Author Topic: Is there a "rule of thumb" for HP vs intake flow for heads?  (Read 1379 times)

0 Members and 1 Guest are viewing this topic.

FERoadster

  • Sr. Member
  • ****
  • Posts: 370
    • View Profile
Is there a "rule of thumb" for HP vs intake flow for heads?
« on: August 03, 2020, 10:00:05 PM »
A friend much more knowledgeable then me and I were discussing head intake flow vs HP potential.
His statement seemed legit so I thought I'd throw it out here as a question/discussion point.

Hypothetical question
427 +017 block RPM intake and 850 Holley carb. 1-7/8 headers, cam: please someone name one that would be appropriate.
Compression 10.5

1st engine heads flow 275 CFM at 600 lift

2nd version exactly the same engine heads flow 300 at 600 lift.
Consider both versions a very detailed custom build

His thoughts are HP can be approximated or have the potential at 2 times the CFM intake flow.  plus or minus 10%
Your thoughts?

Richard >>> FERoadster



Joe-JDC

  • Hero Member
  • *****
  • Posts: 1098
  • Truth stands on its own merit.
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #1 on: August 03, 2020, 10:44:17 PM »
I have tried for years to find a correlation to airflow vs potential, and find that there is a lot more to the question than a simple answer such as you propose.  For years, the formula of  CFM x .257 x #cylinders was used, but every time I use that, it seems optimistic vs the actual dyno results.  I have tried average cfm airflow, and doubled that, which comes closer to actual potential, but that does not always work, either.  What I try to use is airflow through the intake manifold and head together, with the first formula, and it really comes close.  Not a lot of information available for that combination, but it works.  So, just for grins,  275 x .257 x 8 = 565.4 hp, and 300 x .257 x 8 = 616.8 hp.  This is theoretical, so take it with a grain of salt. 275 x 2 = 550 hp, and 300 x 2 = 600 hp.   That 10% fudge factor certainly comes into the parameters, and if you think about it, that is a lot of swing in potential.  Joe-JDC
Joe-JDC '70GT-500

e philpott

  • Hero Member
  • *****
  • Posts: 719
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #2 on: August 03, 2020, 10:45:53 PM »
Most builders say double cfm for potential horse power, 300 has 600 horse capabilities but NHRA Stock racers kind of blow that theory out of the water . But besides 600 lift , flow at 200 lift up is important as 600 lift if flow only numbers of your cam has only a max lift of 600 meaning you can’t have lousy low lift numbers with the 600 lift cam and expect a miracle

WerbyFord

  • Full Member
  • ***
  • Posts: 241
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #3 on: August 03, 2020, 11:32:20 PM »
Most builders say double cfm for potential horse power, 300 has 600 horse capabilities but NHRA Stock racers kind of blow that theory out of the water . But besides 600 lift , flow at 200 lift up is important as 600 lift if flow only numbers of your cam has only a max lift of 600 meaning you can’t have lousy low lift numbers with the 600 lift cam and expect a miracle

The "double your intake CFM" = MAX horsepower potential on pump gas is about the closest to a rule of thumb I could think of.
And that's about the MAX - if everything else is right on.

Think about the top engines of the 1960s - the Hemi, the L72 rat, the Medium Riser. They had intake flows nearing 300, so 300 x 2 = 600 hp.
That doesn't mean you got 600hp from the factory - more like 460hp give or take a little.
But, in NHRA trim, they did indeed get to around 600hp, and that was with very little work to the heads as very little was allowed by NHRA.

jayb

  • Administrator
  • Hero Member
  • *****
  • Posts: 6725
    • View Profile
    • FE Power
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #4 on: August 04, 2020, 08:22:28 AM »
I think the key word is "potential" HP per cfm of intake flow.  As Werby mentioned, you need a race motor calibration to really take advantage of that.

I usually use a factor of 2.1 HP per cfm if I'm building a real strong engine.  Here's a few examples from some of the engines I've done over the years:

511" Medium Riser used at Drag Week 2005, peak intake flow was 340 cfm at .700", HP was 706 at 6700, HP per cfm was 2.076

530" High Riser used at Drag Week 2013, peak intake flow was 401 at 0.800", HP was 850 at 7100, HP per cfm was 2.119

585" SOHC used at Drag Week 2016, raised and welded intake ports flowed 460 at .700", HP was 1004 at 7100, HP per cfm was 2.182

