Isky cam degreeing?

B

bdog_v

New member
P.s. I also posted this on the planet but I believe you guys have experience with offset keys for degreeing cams so I posted here to???? Here is my story.............
Hi guys I was checking the cam in my dads 345 motor he had built about 20 years ago. It still runs good but seeing how my other cams where off I bet his might be also. I need some verifiication to see if I checked it correctly?
The cam is an isky 256 model, the modest cam they make I believe.....
-the cam card says (112 lobe center ): this is the number I was using to decipher if it was advanced or retarded. I assume this is the number to look at for the (intake centerline method) of cam degreeing?
-the cam card does not say whether that number is for (intake or exhaust) just lobe center 112........
-I put the dial gauge on the intake to take the measurement and got 105.75 or about 6 degrees advanced.........
** my questions:
1. Did I use the correct number 112 lobe center off the cam card?

2. I also tried it on the exhaust valve as I was not certian I did it correctly and came up with a huge number way off.... Any idea where the exhaust valve reading would be for exhaust valve centerline. Should it be close to 112?

3. Finally this vehicle is for trailriding and ice drags not worried about mileage more the quickest point a to b so would having an offset key made for 4 degrees be worth it to go from 105.75 to 109.75 help pick up some acceleration? I was told it is good to be advanceed about 2 degrees but I am advanced close to 6 degrees???????? Any ideas?????? What does a offset key cost???????



Thanks guys kinda lost on where to go from here?????
Brandon
 
As before, 6 deg advanced is ok. Close the intake early and you get better cylinder pressure. Cylinder pressure is what you want for a torque centric engine.
All of this assumes your numbers are correct. Could you post some timing information for me to interpret. Intake opening and closing points @ .050.
 
Hello Robert thanks for chiming in. I have been reading some of your work here and it is truly impressive body of knowledge! I hope to rebuild a high end IH motor some day and hope people like you will help me make that possible! Anyway I got my helper back and got these specs for you...

The cam card calls for (@ .050” lift) the intake to open at 5° atdc and close at 27° abdc; for the exhaust to open at 39° bbdc and close at 17° btdc. Lobe center is 112°.

My results are close (@.050” lift) the intake opens at 7.5° atdc and closes at 27° abdc; the exhaust opens at 39° bbdc and closes at 14° btdc. Lobe center is 105.75 or 106.

-I believe I am o.k. With these numbers as they match up with the cam card fairly close and the other person I listed on here with the same cam. However I am not an engine builder and have alot to learn........ I plan on leaving the 6 degrees advance alone unless you suggest otherwise?

-my only thought is while ice racing without spikes in tires just regular snow tires you have to take off lightly and about half way down the strip the gas pedal is floored so more power on the upper rpm is beneficial. Most of the race occurrs in 2nd gear in a 727 transmission. Towards the finish line I am pushing middle 4000 rpm so more revs would help prevent a shift into 3rd gear.

-this last year I did it with my 304 fuel injected Scout with the nv4500 5 speed and used only 2nd and 3rd gear. It did well I actually won a few races and had a chance at winning the season!! The strip is only 1/8 mile long so at best you hit 50-65mph at the finish line...... I figured my 345 with an auto would be faster but so far the 304 is winning even with its stock cam profile and smaller cubic inches plus having to manually shift....its only about half a second faster but that's all that matters in a race!!!!!!

Here is the website that runs the event if anyone is interested!

merrill ice draggers - worlds fastest 1/8th mile auto racing on ice.

Any thoughts on my cam setup? Do you feel changing the intake centerline to 110 or 112 with a offset ket would help????


Thanks for your knowledge!
Brandon
 
If you want more rpm, advanced is not where you want to be if comparing apples to apples. You have cammed it up so that alone will give you more rpm and being advanced will help balance the engines power with the stock compression.

I would recommend leaving it alone..

Is this a contoured piston or "e" engine? If so verify intake valve to piston clearance through out the overlap range. Advancing a cam creates closer distances between the intake valve and the piston as the intake valve opens and the piston goes over tdc. Probably closest at 10-15 atdc but check the range. Easiest to put a very light spring on the valve (only need to do one) and only that pushrod in.
 
Thanks Robert for all the help. I will leave it alone until I can really rip her apart. Its still in the vehicle and runs fine so I won't make any changes for now.... :icon_up:

brandon
 
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