pm
what is the Hp target?
I can't say that I have one really. The obvious answer would be the most out of the heads and cubes selected. I would think somewhere in or around 450 HP isn't unreasonable. Even a solid 425 would be a step function change from the existing iteration.

skinny z
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Re: Minimum Cross Sectional Area: Question

Post by skinny z » Tue Feb 04, 2020 9:58 pm

Stan Weiss wrote:
Tue Feb 04, 2020 6:45 pm
Kevin,
What VE are you looking for and what velocity do you want?

Stan

PS Did you get my last link / download to work?

ab-383-csa-6000.gif
Hi Stan.
Yes I did get the latest link however I'm still struggling with the resolution. I think it's more hardware based than the program. I'm going to keep working at it. Perhaps my now unsupported Windows 7 laptop can do a better job. This desktop of mine is a Frankenstein of sorts. Somewhat troublesome.
Now that said, regarding your questions. VE and velocity are values I haven't got a clear way of knowing exactly. On the velocity side, I'm anticipating the smaller cross section port will improve velocity at lower lifts and engine speeds. In turn, the thinking is that it will improve the VE in the those areas. While perhaps not being able to make big peak numbers, the area below peak might be enhanced.

digger
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Re: Minimum Cross Sectional Area: Question

Post by digger » Tue Feb 04, 2020 11:17 pm

skinny z wrote:
Tue Feb 04, 2020 9:50 pm
mt-engines wrote:
Tue Feb 04, 2020 5:18 pm
1.9 -2" is about where id size it for that, basic tow truck combo.
RevTheory wrote:
Tue Feb 04, 2020 6:57 pm
I don't know if I'd consider that a tow truck combo but I'm with you in ~1.95 probably closer to 2.00" being about right for a 6,000 rpm 383, assuming it slows enough to make the turn without stacking up.
Yeah. I'm seeing that the heads are definitely on the small side for a 6000 RPM 383. That said, I could lower my peak HP RPM and still get satisfying results I would think. Maybe target peak around 5500 with a 5700 RPM shift.
Interestingly, it has been compared to a tow truck.
digger wrote:
Tue Feb 04, 2020 7:51 pm
what is the Hp target?
I can't say that I have one really. The obvious answer would be the most out of the heads and cubes selected. I would think somewhere in or around 450 HP isn't unreasonable. Even a solid 425 would be a step function change from the existing iteration.
IMO 1.8" MinCSA should be adequate for that power level

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Re: Minimum Cross Sectional Area: Question

Post by mt-engines » Tue Feb 04, 2020 11:48 pm

digger wrote:
Tue Feb 04, 2020 11:17 pm
skinny z wrote:
Tue Feb 04, 2020 9:50 pm
mt-engines wrote:
Tue Feb 04, 2020 5:18 pm
1.9 -2" is about where id size it for that, basic tow truck combo.
RevTheory wrote:
Tue Feb 04, 2020 6:57 pm
I don't know if I'd consider that a tow truck combo but I'm with you in ~1.95 probably closer to 2.00" being about right for a 6,000 rpm 383, assuming it slows enough to make the turn without stacking up.
Yeah. I'm seeing that the heads are definitely on the small side for a 6000 RPM 383. That said, I could lower my peak HP RPM and still get satisfying results I would think. Maybe target peak around 5500 with a 5700 RPM shift.
Interestingly, it has been compared to a tow truck.
digger wrote:
Tue Feb 04, 2020 7:51 pm
what is the Hp target?
I can't say that I have one really. The obvious answer would be the most out of the heads and cubes selected. I would think somewhere in or around 450 HP isn't unreasonable. Even a solid 425 would be a step function change from the existing iteration.
IMO 1.8" MinCSA should be adequate for that power level
yeah, and less cam is needed. 220@.050 will do it. only need 5000rpm to boot

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Re: Minimum Cross Sectional Area: Question

Post by GARY C » Wed Feb 05, 2020 12:47 am

Has anyone here dyno tested or know of anyone that has dyno tested MCS alone?
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Re: Minimum Cross Sectional Area: Question

