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latest ideas on head flow

Posted By: 70Cuda383

latest ideas on head flow - 10/17/12 12:07 PM

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).
Posted By: sshemi

Re: latest ideas on head flow - 10/17/12 12:35 PM

Remove 1 cc and get 300 cfm???!!!
Posted By: 70Cuda383

Re: latest ideas on head flow - 10/17/12 12:39 PM

Quote:

Remove 1 cc and get 300 cfm???!!!



That's what I said! I sugested that a 300CFM port on a small block head for a stock stroke 360 is going to have such low velocity at "street" rpm that it will be a total dog, but this guy said, and I quote:

Quote:

When I port heads I also use a velocity probe shoved in the port. As I test airflow (cfm) I also watch velocity I shoot for 350fps. Just becasue a port does not flow much air does not mean it has great velocity. It has to be able to move air to build velocity at a given CSA. We are not changing the volume of the head by porting it in most cases. I would say if we have picked up 1 cc that would be all.





but, I'm not pretending to be an expert who's ported a ton of heads and built hundreds of engines, all I know is what I've picked up from reading about what you guys have done on here. so my mind is open and I'm looking to learn some more, just in case what I THOUGHT I learned about head flow/velocity/port work etc. is wrong.
Posted By: dogdays

Re: latest ideas on head flow - 10/17/12 03:49 PM

I used to think the same thing, now I'm not so sure. Case in point: my '91 SHO has a 3 liter 6 cylinder engine (Yamaha). That means that each cylinder is 30.5 cubic inches. STOCK head flow on it is 220cfm @ 28". That's 7.2 cfm per cubic inch. A 360 using the same ratio would have heads flowing 324cfm.

What I am seeing on the OEM front here in the States is good head flow with shorter cam timing. So you have Hemis with 250 cfm ports making one hp/cubic inch with less than 200 degrees at 50 cam timing.

So he may be on to something.

R.
Posted By: MR_P_BODY

Re: latest ideas on head flow - 10/17/12 04:07 PM

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
Posted By: 70Cuda383

Re: latest ideas on head flow - 10/17/12 06:03 PM

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?
Posted By: sixpackgut

Re: latest ideas on head flow - 10/17/12 06:09 PM

how much more does it cost to remove 1cc and gain 30cfm?
Posted By: Cab_Burge

Re: latest ideas on head flow - 10/17/12 06:25 PM

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
Posted By: 70Cuda383

Re: latest ideas on head flow - 10/17/12 06:58 PM

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.
Posted By: 70Cuda383

Re: latest ideas on head flow - 10/17/12 07:01 PM

Quote:

Remove 1 cc and get 300 cfm???!!!



Try 50 CFM we're talking about heads that MIGHT flow in the 250 range out of the box. the guy who does the work wants $600 to make them flow 275 and $1000 to make them flow 300, all while only removing about 1cc
Posted By: pittsburghracer

Re: latest ideas on head flow - 10/17/12 07:05 PM

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.
Posted By: sshemi

Re: latest ideas on head flow - 10/17/12 07:09 PM

Posted By: MR_P_BODY

Re: latest ideas on head flow - 10/17/12 07:10 PM

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
Posted By: skrews

Re: latest ideas on head flow - 10/17/12 07:23 PM

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.
Posted By: 70Cuda383

Re: latest ideas on head flow - 10/17/12 08:03 PM

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.
Posted By: JohnRR

Re: latest ideas on head flow - 10/17/12 08:25 PM

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 ...
Posted By: justinp61

Re: latest ideas on head flow - 10/17/12 09:44 PM

When I had the 340 in my Dart it was 3240#, the heads flowed 293 @ .650" and the cam was 237/242 @ .050. With 4.30 gears and a 28" tire it had power everywhere, it pulled all the way to the 6400 rpm shift point. It didn't weigh 4000 pounds though.
Posted By: perfmachst

Re: latest ideas on head flow - 10/17/12 09:51 PM

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.
Posted By: dogdays

Re: latest ideas on head flow - 10/17/12 10:19 PM

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.pdf
for 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.
Posted By: 340B5

Re: latest ideas on head flow - 10/17/12 10:23 PM

Quote:

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!

X2 those heads bring a tear to the eye, but they'd be better w/ shaft rockers.
Posted By: MattW

Re: latest ideas on head flow - 10/17/12 11:53 PM

My get as much port velocity as u can. The problem is that too much and you get turbulence? The standard LA head you can only so much. It has to make that sharp turn.
Now a G3 head that's a whole different ball game. Matt
Posted By: Adobedude

Re: latest ideas on head flow - 10/18/12 12:12 AM

Tom...I don't think those are heads Aluminum Magnum heads, only a few sets of those made it out of MOPAR alive, his heads are what some guys call small port Commandos, Indy was blowing them out awhile back.
Posted By: 70Cuda383

Re: latest ideas on head flow - 10/18/12 12:23 AM

Quote:

Tom...I don't think those are heads Aluminum Magnum heads, only a few sets of those made it out of MOPAR alive, his heads are what some guys call small port Commandos, Indy was blowing them out awhile back.



whatever they are, he's asking me what port job he should go with my gut tells me that for what he wants, a 300CFM port job is overkill and money wasted on his stock stroke 360 in a 4,000 lb truck. but then we've got you know who saying that he can make them flow 300 cfm, maintain velocity, AND only increases the port by "around 1 cc"


Thought I'd come over here and see what everyone here thought. maybe I'm mistaken in what I believed about port velocity for lower RPM drivability of a street motor vs all out flow numbers for high rpm race and chasing ETs
Posted By: Adobedude

Re: latest ideas on head flow - 10/18/12 12:39 AM

With a street motor in a heavy truck I'd be more concerned with his mid lift numbers...400 to 500.
Posted By: Adobedude

Re: latest ideas on head flow - 10/18/12 12:41 AM

Part number of the heads in question...Maybe this will help.

P4532900
Posted By: sshemi

Re: latest ideas on head flow - 10/18/12 05:14 PM

For what he wants the RHS heads would be good, aldough they are heavy.
Mine flow 298 cfm at just above 0.5" lift and then gets turbulent.
This is at 185 cc ported by me.
Thats more than 1 cc removed dough.
Posted By: DakFink

Re: latest ideas on head flow - 10/18/12 07:41 PM

I stayed out of that conversation on that site.

But here's my 2-cents worth. He should Send them to Brian @ IMM or Dr. J's and tell them what he wants from them and they will get him what he needs.

I personally like Dr J's phylosohy on the subject: (copied form their website) At Dr J's Performance we do not believe on individual stages of porting, because it does not benefit the costumer. Our goal is to provide the customer with most amount of performance per dollar spent. Every head that leaves Dr J's performance is ported to its maximum potential.
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