504" Medium Riser used as a dyno mule for testing the 351 intakes, if I recall correctly peak intake flow was 330 cfm from Joe Craine ported Edelbrock heads (Joe, maybe you can check this?), peak HP was 723 at 6300, HP per cfm was 2.191


None of these engines were really maxed out; for example, none had 15:1 compression, most were 13:1, and the first one on the list was only 11.5:1 if I recall correctly.  But I have seen legitimate dyno data of numbers of up to 2.4 HP per cfm, on a really high winding small block at another dyno, so it's possible to get pretty far past 2:1 for HP per cfm.  The intake tract is the critical piece...
Jay Brown
- 1969 Mach 1, Drag Week 2005 Winner NA/BB, 511" FE (10.60s @ 129); Drag Week 2007 Runner-Up PA/BB, 490" Supercharged FE (9.35 @ 151)
- 1964 Ford Galaxie, Drag Week 2009 Winner Modified NA (9.50s @ 143), 585" SOHC
- 1969 Shelby Clone, Drag Week 2015 Winner Modified NA (Average 8.98 @ 149), 585" SOHC

   

Joe-JDC

  • Hero Member
  • *****
  • Posts: 1098
  • Truth stands on its own merit.
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #5 on: August 04, 2020, 09:53:36 AM »
The problem I have with the cfm x 2 is the cubic inch of the engine is not taken into the equation.  A 302 with a 280 cfm head, and a 445 with a 280 cfm head will have very different horsepower and torque numbers.  I drove a SBF on the street for years with a 330 cfm TFS head, and thought it was a monster.  Put a 230 cfm head on the same shortblock, and it was just as potent on the street, actually felt stronger at times.  Like Jay, I think compression ratio has to be factored into the equation.  Compression ratio will come into the factor when you start figuring HP/CI and TQ/CI, regardless of the cfm of the cylinder heads.  This year, the Masters of Motors competition was supposed to increase the compression ratio from 10.5 to 11.5 for the Old Iron class.  It will be an interesting comparison to last year's dyno numbers since most everything else will remain the same except the headers must not have steps in the primary tubes.  Will have to wait until next year for that dyno comparison, though, because the MOM was put on hold due to the virus.  Joe-JDC
Joe-JDC '70GT-500

Barry_R

  • Hero Member
  • *****
  • Posts: 1596
    • View Profile
    • Survival Motorsports
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #6 on: August 04, 2020, 09:53:55 AM »
Airflow numbers can provide useful guidance as to power potential when comparing similar parts, but they are not anywhere near a fixed reference.  Most airflow numbers are given at 28"  - a value which has absolutely nothing to do with actual operating characteristics of an engine, but instead is tied to the capabilities of the test equipment in common use at the time the "standard" was adopted.

As examples, you can stick a 340 cfm wedge low riser on an engine, a similar flowing medium riser, a tunnel port, an SOHC, or a filled port high riser - - and you would get significantly different power numbers.  Port targeting relative to the valve, height off of the deck, port volume, runner length and shape are all characteristic not reflected in a simple flow metric.  Raise the flow demand on a given port with extra cubic inches, enhanced efficiency, and/or higher RPM and the flow characteristics of a given port will change as velocity goes up - some may get better, some worse.

My427stang

  • Hero Member
  • *****
  • Posts: 3188
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #7 on: August 04, 2020, 10:03:02 AM »
Joe, your rule seems plausible, but it also isn't far from 2:1 on a V-8 (2.056)

I like the 2:1 on an FE because it's easy and quick to explain differences, it can be conservative.  Not to bring a dirty subject in, the 460 guys usually use 2.2.  You can see from Jays numbers, and supported by Barry's comments, that engine design as a whole matters.  That being said, as Jay improved port design, even on the C intake, the numbers were a little better with the better port.

The key is of course match the entire build to itself, however, often we can explain why something happens too.  The guy with a 260 cfm Edelbrock and a HUGE cam can't make the numbers of a better head and less cam...easy to subtract the difference in flow and multiply by two to explain while bench racing.

Really simplified...fast guys make power with heads...certainly more to it, but assuming the car can hook and parts match properly, usually holds true...
---------------------------------
Ross

- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

blykins

  • Hero Member
  • *****
  • Posts: 3221
    • View Profile
    • Lykins Motorsports
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #8 on: August 04, 2020, 01:26:41 PM »
Joe, your rule seems plausible, but it also isn't far from 2:1 on a V-8 (2.056)

I like the 2:1 on an FE because it's easy and quick to explain differences, it can be conservative.  Not to bring a dirty subject in, the 460 guys usually use 2.2.  You can see from Jays numbers, and supported by Barry's comments, that engine design as a whole matters.  That being said, as Jay improved port design, even on the C intake, the numbers were a little better with the better port.