Post by steve cowan » Wed Feb 05, 2020 3:16 am

My 383 combo I ran last year
Dart 178cc cast iron heads 1.81" pinch
SFT comp oval cam 235-242 @ 0.050"
500" lift 106 ICL 106 LSA
10.6 compression
Stock airgap
950 hp holley
1.94"Intake valve
1.5" Exhaust valve
261 cfm @ 550"
3650 pound streeter 11.71 @ 114.51 mph
1.57 in the 60ft radial tyre.
Ran best et and mph with as cast Vic jnr
2 tenths and 2 mph slower with airgap.
Shift points 6000rpm
Finish line 6300 rpm
After 12 months on track testing, cam timing, lash loops, timing curves and high speed retard and advance testing, 3 x different carbs, different headers and exhaust system, different shift points 5800-7000 rpm, I came to the conclusion that the pushrod pinch was holding it back, also tested 2 x different converters 8" 5600 stall was better than 9"4000stall
The best gain was changing to single plane intake also tried different spacers 1",2" tapered, 4 hole tappered.
What heads are you going to use as in size, what valve combination, what application??
If I was doing this type of combination again I would work for average CSA of 2" and around 185-190cc, run a single plane intake that is complemented with the heads meaning entire intake tract sizing and if using a 230ish cam look at getting as much valve lift as possible, are you porting heads and intake manifold yourself??
How would you approach the sizing of the intake tract from plenum /runner entry down to throat size for your application??
Alot of questions if you want a lot of answers :D
steve c

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Re: Minimum Cross Sectional Area: Question

Post by RevTheory » Wed Feb 05, 2020 8:13 am

skinny z wrote:
Tue Feb 04, 2020 9:50 pm
Yeah. I'm seeing that the heads are definitely on the small side for a 6000 RPM 383. That said, I could lower my peak HP RPM and still get satisfying results I would think. Maybe target peak around 5500 with a 5700 RPM shift.
Interestingly, it has been compared to a tow truck.
You could probably size the pinch at 1.92 and call it a day. Especially if you're after throttle response on the street more than being able to drive over the peak hp before upshifting.

skinny z
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Re: Minimum Cross Sectional Area: Question

Post by skinny z » Wed Feb 05, 2020 10:00 am

steve cowan wrote:
Wed Feb 05, 2020 3:16 am
My 383 combo I ran last year
Dart 178cc cast iron heads 1.81" pinch
SFT comp oval cam 235-242 @ 0.050"
500" lift 106 ICL 106 LSA
10.6 compression
Stock airgap
950 hp holley
1.94"Intake valve
1.5" Exhaust valve
261 cfm @ 550"
Very similar collection of parts to what I have.
The heads are built, ported ("stage 1" by a pro) and my intention is not to spend another nickle on them. I will probably verify the pinch rather than calculate but for now those stay on the current lump (350). So that part of the combination is set. The plan is to maximize their potential with respect to the CID and select a cam to suit. CR will be about 9.8:1.
Torque Master has churned out a spec very similar to yours although duration is given seat to seat and comes in at 284/290 for peak HP RPM of 5700 (IIRC).
As for the rest, I'll build a car around it. Looking for strip performance and the street side I can take care of if past experience has anything to do with it.

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Re: Minimum Cross Sectional Area: Question

Post by skinny z » Wed Feb 05, 2020 10:09 am

RevTheory wrote:
Wed Feb 05, 2020 8:13 am
skinny z wrote:
Tue Feb 04, 2020 9:50 pm
Yeah. I'm seeing that the heads are definitely on the small side for a 6000 RPM 383. That said, I could lower my peak HP RPM and still get satisfying results I would think. Maybe target peak around 5500 with a 5700 RPM shift.
Interestingly, it has been compared to a tow truck.
You could probably size the pinch at 1.92 and call it a day. Especially if you're after throttle response on the street more than being able to drive over the peak hp before upshifting.
The head part of the equation is set. MCA was calculated based on flow although once the rest of the hard parts (shortblock) are built, I'll pull the heads and go over them. Measure what I can as well. But I've zero interest in doing anything more to as they're already overpriced as it is. Two rebuilds plus porting and bench testing after several years but they were inexpensive when I bought them new.
As for street vs track...more track orientated this time around. With a lower redline than the 350, RPM at the stripe should fall in line with just past peak HP.
But I'm trying to concentrate on the engine as a stand alone component as I can build any combination of gearing/converter/etc. to suit.

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Re: Minimum Cross Sectional Area: Question

Post by PRH » Wed Feb 05, 2020 11:20 am

The combo is a 383, vortec heads flowing 260, RPM A/G, headers, 230-240 cam...... and you’re looking for peak power between 5500-6000?

You’re done...... put it together.
Somewhat handy with a die grinder.

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