Author Topic: Stock Exhaust on a Mild Build?  (Read 942 times)

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Offline Deye76

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Re: Stock Exhaust on a Mild Build?
« Reply #50 on: December 17, 2017, 04:51:40 AM »
From Mackie's web site, "Excellent for 80, 88 and 89 inchers. Likes 8.5 to 10.0 C.R. 2000 to 6000+. High performance springs recommended."

EV27 is a bolt in. Mackie doesn't say what max CR is suggested. A half point not too bad, but a full point could be the difference between a strong motor and a ping monster.
East Tenn.
2014 CVO RK, 2015 RGS, 1992 FXRP

Online 1FSTRK

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Re: Stock Exhaust on a Mild Build?
« Reply #51 on: December 17, 2017, 05:52:39 AM »
From Mackie's web site, "Excellent for 80, 88 and 89 inchers. Likes 8.5 to 10.0 C.R. 2000 to 6000+. High performance springs recommended."

EV27 is a bolt in. Mackie doesn't say what max CR is suggested. A half point not too bad, but a full point could be the difference between a strong motor and a ping monster.

You can't take Andrews recommended bolt in compression ratios as the last word, particulairly on the old Evo stuff. Back then half the guys were taking out the junk stock ignition boxes and installing points. Andrews never had a dyno or test bikes they went off 1980's math and feedback from the few builders they talked with.

Now stock bikes crank 205-215 lbs and we have DTT ignitions with custom timing maps, better combustion chambers, higher speed ports, better exhaust or at least no drag pipes so tuning is much better all around. The spec sheeet in the dyno section lists they used a 10.5 dome piston, but does not say what the compression is, the pistons are down -.007, we don't know what head gasket, no head cc's, and he has not done a CCP test. Most guys cut the heads a ton so they don't need to but pistons, he needed pistons so if the chambers grew with the head work and bigger valves, the domed pistons may be making some of that back up. If it did come out to actually be 10.5 static the BB calculator says 201 CCP at 990" with the EV27. I would bet it is no where near that but would be tunable even if it was.

The biggest problem with compression or big cubic inch on the Evo was hard starting and it says no releases, stock battery and starter so I would doubt it was crazy high CCP.
"Never hang on to a mistake just because you spent time or money making it."

Offline Deye76

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Re: Stock Exhaust on a Mild Build?
« Reply #52 on: December 17, 2017, 01:41:05 PM »
All good points. :up:
Still would like to know who ported the heads, as 100hp in a 80" with a bolt in cam is phenomenal. IMHO
East Tenn.
2014 CVO RK, 2015 RGS, 1992 FXRP