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Adventures in Engine Building-Dynamic Compression

pwtjr

pwtjr

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Contemplating two cams for 440:
  • Lunati Voodoo Solid Roller #60332 with 273/279 advertised duration, 243/249 @ .050
  • Comp Extreme Energy Solid Roller XR280R with 280/286 advertised duration, 242/248 @ .050
My static compression ratio is figured right at 10.6:1 and am using aluminum heads and Indiana elevation.
I am wanting this to run on 93 octane, but am realizing I may be on the ragged edge if I am not careful with cam choice.
With the closing point of the intake valve being the X factor, I am having a hard time deciding between these two similar camshafts. Comp gives their specific valve events on advertised duration @ .015 and Lunati gives their valve events on their card at .050.
Lunati has there's at 47.5 ABDC and the comp goes by the longer .015 # and says their intake valve closes at 66.
My questions for you professionals are:
  • What number do you put in the online calculators? I would assume the advertised full duration, right? I would have to call Lunati to get that exact closing number, or just add 15, which is half the difference.
  • So since there is hardly a difference in the .050 numbers, but Comp has a longer advertised, the action on the Comp cam is a bit slower on take off and landing than the Lunati?
  • If so, then the Comp cam would in fact bleed off a little more cylinder pressure, thus helping my dynamic compression a smidge more and give me the best chance to run 93 octane pump gas?
  • What is a good Dynamic figure to shoot for in my situation? I am hoping the modern heart shape chamber of the aluminum Trick Flow heads will allow me to run on the high side of the recommendation.
 
Also, both cams are 110 lobe sep, and installed at 106 int centerline.
 
call lunati and see where they are measuring their advertised numbers. i don't think either are ideal and definitely don't think 110lsa with a 106cl is ideal. i look at at the actual closing event because .050" numbers won't tell you what the ramps are. to me .050" numbers by themselves are worthless.

there are many factors and variables when trying to build detonation resistance. something to keep in mind is your 10.5:1 with clean chambers will be well over 11:1 with some carbon build up. just .010" of carbon build up on the chambers and piston will up the static compression 1/2 point.
 
I would look at some of the hydraulic rollers out there. You could stand to raise the duration and LSA/ICL a tick, especially on the exhaust side. Without knowing what heads and the intake/exhaust ratio along with what intake and exhaust its hard to answer a question like this with only part of the info. If I wanted to run on pump though, I'd run something like a 242/254 on a 113/111 hydraulic roller. Better cam for a pump gas motor in my opinion. Lot's of guys just wanna do things the ways they have always been done. A little more lift with the hydraulic roller, that spec will help bleed off some cylinder pressure even though it will start with a bit more, the dynamic number will be lower
 
lxmodguy said:
I would look at some of the hydraulic rollers out there. You could stand to raise the duration and LSA/ICL a tick, especially on the exhaust side. Without knowing what heads and the intake/exhaust ratio along with what intake and exhaust its hard to answer a question like this with only part of the info. If I wanted to run on pump though, I'd run something like a 242/254 on a 113/111 hydraulic roller. Better cam for a pump gas motor in my opinion. Lot's of guys just wanna do things the ways they have always been done. A little more lift with the hydraulic roller, that spec will help bleed off some cylinder pressure even though it will start with a bit more, the dynamic number will be lower
Click to expand...
I started out this build thinking I would run a solid flat tappet from Hughes. He actually suggested a cam with the durations in the 230's. The thing that changed my mind was the whole wiping of the lobes, breaking in the cam gingerly with a light valve spring, then change the springs, then cross your fingers, etc etc etc.
I then decided to do the hydraulic roller thing, using the same valve springs that I ordered the heads with, work for both kinda thing, so I was convinced the Comp 286HR with 238/242 duration was a good choice...
After a previous post about pushrod choices, and my best friend chirping in my ear the last month, I have now decided the mechanical roller is the best choice for the money.
I am just curious as to why these two cams have similar #'s at .050 lift, but the advertised #'s are significantly different. This leads me to believe that the Comp cam would be better with the extra duration from .050 down to .000 thus bleeding off just a touch more cyl pressure.
I hope I am asking this question the correct way... "Which one of the cams above will produce the lower dynamic compression value?"
 
