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so...after doing a bit of research i found a nice little equation dealing with runner length in relation to TQ and RPM's. there was some discussion about my dyno's after the MACE insulator was added and the drastic fall off of TQ and HP around 6200RPM. it was first considered possibly due to weather, dyno, or other variables than can affect day to day dyno pulls. but after my research...i believe it is directly related to increasing the runner length by adding the 25mm insulator (.984 inch).
here it goes...
david vizard rule:
The general rule is that you should begin with a runner length of 17.8 cm for a 10,000 rpm peak torque location, from the intake opening to the plenum chamber. You add 4.3 cm to the runner length for every 1000 rpm that you want the peak torque to occur before the 10,000 rpm.
so yeah, we don't rev up to 10,000 but our redline is 7,000 and i don't know the actual runner length of our IM. (pre-MACE insulator days) so far i've shown consistent peak HP around 6500RPM and a fairly flat TQ with a steady drop off in TQ starting at 5500RPM @ 240ftlb ---> 7000RPM @200ftlb's. (i know this is backward from the way most people read 5,000,000ftlb's of TQ at 3500RPM but the emphasis is on the RPM, not peak TQ)
moving on...so 4.3cm = 1.69 inches. and 25mm = .984 inches. fyi...4.3cm is 43mm...if that isn't mind bottling then your doing good. so according to Mr. Vizard's theory, my peak TQ should shift to the left by roughly 580RPM.
25mm/43mm = .581 x 1000(RPM) = 581RPM
.984in/1.69in = .582 x 1000(RPM) = 582RPM
according to my dyno sheets with the MACE 25mm insulator, my peak TQ is now right around 5000RPM at 245ftlb's with a slightly more drastic fall off starting around 6200RPM reaching 200ftlb of TQ at 6550RPM.
its rough math and im not an engineer but thought i'd share my thoughts on what i found using the internets.
enjoy
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