to wrap up the cam selection saga for the D-150,,

decided to go with the Oregon 1333 intake profile on the intake and the 1527 intake profile on the exhaust,,
will give a 265 / 250 duration with valve lifts in the .431 range. Should work well for the low rpm / torque...

Now that the cam profiles are selected,, I need to know where to set the cam timing..

finished the head clean up yesterday cc'd the combustion bowls again,
for the block, put in the crank, a rod and one of the pistons that I will be using and verified piston recession..again.

put the combustion volume info into the Pat Kelly calculator,,
to get to my target dynamic compression of 8.0, which gives me a static compression of 9.15, I need to reduce the combustion chamber volume from 57 to 47 cc, so will be milling .068 off the head. I decided to do it all in the head and leave the case alone..

with the combustion chamber volumes set, I wanted to see how the intake centerline setting affects the dynamic compression ratio.
that info is on the spread sheet linked below:

(see below, found an error in one of the input values)

I am going to target for the 102 Intake centerline,, but if the engine is sensitive to octane I can move to a 106 Intake centerline and lower the dynamic,, If it looks like there is more to be had on regular gas,, I can move to a lower intake center and raise the dynamic.

I'll give Oregon a call early next week and get the cam headed their way.


regards
DT

well i went from 56cc to 44cc with .110 off so you may need more than .068 off...

but what is the cam duration at .050? .431 lift seems kinda low...

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I went back and re did the calculations using the Silvolite calculator,,
found the static and dynamic ratio's to be about 2% lower on that calculator with 47 cc chambers that what I had posted using the Pat Kelly calculator.

so, heck, went back through my notes and did the process again, found that yesterday I had put the rod length in at 6.999,, corrected that to 6.699 and re ran it
here is the corrected work sheet, I deleted the link in the 1st post. The one below uses the correct rod length values and shows the static and dynamic ratio's with 47 and 45 cc chambers.
The PK and Silvolite calculators bring near identical results.

http://www.flickr.com/photos/13718356@N ... 274662383/

so to get to the target of just above an 8.0 dynamic, with the cam and settings I am looking at, will need to get to 45 cc chambers.
so 58-45=13,,,
I am using the 1cc=.0068 to calculate the mill amount, so now that looks like .088 will be coming off the head.

the duration at .050 is 212 and 206,, this a low rpm tow vehicle motor,,I am targeting to have power in the 1500 to 3500 band. And the goal is to be able to run regular gas with a fair amount of advance.

thanks

DT

What LSA? I would make it 106 or so. 225s like more overlap than more square/oversquare motors. You might need premium gas with that (basically stock) cam profile and 9.1 static comp. Ign timing curve will have to be smithed to give no pinging under both load and light throttle conditions. 102 centerline looks right to me with that cam. I would not go above that or low end will really suffer.

Personally, I just design everything for premium, since it is only slightly more expensive than 87 (6-8%).

Lou

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Lou

the LSA is 105,, there is over 40 degrees of overlap,,

yep, 102 is the target intake centerlne,,

I though I read where with the right timing, regular gas will run with a dynamic compression of up to 8.25 and regular runs fine at a dynamic compression of 8.

let me do some more looking.

thanks
DT

OK, with 105 LSA you are probably OK. Most cams that small have LSA around 110. I am not a DCR user or aficionado, but my experience tells me it will not be a piece of cake to get 87 to run ping free on a combo like yours. I'm sure it can be done, but will take some futzing with dist (timing curve). Just a word that significant tuning will be required.

Happy building,

Lou

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