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Author Topic:   Need some advice on compression, 9:1 or 12:1
xhubby
Member
posted November 04, 2003 06:48 PM
I need some sound advice, so naturally I came to this forum. Our local track is having their rules meeting this Sunday for our limited mod class. One of the issues to be voted on is whether to run 9:1 motors with small(7.25" single disk) clutches, or stay with the current rule that is "no compression limit(we run about 12.5:1),360cid with a minimum 10" stock single disk clutch. We may be given the option of running one or the other.We can only run 2-link or leaf spring rear suspensions.Which engine/clutch set up would be more advantages over the other? Our track is a semi banked 3/8 that is usually dry slick by feature time, and the driver is very smooth on the throttle. I would like to make a knowledgeable decision. Thanks guys.


racer17j
Member
posted November 04, 2003 07:20 PM
we run the 9:1 rule at our track in our 360 mods and it's good close afordable racing if i had a vote i would definatley vote for the 9:1. the pistons are cheaper for one thing and the lower compression is easier on the bottom end. another thing it limits the heads a guy can use to a 76 cc head which also makes the racing more afordable because you can get those heads everywhere instead of haveing to hunt for hi priced double humps or vortecs


Eljojo
Member
posted November 04, 2003 08:15 PM
The answer lies in the depth of your pocket. If you've got the 12.5 motor and the light weight 10" clutch--why make the swap? However if you have to purchase a motor and clutch....so? I have raced against the Tazwell purestocks and they are required to run dish pistons. Those guys spend some big bux making the low compression motors put out the ponies--but they ROCK AND ROLL! I would stick with whe stuff I already had and see how the guys who switch fare.


xhubby
Member
posted November 04, 2003 09:21 PM
Right now, the motor we have is a 6" rod flat top 355 with 50cc pro action heads. Our engine claim rule is $525.oo or swap. I was thinking that with the 9:1, & a cheaper set of heads, I would have my money in the clutch (not claimable) as opposed to my heads. I was just confused (I'm not much of an engine guru) as to the difference in the two options, performance wise. How would a 9:1 with a small clutch perform on a dry slick track as opposed to a 12.5:1 with a stock clutch (ours is an 11" clutch & pressure plate with an aluminum flywheel, not all that light, but it was free).


xhubby
Member
posted November 06, 2003 06:03 AM
Wow, I thought there would be alot more opinions on this than just two. Thanks racer17j & eljojo for your thoughts. No one has said what performance difference there would be though.


RCRacing #08
Member
posted November 06, 2003 06:39 AM
Performance wise you will be better off with the 12.5:1 engine.

Cost wise you will be better off with the lower compression 9:1 engine

ok
Joe


Eljojo
Member
posted November 06, 2003 07:55 AM
X-Hubby? Where do you race? I have been wanting a set of the Pro Toplines and $525 sounds like a great price! LOL!! If your stuff hasn't been claimed (yet) I think I would thank the guy who gave me the 11" clutch for letting me use it. Then I would sprend the $ on a 10000 rpm lightweight set up. They are pricey... but then you jave the best (of both worlds) Good luck!


budman14
Member
posted November 06, 2003 08:14 AM
hey eljojo i read ur post and saw u raced at the taz i raced there in the pure street class for 8 years ran in top 5 most of the time me and 56 car gavem **** anyways i quit sold my cars an went back to spectateing that place has become a joke if ur buddies with the tech guys u can get away with anything didnt mean to change subject of this post but couldnt pass up on spilling the beans on tazwell speedway ps i know guys in that class runing 406,383,434,377 go figure


budman14
Member
posted November 06, 2003 08:17 AM
xhubby i think i would go with 9.1 rules save u alot of money and with the right combo that 9.1 motor will be right up there with the high comp motors my theory is a well handleing car with a low comp motor can run with any ill handleing car with high comp an i bet that low comp motor will live longer just my opinion.

[This message has been edited by budman14 (edited November 06, 2003).]

xhubby
Member
posted November 06, 2003 11:52 AM
Eljojo, Thats why we are looking at the 9:1 motors. A guy should not have to run that kind of motor to be competitive in a limited mod class. Believe it or not, there were several motors out there that made mine look like a pooch, including one that had ported & polished Dart heads that were port matched & setting in a brand new $15,ooo,oo car.Quite a limited class huh. There were no claims at all last year.
Budman14, I agree with you. Our car handles really well & think we can be just as fast with the 9:1, but I wanted some input because like I said, I'm not really into engines that much & was'nt sure how the smaller motor would fair against the bigger ones. I was guessing that a small clutch would liven up a 9:1 pretty good. Thanks guys.


xhubby
Member
posted November 06, 2003 08:18 PM
Eljojo, I sent you a PM


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