running a 7.90 engine in 8.90 class

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running a 7.90 engine in 8.90 class

Postby sprayed347 » Tue May 01, 2018 9:34 am

besides trying to slow it down . any disadvantages?
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Re: running a 7.90 engine in 8.90 class

Postby coburja » Wed May 02, 2018 11:10 pm

It sounds doable but it's a nightmare. Unless you're a fan of inconsistency and going out in early rounds, I'd avoid it like the plague.
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Re: running a 7.90 engine in 8.90 class

Postby RNorton » Sat May 05, 2018 9:31 pm

Not buying the inconsistency argument...

An intake restrictor and a little weight will get you were you need to go easily, our engine went 7.50's with a slightly bigger cam and 42mm carb at similar weight.

It really depends on how you slow it down, its going to take some work but I believe its not as bad as it sounds. We ran an 0.9" intake restrictor and 75 lbs to go from 8.0's to 8.90's with pretty good luck. We went to three finals and one win in 14 races with a rookie driver, for most of the season we battled a bog from not leaving at a high enough RPM for our engine combination. If it were not for that we would have had better luck I think, that was most definitely nothing to do with slowing an engine down.

This year we took the intake restrictor out and went to a 2.5 gear, still working the kinks out. A setup like this I can already tell you will take some major clutch tuning to make it play nice. Right now we are running 8.90s at 79 MPH, there is more left in it for MPH when I get the shift right. It shifts a lot later, you'll need a high angle helix on the driven to get it to shift in the typically range most people recommend.

You will work the belt hard and need more clutch flyweight for a given flatline RPM than a "standard" setup.
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Re: running a 7.90 engine in 8.90 class

Postby sprayed347 » Mon May 07, 2018 2:53 pm

are you guys making your own restrictor or buying them
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Re: running a 7.90 engine in 8.90 class

Postby sprayed347 » Thu May 17, 2018 4:22 pm

I have a 33 sleeved down to a 28 also has anyone tried that?
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