[64nailhead]

I've put my engine numbers into Patrick Kelley's and KB's calculator and the DCR number's are no where near each other. The KB uses intake valve closing point at .050" lift + 15 degrees and Patrick Kelley's uses the actual intake valve closing point (my cam card uses at .006".) They differ by more than 1.6:1!!??

My engine info :
bore : 4.030
stroke : 3.25
rod : 6.25
head cc : 69
piston cc : 3.25 dome/pop up
head gasket : .039
head gasket bore : 4.166
piston to deck clearance : .020

Cam :Speed Pro CS1062R
Duration at .006" Int/Exh 304/287 deg ITC 78 deg
Duration at .050" Int/Exh 220/231 deg ITC 36 deg
Gross Lift Int/Exh .312"/.320" with 1.6 rockers
LSA : 110 deg
Intake centerline 106 deg (calculated from midpoint of opening and closing points)


Questions : 1st, which calculator is correct/more accurate?
2nd, am I missing something on my cam card or could it be incorrect? I ask because 42 degrees of crank rotation seems like alot of degrees for the intake lift to go from .050" to .006". And, according to the cam card there is more intake duration than exhaust at .006 lift, but vise versa at .050 lift. If my card is accurate, then that is ONE LOW ramp rate between .050 & .006 for the intake, and the ramp rate is a fair amount faster for the exhaust lobe in the same range. I checked a bunch of other cams and could not find one where the int duration was greater than the exh at .006" and then lower at .050" lift.
3rd, how low can the DCR be before issues develop?



FYI - I did not degree the cam when I installed it.

What do you think?

As always, all help and advice is greatly appreciated - Jim

[hcompton]

I use this one andit seems to be accurate. Now you need to read the foot note and make sure the numbers you are putting in are correct.

United Engine & Machine Co. Incorporated

Now if your numbers are at .050 then you need to add 15 degrees but if its at .006 then that number is pretty close and can be used. I do not know of anyway to convert to zero. Just keep in mind some cams have longer ramps then other so .006 can be longer on different cam types and mfr.

Dcr veries with head material and setup and how tight the squish is when complete.

[hcompton]

And did you put your piston dome in as - number or negative number. In the link i posted itnshould be neg if pop up.

[techinspector1]

OK, we have the following values.....
679.3 cc's in the cylinder
4.2 cc's in the piston deck height
8.7 cc's in the gasket
0 cc's in the piston crown (we sliced off the pop-up and put it in the chamber)
65.5 cc's in the chamber
Total 757.7
Divide by 78.4 and find 9.66:1 SCR

On the KB calculator (only one I have used for years).....
compression ratio 9.66
stroke 3.250
rod length 6.250
intake closing point 36 + 15 =51.000
DCR = 8.398:1

Looks like a good build to me, except the squish at 0.059". I would have either cut the decks or used a thinner gasket to get closer to 0.040".

[hcompton]

I see your problem.

I get 10.28:1 and 7:1 with .015 gasket.

You need to work out the deck height. If possible did you order your pistons yet. Get them so the deck will be .010 on down to zero if possible.

With .010 and .015 gasket i get 10.55:1 and 7.37:1 for dcr. Your engine will be alot happier with proper squish and scr. This should be happy on the street with good heads and proper setup.

Have you purchased the heads. 59cc will open up a lot of options to you. 59cc procomps is what i am using on my current build because the cam is so big.

[hcompton]

Oh crap i read that wrong. Ignore me.

[cdminter59]

64nailhead, the easiest way to check out what you want to know is to install a degree wheel and degree your cam. This way you can find out if the intake valve is closed at .050 or just partially closed. IDK about the brand of cam you have installed but Comp Cams valve opening and closing are at .006 on the cam card. Crane cams opening and closing are at .004 on their cam card. The Crower cam I have the opening and closing are at .050. It seems all these manufacturer just want it so confusing.

[64nailhead]

Originally Posted by techinspector1

intake closing point 36 + 15 =51.000

The intake closing point is where my concern is. If I use the closing point, at .050, of 36 deg and then add 15 deg, then all is well, BUT if I use the actual closing point at .006 of 78 deg then all is not well.

Should I assume that the KB calculator is saying that the intake valve is closed at 15 degrees past the .050 lift point? If that is the assumption, then my DCR is actually much lower because, according to cam card, my intake valve isn't closed until 78 deg. Unless, the intake valve is considered closed for DCR calculations at 51 degrees.

What do you think?

FYI - I tried to word my question so that it isn't confusing - I can't say that I succeeded, but I tried.


