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Tue Apr 26, 2022 6:10 am

experimenting with these on a small dual port engine.

at what rpm do they actually start making boost?

Is it possible for a basically stock engine to "starve" itself prior to boost?
IE.pulling far more vacuum while trying to pull air/fuel through the unit prior to boost?

Is there a base line pulley size to match the engines minimal air/fuel needs.
-mainly the minimal rpm the unit must spin for the engine to operate as if the super charger wasn't inline "blocking" the induction in a draw through application.

Tue Apr 26, 2022 6:24 am

There are tons of threads about this on STF. There is also a calculator for determining proper pulley size.

Ive always wanted to see someone stuff two AMR300's on a set of single throat dual carbs.

Tue Apr 26, 2022 6:29 am

Chickensoup wrote: There are tons of threads about this on STF. There is also a calculator for determining proper pulley size.

Ive always wanted to see someone stuff two AMR300's on a set of single throat dual carbs.

This just activated my Kadron stiffy :D

Those AMR500 sure are cheap, I've been reading about them recently. May be fun on a big-bore 40 horse or 36 horse setup like a poor-mans Judson 8)

Tue Apr 26, 2022 8:12 am

vwinnovator wrote: experimenting with these on a small dual port engine.

at what rpm do they actually start making boost?

Is it possible for a basically stock engine to "starve" itself prior to boost?
IE.pulling far more vacuum while trying to pull air/fuel through the unit prior to boost?

Is there a base line pulley size to match the engines minimal air/fuel needs.
-mainly the minimal rpm the unit must spin for the engine to operate as if the super charger wasn't inline "blocking" the induction in a draw through application. wow what a question. starve the engine for fuel&air....really?? there is a very simple fix for that. it's called a idle screw. but there may not be a fix for the other thing.sorry. before boost it will have either vacuum or no vacuum.kinda like a engine normaly has. perhaps all that stock vacume will pull the super charger faster and make it turn the crank so the engine will make more horsepower with out any boost or lost hp from spining the supercharger, and then you could just shut off the fuel and let perpetual motion take over......somethen to think on.

Tue Apr 26, 2022 10:17 am

If I recall, the max continuous rpms on the AMR is 16,000. So if you keep your engine under 5,500 rpm you can easily get away with a 3:1 ratio. I don't know how much boost this makes. Verify the max rpm on your blower before doing anything though. These things are really made for tiny engines, smaller than a VW.

Tue Apr 26, 2022 10:29 am

Japanese micro-compact kei cars and cappucino types seem to be perfect for stuff like this.

Tue Apr 26, 2022 4:04 pm

mark tucker wrote: vwinnovator wrote: experimenting with these on a small dual port engine.

at what rpm do they actually start making boost?

Is it possible for a basically stock engine to "starve" itself prior to boost?
IE.pulling far more vacuum while trying to pull air/fuel through the unit prior to boost?

Is there a base line pulley size to match the engines minimal air/fuel needs.
-mainly the minimal rpm the unit must spin for the engine to operate as if the super charger wasn't inline "blocking" the induction in a draw through application. wow what a question. starve the engine for fuel&air....really?? there is a very simple fix for that. it's called a idle screw. but there may not be a fix for the other thing.sorry. before boost it will have either vacuum or no vacuum.kinda like a engine normaly has. perhaps all that stock vacume will pull the super charger faster and make it turn the crank so the engine will make more horsepower with out any boost or lost hp from spining the supercharger, and then you could just shut off the fuel and let perpetual motion take over......somethen to think on.

no shit...

but let's look at it another way.
Assume there was no belt driving the super charger. In this case, the lobes/rotors would be an obstruction in the path of the air/fuel flow.
The vacuum of the engine would not freewheel the super charger to an rpm equivalent high enough to provide the same flow of air/fuel as an intake manifold without any obstructions (lobes/rotors)
The vacuum of the engine would be very high essentially "starving" for air/fuel.

That said, with a belt driving the super charger, to match the flow under the vacuum of a non super changed engine, the super charger will have to run at a certain rpm.

guess the questions comes down to:

how many CFM flow through a stock manifold at idle on a bone stock engine?
how many rpm must the amr500 spin to provide the equivalent CFM?

Tue Apr 26, 2022 5:35 pm

If you have a 2000cc engine, that means it could move 2000cc in one engine cycle (two revs)

The 500cc supercharger moves 500cc in one revolution

So it would need 2:1 ratio on the belts to just break even.

Engines or superchargers do not have exactly 100% VE, but it gets you in the ballpark.

