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Minimum Cross Sectional Area: Question

General engine tech -- Drag Racing to Circle Track

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steve cowan
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Re: Minimum Cross Sectional Area: Question

Post by steve cowan » Thu Feb 06, 2020 1:08 am

would end badly i think lol :lol:
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Re: Minimum Cross Sectional Area: Question

Post by Orr89rocz » Thu Feb 06, 2020 7:37 am

So not trying to be a jerk, but for a daily driver, what would you consider a pleasant cruise RPM? What would you do to optimize it for use in its predominantly used RPM range? I love hearing others ideas and thoughts as open thinking and dialogue lifts the whole group.
For a true daily driver? I would leave it stock ish. My dd has been a 2010 sierra 6.2 and now a 17 sierra 5.3. Lol. My 89 camaro was an occassional nice spring/summer/fall day driver. But its been years since its be naturally aspirated. For a true daily driver i wouldnt want anything much beyond what the factory oems produce. If absolutely stuck with a built motor sbc like this thread, i certainly wouldnt want a 240 deg cam in it. My 383 was 11:1 with afr 195 heads and a 230/245 hyd roller .600”. Drove fine. 3.42 gear. Lock up converter for highway. Overdrive .70 gear. No drivability problems. Efi car. I could see driving that most days.
Thats 2200 rpm in OD on a 26” tire at 70 mph. Fantastic.

Thats how you need to do it imo. Efi is a must, OD lockup trans to handle sub 2500 rpm 70 mph highways. You can make alot of power and still drive nice this way. Ls guys easily do it. But not using small ports and wringing its neck with over duration cams


What you built, that runs 40’min commutes with no ac in 100-130 deg weather, i would never want lol. You need a different car for that.

My current “street car” has been th400, non lockup but 28” tire 3.42 gear soon to be 3.08. Turbo combos. Closer to 2500 rpm for 60 mph with some converter slip im sure. I dont like it but its tolerable for short trips. Certainly not a daily imo lol. But its gonna make 2000 hp

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Re: Minimum Cross Sectional Area: Question

Post by skinny z » Thu Feb 06, 2020 10:31 am

raynorshine wrote:
Wed Feb 05, 2020 11:24 pm
Skinny: what do your computer sims recommend for duration at .050"...6000 RPM redline...3.75" stroke...? (intake specifically)

-i feel 240 degrees is excessive :shock: not many small-block tow-trucks have 240 intake degrees duration.. :P
I'll look into my results and post up. Probably a dozen iterations to date with examples from the pro's recommendations to ideas drawn from other builds (namely DV's) plus what Torque Master has churned out. Although with the latter, I haven't run any simulations yet. Those results intrigue me the most.
For the record, the 240 cam was aimed specifically at the small MCA heads as executed by DV in one of his magazine articles. That one caught my attention. Not a lot of RPM involved.

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Re: Minimum Cross Sectional Area: Question

Post by skinny z » Sat Feb 08, 2020 1:30 pm

raynorshine wrote:
Wed Feb 05, 2020 11:24 pm
Skinny: what do your computer sims recommend for duration at .050"...6000 RPM redline...3.75" stroke...? (intake specifically)
-i feel 240 degrees is excessive :shock: not many small-block tow-trucks have 240 intake degrees duration.. :P
As far as the cam recommendations go, as well as the computer simulations, almost all peak at 6000 RPM. Makes perfect sense in that the CID, heads (in particular)and compression ratio are the same across the board. That said, I place my red line about 500 RPM beyond the peak HP RPM.
Professional picks ranged from 232 to 242 @ .050" on the intake. All peak at 6000 (so a 6500 red line shift). The lower duration tends to be flatter at peak. Essentially flat from 5500-6000. Then they all fall off the map after that as, I assume, the heads run out of steam.
My latest experiments use Torque Master as a guide and moving the inputs around to see the trends that develop. As an example, all else being equal, at 9.8:1, duration at .050" is 231. LSA 106, ICL 102. Push that compression up to 10.4 and suggested duration is 224 with 107/103.
There's one more iteration I want to study and that's the "too big a cam" in DV's write-up on a small headed 383. That particular combination used a small head (Edelbrock Performer RPM 170 cc) but the cam spec was 288/293, 236/242 (no spec on the LSA although given that is was described as Comps so I'd guess a 110 LSA). Plenty of low end torque which was attributed to the higher port velocity while the longer duration helped the top end.
I'm less enthusiastic than I was about the approach though.

