A camshaft duration Dyno comparison (comp hyd. flat tappets) SBC

[Jersey Devil]

Looking at my magazines, I found this old article comparing 4 Comp cams (252, 268, 280, 292 High energy flat tappets).

I, thought you guys might find it Interesting for comparisoning Dyno curves and the only article that includes. Vacuum recorded for those running (power brakes,etc.).

The engine is a 350sbc, BUT it has AFR heads that flow slightly less than SBM TFS 190 heads / probably like ported Edelbrock Heads. Also had 9.7:1 compression an Edelbrock RPM manifold and 750 carb, so comparable to mopar parts.

The cams are exactly like the Comp Mopar cams. 252H, 268H, 280H, 292H

 

[Dart Frog]

Yes that's meat and potatoes article. There's always a trade-off and so many variables when picking a camshaft. Vehicle weight rear end ratio, exhaust efficiency compression ratio, intake design, automatic transmission, manual transmission and the list goes on and on... That's what makes it so much fun!

 

[273]

It shows depending what's the goal you can go with a fair size cam without effecting down low too much.

Plus down low HP is less sensitive to torque changes, hp as a percentage of torque =
At 2500 rpm hp is 47.5% of torque, At 3000 rpm hp is 57% of torque.

 

[Newbomb Turk]

Again, that’s bad testing.

There is no way you’d run the same compression with a 252 cam as you would with a 292 cam.

If you do, you’d see the same piss poor results like the test shows.

 

[crackedback]

Again, that’s bad testing.

There is no way you’d run the same compression with a 252 cam as you would with a 292 cam.

If you do, you’d see the same piss poor results like the test shows.

Did they change the distributor for initial to clean up the pull from the bottom as well? Little things that matter.

It's info, which is always interesting to read and dissect.

 

[Jersey Devil]

Again, that’s bad testing.

There is no way you’d run the same compression with a 252 cam as you would with a 292 cam.

If you do, you’d see the same piss poor results like the test shows.

Yeah, they mentioned how the combo is optimized for the 268H/280H cams. They said the 252 would make more with s regular perfomer intake and 1-5/8 headers. They mention the 292 would work better with a victor intake and 1-7/8. And probably a 1 bump in compression.

I think they tested it like that to show guys what too big for a combo looks like.

 

[Jersey Devil]

Did they change the distributor for initial to clean up the pull from the bottom as well? Little things that matter.

It's info, which is always interesting to read and dissect.

They tuned the timing and carburetor for each camshaft.

 

[junkyardhero]

the last line in that article should be etched into the lids of a million toolboxes and printed on a million more t-shirts.

 

[mario03srt]

If I’m. It mistaken Comp has dyno plots on their site for all of those XE cams plus the 274. Which was my choice @ 10.4 to 1.

 

[Jersey Devil]

If I’m. It mistaken Comp has dyno plots on their site for all of those XE cams plus the 274. Which was my choice @ 10.4 to

Yeah but Most of them are built as a complete combo, heads, intake, carb, cam and compression were all selected together.( Which is what I am trying to do). This is more relatable for 99% of people as you have an engine and usually are trying to find the cam with the Best "Compromise". Idle quality, drivability in traffic/daily, low end torque vs. high rpm power.

the last line in that article should be etched into the lids of a million toolboxes and printed on a million more t-shirts.

Yeah I worry about that too much and am always regretting getting the "Too Safe" choice. I always seem to buy the one, one step Under the one I should have gotten.

Trying NOT to do it with my current build... But I probably will have to get 2 cams or more to find exactly what I want.

 

[273]

Yeah but Most of them are built as a complete combo, heads, intake, carb, cam and compression were all selected together.( Which is what I am trying to do). This is more relatable for 99% of people as you have an engine and usually are trying to find the cam with the Best "Compromise".

100%

Idle quality, drivability in traffic/daily, low end torque vs. high rpm power.

Problem is these test don't really show driveability, people equate full throttle low speed torque and driveability as the same thing which I believe mostly to be untrue.

Be nice if someone would do a similar in car test.

Yeah I worry about that too much and am always regretting getting the "Too Safe" choice. I always seem to buy the one, one step Under the one I should have gotten.

Trying NOT to do it with my current build... But I probably will have to get 2 cams or more to find exactly what I want.

Probably will to get it dial right in the way you want it.

 

[Jersey Devil]

100%

Problem is these test don't really show driveability, people equate full throttle low speed torque and driveability as the same thing which I believe mostly to be untrue.

Be nice if someone would do a similar in car test.

Probably will to get it dial right in the way you want it.

If the rest of the car is dialed in... gearing, transmission wise for the weight if the vehicle.

I think, " What can work" for daily driving can be fairly wide.

If the gearing is way off or the tq converter is too tight... "What can work" narrows Dramatically.

I think Needing power brakes and at what rpms I want my hp, makes my choice pretty specific.

