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latest ideas on head flow
#1321659
10/17/12 08:07 AM
10/17/12 08:07 AM
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Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
70Cuda383
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Marysville, O-H-I-O
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I know that head flow is key to making good power, but is it possible to have too much of a good thing? example: there's a guy with a 5.9L Magnum, Dakota R/T truck. he wants to hop it up some, but keep it a street truck. it's a 4,000 lb regular cab. he has 4.56 gears and a 2800 rpm stall, so I'm thinking as far as a cam goes, he probably shouldn't go much bigger than 230° @ .050, and 110 LSA. He's got a set of the mopar aluminum magnum heads, and is sending them out to get ported. he's wanting to know if he should pay to have them ported to flow 275 cfm or spend the extra money to get them to flow 300 cfm. my thoughts were that a 300cfm port on a stock stroke 360 is overkill, and is likely to be a total dog at low RPM due to poor port velocity, but the guy doing the port work claims that he can open the ports up to flow 300 cfm, while maintaining 350 fps, and only removing 1cc of metal from the port.  What kind of head flow and cam specs would you guys suggest for a 4,000 lb sport truck with a stock stroke 360, stock dished pistons, with other constraints being a 2800 rpm stall and 4.56 gears (w/ 28" tires).
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Re: latest ideas on head flow
[Re: 70Cuda383]
#1321663
10/17/12 12:07 PM
10/17/12 12:07 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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It would only be a dog due to the conv.... more flow you move everything up higher in the RPM range, both torque and HP 
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Re: latest ideas on head flow
[Re: 70Cuda383]
#1321666
10/17/12 02:25 PM
10/17/12 02:25 PM
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Joined: Aug 2003
Posts: 43,163
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,163
Bend,OR USA
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The right foot, and the brain, control how far the throttle opens  Street driving versus all out drag racing are two different things, right I think having more air flow at WOT than you need is probally a good thing, street or strip  I think the smallest restrictor in the intake side of the valves determines how much air goes into the cylinders, not just the intake ports and cam
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: latest ideas on head flow
[Re: Cab_Burge]
#1321667
10/17/12 02:58 PM
10/17/12 02:58 PM
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Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
70Cuda383
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Quote:
The right foot, and the brain, control how far the throttle opens Street driving versus all out drag racing are two different things, right I think having more air flow at WOT than you need is probally a good thing, street or strip I think the smallest restrictor in the intake side of the valves determines how much air goes into the cylinders, not just the intake ports and cam
so the old school of thought about port velocities and needing good velocity to make torque is out the window? I'm not talking about restrictions in airflow and how much air goes into the cylinders at WOT. I'm talking about low RPM, part throttle driveability, and street manners.
so what you guys are saying is that more CFM is better. Period.
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Re: latest ideas on head flow
[Re: 70Cuda383]
#1321669
10/17/12 03:05 PM
10/17/12 03:05 PM
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Joined: Feb 2005
Posts: 20,174
PA.
pittsburghracer
"Little"John
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"Little"John
Joined: Feb 2005
Posts: 20,174
PA.
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Something to think about here guys. So-called 300cfm head flows 300cfm@.700 or maybe .750 not .500 or .550 lift. The cam determines your usable cfm range.
1970 Duster
Edelbrock headed 408
5.984@112.52
422 Indy headed small block
5.982@112.56 mph
9.42@138.27
Livin and lovin life one day at a time
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Re: latest ideas on head flow
[Re: 70Cuda383]
#1321671
10/17/12 03:10 PM
10/17/12 03:10 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
Quote:
It would only be a dog due to the conv.... more flow
you move everything up higher in the RPM range, both
torque and HP
exactly. more converter....more RPM....less streetable.
the kid wants a street truck, not an all out race only track vehicle.
so, with a smaller cam, tighter converter, will low RPM driveability suffer with a 300 cfm port on a 360 cubic inch motor?