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Re: Minimum Cross Sectional Area: Question

Post by steve cowan » Sat Feb 08, 2020 3:24 pm

skinny z wrote:
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.
Can I ask why such low compression??
It will run fine with 9.8:1 but why not bump it higher, 11.5:1 on pump gas is doable if your tune up is good.
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Re: Minimum Cross Sectional Area: Question

Post by skinny z » Sat Feb 08, 2020 4:05 pm

steve cowan wrote:
Sat Feb 08, 2020 3:24 pm

Can I ask why such low compression??
It will run fine with 9.8:1 but why not bump it higher, 11.5:1 on pump gas is doable if your tune up is good.
Couple of things. Iron heads for one. Cast pistons (hypereutectic) was another. And the potential application.
That said, the new short is all forged internals.
Previous builds into "streetable" projects (although the relevance of that term in this build is undetermined) with 10.5:1, dynamic compression approaching 8.5 and cranking compression north of 200 PSI didn't play nice with 94 octane and decent timing. The cam on that was about 224 on a 106 ICL.
If I had aluminum heads, I'd have no fear. But the choice of the iron heads is set so I have to deal with it.
Interesting question though as I'm toggling back and forth between 9.8 and a smaller cam or back to 10.5 with something larger. What I'm learning though is that these heads limit any gains from the higher RPM that would result from a more duration and the accompanying higher compression. Simulations and similar combinations show that the power simply drops off past 6000 RPM.
If I touch on the potential application mentioned earlier then things shake out differently. If I forgo the idea of driving anywhere, anytime then I can build more towards WOT. If I want to cruise on the highway and not get crushed with poor fuel economy then I'll scale back the aggressiveness and live with less. That part is undecided.
The more I get into it the more I'm thinking of targeting peak HP RPM around 5500. That lets the lower compression work nicely with the cam needed.
As has been suggested here (more than once!) is go with 230 on the intake and call it a day. Been done for decades and this one is nothing special.

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Re: Minimum Cross Sectional Area: Question

Post by steve cowan » Sat Feb 08, 2020 6:15 pm

skinny z wrote:
Sat Feb 08, 2020 4:05 pm
steve cowan wrote:
Sat Feb 08, 2020 3:24 pm

Can I ask why such low compression??
It will run fine with 9.8:1 but why not bump it higher, 11.5:1 on pump gas is doable if your tune up is good.
Couple of things. Iron heads for one. Cast pistons (hypereutectic) was another. And the potential application.
That said, the new short is all forged internals.
Previous builds into "streetable" projects (although the relevance of that term in this build is undetermined) with 10.5:1, dynamic compression approaching 8.5 and cranking compression north of 200 PSI didn't play nice with 94 octane and decent timing. The cam on that was about 224 on a 106 ICL.
If I had aluminum heads, I'd have no fear. But the choice of the iron heads is set so I have to deal with it.
Interesting question though as I'm toggling back and forth between 9.8 and a smaller cam or back to 10.5 with something larger. What I'm learning though is that these heads limit any gains from the higher RPM that would result from a more duration and the accompanying higher compression. Simulations and similar combinations show that the power simply drops off past 6000 RPM.
If I touch on the potential application mentioned earlier then things shake out differently. If I forgo the idea of driving anywhere, anytime then I can build more towards WOT. If I want to cruise on the highway and not get crushed with poor fuel economy then I'll scale back the aggressiveness and live with less. That part is undecided.
The more I get into it the more I'm thinking of targeting peak HP RPM around 5500. That lets the lower compression work nicely with the cam needed.
As has been suggested here (more than once!) is go with 230 on the intake and call it a day. Been done for decades and this one is nothing special.
Thanks for your response,
Just for informations sake -
My last year 383 combination with cast iron darts was pump fuel,put over 50 passes on it plus driven 3 hrs plus to the track towing a small trailer with tools, spares etc, 60 mph @ 3200 rpm, best timing was 32 deg locked with programmable msd ignition.
In process at the moment, short block assembled with Howard roller 241-252 @0.050,.600" lift 108 lsa in at 104.
Same heads reworked - ported to peak at 6500rpm, angle milling for 11.3:1 compression, steeper valve seat angles, modified victor junior intake.
Tighten quench to 31"
Still going to run pump gas.
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Re: Minimum Cross Sectional Area: Question

