I have read about head flow for years,But?????

General engine tech -- Drag Racing to Circle Track

Moderator: Team

oldhead
Expert
Expert
Posts: 638
Joined: Sat Aug 13, 2005 9:49 am
Location: NE.Phila.

I have read about head flow for years,But?????

Post by oldhead » Thu May 03, 2018 8:36 am

Oldhead again with one of his dumb questions....I have read about head flow for years,But what about the manifold and carb?? Do they flow so high that its not worth talking about?? Say heads flow 300 at .700. Install manifold, still 300, install carb, now flow 675...Needs bigger carb..........Oldhead
Quicker then most

Carnut1
Guru
Guru
Posts: 3991
Joined: Tue Jun 11, 2013 6:32 pm
Location: Melbourne fl.

Re: I have read about head flow for years,But?????

Post by Carnut1 » Thu May 03, 2018 8:40 am

Check out the last page of my Dart 215 thead. Working on this. Thanks, Charlie
Servedio Cylinder Head Development
631-816-4911
9:00am - 9:00pm EST

oldhead
Expert
Expert
Posts: 638
Joined: Sat Aug 13, 2005 9:49 am
Location: NE.Phila.

Re: I have read about head flow for years,But?????

Post by oldhead » Thu May 03, 2018 9:55 am

I THANK YOU CHARLIE,,,,BUT,How do I find your thread?? I tried :D :D :D :D Oldhead
Quicker then most

Carnut1
Guru
Guru
Posts: 3991
Joined: Tue Jun 11, 2013 6:32 pm
Location: Melbourne fl.

Re: I have read about head flow for years,But?????

Post by Carnut1 » Thu May 03, 2018 10:20 am

oldhead wrote:
Thu May 03, 2018 9:55 am
I THANK YOU CHARLIE,,,,BUT,How do I find your thread?? I tried :D :D :D :D Oldhead
Just scroll down, it is on the first page of ST engine tech.
Servedio Cylinder Head Development
631-816-4911
9:00am - 9:00pm EST

andyf
Guru
Guru
Posts: 1338
Joined: Tue Oct 05, 2004 12:55 pm
Location: Oregon
Contact:

Re: I have read about head flow for years,But?????

Post by andyf » Thu May 03, 2018 11:32 am

Head flow is easier to measure than head + manifold + carb. Also, head mfgs don't know which intake and carb you are going to use so they just publish the head flow and let you figure out the rest.

But yes, the intake and carb flow do matter. You can kill the performance of the head with a bad intake manifold. Put a stock cast iron dual plane intake on a set of race heads and you'll lose 100 hp or more.
Andy F.
AR Engineering

PackardV8
Guru
Guru
Posts: 5542
Joined: Sun Jul 30, 2006 2:03 pm

Re: I have read about head flow for years,But?????

Post by PackardV8 » Thu May 03, 2018 12:08 pm

Yes, it's been discussed here for several years and times. And yes, the race teams with the budget do flow head, intake and carb/throttle body as a unit.

Yes, it's not new news. Many years ago, I saw a NASCAR setup where the vacuum for the intake flow was pulled out of the bottom of the oil pan. That flowed the air filter, carburetor, intake manifold, head ports and cylinders as well.

I do remember that team being frustrated, as much of their flow bench and dyno work went to shit when run into the corners on the high banks at 200+MPH. In the shop, they couldn't simulate the centrifugal forces pushing more A/F mixture to the right side.
Jack Vines
Studebaker-Packard V8 Limited
Obsolete Engineering

pcnsd
Pro
Pro
Posts: 458
Joined: Thu Dec 13, 2012 12:04 am
Location: North County San Diego CA

Re: I have read about head flow for years,But?????

Post by pcnsd » Thu May 03, 2018 2:42 pm

oldhead wrote:
Thu May 03, 2018 8:36 am
Oldhead again with one of his dumb questions....I have read about head flow for years,But what about the manifold and carb?? Do they flow so high that its not worth talking about?? Say heads flow 300 at .700. Install manifold, still 300, install carb, now flow 675...Needs bigger carb..........Oldhead
Pressure loss (and so flow rate loss) is cumulative in series. As you add parts to your intake system the pressure loss increases. I have wondered about the common recommendations for port velocity in cylinder heads also, since it is apparent that if you flow at some particular rate on the bench at 28" H2O seeking a CSA that provides 300 afps and then add on a manifold, carb and air filter. That flow rate and its attendant velocity is going to fall. I work with IR systems only and have a few general rules. I want the manifold and carb to flow ~140% the bare head rate and the air filter to flow 300%+ the bare head rate at the same pressure. I also have a formula I use to estimate the expected total flow rate when assembling components that are tested separately and use that to estimate the expected system CSA.
- Paul

GARY C
Guru
Guru
Posts: 4757
Joined: Tue May 14, 2013 10:58 pm

Re: I have read about head flow for years,But?????

Post by GARY C » Thu May 03, 2018 2:50 pm

oldhead wrote:
Thu May 03, 2018 8:36 am
Oldhead again with one of his dumb questions....I have read about head flow for years,But what about the manifold and carb?? Do they flow so high that its not worth talking about?? Say heads flow 300 at .700. Install manifold, still 300, install carb, now flow 675...Needs bigger carb..........Oldhead
I have had the same question but it usually goes unanswered, the first head I worked on with a flow bench was a Dart Pro 1 230cc head, advertised flow was 301, on my bench it was 280, after porting I had it in the 317 range, I bolted a Super Viclor on it and it went back to 280.