The key is of course match the entire build to itself, however, often we can explain why something happens too.  The guy with a 260 cfm Edelbrock and a HUGE cam can't make the numbers of a better head and less cam...easy to subtract the difference in flow and multiply by two to explain while bench racing.

Really simplified...fast guys make power with heads...certainly more to it, but assuming the car can hook and parts match properly, usually holds true...

The 2.2 rule for 460 guys seems reasonable.   1206 hp with a 550 cfm head here recently.
Brent Lykins
Lykins Motorsports
Custom FE Street, Drag Race, Road Race, and Pulling Truck Engines
Custom Roller & Flat Tappet Camshafts
www.lykinsmotorsports.com
brent@lykinsmotorsports.com
www.customfordcams.com
502-759-1431
Instagram:  brentlykinsmotorsports

plovett

  • Hero Member
  • *****
  • Posts: 1334
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #9 on: August 04, 2020, 04:15:25 PM »
Discharge coefficient may help compare two heads with similar flow numbers?   Or average cross sectional area.  Or port volume.  In any case you will end up with ratios of flow to area or volume.   That might "flesh out" the simple flow numbers to some extent   

http://www.wallaceracing.com/discharge-coef.php

pl
« Last Edit: August 04, 2020, 07:23:49 PM by plovett »

FERoadster

  • Sr. Member
  • ****
  • Posts: 370
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #10 on: August 04, 2020, 09:32:45 PM »
Here is my cam card.  engine is a +030 427 with a 3.98 crank  Cam purchased new from Gene Kitchen about 8 years ago. I bought it primarily due to the larger exhaust potential for 100% street driving in a car right at 3000# with a 4.57 gear and wide ratio toploader. Intake will be the 6X2 Edelbrock with Edel. heads and 2.19 valves .  Heads flowed 306 at 600 lift.

Hope this helps with  the 2X HP rating

Richard
« Last Edit: August 04, 2020, 11:39:41 PM by FERoadster »

My427stang

  • Hero Member
  • *****
  • Posts: 3188
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #11 on: August 04, 2020, 10:15:51 PM »
I think the limiting factor will be your intake manifold but it should be a pretty stout combo

Of course the intake has a cool factor....I’d guess there’s probably 50 hp more with a modern intake

Super cool though!
---------------------------------
Ross

- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

FERoadster

  • Sr. Member
  • ****
  • Posts: 370
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #12 on: August 04, 2020, 11:50:41 PM »
Ross thanks for the reply. Yes the intake is totally for the wow factor.
The rest of the build: C3 Long CI headers. RC blowproof BH. Vertex Mag.  6 Stromberg WW carbs, Aluminum WP, Edelbrock Marine TC cover with the legs cut off.  Mustang II disc frontend with PS (way less weight than the 60 Vette huge cross member),  No conv. top, heater delete (not needed in SW Oregon) no wipers body stripped to the bare minimum.  Hoping for just under 3000#

BTW Jays testing showed that the Edelbrock 6X2 performed in the top 1/4  of his tests, Tuning will be the issue.

Richard
« Last Edit: August 04, 2020, 11:54:17 PM by FERoadster »

jayb

  • Administrator
  • Hero Member
  • *****
  • Posts: 6725
    • View Profile
    • FE Power
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #13 on: August 05, 2020, 09:31:03 AM »
That 6X2 intake did a lot better than I thought it would, peak power with that intake was almost as high as the top intakes.  It lagged a little in the midrange, but still a really good intake.
Jay Brown
- 1969 Mach 1, Drag Week 2005 Winner NA/BB, 511" FE (10.60s @ 129); Drag Week 2007 Runner-Up PA/BB, 490" Supercharged FE (9.35 @ 151)
- 1964 Ford Galaxie, Drag Week 2009 Winner Modified NA (9.50s @ 143), 585" SOHC
- 1969 Shelby Clone, Drag Week 2015 Winner Modified NA (Average 8.98 @ 149), 585" SOHC

   

cjshaker

  • Hero Member
  • *****
  • Posts: 3839
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #14 on: August 05, 2020, 09:46:48 AM »
Am I getting this right? You're putting a 427 FE into a '60 Vette?
Doug Smith


'69 R-code Mach 1, '65 427 MR, 2x4, 4-spd, 4.30 Locker
2 1965 Galaxies with 390s
1970 F-350 390
1958 Ford Ranch Wagon 390