More conv doesnt make it less street friendly...
plenty of people(me included) run much higher stall
on the street... with the gear (4.56) the revs will
come up pretty quick and he wont spend much time
at low rpm.... if he doesnt want to change conv then
I would just leave it alone and go with the gear...
back when I played on the street I always did a gear
first then conv then the engine... that was always
the biggest improvement for the money spent... JMO
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Re: latest ideas on head flow
[Re: skrews]
#1321673
10/17/12 04:03 PM
10/17/12 04:03 PM
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Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
70Cuda383
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Quote:
300 cfm out of RT heads by increasing port volume 1cc, no chance in hell. Find another shop that's not trying to screw you over. $1000 to remove 1cc worth of metal, wish I was making that kind of dollars per cc when porting heads.  Turn up the gain on your BS meter. 
Yea, well, I already knew he was full of it when he said they didn't remove very much metal "maybe 1 cc"
My main question was about how streetable 300CFM heads would be on a stock stroke 360.
Everything I've read/learned up to this point has been about velocity, and using the velocity and harmonics of the pulse waves to tune the RPM where you make peak torque, and that's why some guys use 1 5/8" primary headers with a 2.5" exhaust, and some guys use a 1 7/8" primary with a 3" exhaust, or a long runner dual plane intake vs a short runner single plane design, where you have to keep in mind the operating range of the engine and it's intended use. a street engine that spends 80-90% of the time below 3,000 rpm ought to be built for low end torque, especially in a 4000 lb truck, whereas if it was a race only car, you could build it for peak power at 6000 rpm, but it's going to lug and surge around at part throttle cruise unless you keep it tached up to 3500 rpm with numerically high gears.
I just figured that a 300 CFM port would fall into the category of "not ideal for the street" and would lose port velocity and the harmonics for maximum efficiency at lower RPM.
but as pointed out earlier, apparently the manufacturers are going to big flowing heads with smaller cams.
I'm trying to understand this theory and how it all plays together with the rest of the parts in the combo.
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Re: latest ideas on head flow
[Re: pittsburghracer]
#1321674
10/17/12 04:25 PM
10/17/12 04:25 PM
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Joined: Jan 2003
Posts: 75,005
U.S.S.A.
JohnRR
I Win
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Joined: Jan 2003
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U.S.S.A.
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Quote:
Something to think about here guys. So-called 300cfm head flows [Email]300cfm@.700[/Email] or maybe .750 not .500 or .550 lift. The cam determines your usable cfm range.
I was thinking something similar , what lift is that 300cfm number at ? The more important numbers are the low lift flow numbers on a street type build, it only sees peak lift once and all the other lifts twice ...
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Re: latest ideas on head flow
[Re: 70Cuda383]
#1321676
10/17/12 05:51 PM
10/17/12 05:51 PM
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Joined: Sep 2010
Posts: 170
renton , washington
perfmachst
member
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member
Joined: Sep 2010
Posts: 170
renton , washington
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hi, 300 CFM will be too much for what he needs. i attended a super flow seminar, years ago, mr betts, statement was, do not get hung up on big flow numbers, port velocity and port shape are everything. faster moving air will fill cylinder faster than a big number with low velocity. higher port velocity, gives you better throttle response, more torque. torque is what moves car.granted, you do need more flow, but not at a loss of velocity. just food for thought.
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Re: latest ideas on head flow
[Re: perfmachst]
#1321677
10/17/12 06:19 PM
10/17/12 06:19 PM
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Joined: Jan 2003
Posts: 16,376
dogdays
I Live Here
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I Live Here
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Posts: 16,376
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You don't have to have giant ports to flow good. In my storage is an AFR 1034, which is a street legal head for smallblock chevies, 195cc intake runner, 2.05" valve that flows up to 280 cfm at .550 lift and 28" depression. Exhaust flow is 76% of intake flow. I sure wish they put their magic to work on LA motors! R. One thing troubles me, though. I seem to remember something about sonic velocity through a restriction limiting flow no matter how much delta P there was. See http://www.therebreathersite.nl/04_Links/Downloads/Choked.pdffor an explanation. One area where I didn't remember correctly is that it is the velocity that stays constant, not necessarily the mass flow rate. If the density of the upstream air increases, while the velocity remains the same, the mass flow rate increases. Logically this brings us to superchargers.
Last edited by dogdays; 10/17/12 06:25 PM.
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X2 those heads bring a tear to the eye, but they'd be better w/ shaft rockers.