Wanna hit 40-45 mph on predator 212

[boostedskyline]

Like the title states these are my hopes

Parts list
- 6" wheels
- ARC billet flywheel with key with 8° advanced timing
- max torque ss clutch 12 tooth
- 72 tooth sprocket (should I find smaller and less teeth sprocket considering I have the max torque, or does the billet flywheel compensate somehow? )
- intake with upgraded carb jets
-pipe header with removable muffler
-ngk plug and boot

Where am I bottlenecking right now (parts are Still coming in) I'm asking because my friend has pretty much the same setup except he has smaller tires and no upgraded flywheel on his and he only clocked it at 29mph, he's thinking its the huge sprocket that's messing up the gearing

 

[Kelly Wood]

Doing the math: Assume your 6" wheels are 12" in diameter and your hop-ups get you 6000 rpm.

You'll only hit a max of 36mph in a perfect world.

Go down to a 60T in the back & you'll start approaching your target speed.

 

[boostedskyline]

What would be the smallest sprocket I could go? I'm trying to not remove the governor altogether, but I am planning on relocating the spring to max it out art 5000-5200 rpms

 

[bob58o]

Since you got the flywheel, get a billet connecting rod and upgrade your valve springs.
If your friend has 12" Tires, he is revving to 5300 RPMs where the stock valves springs act as a rev limiter. Valves float or flutter or bounce or ....

Normally the stock rod is good unless you switch from the stock springs. And normally the rod goes before the flywheel. So IMHO, you should have gotten the rod before the flywheel.

But anyway, Stiffer Valve springs should get you some more RPMs, which means higher top speed. Only if you remove the governor.

Or like Kelly said, a smaller sprocket on the rear will increase top speed, but it will also cost you low end acceleration and the ability to climb (it will also be a little tougher on the clutch).

I'd probably get a billet connecting rod, 18 - 22lb valve springs, and a 60T sprocket. AND remove the governor!

---------- Post added at 09:20 AM ---------- Previous post was at 09:13 AM ----------

I wouldn't go much lower than 60T on the rear. Maybe 54??? With 12 on the front, the 60T gives you 5:1. That's good for 12" Tires and a Clutch. If you wanted less than 60T on the rear for reasons of higher top speed (at relatively low RPM), then a torque converter may have been a better option over the clutch.

---------- Post added at 09:25 AM ---------- Previous post was at 09:20 AM ----------

Are your tires 12" diameter?

 

[boostedskyline]

I'm not too worried about climbing ability since it'll only be for putting around the neighborhood/ whenever I go camping, also figured the clutch would help with increasing low end torque.

I'm not so mechanically inclined that i wanna get into pulling the motor apart to change things like rods, pistons, valves/ springs etc. I'm only doing the flywheel because I do plan on tampering with the governor. But if I do remove it completely, what's a relatively safe rpm to ride at since I'm installing a tach to keep an eye on it

But other than an engine build, getting a 60t sprocket on the back will help with getting closer to 40mph?

The rims are 6 diameter, with the tires will probably take it to 12 diameter

 

[Kelly Wood]

Exactly. But all of this, depends on what you're pushing around with that engine.

 

[boostedskyline]

The valves seem easy enough to replace, is the billet connecting rod an absolute must if I get 18 lb valve springs?

 

[Panhead5496]

also figured the clutch would help with increasing low end torque.

I thought Torque converters were better for low end torque and gave up a few mph top speed?

 

[anickode]

I thought Torque converters were better for low end torque and gave up a few mph top speed?

They do if you don't change your sprocket, but the low end torque the torque converter provides can allow you to run a bit taller final drive ratio. Plus the 10% overdrive.

 

[bob58o]

6:1 with a clutch is 6:1 at 2000 RPM and 6:1 at 5300 RPM.

6:1 with a TC is like 16:1 at 2000 RPM and will be like 5.4:1 at 5300 RPM.

With 12" tires, at 5300 RPM, geared 6:1 with a clutch... you are going 31.5 mph.
With 12" tires, at 5300 RPM, geared 6:1 with a TC........ you are going 35 mph.

10% increase in top speed due to 0.90:1 overdrive in the 30 series TC's with the 6" driven.

 

[mckutzy]

Flywheel isn't so much of a problem but the con rod is. Stock rod and FW, will be fine if you leave the stock springs in...with a gov delete/mod. Changing the springs won't allow the valves to float at a safe rpm level for the rod, and at which time it will soon let go.

 

[Panhead5496]

They do if you don't change your sprocket, but the low end torque the torque converter provides can allow you to run a bit taller final drive ratio. Plus the 10% overdrive.

Gotcha, that makes sense now