OT:Camshaft correlation between cubic inches ?

[Joe-JDC]

We all know that if you put a camshaft in a 352 FE with 230* @ .050", it will be fairly lumpy, but in a 390, not so much, and in a 428 CJ, even less.  So my question to all you math geniuses and those with engine programs, have you ever seen a correlation with the same cam in different cubic inch engines?  The reason I ask is this, If I have a 302W cubic inch engine and a 383W(351 with 3.75" crank) cubic inch engine of same family, and the 383W makes 540 hp with a 248/252* @ 050", @6500 rpm, what will be the affect if I install that same camshaft with comparable heads, intake, headers, etc.?  Where will the hp and tq band move to?  Ideas?   Joe-JDC

[plovett]

I hesitate to reply because it sounds like a can of worms, but I am happy to put myself out there if it gets the discussion started. 

From what I have seen with engines of different displacements with the same induction, the rpm change is almost directly proportional to the displacement change.  It is more complicated than that, for sure.  A larger engine has more ring drag and possibly heavier parts, while a smaller engine has less cylinder displacement per unit of time (at the same rpm).

So, figure the percent change in displacement and that is roughly the change in rpm.   Going from a 383 to a 302 is roughly a 20% drop so the rpm will increase by roughly 20%.  6500 to 7800.  It really is that simple if you look at displacement over time, which is just displacement combined with rpm.   

JMO,

paulie

check out the Boss 302 and Boss 351 in this article.  Same cam and essentially the same induction. 

https://www.hotrod.com/articles/hrdp-1001-muscle-car-engine-shootout/

edit:  also check out the Chevy 327 and 302.  Basically displacement is the only change.

[blykins]

Joe, I'd expect the horsepower peak to move up about 1000 rpm.

[plovett]

Sounds like we need another dyno test! 

[blykins]

I've used the same parts on two different engines many times, but I don't think I've ever dropped 75 cubes before.

[machoneman]

O/T but I had forgotten about that old article. I drove a pal's near new 100% stock '71 351 Boss Mustang back in the day and that car was about the fastest I'd ever driven or encountered. And that was against all kinds of big block cars!

I hesitate to reply because it sounds like a can of worms, but I am happy to put myself out there if it gets the discussion started. 

From what I have seen with engines of different displacements with the same induction, the rpm change is almost directly proportional to the displacement change.  It is more complicated than that, for sure.  A larger engine has more ring drag and possibly heavier parts, while a smaller engine has less cylinder displacement per unit of time (at the same rpm).

So, figure the percent change in displacement and that is roughly the change in rpm.   Going from a 383 to a 302 is roughly a 20% drop so the rpm will increase by roughly 20%.  6500 to 7800.  It really is that simple if you look at displacement over time, which is just displacement combined with rpm.   

JMO,

paulie

check out the Boss 302 and Boss 351 in this article.  Same cam and essentially the same induction. 

https://www.hotrod.com/articles/hrdp-1001-muscle-car-engine-shootout/

edit:  also check out the Chevy 327 and 302.  Basically displacement is the only change.

[Joe-JDC]

Well, I am in the process of building an engine that is in complete new territory for me.  I have built many small blocks over the years, and this one is a head scratcher on camshaft selection.  I have several companies that suggested camshaft specifications, but I am not happy with what is being suggested.  Seems wrong, but I have been fooled in the past with what works vs what seems like it should work.  If anyone has a program that can give that kind of advice, I would be glad to correspond by private messages.  Thanks, Joe-JDC     e-mail     joe dot d dot craine@gmail.com

[blykins]

Joe, shoot me an email.  I'll help you out.  brent@lykinsmotorsports.com

[gt350hr]

    Joe ,
      I agree with Brent. The power band will raise at least 1,000 rpm and below that the power will be FAR less than with the smaller 302 cam. I ran 289's from '66 on and went from solids to rollers during that time. (there were no hydraulic rollers back then) . The Mustang I was racing back then was a stick and with the larger cam I needed more gear and more starting line rpm to go faster. Shift point rose to 8,000 as well Brent has a ton of dyno experience with cam changes . I was a poor guy and has to use the track to see if I made an improvement.
    Randy

[My427stang]

I will say that I don't like using things like "lumpy" because dilution due to overlap doesn't really go away in a linear basis with cubes

However, I can absolutely agree that the curve shifts in some sort of pattern with displacement, it's basic airflow, although how hard it pulls on the intake changes somewhat.

I'd defer to Brent or other small block guys on the specific question, but my gut is if all is the SAME, smaller engine, slight decrease in HP but it will have to spin another maybe 800-1000 to do it in your example.  However, if the heads and intake are even a little different, game's off

[Joe-JDC]

Ok, here is some data for thought.

289 heads flow 170/130
302 E-7 heas    169/135
302 Boss           285/190
351W                175/135
351C                 290/190ish
GT-40  302W     179/145
AFR  165            250/170
AFR  185            290/190
AFR  205            312/220
AFR  225            330/228
NEW AFR CNC     340/230
TFS TW               283/205
TFS R CNC          340/236
TFS HP 225         340/238
I could go on, but all these heads will fit on a 289-302-351W style engine.  I have had them on just about every conceivable type of build over the years, and had some really strong 306W style engines with heads that flow up to 340cfm on the street.  I never felt a loss of power or torque, but now I know there was a lot to be gained by using a much smaller port and higher velocity that I used to play with.  The engine I am building is 302-303 cubic inches, and heads will flow only 260 cfm with 10.5 compression, and max lift of .600".  Not worried about the rpm, but it will have a rod ratio of 1.94 which should rpm quite easily.  Joe-JDC               

[My427stang]

Ok, here is some data for thought.

289 heads flow 170/130
302 E-7 heas    169/135
302 Boss           285/190
351W                175/135
351C                 290/190ish
GT-40  302W     179/145
AFR  165            250/170
AFR  185            290/190
AFR  205            312/220
AFR  225            330/228
NEW AFR CNC     340/230
TFS TW               283/205
TFS R CNC          340/236
TFS HP 225         340/238
I could go on, but all these heads will fit on a 289-302-351W style engine.  I have had them on just about every conceivable type of build over the years, and had some really strong 306W style engines with heads that flow up to 340cfm on the street.  I never felt a loss of power or torque, but now I know there was a lot to be gained by using a much smaller port and higher velocity that I used to play with.  The engine I am building is 302-303 cubic inches, and heads will flow only 260 cfm with 10.5 compression, and max lift of .600".  Not worried about the rpm, but it will have a rod ratio of 1.94 which should rpm quite easily.  Joe-JDC               

Joe, 2 questions

1 - Are you willing to share specific details on the new build?

2 - What were all the cam specs and the overall build on the 383W?  I could easily plug in everything and change cid to 306 along with rod length, etc and see what happens

The electronic programs are just trending ools, they aren't great, but it's so darn easy to plug in and then cut/paste the curves

[hwoods]

https://steviescrazygarage.com/

[Joe-JDC]

The 383W has a Comp Cams solid roller,  I will have to find the cam card, but it was ~248/252  .612" lift/112 LSA.  EFI in '86 Fox GT.  Runs strong on street and idles fair with the 112 LSA.  The question above will be non-specific about this engine, just trying to get a handle on choosing a camshaft for a much smaller engine.  I have several Comp roller camshafts in hyd and solid roller for the SBF.  Several Motorsports cams, also.

Joe-JDC

[blykins]

It will just depend on where you want it to peak and what kind of horsepower you're wanting.   There could literally be a 50° swing in duration depending on your goals.