lewtot184 said:
call lunati and see where they are measuring their advertised numbers. i don't think either are ideal and definitely don't think 110lsa with a 106cl is ideal. i look at at the actual closing event because .050" numbers won't tell you what the ramps are. to me .050" numbers by themselves are worthless.

there are many factors and variables when trying to build detonation resistance. something to keep in mind is your 10.5:1 with clean chambers will be well over 11:1 with some carbon build up. just .010" of carbon build up on the chambers and piston will up the static compression 1/2 point.
Click to expand...
Knowing where Lunati is measuring would be a big help indeed. I am envisioning being on hold for ever, so thought a post on FBBO over the weekend may suffice.
For the sake of argument though, lets assume they are doing it at .015 lift like Comp. If this is the case, the Comp cam is definitely holding the intake valve open longer (7 degrees) and would be my safer choice of the two.... right?
 
lxmodguy said:
I would look at some of the hydraulic rollers out there. You could stand to raise the duration and LSA/ICL a tick, especially on the exhaust side. Without knowing what heads and the intake/exhaust ratio along with what intake and exhaust its hard to answer a question like this with only part of the info. If I wanted to run on pump though, I'd run something like a 242/254 on a 113/111 hydraulic roller. Better cam for a pump gas motor in my opinion. Lot's of guys just wanna do things the ways they have always been done. A little more lift with the hydraulic roller, that spec will help bleed off some cylinder pressure even though it will start with a bit more, the dynamic number will be lower
Click to expand...
Also, the heads are Trick Flow, 78cc chambers, 2.19 Intake valve, 1.76 exhaust valve (these things flow pretty good for stock intake port window). Intake is an Edelbrock Torker2 that has had a deep port match done (fits under a stock ramcharger hood), QF 850, and the exhaust is 1 7/8 TTI headers with matching TTI 3 inch exhaust with H-pipe.
Car is a 69 Bee, 4 speed, 3.55 gears.
 
Call comp and tell them what you want and how you intend to use the car and they will custom grind a cam for you. It's not that much more
 
i use an old fashioned engle solid with a long closing ramp, [email protected]"-.510 lift. the asymmetrical lobe gives me some wiggle room on closing the intake valve. i have less static compression than you have but the engine is very pump gas friendly.
 
its funny people worry about dynamic . I kept getting the "where does your intake close "you will kill compression . I talked to a few cam companies , they didn't seem too worried they recommended a shelf or custom off my requirements . Jones Cams went so far as say it was immaterial as with various rpm the dynamic compression changed . Mike does seem a pretty clued in character .
Tex
 
Here's a data point for you, maybe it's apples and oranges but...

528hemi, Iron Heads, true 10:1 (I cnc'd every chamber) doesn't ping on 93 octange. Dinky Comp solid lifter cam 270 advertised 235 @.050 106LSA.

I'm in between Muncie and Ft. Wayne.
 
I would just put it this way, you can think about things "the way guys have always done it" or you can think out of the box a little bit. Most places are using 40 year old designs that use what they knew worked back then. I wouldn't buy a cam from anyone that doesn't want to know the head flow numbers from .100 to .700 lift. If they don't ask you lots and lots of questions that are very technical, then they don't have enough data to suggest the perfect cam for you.
 
TetanusShot said:
Here's a data point for you, maybe it's apples and oranges but...

528hemi, Iron Heads, true 10:1 (I cnc'd every chamber) doesn't ping on 93 octange. Dinky Comp solid lifter cam 270 advertised 235 @.050 106LSA.

