SpeierRacingHeads wrote: ↑Sun Nov 24, 2019 9:13 pm
What Randy doesn't understand, and I'm not sure why, If both heads are 205cc and one flows 270 at desired lift and then stops and the other flows 280 at desired lift and carriers the flow curve all the way until the valve touches the retainers, the second head is always better and more versatile.
The porters vision and ability to get the shape correct to carry the curve is critical in making power.
Thinking all you need if flow to your lift is correct, better do something more than 550hp engines.
Not one mention of velocity in this senerio. Always cfm.. Thought the difference was explained a long time ago.
i don't know much, but i know enough to be able to know that you cant say one head is better than another based purely on the flow curve and be correct 100% of the time
I'd wager a bet. Going back to that 28" on the flowbench again.
SpeierRacingHeads wrote: ↑Sun Nov 24, 2019 9:13 pm
What Randy doesn't understand, and I'm not sure why, If both heads are 205cc and one flows 270 at desired lift and then stops and the other flows 280 at desired lift and carriers the flow curve all the way until the valve touches the retainers, the second head is always better and more versatile.
The porters vision and ability to get the shape correct to carry the curve is critical in making power.
Thinking all you need if flow to your lift is correct, better do something more than 550hp engines.
Not one mention of velocity in this senerio. Always cfm.. Thought the difference was explained a long time ago.
i don't know much, but i know enough to be able to know that you cant say one head is better than another based purely on the flow curve and be correct 100% of the time
I'd wager a bet. Going back to that 28" on the flowbench again.
In fact I do wager that bet with every customer.
i think first what needs to be defined is what 'better' is.
i don't know much, but i know enough to be able to know that you cant say one head is better than another based purely on the flow curve and be correct 100% of the time
I'd wager a bet. Going back to that 28" on the flowbench again.
In fact I do wager that bet with every customer.
i think first what needs to be defined is what 'better' is.
Ask Randy.
Better to me is faster down the drag strip or around a corner.
I can't believe all this has been hashed out for years and now it suddenly different..
digger wrote: ↑Sun Nov 24, 2019 9:31 pm
i don't know much, but i know enough to be able to know that you cant say one head is better than another based purely on the flow curve and be correct 100% of the time
SpeierRacingHeads wrote: ↑Sun Nov 24, 2019 9:13 pm
What Randy doesn't understand, and I'm not sure why, If both heads are 205cc and one flows 270 at desired lift and then stops and the other flows 280 at desired lift and carriers the flow curve all the way until the valve touches the retainers, the second head is always better and more versatile.
The porters vision and ability to get the shape correct to carry the curve is critical in making power.
Thinking all you need if flow to your lift is correct, better do something more than 550hp engines.
Not one mention of velocity in this senerio. Always cfm.. Thought the difference was explained a long time ago.
Chad, are you talking about the flow continuing to increase the odd cfm all the way up being good? I did a Vortec awhile back and we targeted .550 to represent a decent hyd/roller and the flow basically leveled off around .525/.550 but picked up a cfm per .100 up to .800" lift.
Maybe I’m not being analytical enough, and just going by what I “think” the results would be.
But here’s how I see it......
Chads heads have already shown they can make 675hp on a 383.
Not trying to take anything away from Steve’s efforts here, but if he ends up with what he says he’s shooting for......which is starting out with a Dart SHP 180 head, doing some rework to arrive at 270-280cfm with a finished runner volume in the 200-ish cc range....... and you removed the SRH 205’s from that 675hp 383 and swapped them for Steve’s Dart’s....... I’d be expecting the motor to take a pretty big hit in the HP dept.
PRH wrote: ↑Mon Nov 25, 2019 10:34 am
Maybe I’m not being analytical enough, and just going by what I “think” the results would be.
But here’s how I see it......
Chads heads have already shown they can make 675hp on a 383.
Not trying to take anything away from Steve’s efforts here, but if he ends up with what he says he’s shooting for......which is starting out with a Dart SHP 180 head, doing some rework to arrive at 270-280cfm with a finished runner volume in the 200-ish cc range....... and you removed the SRH 205’s from that 675hp 383 and swapped them for Steve’s Dart’s....... I’d be expecting the motor to take a pretty big hit in the HP dept.
Chris Cobb has a 383 in the works right now and the goal is 700.. I will be sure to post it up so the house mafia can pick it apart.
i think Randy's question -how much cfm do you need in a running engine??
was valid as different depressions have not really been mentioned here,please bare with me as i am not the smartest person around.
some calculations i made (only rough )
383 ci
cfm demand at peak piston speed approx 76deg atdc
5000rpm-234
5500rpm-257
6000rpm-281
6500rpm-304
7000rpm-327
7500rpm-351
8000rpm-374
i would assume that demand varies to piston position and rpm through the range.
port velocity will vary through rpm/valve lift sequence etc
if port is stable and airspeeds stable port in theory should keep flowing till choke ??
flowbench flow air one way at a time-engine dont but i think we would like it to flow one way from intake to cylinder.
i wont put all the numbers up but i played around with a set of sportsman 2 heads a while back.
198cc as cast
227cfm@.600''@28'' turbulent @ 0.400''
velocity
pinch-240ft/sec
floor-345ft/sec
apex ssr-245ft/sec
these heads had a 3 angle valve job previously and at 86% throat
i set pinch to 2.3''
blended throat to 87%
narrowed guide boss
did not touch SSR just blended through port and polished apex of SSR
so lifts above 0.500'' it picked up 12% cfm
260cfm @ 0.600''@ 28''
velocity
pinch 285ft/sec
floor 330ft/sec
apex 330ft/sec
port was smooth through the lift range and reckecked at 202cc
so then i tested at 35'' depression
wont bother with all the numbers
500''-277
550''-285
600''-288
650''-291
700''-296
velocity
pinch 310
floor 420
apex ssr 398
what i am trying to say is flow and velocity increase with depression,how much depression does running engine have at peak demand ??
i have read Larry Meaux early readings about sonic choke
can a engine choke from to much cfm??
could be a stupid question (maybe)
I can’t answer that, but it seemed to me the implication was that....... if you’re not using it “all”, then there’s somehow something wrong with the head.
I’m pretty sure I’ve never built a motor where I’ve gotten every last hp out of the heads.
I can’t answer that, but it seemed to me the implication was that....... if you’re not using it “all”, then there’s somehow something wrong with the head.
If "all" means in the entire flow curve, that is wrong, IMO. If one believes a running engine is pulling more than what the bench is showing, where you end that positive flow will show up earlier in the curve, even with the manifold attached.
If "all" means at the lift of your cam, that is a valid point.
When you access "all" of the flow at your lift, it's a pretty good indication shape and velocities are correct.
steve cowan wrote: ↑Mon Nov 25, 2019 1:22 pm
what i am trying to say is flow and velocity increase with depression,how much depression does running engine have at peak demand ??
Right, on a flow bench we keep re-setting the depression to the industry standard of 28",..
and take how long to make a flow test at any given lift ??
How directly does that relate to something happening in a fraction of that time ??
Published intake-to-cylinder pressure delta traces I've seen from running race engines vary during the intake cycle from well over 100"Hg. to single digits.
