high-comp 420 piston

[OPmini]

In an effort to get away from the predator 420's measly 8:1 stock compression ratio I am looking for a high comp piston 12:1 or more. I have found a few 90mm wiseco pistons and namura pistons but I cant find the wrist pin size, can anyone point me to the direction of a high comp piston that would fit on a 420? thanks!

 

[madprofessor]

I'll be watching this thread closely, want to learn about what hotrodding can be done to a 420 with current parts availability.
Note: Research also over-length billet rods, any billet rod at all is always a good idea, longer ones even better. Got a feeling you'll need to combine that with a piston to reach the kind of ratio you want.

 

[OPmini]

I'll be watching this thread closely, want to learn about what hotrodding can be done to a 420 with current parts availability.
Note: Research also over-length billet rods, any billet rod at all is always a good idea, longer ones even better. Got a feeling you'll need to combine that with a piston to reach the kind of ratio you want.

oh yeah, this engine is already hot rodded (5lb flywheel, 30mm carb, billet rod, springs, governer delete) , im getting ready for a next level of upgrades, piston, cam, port, oil cooler, and maybe propane injection with a turbo. I might also add a billet crank, pvl, and efi, maybe.

 

[Denny]

You could send them a wrist pin so they could fit it to a piston. Just make sure you have enough piston to head clearance or enough meat in the crown to clearance it.

 

[vpd66]

oh yeah, this engine is already hot rodded (5lb flywheel, 30mm carb, billet rod, springs, governer delete) , im getting ready for a next level of upgrades, piston, cam, port, oil cooler, and maybe propane injection with a turbo. I might also add a billet crank, pvl, and efi, maybe.

If you plan to add a turbo you might want to keep the compression at 8:1.

 

[Bansil]

I agree with 8:1 with turbo BUT that was from days of HEI ignition

 

[65ShelbyClone]

Propane has a high octane rating of something like 105-110 so using it with 12:1 wouldn't be outlandish. Using it with boost wouldn't be either. However....

and maybe propane injection with a turbo. and efi, maybe.

Think about what you really want to do with the engine and decide on that before buying all the hardware or you're going to end up wasting money to get a mismatched combination that doesn't do anything as well as it should.

 

[Bansil]

You are correct, I didn't see propane.

We used to run propane on our trucks before fi kits and ls engines

 

[madprofessor]

My propane van of long ago was a very good example of propane making for a smoother acceleration than the gasoline vans they had. Propane just isn't as explosive as gasoline. I think it could be a lot of trouble to make for unsatisfactory results, just my opinion.

 

[Denny]

Propane is plenty explosive, it just does not have the energy content that gasoline does. Lower BTUs.

 

[madprofessor]

I know exactly how explosive propane can be. I bent over into the middle of 200 cubic feet of it with a pilot igniter. Used to actually have a unibrow, blew them completely off. They grew back properly spread apart, unibrow gone, but now brows go all the way down the sides around my eyes. BTW: Me as a165 lb. body was blown 20' away in that blast.

 

[65ShelbyClone]

Methanol has a lower BTU/unit mass than gasoline, but it makes more power. Same with nitromethane(it is even denser than gasoline, yet has lower BTU/lb). Two fun counter-examples.

Gaseous propane displaces a lot of space that could otherwise be intake charge air. That's the main reason it makes a lot less power than gasoline with all things being equal. In the context of this discussion, propane is not usually preferred as a high-performance fuel for that reason. It's just about mandatory to run boost or high compression to get the losses back from that and then you have to push even further to start realizing power gains.

It's also effective at increasing power with diesels, but only because diesels commonly run very lean air:fuel ratios and there is a lot of unused oxygen after the burn that can be used to burn propane. Spark ignition engines have very little residual oxygen in the exhaust and operate over a comparatively narrow AFR range. Adding propane as a secondary fuel requires either more air or less of the primary fuel in order to maintain proper running.

 

[Denny]

The only reason methanol and nitromethane/methanol make more power is you have to use twice as much or more as gasoline. They still have lower BTUs pound for pound. Octane is higher with methanol.
Propane and natural gas have lower BTUs also. With less heat the engine makes less power. Sorry but physics is physics. It’s not the alcohol that is corrosive so much as it is the water it absorbs. The alcohol just eats the rubber and plastic. I did stand in crew for top fuel teams for a season in the early 90s. Might have been the gofor chute guy most days, but I got taught a lot of other things.

 

[65ShelbyClone]

The only reason methanol and nitromethane/methanol make more power is you have to use twice as much or more as gasoline. They still have lower BTUs pound for pound. Octane is higher with methanol.
Propane and natural gas have lower BTUs also. With less heat the engine makes less power. Sorry but physics is physics.

Yes, but you didn't explain the physics (really chemistry) of it. I was just poking fun at that with examples showing that the opposite also occurs.

Propane is also not explosive nor is gasoline, natural gas, alcohols, diesel, etc. Explosives detonate supersonically by violent chemical decomposition with or without air being present. Nitromethane is the only one we've talked about that is capable of doing that under certain conditions. The others require air and they only deflagrate subsonically.

 

[Denny]

You are totally right about nitromethane being the only one capable to auto ignite under certain circumstances. It carries some of its own oxygen too. Add a little of the magic H (hydrazine) and on a hot day and it will detonate at random. In the engine or in the tank it don’t care. It makes the nitro super unstable.

 

[Bansil]

at the same time a lighter and a fart makes an explosion, or a fireball
Ya'll are above my early 80's science class, we just played with rolls of magnesium and a match

 

[Denny]

Everybody has lit farts. Drugs are bad! Mmkay. Magnesium + fire = fun. Unless you are a fireman or it is your car burning.

 

[65ShelbyClone]

Add a little of the magic H (hydrazine) and on a hot day and it will detonate at random. In the engine or in the tank it don’t care. It makes the nitro super unstable.

If the ground is shakin' and the flames are green, they must be runnin' that hydrazine.