I need X amount of duration for the power I want and the width of the lsa will get me enough Vacuum for P/B.

 

[273]

If the rest of the car is dialed in... gearing, transmission wise for the weight if the vehicle.

I think, " What can work" for daily driving can be fairly wide.

If the gearing is way off or the tq converter is too tight... "What can work" narrows Dramatically.

True, A lot really handicap themselves with gearing and stall etc.. choices.

 

[TT5.9mag]

Again, that’s bad testing.

There is no way you’d run the same compression with a 252 cam as you would with a 292 cam.

If you do, you’d see the same piss poor results like the test shows.

I’m not sure I agree with “bad” testing. I’d be more inclined to say “representative” testing because that’s exactly how most jack hole engine assemblers pick camshafts.

 

[273]

Wasn't meant to be you should use X camshaft for Y engine.

To me the point of the test was to show the basic trends (curves) when going from mild to wild ish in a basic build, to help some to understand the effect of different cam choices.

 

[Jersey Devil]

Wasn't meant to be you should use X camshaft for Y engine.

Thats the dilemma we All have to face. I'm probably start with something in the middle and choose something bigger/smaller depending on how it runs.

Probably a Howard’s custom 235/243@0.050 0.640" lift. on a 112lsa. I can trade some of the power oeaks for a wider powerband+vacuum.

 

[273]

I'd just ditch the power brakes.

 

[Jersey Devil]

I'd just ditch the power brakes.

Yeah, if it needs manual brakes then it's too much toward the strip of street/strip. I don't want the bottom end of a Honda Civic where I have to rev to 3 grand just to move it, and falls on its face <3,000.

Also it's going a gen1 Dakota not a 3,200lb A body. Not going to tow anything, but will see payloads.

I come on here because there is No body on the truck forum. Also, here people are more small block oriented.I probably need to spend time on the E/B body forums.

 

[Newbomb Turk]

I’m not sure I agree with “bad” testing. I’d be more inclined to say “representative” testing because that’s exactly how most jack hole engine assemblers pick camshafts.

Yeah, that’s more like it. The testing should be used to show what not to do.

I mean, I hate to say it but how many guys on here have to do things like use manifold vacuum to get the engine to idle?

Or worse yet they (or maybe equally as bad) they lock out the timing.

This **** gets old. What really gets old is some guys NEVER learn.

 

[Newbomb Turk]

Thats the dilemma we All have to face. I'm probably start with something in the middle and choose something bigger/smaller depending on how it runs.

Probably a Howard’s custom 235/243@0.050 0.640" lift. on a 112lsa. I can trade some of the power oeaks for a wider powerband+vacuum.

That’s waisting time and money. You should be able to get one cam that is so close any other cam tilts the curve a bit.

You shouldn’t have to advance the cam to make it run either. That’s another crutch that’s used to try and unscrew a bad combo.

 

[Jersey Devil]

That’s waisting time and money. You should be able to get one cam that is so close any other cam tilts the curve a bit.

You shouldn’t have to advance the cam to make it run either. That’s another crutch that’s used to try and unscrew a bad combo.

I can get close...as close as any "expert". I called different companies every few months and get different suggests, from different salesman.

It's easily proven by the cam challenge online. Cam grinders, cam companies and engine builders were given ALL the specs and None of the cams had the same specs.

$500 for a roller cam that I can sell for 1/2, isn't a bad deal. Hell, The dyno time is the expensive part. I could basically do my own version of this test. If anything I could build another engine "for" that cam.

 

[Dave999]

i went to the cam grinders and told them what i had to work with,
gearing the resultant CR of the block crank head and piston combo
my carburetor and exhaust plans...

they said no problem

I adjusted my build plan slightly to fit, checked what he said by using tools/calculators and my measured data (tools that cause arguments here due to bad use of terms and naming conventions)

the "effective" compression ratio was key to the choice, a compression ratio that takes into account rod ratio and position of piston at the point the inlet closes. call it what ya like
it gave me some assurance that i wasn't being lead down a path that would result in failure

focused on this because the suggested static CR of 12.5:1 made me very very worried given the general consensus that 10:5.1 is king for streetable motor

i had little choice about static my virgin bore rebuilder turned out to be a mess and it was the only spare engine in the country massive cuts to head and deck that wasn't mentioned at time of purchase

very happy with the outcome

happy to pay a little more for his advice and the right cam.
If id gone with the safe option, the magazine's favorite, the one every says in the right one, mesageboard and face to face, you'd be calling me detonation dave and id be extolling the virtues of a locked out distributor at 15 BTDC.

