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Old 12-30-2019, 02:07 PM
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Default Any Predator 420cc non hemi gurus?

Are the 420cc engines that much different that they can have a big difference in the piston height? Or are they mainly about the same? Iím trying to bump up the compression a bit in my mild 420 predator non hemi. I donít really want to mill the head at this time as that may take a while to do. Then getting pushrods to length. Just thinking of upgrading the rod and maybe the piston to a flat top. Any one know if a .040 rod from arc, is too long and will make the piston come out of the hole? Anyone know how much it may be out of the hole? Then Iíll have to get it cut and that may take time to find a machine shop that will jump on it and not wait a month to do it. Or is putting a stock length arc rod, a flat top piston and a thinner head gasket possibly the quicker way to go? Not trying to get big compression numbers, just something to bump it up for now and have fun with it as I am building another engine.
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Old 12-30-2019, 03:40 PM
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My 420cc was Powerland brand. The piston was only a few thousands in the hole. Around 0.005” IIRC. I think I shaved the head 0.075” or 0.085”. A longer rod wasn’t really an option. I don’t remember how thick the gasket was. But you want about 0.030” between the piston and the head. So if you have 0.015” pop out, you want a 0.045” gasket. If 0.005” in the hole, you can run 0.025” gasket. I think I used a copper gasket around 0.027”. Possibly from Bullfrog Motorsports??? I think that the stock gasket was around 0.045”. I can’t really help too much. Got to pop the head off, see whatcha got, and go from there.

---------- Post added at 04:09 PM ---------- Previous post was at 04:05 PM ----------

You can put a flattop piston and a thinner gasket and keep the stock size rod. I’m sure I mentioned some of this in the thread you looked at, but I don’t remember many of the details. I gave that engine away with the buggy it was on.

PS. I have a flattop piston I never installed. I think I paid $20 for it. I’ll ship it to you for $10 plus shipping if you want.

---------- Post added at 04:40 PM ---------- Previous post was at 04:09 PM ----------

This is from the Buggies Gone Wild post by Geoff, the guy at Vegas Carts....

...I ran a stock rod and valves for ALONG time and ALOT of abuse. I didnt have 1 problem until the day I put a cam in it....
With regards to bang for buck, a 420 clone with the following mods will make 20-22hp and doesnt need a billet rod:

-Timing Key
-Ported & Milled Head
-28-32mm ATV/Motocycle Carb
-Header & Free Flowing Exhaust
-HD ValveSprings

Can be done for $400 including the engine.


-Geoff Warner
There are two types of people. Those who can extrapolate from incomplete data
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Old 12-30-2019, 04:21 PM
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Looks like I’m short on the timing key and the ported & milled head in my build.
I have a 32mm pwk carb. It seems ok and tuned ok, but a stock $45 Vegas carts 24mm carb made me quicker in the 1/8th mile vs that 32mm carb by 1/2 a second. My mph was lower by 5mph but my 60’ and 330 were quicker. Bigger carb wasn’t better on this build or maybe it’s just the carb as I’d like to get a genuine mikuni.
Everything in/on the engine was the same except the carb swap.
I have the NR twister cam, 35# valve springs, 1-1/8th ID heade
I just want to up the compression a lil bit and leave it alone and have fun with it.
I have another engine that I am building to make more power with billet rod & flywheel.
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