Box Stock

Supercharged Predator 212

Gappin Foos

Gappin Foos

Member
So I bought an AMR500 supercharger for a mini cooper or vw. But I am putting it on a 212. I've tried to supercharge this motor before with a smog pump but I spun it in reverse and blew the smog pump up. My engine has Chromoly push rods, 28lb valve springs, stock crank, billet rod, flat top piston, 1-inch exhaust all the way out, ported intake, 2 degrees colder plug, and a 26mm Chinese Mikuni carb. My cam I did myself, I chopped the lobes and welded higher for more lift, the lift is unknown but better than stock. So my motor is pretty built. Im just wondering what other things I should do for ensuring the safety of the engine when supercharging it. Should I run higher octane fuel than just 91? What psi should I not go over? I also bought a boost gauge and a blow-off valve so I can control what kind of boost goes into the engine.
 
flattop1 said:
No billet rod or flywheel?
One Pound too start .
Or all in and a dust pan .
Click to expand...
Stock crank but has billet rod.

As for how much boost regulate it to one then slowly creep up at it. With the setup you have I wouldn't expect much gain. All these little engines are, are air pumps. The more air you can cram through it the higher the numbers. But without seriously modifying the head and carb for a blow through application the gain will be very little.
 
You're probably going to want to drop your compression, as well as o-ringing the head because cylinder pressure is going to increase a good bit.
Supercharging will also increase heat during combustion. The Hanson superchargers for the flathead used to tell you to add a nut to the head bolt next to the exhaust valve to help keep it from pulling out due to heat.
I'd go ahead and set the carb up for methanol.
Seems to me that might be too much supercharger for a Predator, reciprocating weight will be a problem.
Probably shouldn't go over 7 to 10 lbs boost, that should get you around a 5 to 7 hp increase with a properly sized blower.
 
yeah, I was figuring that an amr500 was on the bigger side so I'll just run her on low boost. My goal was 10lbs because Big Boys Boosted Toys put a 69 vw smog pump on a stock predator and was able to make a lot of boosts and the power was noticeable. I could run it on some E85, I think there's a pump near me. But if I'm wrong I'm probably just going to need to bump up the octane. I'll definitely run a 1:1 pulley ratio or even underdrive the supercharger. For toning down the compression, do yall suggest I put the stock piston back in ?
 
Gappin Foos said:
I was figuring that an amr500 was on the bigger side so I'll just run her on low boost
Click to expand...
The AMR500 is a Rootes style blower for motors around 1200 cc, or so. What I meant was that you would be wasting hp turning the blower.
Gappin Foos said:
My goal was 10lbs because Big Boys Boosted Toys put a 69 vw smog pump on a stock predator and was able to make a lot of boosts and the power was noticeable.
Click to expand...
Never heard of them, but 10 lbs sounds reasonable.
You might check some places like arcracing.com and dynocams.com
They might have some off the shelf parts that could help you out.
Gappin Foos said:
For toning down the compression, do yall suggest I put the stock piston back in ?
Click to expand...
You'll want the strongest piston available, I would suggest a shorter billet rod to lower compression.
I'm sure there are formula's for selecting optimum compression ratio for boost level out there.
 
While at lower boost numbers, under 15psi stock compression ratio is fine (9.0-9.5), lower wouldn't hurt. But, it's not going to matter till you're over 15psi. Which you'll never achieve most likely.

What Bob is trying to say while being nice, you're effectively pissing in the wind.

The reason is that blower is about 4-5 times or even more too big for the engine you're trying to put it on. What that means is IF you ever turn it enough RPM to produce boost. It will rob more HP to turn the compressor than it will gain back from the boost it does manage to produce. Yes, while a supercharger setup is the most effective method for a single cylinder engine, You'll need something a lot smaller.

You effectively have about 0.2L and you're trying to boost it with something designed for up to 2.0L. Even at the lowest 0.8L tolerance for this blower, you're WAAAAAAAAAAAAAAY out of it's efficiency range. You'd need something around 1000-1500 or 2000cc to utilize this blower effectively.

(Edit) It's been proven time and time again, especially with normal turbo type setups on single cylinder engines. Unless it's VERY appropriately sized and designed. It might produce 7-10psi or more, but the HP gain is usually 0, or in many cases actually negative.
 