The thing I wondered was if people use head flow to spec a cam then why not come up with a way to include intake or if it doesn't matter, why not?.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBER AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!

Casper393W
Pro
Pro
Posts: 423
Joined: Wed Jul 06, 2016 7:18 am

Re: I have read about head flow for years,But?????

Post by Casper393W » Thu May 03, 2018 5:24 pm

On my engine build my heads alone flowed 315 cfm @ .625" once I bolted on my Tunnel Ram "which was for a 302" the flow dropped to 258 cfm and reached this max number at around .425" lift.

I have spent many hours porting to get the Cross section larger and it now flows around 270-275cfm.

In big conversation I had with David Vizard " he ported my heads" he said he has seen many times a manifold that will flow more on the bench will make less power than one that flows less... Many factors come into play regarding how the engine "sees" the manifold! Sometimes it's not about max flow... Just something to think about. I'm sure more know about this subject than I do

stealth
Guru
Guru
Posts: 1054
Joined: Fri Jun 30, 2006 9:37 am

Re: I have read about head flow for years,But?????

Post by stealth » Thu May 03, 2018 5:31 pm

There are pictures around of Smokey Yunick pulling air through the entire intake track threw the bottom of the block...
The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man.

GARY C
Guru
Guru
Posts: 4757
Joined: Tue May 14, 2013 10:58 pm

Re: I have read about head flow for years,But?????

Post by GARY C » Thu May 03, 2018 5:38 pm

Casper393W wrote:
Thu May 03, 2018 5:24 pm
On my engine build my heads alone flowed 315 cfm @ .625" once I bolted on my Tunnel Ram "which was for a 302" the flow dropped to 258 cfm and reached this max number at around .425" lift.

I have spent many hours porting to get the Cross section larger and it now flows around 270-275cfm.

In big conversation I had with David Vizard " he ported my heads" he said he has seen many times a manifold that will flow more on the bench will make less power than one that flows less... Many factors come into play regarding how the engine "sees" the manifold! Sometimes it's not about max flow... Just something to think about. I'm sure more know about this subject than I do
Yes, Wilson manifold told me the same thing, it seems the only way to know when it's to big is to test it until you reach that point, then buy another intake and stop porting a little sooner. :D
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBER AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!

ptuomov
Guru
Guru
Posts: 2140
Joined: Fri Aug 07, 2009 3:52 am

Re: I have read about head flow for years,But?????

Post by ptuomov » Thu May 03, 2018 6:24 pm

PackardV8 wrote:
Thu May 03, 2018 12:08 pm
Yes, it's been discussed here for several years and times. And yes, the race teams with the budget do flow head, intake and carb/throttle body as a unit.

Yes, it's not new news. Many years ago, I saw a NASCAR setup where the vacuum for the intake flow was pulled out of the bottom of the oil pan. That flowed the air filter, carburetor, intake manifold, head ports and cylinders as well.

I do remember that team being frustrated, as much of their flow bench and dyno work went to shit when run into the corners on the high banks at 200+MPH. In the shop, they couldn't simulate the centrifugal forces pushing more A/F mixture to the right side.
Couldn’t you tilt the whole apparatus to its side by 45 degrees to simulate a constant 1g turn? Wet flow necessary, of course.
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU

Warp Speed
Guru
Guru
Posts: 2693
Joined: Wed Jun 25, 2008 1:46 pm
Location: NC

Re: I have read about head flow for years,But?????

Post by Warp Speed » Thu May 03, 2018 6:39 pm

Why does a port need to flow 300cfm, when the engine running full song doesn't pull 800 total?!?

cgarb
Guru
Guru
Posts: 1656
Joined: Wed Jul 09, 2014 11:50 am
Location: Maryland

Re: I have read about head flow for years,But?????

Post by cgarb » Thu May 03, 2018 7:00 pm

Different inches of vacuum....heads are flowed at 28" and I believe a carb is flowed at only 10" or less. I asked a similar question to my local machine shop that I use his flowbench to test my ports, he said on restricted intake classes, even if the intake flow is less than the heads flow, improving the cylinder head flow always netted him more power on the Dyno. He said that he thought the stronger intake port pulled on the manifold and carb more.

Warp Speed
Guru
Guru
Posts: 2693
Joined: Wed Jun 25, 2008 1:46 pm
Location: NC

Re: I have read about head flow for years,But?????

Post by Warp Speed » Thu May 03, 2018 7:44 pm

cgarb wrote:
Thu May 03, 2018 7:00 pm
Different inches of vacuum....heads are flowed at 28" and I believe a carb is flowed at only 10" or less. I asked a similar question to my local machine shop that I use his flowbench to test my ports, he said on restricted intake classes, even if the intake flow is less than the heads flow, improving the cylinder head flow always netted him more power on the Dyno. He said that he thought the stronger intake port pulled on the manifold and carb more.
So your saying it is the restriction at the inlet, and that if you put a 2400 cfm throttle body on said engine, it would move that through it at max rpm, or is it still a "different inches of vacuum"?
Last edited by Warp Speed on Thu May 03, 2018 7:47 pm, edited 1 time in total.

Post Reply