FERoadster

  • Sr. Member
  • ****
  • Posts: 370
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #15 on: August 05, 2020, 10:37:04 AM »
Doug yes. I bought the basket case 60 Vette in 1977 for $2400 and it has a new interior carpeting instrument panel etc.
It was taken all apart by my 2nd cousin who gave up on it and moved to Florida. Never saw or heard from him since.
I've been offered crazy money for it but it would cost me a lot more to  get a Cobra or an equivalent sports car. I've got a 1969 Mustang 9" that is the same width as the original Vette axle. The Mustang II is a tubular A arm setup by Fatmans that was in my 56 Ford PU that I ended up scrapping. (Michigan Rust victim)

Here is  a picture of the engine compartment. Huge empty space just waiting for the FE.

Richard

Chrisss31

  • Full Member
  • ***
  • Posts: 115
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #16 on: August 05, 2020, 10:41:13 AM »
Payback for all the LS powered Mustangs.  Love it!!

jayb

  • Administrator
  • Hero Member
  • *****
  • Posts: 6725
    • View Profile
    • FE Power
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #17 on: August 05, 2020, 10:48:06 AM »
Richard, have you seen the old Hot Rod article where somebody put a 427 FE engine in a 64 or 65 Corvette?  Somebody here probably has a copy...
Jay Brown
- 1969 Mach 1, Drag Week 2005 Winner NA/BB, 511" FE (10.60s @ 129); Drag Week 2007 Runner-Up PA/BB, 490" Supercharged FE (9.35 @ 151)
- 1964 Ford Galaxie, Drag Week 2009 Winner Modified NA (9.50s @ 143), 585" SOHC
- 1969 Shelby Clone, Drag Week 2015 Winner Modified NA (Average 8.98 @ 149), 585" SOHC

   

thatdarncat

  • Hero Member
  • *****
  • Posts: 1541
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #18 on: August 05, 2020, 12:09:43 PM »
Richard, have you seen the old Hot Rod article where somebody put a 427 FE engine in a 64 or 65 Corvette?  Somebody here probably has a copy...



Kevin Rolph

1967 Cougar Drag Car ( under constuction )
1966 7 litre Galaxie
1966 Country Squire 390
1966 Cyclone GT 390
1968 Torino GT 390
1972 Gran Torino wagon
1978 Lincoln Mk V

Royce

  • Hero Member
  • *****
  • Posts: 528
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #19 on: August 05, 2020, 12:41:02 PM »
I was there at Jay's for that dyno test of the 6x2 intake.. I think with about 2 weeks more carb fiddling linkage engineering and cam changes we could have knocked the Perfomer RPM off it's perch  Jay cut it short due to the potential fire hazard of 6 leaky Holley 94s.  Would love to rerun it with a sextet of brand new Stromberg 97s.. Let's see   that's about 4k worth of carbs  lol
1955 Thunderbird Competition Coupe Altered Chassis "War Bird" 383 Lincoln Y block 520 hp
1955 Thunderbird 292 275 hp Y Block
1956 Ford Victoria 292 Y block
1956 Mercury "Thumper"433 cu in 445 hp Lincoln Y Block
1957 Mercury 2dr Wagon "Battle Wagon" drag car  Currently engineless,  Boss 9 transplant coming soon.
1957 Thunderbird Glass body Tube Chassis drag car 333 cu in 500 hp Ford Y block
1958 Mercury Monterey  430cu in 400hp 3x2 Super Marauder
1961 Starliner 390/375 clone
1960 Starliner 352/360hp, real one
1966 Falcon Pro Touring project

My427stang

  • Hero Member
  • *****
  • Posts: 3188
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #20 on: August 05, 2020, 01:00:16 PM »
That 6X2 intake did a lot better than I thought it would, peak power with that intake was almost as high as the top intakes.  It lagged a little in the midrange, but still a really good intake.


I was there at Jay's for that dyno test of the 6x2 intake.. I think with about 2 weeks more carb fiddling linkage engineering and cam changes we could have knocked the Perfomer RPM off it's perch  Jay cut it short due to the potential fire hazard of 6 leaky Holley 94s.  Would love to rerun it with a sextet of brand new Stromberg 97s.. Let's see   that's about 4k worth of carbs  lol

I would stay I stand corrected, but better would be "I fell over in amazement"  that's cool and suprising!