Post by skinny z » Sat Feb 08, 2020 6:51 pm

steve cowan wrote:
Sat Feb 08, 2020 6:15 pm

Thanks for your response,
Just for informations sake -
My last year 383 combination with cast iron darts was pump fuel,put over 50 passes on it plus driven 3 hrs plus to the track towing a small trailer with tools, spares etc, 60 mph @ 3200 rpm, best timing was 32 deg locked with programmable msd ignition.
In process at the moment, short block assembled with Howard roller 241-252 @0.050,.600" lift 108 lsa in at 104.
Same heads reworked - ported to peak at 6500rpm, angle milling for 11.3:1 compression, steeper valve seat angles, modified victor junior intake.
Tighten quench to 31"
Still going to run pump gas.
Any specs on those heads? CFM, MCA, Valve size? Your better valve job will change the cam spec too. Last I had these heads rebuilt I think the shop gave me a very pedestrian result. Invoice read: "Standard 3-angle valve job". The heads out of the box had radiused exhaust seats. That's probably gone.
Your peak HP RPM is way beyond what I can make with these heads. With 230@.400", 254@.500", 247@.600" there's not a lot to feed the CID at higher RPM. I haven't measured but would say the MCA is about 1.8 sq in.
This isn't to say that a 240 degree intake and a 1.8 MCA head can't make decent power provided enough CFM is there. That's the whole deal with this wormhole of the small head/big cam DV thing I was following. I say was because now I'm not so sure I want to go that route. Besides the DV build, I've got little to no support otherwise.

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Re: Minimum Cross Sectional Area: Question

Post by steve cowan » Sat Feb 08, 2020 7:40 pm

Heads and intake still in progress
I will send you a PM
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Re: Minimum Cross Sectional Area: Question

Post by gmrocket » Sat Feb 08, 2020 9:25 pm

skinny z wrote:
Sat Feb 08, 2020 4:05 pm
steve cowan wrote:
Sat Feb 08, 2020 3:24 pm

Can I ask why such low compression??
It will run fine with 9.8:1 but why not bump it higher, 11.5:1 on pump gas is doable if your tune up is good.
Couple of things. Iron heads for one. Cast pistons (hypereutectic) was another. And the potential application.
That said, the new short is all forged internals.
Previous builds into "streetable" projects (although the relevance of that term in this build is undetermined) with 10.5:1, dynamic compression approaching 8.5 and cranking compression north of 200 PSI didn't play nice with 94 octane and decent timing. The cam on that was about 224 on a 106 ICL.
If I had aluminum heads, I'd have no fear. But the choice of the iron heads is set so I have to deal with it.
Interesting question though as I'm toggling back and forth between 9.8 and a smaller cam or back to 10.5 with something larger. What I'm learning though is that these heads limit any gains from the higher RPM that would result from a more duration and the accompanying higher compression. Simulations and similar combinations show that the power simply drops off past 6000 RPM.
If I touch on the potential application mentioned earlier then things shake out differently. If I forgo the idea of driving anywhere, anytime then I can build more towards WOT. If I want to cruise on the highway and not get crushed with poor fuel economy then I'll scale back the aggressiveness and live with less. That part is undecided.
The more I get into it the more I'm thinking of targeting peak HP RPM around 5500. That lets the lower compression work nicely with the cam needed.
As has been suggested here (more than once!) is go with 230 on the intake and call it a day. Been done for decades and this one is nothing special.
I don't think you've said what type of cam you want to run? maybe I missed it...hyd flat? anyway, with your comp a bit on the low side you might be best to keep your seat timing on the shorter side and go with a more aggressive lobe to get you into the bigger .050" numbers.

it will build more cyl pressure, TQ , on the low end and the bigger .050" will help make more pwr on the top end of the rpm range and will not fall off as quick.

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Re: Minimum Cross Sectional Area: Question

Post by PRH » Sun Feb 09, 2020 12:18 pm

365” SB Mopar, 9.7:1cr.
Stock J heads with 2.02/1.60 valves and mild porting. Peak flow of 230@.500 lift.
Old school dual plane intake-divider cut down, Holley 4779, 1-3/4” headers(probably too big).
Small solid cam.

Peak tq@4800, peak hp@6200.
Within 10hp of peak from 5300-6600.
Down 13hp from peak at 6800.

I would expect something like a Voodoo 741 cam in a vortec headed 383 could easily make the target power level(450hp).
Somewhat handy with a die grinder.