I benefit from a semi hemi head (2/3 of a poly shape) great carburetion and a labyrinthine quench caused by my weird raised centre, piston set up, and the way it fits into the chamber

i feel luck played a part, i depended very much on talking to the right guys, using their experience, I got help from an expert cam grinder and a helpful machinist with experience in building everything from jaguar race engines highly strung ford zetec to Briggs n stratton cart engines... the only part i ignored from him was his suggestion that i sculpt epoxy in the inlet ports to take up some of what he termed the wasted space..
His view was aim for near supersonic speeds through the inlet at WOT, really packs it in when the valve opens, very much a road race, rally and circuit race focused guy.... mine was, maybe next time...

cam grinder knew my engine street and drag use.
machinist knew how to make any engine work in just about every application, drag racing was not the main area of his work.... more formula 5000 and v8 super saloon racing than drag
was a good combination

work out what you have chat to a range of people, choose what you think is best advice find away to test it, simulation, basic calculation, make your purchase

Dave

 

[QuickDart360]

Yeah, they mentioned how the combo is optimized for the 268H/280H cams. They said the 252 would make more with s regular perfomer intake and 1-5/8 headers. They mention the 292 would work better with a victor intake and 1-7/8. And probably a 1 bump in compression.

I think they tested it like that to show guys what too big for a combo looks like.

Reminds me of when I went from the 280 mopar cam to the 292 mopar cam. I have flat top KB107 pistons so compression is probably not so high for the 292. So on Crackedbacks advise I advanced it @ the crank 4°. It runs sweet from low to upper rpms.

 

[Newbomb Turk]

I can get close...as close as any "expert". I called different companies every few months and get different suggests, from different salesman.

It's easily proven by the cam challenge online. Cam grinders, cam companies and engine builders were given ALL the specs and None of the cams had the same specs.

$500 for a roller cam that I can sell for 1/2, isn't a bad deal. Hell, The dyno time is the expensive part. I could basically do my own version of this test. If anything I could build another engine "for" that cam.

I understand that. Most of the guys answering the phone are reading from the same catalogue you and I can get. Unless you have a “guy” at the cam company who knows this stuff, calling a cam company is a crap shoot at best.

There is math out there that can get you very close IF you know all the data it asks for. You can’t fudge on any of he numbers.

I’ve posted where the math is before, but you can also get the same results with certain computer programs.

Of note, most guys building street/strip engines use way more cam than the compression they run wants.

As the engine goes more towards strip/street most guys under cam for the compression ratio.

When you see enough engines on the dyno and look at the curves you see this isn’t just a trend, it’s the reality. Peak torque and power are 700-1000 rpm LOWER than they think it is.

I see it just as much on under headed stroker engines.

You can get far closer than a phone call will get you with some math.

 

[Newbomb Turk]

i went to the cam grinders and told them what i had to work with,
gearing the resultant CR of the block crank head and piston combo
my carburetor and exhaust plans...

they said no problem

I adjusted my build plan slightly to fit, checked what he said by using tools/calculators and my measured data (tools that cause arguments here due to bad use of terms and naming conventions)

the "effective" compression ratio was key to the choice, a compression ratio that takes into account rod ratio and position of piston at the point the inlet closes. call it what ya like
it gave me some assurance that i wasn't being lead down a path that would result in failure

focused on this because the suggested static CR of 12.5:1 made me very very worried given the general consensus that 10:5.1 is king for streetable motor

i had little choice about static my virgin bore rebuilder turned out to be a mess and it was the only spare engine in the country massive cuts to head and deck that wasn't mentioned at time of purchase

very happy with the outcome

happy to pay a little more for his advice and the right cam.
If id gone with the safe option, the magazine's favorite, the one every says in the right one, mesageboard and face to face, you'd be calling me detonation dave and id be extolling the virtues of a locked out distributor at 15 BTDC.

I benefit from a semi hemi head (2/3 of a poly shape) great carburetion and a labyrinthine quench caused by my weird raised centre, piston set up, and the way it fits into the chamber

i feel luck played a part, i depended very much on talking to the right guys, using their experience, I got help from an expert cam grinder and a helpful machinist with experience in building everything from jaguar race engines highly strung ford zetec to Briggs n stratton cart engines... the only part i ignored from him was his suggestion that i sculpt epoxy in the inlet ports to take up some of what he termed the wasted space..
His view was aim for near supersonic speeds through the inlet at WOT, really packs it in when the valve opens, very much a road race, rally and circuit race focused guy.... mine was, maybe next time...

cam grinder knew my engine street and drag use.
machinist knew how to make any engine work in just about every application, drag racing was not the main area of his work.... more formula 5000 and v8 super saloon racing than drag
was a good combination

work out what you have chat to a range of people, choose what you think is best advice find away to test it, simulation, basic calculation, make your purchase

Dave

The paragraph that starts with “the effective” should be copied, put in bold, italicized, out in the biggest font it can and then be made a sticky.

Then it should be added to the TOP of the forum RULES that you must sign and agree to before you can even join FABO.

Then when anyone asks about cam selection they should be given the punishment of typing out that paragraph 100 times exactly as it’s written in whatever forum the question is asked before they can post again.

Just my suggestion to help clear up cam selection threads.