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Question For Mike Jones - Duration Vs Rod/Stroke Ratio

General engine tech -- Drag Racing to Circle Track

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Stan Weiss
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Re: Question For Mike Jones - Duration Vs Rod/Stroke Ratio

Post by Stan Weiss » Mon Mar 23, 2020 11:58 am

CamKing wrote:
Sun Mar 22, 2020 2:59 pm
tjs44 wrote:
Sun Mar 22, 2020 2:45 pm
Mike,what do you think for a engine for a 100% street car that has a OD trans and will operate from off idle to about 2500 with occasional bursts to 3500-4000?I know we always regress to race engines but a lot of HiPo street engines are being built these day.s with ODs.Tom
Well, first you would want to design the cam to make the most power between stall converter RPM, and 4,000rpm, but that can be tricky. Sometimes when you're working with these short duration cams, you can over-cam it, and actually make more power, thru-out the usable power curve.
Say you have an 1,800 stall, and a max RPM of 4,500. A cam designed to make power to 5,000rpm, may make more power from 1.800-4,500, then a cam designed for 4,500rpm. Even though the larger cam moves the peak torque rpm up, it can still make more torque, at the RPM the smaller cam made peak torque.
CamKing wrote:
Mon Mar 23, 2020 11:34 am
tjs44 wrote:
Sun Mar 22, 2020 7:39 pm
Mike and Stan,yes TKO 5 speeds with .64 OD.Tom
Not sure what you want to know ?

If you want to know what cam it would need, that's what my cam recommendation form is for: http://jonescams.com/street-performance/
Mike,
You answered Tom's question based on him having an auto trans and torque convertor. Which in this case is not the case.

Stan
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Re: Question For Mike Jones - Duration Vs Rod/Stroke Ratio

Post by CamKing » Mon Mar 23, 2020 12:05 pm

Stan Weiss wrote:
Mon Mar 23, 2020 11:58 am
Mike,
You answered Tom's question based on him having an auto trans and torque convertor. Which in this case is not the case.
Then you just replace the converter RPM with the lowest RPM you will be cruising at.
Mike Jones
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Re: Question For Mike Jones - Duration Vs Rod/Stroke Ratio

Post by tjs44 » Mon Mar 23, 2020 9:20 pm

Mike,usually 1500 for street driving and 1900-2000 freeway.Tom

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Re: Question For Mike Jones - Duration Vs Rod/Stroke Ratio

Post by tjs44 » Mon Mar 23, 2020 9:22 pm

I guess what im asking at that low RPMs does R/S ratio mean really anything when choosing a cam.Tom

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Re: Question For Mike Jones - Duration Vs Rod/Stroke Ratio

Post by CamKing » Tue Mar 24, 2020 11:14 am

tjs44 wrote:
Mon Mar 23, 2020 9:22 pm
I guess what im asking at that low RPMs does R/S ratio mean really anything when choosing a cam.Tom
When you're not turning over 4,000rpm, the R/S ratio plays a very small part.
Designing the cam for the correct R/S ratio will make it more efficient, but by such a small amount, you probably would never notice.
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Re: Question For Mike Jones - Duration Vs Rod/Stroke Ratio

Post by hoffman900 » Tue Mar 24, 2020 2:36 pm

CamKing wrote:
Tue Mar 24, 2020 11:14 am
tjs44 wrote:
Mon Mar 23, 2020 9:22 pm
I guess what im asking at that low RPMs does R/S ratio mean really anything when choosing a cam.Tom
When you're not turning over 4,000rpm, the R/S ratio plays a very small part.
Designing the cam for the correct R/S ratio will make it more efficient, but by such a small amount, you probably would never notice.
Shouldn't we be thinking in terms of piston speed and not rpm?

A tractor motor at 4k rpm could have the same piston speed as a 600cc sportbike at 15,000rpm.
-Bob

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Re: Question For Mike Jones - Duration Vs Rod/Stroke Ratio

Post by CamKing » Tue Mar 24, 2020 3:01 pm

hoffman900 wrote:
Tue Mar 24, 2020 2:36 pm
Shouldn't we be thinking in terms of piston speed and not rpm?
Yes, but the subject for this question was a Pontiac street engine, that turns a max of 4,000rpm.
I didn't want to be too confusing, switching to average piston speed.
Mike Jones
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Re: Question For Mike Jones - Duration Vs Rod/Stroke Ratio

Post by falcongeorge » Thu Mar 26, 2020 4:41 pm

Stan Weiss wrote:
Sat Mar 21, 2020 7:31 pm
David,
What I used was different engine families which could have the sane stroke, but they have about an inch difference in deck height.

Yes I have looked at wrist pin offset, but there is a very small limit that you can do there. Where it really becomes interesting is in inline engines where there has been some large offset of the crank center line. I need to see if I can find some numbers I had where the engine had a 10mm crank center line offset.

Here are a couple of graphs I did sometime ago for a 350 SBC 0.060" offset in both directs and the pin centered.

Stan

ab-ra-350-wpo.gif

ab-sf-350-wpo.gif
Interesting post. Thanks for posting that.

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