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Re: Minimum Cross Sectional Area: Question

Post by skinny z » Sun Feb 09, 2020 12:40 pm

gmrocket wrote:
Sat Feb 08, 2020 9:25 pm
I don't think you've said what type of cam you want to run? maybe I missed it...hyd flat? anyway, with your comp a bit on the low side you might be best to keep your seat timing on the shorter side and go with a more aggressive lobe to get you into the bigger .050" numbers.

it will build more cyl pressure, TQ , on the low end and the bigger .050" will help make more pwr on the top end of the rpm range and will not fall off as quick.
This is a hydraulic roller.
I'm certainly starting to go in that direction. The heads are obviously the limiting factor (and they aren't going to change) so I find I'm RPM limited with the CID. Not so much so that so it'll stop it from making decent power but the peak HP RPM is going to be lower than i had started off going for initially.
So yeah, nothing special now I guess as I had wanted to work this in another direction but it appears it's going to be a fairly traditional "Vortec 383" spec. Or at least modified Vortec 383.
The aggressive lobe is subjective though. An Xtreme Energy from COMP is easy to handle while I found their XFI profile to be little harder on parts. The latter being 274/224 w/ .575" and 1.6 RR. It looks though that the current cam spec is going to be in around 283/231 with .550" lift. That's tame in relative terms and I'll be looking for other lobe profile lists (like Mike Jones' offerings) to compare.

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Re: Minimum Cross Sectional Area: Question

Post by skinny z » Sun Feb 09, 2020 12:46 pm

PRH wrote:
Sun Feb 09, 2020 12:18 pm
365” SB Mopar, 9.7:1cr.
Stock J heads with 2.02/1.60 valves and mild porting. Peak flow of 230@.500 lift.
Old school dual plane intake-divider cut down, Holley 4779, 1-3/4” headers(probably too big).
Small solid cam.

Peak tq@4800, peak hp@6200.
Within 10hp of peak from 5300-6600.
Down 13hp from peak at 6800.

I would expect something like a Voodoo 741 cam in a vortec headed 383 could easily make the target power level(450hp).
I think your peak HP RPM is beyond what I'm able to reach. Now that said, if I knock 20 cubic inches off of the spec, it does raise the potential peak RPM of these heads. But as it is, it looks like 5500-5700 is a more likely peak given a max CFM of 250-255 (which I've got covered) and the MCA at <1.80. Data suggests a max HP of about 480 with that RPM. So it's looking like 450 HP is very reachable.

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Re: Minimum Cross Sectional Area: Question

Post by gmrocket » Sun Feb 09, 2020 1:40 pm

skinny z wrote:
Sun Feb 09, 2020 12:40 pm
gmrocket wrote:
Sat Feb 08, 2020 9:25 pm
I don't think you've said what type of cam you want to run? maybe I missed it...hyd flat? anyway, with your comp a bit on the low side you might be best to keep your seat timing on the shorter side and go with a more aggressive lobe to get you into the bigger .050" numbers.

it will build more cyl pressure, TQ , on the low end and the bigger .050" will help make more pwr on the top end of the rpm range and will not fall off as quick.
This is a hydraulic roller.
I'm certainly starting to go in that direction. The heads are obviously the limiting factor (and they aren't going to change) so I find I'm RPM limited with the CID. Not so much so that so it'll stop it from making decent power but the peak HP RPM is going to be lower than i had started off going for initially.
So yeah, nothing special now I guess as I had wanted to work this in another direction but it appears it's going to be a fairly traditional "Vortec 383" spec. Or at least modified Vortec 383.
The aggressive lobe is subjective though. An Xtreme Energy from COMP is easy to handle while I found their XFI profile to be little harder on parts. The latter being 274/224 w/ .575" and 1.6 RR. It looks though that the current cam spec is going to be in around 283/231 with .550" lift. That's tame in relative terms and I'll be looking for other lobe profile lists (like Mike Jones' offerings) to compare.
Are the advertised ratings for the 274 and 283 taken at same lift?

You may better off with something like 275 and 235 or more...with 1.6 on intake only.They are out there.

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Re: Minimum Cross Sectional Area: Question

Post by skinny z » Sun Feb 09, 2020 3:10 pm

gmrocket wrote:
Sun Feb 09, 2020 1:40 pm

Are the advertised ratings for the 274 and 283 taken at same lift?

You may better off with something like 275 and 235 or more...with 1.6 on intake only.They are out there.
The 274/224 w/.575" is right out of COMP's profile catalogue and is based on a 1.6 RR. That's an XFI intake lobe. The 283/231 was spec'd by Torque Master but there's no XFI lobe with that duration. 280/230 and 286/236 is as close as it gets with lifts around .575". My job will be to find a cam supplier that can deliver that duration with similar lifts of .575". There are two lobes in the Xtreme Energy category at 282/230. One with .544" and the other with .622". The .622" is too much IMO. The .544"....maybe.
Like you said, they are out there.
I have to get back into Jones' catalogue as I believe he has lobes that fit that bill.

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