Doug yes. I bought the basket case 60 Vette in 1977 for $2400 and it has a new interior carpeting instrument panel etc.
It was taken all apart by my 2nd cousin who gave up on it and moved to Florida. Never saw or heard from him since.
I've been offered crazy money for it but it would cost me a lot more to  get a Cobra or an equivalent sports car. I've got a 1969 Mustang 9" that is the same width as the original Vette axle. The Mustang II is a tubular A arm setup by Fatmans that was in my 56 Ford PU that I ended up scrapping. (Michigan Rust victim)

Here is  a picture of the engine compartment. Huge empty space just waiting for the FE.

Richard

Richard, that's going to be awesome.  I am not one for Chevy punishment, but I love the idea based on how a big FE will run.  Thant's a cool machine!
---------------------------------
Ross

- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

FERoadster

  • Sr. Member
  • ****
  • Posts: 370
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #21 on: August 05, 2020, 01:42:01 PM »
Royce and others: The Stromberg WW flows about 20% more than the 97. They are carbs that came out in the late 50"s or early 60's. My first one was on a 1965  2 ton GMC 305 CI V6 (can't remember the Cubes) but the carb was really smooth. Since then I've collected more then 20  complete WW's and have somewhere near 10 new ones. I usually pick them up for around $20 each. I've also got near 10 parts carbs.
A few years ago I posted CFM rates for 94's 97's and WW's on here.  I'll see if I can find the post
Richard

Here is the post

Jay and others: Did some searching  on HAMB  for a short time today and looked for CFM data on 94's
Here is my preliminary finding. First off. 2bbl carbs are rated at 3" vacuum where 4bbl carbs are at 1.5" so I'm including some # for each.
The Holley-Ford carbs are designated by the venturi size in decimals of an inch. ie 94=.94, 81, 48 and Stromberg 97 as well .97

So flow ratings are as follows

Carb Model    CFM@3.0"  CFM@1.5"

94                   251            176
81                   192            135
48                   250            175
LZ                   229            160
ECG                264             185

Strom 97         214             150
Strom WW       357             250   not sure of which venturi size 2 variations one @ 1.125 and another @ 1.1875



« Last Edit: August 05, 2020, 01:48:59 PM by FERoadster »

frnkeore

  • Sr. Member
  • ****
  • Posts: 356
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #22 on: August 05, 2020, 03:42:43 PM »
Is your 6x2 manifold a 3 bolt or 4 bolt flange?

If 3 bolt, the 2100 Holley, with a 1 1/16" venturi ( a 94 but, with 1 1/16 on the side) would be best. If it's a 4 bolt, the WW's are much lighter but, the Rochester, 2CG carbs, offer 350 and 500 cfm @3".

BTW, the Stromberg 48, has a 1 1/32" venturi. The 48, comes from the Ford part number 48- of 1934. Harder to find and more expensive, only used 2 years.
« Last Edit: August 05, 2020, 03:46:29 PM by frnkeore »
Frank

WerbyFord

  • Full Member
  • ***
  • Posts: 241
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #23 on: August 06, 2020, 10:22:33 AM »
Royce and others: The Stromberg WW flows about 20% more than the 97. They are carbs that came out in the late 50"s or early 60's. My first one was on a 1965  2 ton GMC 305 CI V6 (can't remember the Cubes) but the carb was really smooth. Since then I've collected more then 20  complete WW's and have somewhere near 10 new ones. I usually pick them up for around $20 each. I've also got near 10 parts carbs.
A few years ago I posted CFM rates for 94's 97's and WW's on here.  I'll see if I can find the post
Richard

Here is the post

Jay and others: Did some searching  on HAMB  for a short time today and looked for CFM data on 94's
Here is my preliminary finding. First off. 2bbl carbs are rated at 3" vacuum where 4bbl carbs are at 1.5" so I'm including some # for each.
The Holley-Ford carbs are designated by the venturi size in decimals of an inch. ie 94=.94, 81, 48 and Stromberg 97 as well .97

So flow ratings are as follows

Carb Model    CFM@3.0"  CFM@1.5"

94                   251            176
81                   192            135
48                   250            175
LZ                   229            160
ECG                264             185

Strom 97         214             150
Strom WW       357             250   not sure of which venturi size 2 variations one @ 1.125 and another @ 1.1875



Great chart!
Similar data in Tex Smith's "the complete (old) Chrysler Hemi" by Ron Cerdano.
It lists those same carbs but not the "WW".
Seems the "WW" was uised quite a few years -
My scroungy data shows venturi & throttle sizes & cfm at 3" Hg of
1.08 x 1.436 256cfm
1.18 x 1.436 287cfm
1.24 x 1.436 294cfm
1.31 x 1.562 356cfm (a guess on that last one, but that' where I get flow of 356cfm at 3" Hg)
Since you have so many WW's, wondering if you can confirm if these or other sizes actually existed & when.