I'm in between Muncie and Ft. Wayne.
Click to expand...
In your case thats an incredibly small cam in a really big motor. I would guess (and its just a guess because there aren't enough cam specs there to tell me much) that your dynamic compression is under 9:1. Cubic inches are a wonderful thing. I would also guess that motor makes maybe 600 horsepower
 
Pwtjr;

Good questions. Well thought out and precise. I can not help in the specifics. I have not been there and done that with a big block or these cams.

But what I can share is my 360 small block builds. All ran pump 93 w/10 ethonal.

360/.030, zero deck on both builds. 1 iron head open chamber for a 9.8-1 ratio and the other an Edelbrock head for a 11-1 ratio.

The iron head used the Purple cam two separate times. The smallest one was a 288 advertised, [email protected]. Then a move to a 292/.509. I switched to the Edelbrock head on the engine. The second build was the same but switch the cam to a Comp Cam of [email protected].

You should have no problems running ether of those cams with the aluminum heads. Take your time dialing in the distributor and carb jetting.
 
TetanusShot said:
Here's a data point for you, maybe it's apples and oranges but...

528hemi, Iron Heads, true 10:1 (I cnc'd every chamber) doesn't ping on 93 octange. Dinky Comp solid lifter cam 270 advertised 235 @.050 106LSA.

I'm in between Muncie and Ft. Wayne.
Click to expand...
Interesting, thank you for posting.
That is very encouraging.
 
lxmodguy said:
In your case thats an incredibly small cam in a really big motor. I would guess (and its just a guess because there aren't enough cam specs there to tell me much) that your dynamic compression is under 9:1. Cubic inches are a wonderful thing. I would also guess that motor makes maybe 600 horsepower
Click to expand...
Lol 600 I wish! Its probably making barely 1hp per cube before adding accessories. Its stock appearing with iron exhaust manifolds and a factory intake.
You were very close on dynamic, it was a little under 9 if I remember right.
I'm not sure how relevant it is to the OP but thought I'd post it up since we're from similar areas/elevation/fuel quality
 
rumblefish360 said:
Pwtjr;

Good questions. Well thought out and precise. I can not help in the specifics. I have not been there and done that with a big block or these cams.

But what I can share is my 360 small block builds. All ran pump 93 w/10 ethonal.

360/.030, zero deck on both builds. 1 iron head open chamber for a 9.8-1 ratio and the other an Edelbrock head for a 11-1 ratio.

The iron head used the Purple cam two separate times. The smallest one was a 288 advertised, [email protected]. Then a move to a 292/.509. I switched to the Edelbrock head on the engine. The second build was the same but switch the cam to a Comp Cam of [email protected].

You should have no problems running ether of those cams with the aluminum heads. Take your time dialing in the distributor and carb jetting.
Click to expand...
Thanks for the reply. This whole "picking out the cam" should have been done 1st, then build the rest of the drivetrain to suit it. I'm learning...
I talked to Dave Hughes and he was really specific with his questions. Like I said earlier, his solid flat tappet cams are interesting, and I almost went that route. He was suggesting tighter cams than the two I am contemplating now. Heavy car and modest gear ratio being my bottle necks for sure suggests a mild cam, but with my static compression ratio I think I am better off opening things up a bit more.
I appreciate everyone's input.
 
TetanusShot said:
Lol 600 I wish! Its probably making barely 1hp per cube before adding accessories. Its stock appearing with iron exhaust manifolds and a factory intake.
You were very close on dynamic, it was a little under 9 if I remember right.
I'm not sure how relevant it is to the OP but thought I'd post it up since we're from similar areas/elevation/fuel quality
Click to expand...
The calculators I am using show me with a dynamic of 8.15 with the Comp and 8.3 with the Lunati stick. I have read that 8.2 is the target for those of us running pump gas. Maybe those of us fortunate enough to live around sea level elevation can get away with a bit more if yours figures to be 9.
Once again, very encouraging for me.
Thanks again for posting.
 
I agree with the notation of the cars weight and gear ratio with the cams being considered. Mostly gear ratio.

If it were myself doing this, it would ether be 4.10-4.30 gears or a smaller cam by an approx. 10*'s.

Edited the reply.
 
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