28.5 vs 30.5

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The Rally that's coming has a 28.5. Assuming that its good, should I leave it in there? I know the 28.5 should rev higher than a 30.5, but how much. I'm going to use a side mount mid bleed Jetpro for the pipe. This pipe will develop low to mid and is not built to let the engine rev to the moon.


I have a couple of 30.5 HY Redcat pull outs that only have a few tanks through them. I was thinking about using one instead of the 28.5. So, neither of the motors are ported.


I'm going to gear it .7:1 which is about the same as 35-25 gears. I believe the Rally comes stock 29-31. The taller gearing would benefit from any added torque the 30.5 has over the 28.5.


The motor of choice is a 27.2 FMLR, but I want to start on the FG sports line project so the budget is somewhat limited for the Rally at least for now.
 
28.5? Thats the displacement of the cy 29? here are photos of a cy29 top end bolted to a hy bottom end- i just added nachi bearings-zen seals. this little guy has hads been wrung out many, many times. always kept the filters clean. look closely @ the bottom of the jug- no wet spots! use the graphite-ss gasket. i swear, this mill is as good as new.- same compression as new- its had approx 4 gallons@ 32/1 klotz ran tru it. took a licken and still keeps on ticken. this 29 puts out good mid range- not really a high rever though. i use the gitmo lighten flywheels- after about 80-90 degrees it might be a good idea to use the stocker- heat.
 
forgot to say-- for me- this hybred top-bottom engine will walk the dog on the 30.5 - from idle to max rpm. just my opinion. nachi bearings are a must have replacement on the hy-cy engines. they can be bought fro 4 bucks each @ vxb bearings in califorina.
 
Thanks for the input.

I'll leave it and beat on it some, at least for awhile. :)
 
used 2 pipes. a ddm v1 5b pipe converted to a sidemount, and the jetpro rear mount. the jetpro overall was better.- yea, ada 990 or 813, either the 1 inch or the 3/4 inch velocity stack.- most times 990-1" stack. the 29 seemed to have a bunch of cranking compression, pulled really hard from idle up. must be the way the jug was cut-factory ported?
 
Both end bleeds. I prefer the performance of the end bleeds myself. I like to let the cars stretch their legs. We'll see how the mid bleed Jetpro performs on it. This is the one that's go'n on there.

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I would say both engines are a draw. It would come down to gearing and how you plan on using the benefit of each engine. Look at diesel trucks, low redline but huge torque numbers, twice the horsepower rating usually. They will beat out comparable gas trucks with higher HP and less TQ. You would just need gearing.

I think making your power quickly, using gearing to substitute for RPM loss would be better for all around performance, not so much with single gear cars, but multi gear more or less.. If your engine revs to the moon, what good is that if the gearing is not matched to the Peak HP range of the engine? You simply bog untill HP is made.

With Torque, it is easier to utilize power from the bottom. A 2-3 speed tranny would make a TQ motor the ideal choice to run for sure. I would run the 30.5cc motor and play with gearing.

Forgot to mention, the high flow rear exit pipe will help the torque motor open up more, could help balance the motor up more and give even more potential.
 
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The Rally is even lighter than the the X-series platform. It wont take as much torque to get it moving. However, for the best performance the pipe also needs to match the motor and driving style. The mid bleeds improve more on the bottom to mid while the end bleeds improve the mid to the top. There is limited gearing available and currently only single speed. So I have to work with what's currently available.

I high revving motor seems better since the ratio never changes. The 27.2 in my XB is currently my favorite setup.

When running the higher hp motors you can run much taller gearing and still spin all 4 tires on the launch. However, you can only gear so high, due to product availability. So to go faster you end up needing more rpms.
 
The rally is even lighter than the xb?-- cool. After ya run the engine that the car came with a while, I bet the 27.2 with a rev pipe would really get with the program! big motors- little motors- its great to have these choices.
 
Ive read low 20lb range. Ill weigh it when it gets here. It might not stay lighter. I plan on adding the aluminum suspension goodies. I have read the plastic didn't hold up the best. I would like to stiff'n up the chassis, then hollow it out to shave some weight. It's going to only be a parking lot basher so NBD.
 
alfred e numan said:
The rally is even lighter than the xb?-- cool. After ya run the engine that the car came with a while, I bet the 27.2 with a rev pipe would really get with the program! big motors- little motors- its great to have these choices.
Click to expand...
22.5 with no body. Everything else installed, like battery and even 1/3 tank of fuel.

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