When I put this engine together, I relied on the machine shop to recommend the cam and pistons. He thought the engine should easily make 1 hp/cube, but I haven't been able to pull it off. The best I've done is a little less than 310. The 310 was calculated from the dyno owner's software based on actual rwhp. I realize that all dyno's are not alike, but, this got me checking into the DCR just to see whether it was OK. When I found the discrepency between the two calculators then I thought this could be some of the issue. But I don't have a good enough understanding of exactly how DCR is calculated. And that is how I got into this conundrum.


Do any of you know what happens when the DCR is at or below 6.7:1? Will the engine still run well and be low on power, or will it run poorly all the time, certain RPM ranges, or what?

For some background, this engine was put together in the spring and driven for most of this last summer and fall - about 4000 miles. I can say safely, based on driving it, that I need more stall for launch, but other than that it seems like a rocket in the car. The is quite light, around 2600 lbs. At 40 mph it feels like it's shot of gun when you lay into the throttle.

Thanks - Jim

[64nailhead]

Originally Posted by cdminter59

64nailhead, the easiest way to check out what you want to know is to install a degree wheel and degree your cam. This way you can find out if the intake valve is closed at .050 or just partially closed. IDK about the brand of cam you have installed but Comp Cams valve opening and closing are at .006 on the cam card. Crane cams opening and closing are at .004 on their cam card. The Crower cam I have the opening and closing are at .050. It seems all these manufacturer just want it so confusing.

Hey, we were posting at the same time. I agree with that lack of a uniform standard from cam companies. I think that it is the same deal with the lobe profiles. In checking out this DCR question I looked up a lot of cam specs, how much handier would it be when choosing a cam if you knew the ramp rates, or lift at more positions than max and .050. I think some of it is smoke and mirrors, but I could be wrong. Maybe Comp, Crane, Lunati, etc. want you to call them. Anyway............I think that is a subject for another thread.

I would love to degree the cam, but it can't be done in the car due to clearance issues - we currently have about .5" from the water pump pulley bolts to the radiator (using electric fan). I could try doing it with timing tape, but I don't know if that would be very accurate with a small balancer.

Thanks.

[cdminter59]

In this article by Pat Kelly he says the correct way of figuring the DCR is by using the cams advertised duration. That using the .050 reading is incorrect. But KB calculator is adding 15* so IDK who is right. I wish I had found these articles when my engine was on the stand so I could check for myself. He also says if the DCR should be in a range of 7.5-8.5. If it drops below 7.5 like you suspected the torque drops off and you also lose power on the top end. If it is in a higher range tha 8.5 no problem add racing gas. Dynamic CR

[64nailhead]

Originally Posted by cdminter59

I wish I had found these articles when my engine was on the stand so I could check for myself. . Dynamic CR

X2!

If at 1st you don't succeed, then read the directions and try again

[GMC boogie]

That is one low intensity cam lobe. Intake duration at .006 304
Intake duration at .050 220

That is a difference of 84. Sure that advertised number is at .006?

[techinspector1]

Originally Posted by GMC boogie

That is one low intensity cam lobe. Intake duration at .006 304
Intake duration at .050 220

That is a difference of 84. Sure that advertised number is at .006?

Lots of ramp. That's the way the OEM's used to grind hot cams. Speed Pro, Melling and a few other grinders still do it that way. I like 'em. Easy on the valvetrain.

[GMC boogie]

I calculate a 9.63:1 CR and a DCR of 6.76 if those numbers are correct. That is using the Pat Kelly calculator.

[64nailhead]

Originally Posted by GMC boogie

That is one low intensity cam lobe. Intake duration at .006 304
Intake duration at .050 220

That is a difference of 84. Sure that advertised number is at .006?

Exactly! Yes, that is the number on the card.

I haven't contacted SpeedPro/Federal Mogul, because I can't find a phone number, but I've confirmed this number on several different websites of companies selling this cam. The other cams that appear on the same listing from Speed Pro do not follow this grind pattern.

Does anyone have a contact number you've found for SpeedPro?

Has anyone encountered a dual grind cam where the the intake duration is greater than the exhaust at .006 and vise versa at .050 lift? And if this is accurate and other manufacturers make a cam similar, then what is the purpose of this?

As cdminter59 mentioned, I'm kicking myself for not degreeing the cam when I installed it!!! Currently I'm in the process of installing a multiport setup on this and hope to have it done in a couple of weeks and then I'm pulling the trans for a rebuild. The more I think about it, I'm thinking I'm gonna pull the engine while I'm waiting for the trans to get rebuilt to degree the cam.

Like I mentioned in the original post, if you check my DCR using Pat Kelly's calculator, you'll see what my concern is. Basically, that is the reason for my starting this thread. I have to admit that I believe what TechInspector said, but......, I can't understand how two different and reputable DCR calculators could be so far off from each other.?.