Last edited:
****, what I should have done is an AMR300. Once I get the AMR500 I'll just return her cause I bought it on amazon and buy an amr300. Even then it might be a little big.
 
Flattop's post is your best bet, twins or a common case Vtwin or anything with two or more cylinders around the 640-800cc range would be good.

Read this, there seems to be some decent info there for this. The 300 might work. But the last post goes over how inefficient it will be from heat. Which also takes away a lot of your gains. Which is another reason boosting on single cylinders isn't great. You'd really need a air to water intercooler to be remotely effective.

But, if you're having fun then that is all that matters. But, don't expect huge gains.


https://www.diygokarts.com/community/threads/amr-300-supercharger.41512/
 
Depends on how it's setup, it either starts to build up in the intake tract, which is why you run a boost controller. Or, depending on how much boost it is, it won't hurt anything and just gets ready for the next stroke.
 
Yeah so I would be running a blow-off valve, so when it builds up it'll just open up and dump at the desired psi. It would be awesome if I could retard the timing. I guess I could mark TDC with a sharpie then go to BDC and mark there on the flywheel then make marks from there to figure out the timing. I saw a picture with three blowers, a 68-69 VW smog pump for 33cc-300cc motors, then the AMR300 for 250cc-1000cc motors, and the AMR500 for 1000cc-2000cc motors. So furthermore the AMR300 is a little big but if I overdrive the supercharger so that when the crank rotates once, it rotates the supercharger twice, I can make up for the consumption of power used by the supercharger from the crank. Boom problem solved. So the only thing It needs is to retard the timing, keep the engine and supercharger cool, and get the air-fuel mix right. Now maybe, just maybe, the stock timing will be good enough for 10psi. Cause, correct me if I'm wrong, but the more boost the more retarding of the timing. So I'll probably try and leave stock timing for now, and run it on 91 with some octane booster. Any other thoughts or suggestions.

Heres the guy I was talking about
 
ted said:
just a Thought. what happens to the boost when the intake valve is closed?
Click to expand...
the manifold / plenum is to small for an efficient pressure system. If you remember the Hanson system, they had a added surge chamber / plenum to have an additional volume to absorb and supply volume as the engine went through induction cycles. I would duplicate such a system with a volume equal to twice (minimum) the displacement of the engine.
 
^^^ I was thinking plenum Volume as well.
Accurately measure flywheel circumference divide by 360 = degrees per inch of circumference.
Relating this too crank degrees is the trick as moving the flywheel also moves its relationship too TDC .
Thus you have to relocate tdc after each adjustment.
 
Direct drive (1:1) will take less power than over driving the compressor. (1:2)
It will take twice the power to overdrive it in the manner you describe.

Perhaps you were thinking under driving the compressor?

The ultimate setup would produce the exact boost pressure required without wasting any energy by blowing off excess pressure.
 
95 shaw said:
Direct drive (1:1) will take less power than over driving the compressor. (1:2)
It will take twice the power to overdrive it in the manner you describe.

Perhaps you were thinking under driving the compressor?

The ultimate setup would produce the exact boost pressure required without wasting any energy by blowing off excess pressure.
Click to expand...
If I have a bigger pulley on the crank than on the blower how would it consume more power to drive it?

Cause the crank would be spinning the blower pulley more. The bigger pulley on the crank would spin the blower faster.
 
Years ago, I machined the silver one and had it on a ATC70 that had many custom one off parts. After the proof of concept, I CNC'd the black/purple one to put on a Briggs but never got to it. The 70 had 12:1 compression and I used a Tillotson carb on methanol and made 14lbs of boost
88E1058C-0642-420B-9D1E-1BEF8BA22156.jpeg
. It was a mean machine!
 
Gappin Foos said:
If I have a bigger pulley on the crank than on the blower how would it consume more power to drive it?

Cause the crank would be spinning the blower pulley more. The bigger pulley on the crank would spin the blower faster.
Click to expand...
If you do not understand that driving the blower faster requires more power from the crankshaft , I fear the rest of the build is way above your pay grade.
 
You must log in or register to reply here.
Back
Top