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Cast 421cub


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How much compression should I run with +7 timing & 39pwks? Im looking to get a set of 39's or 35's really soon. What the difference in performance going with the 39's over the 35's? Remember this is a cast 421

 

the one i just put together is an "out of the box" cylinder, really fun little motor.

it has mid/low 170ish psi cranking compression. some 39's will give you more power all over, at least they did on my motor...

if you are having traction issues, sort those out first.

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I use to run a stock stroke HJR dune ported stock cylinder engine that was a really hard runner. I always wanted to make it accellerate faster & just about maxed it out. As everybody should know by now I blew the engine two times in less than a year. Long story, so I was convinced to get a 421 cub if I wanted more accelleration & I could later on down the road port it for more accelleration. So I jumped on the 421 cub & used the previous bolt-ons that I already had because I was told by a few site sponsors that my bolt-ons work well with the 421cub. My current set-up is in my sig. & I do agree that my 421 cub pulls alot harder than my ss dune ported cylinders but it's not exactly pulling hard enough for me. Im trying to get as much bottomend accelleration out of the cylinders as cast before getting it ported. I love the mid to top side but it's the 1st-3rd gear that gets me. I am making this thread to get opinions on what i could do to help my accelleration from 1st-3rd. I want that arm snatching hit from the start. Now it could be that im missing the power cause when my tires just spin from take off & when I switch to second it hooks then. What are some of you guys opinions on how you would set up a cast 421cub to run on 100LL? Even the guys that dont like 100LL how would you set it up on 110 race gas? Thanks in advance Reek

 

 

 

You can't have top without losing bottom G. You could have the cyls decked and see if that helps out a little bit?

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Thanks for all the advice.....I'm going with the 39's cause soon as I get back from busco next weekend. I am pulling my motor out of this duner chassis & installing it in a stock rolling chassis set-up for drag racing. I will be running it an 1/8th mile on asphalt & 300ft on dirt. What are some good gearing combinations for 1/8th mile & 300ft. I know one will not work best for both.....Thanks for all the help.

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Port that cub night and day difference alcohol To race gas alcohol is so worth it and some timing will be awesome 12 paddle extremes or mini staggered and American racers also for either sand or asphalt slingshot lockup is the shit it's a must and you don't go through clutches as fast as the lockup and stealth mode under a stock cover as far as gearing look in the search for ur setup weight and how much slippage in the clutch you want for asphalt racing

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Port that cub night and day difference alcohol To race gas alcohol is so worth it and some timing will be awesome 12 paddle extremes or mini staggered and American racers also for either sand or asphalt slingshot lockup is the shit it's a must and you don't go through clutches as fast as the lockup and stealth mode under a stock cover as far as gearing look in the search for ur setup weight and how much slippage in the clutch you want for asphalt racing

 

Thanks alot.....good info right here is just what I needed. :headbang:

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  • 4 weeks later...

Thanks for all the advice.....I'm going with the 39's cause soon as I get back from busco next weekend. I am pulling my motor out of this duner chassis & installing it in a stock rolling chassis set-up for drag racing. I will be running it an 1/8th mile on asphalt & 300ft on dirt. What are some good gearing combinations for 1/8th mile & 300ft. I know one will not work best for both.....Thanks for all the help.

 

Well the rolling chassis I was suppose to buy didnt happen. The guy didnt hold his end of the bargain. So I have to stick with what I have & work from there. I need some 39 pwk's, lockup/cover, 39mm intakes & 21cc cub domes. If anybody have these parts for sale let me know.

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  • 2 weeks later...
if you are having traction issues, sort those out first.

Listen to those words. If you spend time/money on setting up your bike with your current power level, it will perform much better than slapping on some sniper pipes or any pipes that you want so badly. My bike used to hook in 4-6th. I got tired of playing catch up to the point where i was aggravated with me bike. Then i found out about pro wedge 2 tires and that was history. I've been seeing 4sno i think it's called. But i know my current tire well.

 

Then over ride and lock up. It can be VERY hard to nearly impossible to shift a high hp banshee with a lockup and no override.

 

Vito's sells an undercover slingshot style lockup. It's what i use. I like it because it works with the stock case. I want to say it was close to $220 but dont quote me on that, it was years ago when i got it. Heck, i dont even know if they still make/sell them. But if so, it's a good bit cheaper than the other type and you can adjust it A LOT. Since mines a play bike, i put a little more metal balls than what the instructions called for.

Edited by RagunCajun
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