WerbyFord

  • Full Member
  • ***
  • Posts: 241
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #24 on: August 06, 2020, 10:37:17 AM »
Here is my cam card.  engine is a +030 427 with a 3.98 crank  Cam purchased new from Gene Kitchen about 8 years ago. I bought it primarily due to the larger exhaust potential for 100% street driving in a car right at 3000# with a 4.57 gear and wide ratio toploader. Intake will be the 6X2 Edelbrock with Edel. heads and 2.19 valves .  Heads flowed 306 at 600 lift.

Hope this helps with  the 2X HP rating

Richard

More to the original question:
I Gonkulated your buildk using the same carbs Jay used in his dyno tests I think, 2110 Holleys at 185cfm each at 1.5" Hg. At 1110cfm total plenty of air!
Gonkulator says
Torq 514 at 4400
Powr 546 at 6500

Now, on the heads:
Cut intake flow by 10% => down 14hp
Cut exhaust flow by 10% => down 16hp
Cut BOTH by 10% => down 23hp
I think engines always want more flow- - just not necessarily more port area.
For example, let's de-stroke your engine with a 390 crank, down 23cid.
Results:
Torq -23 ftlb about as expected
Powr -8 hp
So those extra 23cid only gain you 8 hp on top. Not enough airflow, but that's not unusual.
As you add inches, most engines gain torque 1-for-1 or so, but only gain power at 1/4 to 1/2 hp/CID - yours is about in the middle there.

Big Ford power in a little 60 Vet - should run good!

C6AE

  • Full Member
  • ***
  • Posts: 157
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #25 on: August 06, 2020, 10:37:29 PM »
This is a great project, Best Corvette ever!
Please keep us informed of your progress?

FERoadster

  • Sr. Member
  • ****
  • Posts: 370
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #26 on: August 06, 2020, 11:23:09 PM »
Frank: my 6X2 is the 3 bolt version but the WW throttle  shaft on the drivers side hits the VC so I've got spacers. A novel thought I've had is to turn the drivers side carbs backward and use a bell crank with  the top pushing and the bottom pulling in that way both would open with no issues and all linkage would be between the carbs. (a much cleaner install). I will have to figure out how hard the pedal pressure will be and balance springs.
A picture of the intake with carbs in the normal positions. Planning on using 2 sets of FE 3X2 linkage for progressive action.
When I finish my 1948 Continental in a few months I'll start a member project thread on the Vette.
Richard
« Last Edit: August 06, 2020, 11:27:18 PM by FERoadster »

Falcon67

  • Hero Member
  • *****
  • Posts: 1526
    • View Profile
    • Kelly's Hot Rod Page
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #27 on: August 07, 2020, 09:59:19 AM »
I use the 1 x Time Slip method.  (MPH/187)^3 x Weight =  1/8 mile RWH.  Then swag some bogus drive train loss percentage to get flywheel, more or less.

frnkeore

  • Sr. Member
  • ****
  • Posts: 356
    • View Profile
Re: Is there a "rule of thumb" for HP vs intake flow for heads?
« Reply #28 on: August 07, 2020, 12:55:11 PM »
I'm from a different era, 6x2 wasn't uncommon, in the late 50's threw the 70's. I feel in love with multi carb engines (more than 3) in 1959. I lived on a rural road with a straight stretch of at least 1.5 miles. One day a '32 or '34 Ford coupe, made a run on my street. It had a nail head engine, with 6x2's and I'll never forget the sound of the carbs, as it pasted me.

In those days, most where called "log" manifolds. You could even by kits, with a piece of round tubing, intake flanges and tubing, to fit the flanges, then weld it together.

In 64/65, I had a 410 MEL, I bought a 6x2 manifold for it and two sets of 348 Chev tri-powers to put on it. I was going to put it in my '60 Galaxy, to replace the 352 but, I got drafted in '65 and while I was in the Army, my dad hauled the engine off, for scarp. I kept the manifold for a long time after that but, threw it in the scrap pile, at work, in '76 when I moved out of SoCal.

Did Jay have that 6x2 ported in his test? If not, I bet a good porter could take it up a notch or two, on the manifold test scale.
Frank