Tue Apr 26, 2022 7:03 pm

I don't see why ppl spend their time on these, a turbo will put out way more boost without robbing horsepower too. not to mention, have yall seen these units that have failed and the coating coming off the rotors? probably a lesser concern, but what about the added side load on the crank snout / bearing?
I once thought about putting an m90 supercharger on a vw but at something like 12lbs of boost it took 50hp just to turn the supercharger. look it up.

don't get me wrong it is a cool setup but I just don't think they can compare to a turbo.

far as the OP, I don't think an underdriven supercharger will choke down an engine when you consider how closed off a butterfly is at part throttle. or the difference an air bleed makes at idle. I don't know the math but consider how much air that supercharger has to move in order to feed an engine even 10lbs of pressure, if it can do that it can feed the engine plenty of air without and boost at all even at low rpms of the supercharger

Tue Apr 26, 2022 7:19 pm

Same here. I got excited about it once, didn't get very far.
I have a sc14 supercharger but if it goes on anything it will probably be a toyota.

Wed Apr 27, 2022 6:01 am

Turbos are not free HP as so often is wrongly told. A turbo has to create back pressure in order to spool up and that costs power. The higher your boost the more back pressure it causes so yes a turbo robs power too! It's just less than a supercharger mostly I believe because you don't have the friction losses of belts, pulleys and high belt tension. There is also a smaller rotating mass in a turbo.

It would be interesting to put an engine with a turbo on a dyno, not hook up the intake side and make a few runs compared to runs without the turbo and a standard header.

Wed Apr 27, 2022 6:49 am

You're not going to get near the power with a blower that you will with a turbo. The best case scenario with these AMRs on a stock engine is to achieve Judson like numbers. These things were built to make small modern engines more efficient and have better emissions. But they were made to do that with modern fuel injection and computer controlled timing. So while you can gain hp and torque with one, it's not going to turn your bug into a race car, not by itself.

Also in response to richardcraineum's comment about the coating on the rotors, I think this may be due to gas degrading the coating and poor remanufacturing. All of these blowers I have seen in their original engines don't seem to let any fuel touch them. They also usually have intercoolers.

Wed Apr 27, 2022 7:33 am

Email these people. They should have the answers.
https://www.thesamba.com/vw/classifieds/detail.php?id=2522021

Wed Apr 27, 2022 8:28 am

or Speak with Mario at TheDubShop, he has done EXTENSIVE testing with super chargers on small engines with very good results.

and as to why super charger over turbo? theres definitely pros and cons to each. A super charger makes power differently than a turbski.

https://thedubshop.com/products/packaged-kits/amr-supercharger-with-efi/

Wed Apr 27, 2022 8:33 am

Well we've been having some fun testing upper limits of the unit so far.

Free wheeling (open ended, no load) we've run the unit up to approx 24,000 rpm without failure.

these things SCREAM!!

next up we'll be trying to break the 30,000rpm mark.

short 3-5min runs intending to only see if it will explode or seize.
If we can make it do so, we will surly post some video :wink:

SO, since we are comfortable these will be ok in their 16,000 rpm rating, we attached it to a test engine.

First attempt with our intake set-up though posed issues that led to my initial questions.

We mocked up some thick rubber elbows (to see if they would swell and burst as a safe guard to the engine) from the outlet to the intake manifold.

Oddly, the super charger has not been able to overcome the engines vacuum, up to approx 3500 engine rpm. and thats even with up to a 5:1 pulley set-up.

It sucks the boots nearly closed. (again, this is a bone stock 1300cc with DP heads)

hence the question..At what rpm are these units supposed to start boosting?
The assumption of a "linear" rpm to boost doesn't seem to be here...

Probably going to add a bypass to the intake so little/nothing flows through the super charger at idle, with a valve to redirect at high rpms.

Does anyone who's run these have an idea of when they seem to "feel" the boost or have a gauge set up matching an RPM to the start of boost?

Wed Apr 27, 2022 10:59 am

oprn wrote: Turbos are not free HP as so often is wrongly told. A turbo has to create back pressure in order to spool up and that costs power. The higher your boost the more back pressure it causes so yes a turbo robs power too! It's just less than a supercharger mostly I believe because you don't have the friction losses of belts, pulleys and high belt tension. There is also a smaller rotating mass in a turbo.

It would be interesting to put an engine with a turbo on a dyno, not hook up the intake side and make a few runs compared to runs without the turbo and a standard header.

My turbo engine has a 1.13:1 back pressure ratio. In turbo speak it is a non issue. That was testing to 26 lbs boost.
A N/A engine usually has backpressure too so it isn’t worth worrying about as far as power loss through a turbo.
A blower makes intake heat all the time and it is usually substantial unles you have a draw thru carb.
The loss through intake heat is noticeable….. and it is all the time.. even during cruise.

Wed Apr 27, 2022 11:54 am

clonebug wrote: My turbo engine has a 1.13:1 back pressure ratio. In turbo speak it is a non issue. That was testing to 26 lbs boost.
I do not doubt that those are good numbers. I have not calculated turbo back pressure ratio so does that mean that at 26psi on the intake your exhaust system back pressure is 29psi, or 23psi?
clonebug wrote: A N/A engine usually has backpressure too so it isn’t worth worrying about as far as power loss through a turbo.
I just went through this issue recently and asked on this forum at what pressure does one consider to be excessive back pressure on a N/A engine. Guess what? Nobody knows! The best answer I could get out of all the experts on this site was "It should be next to nothing".

Well sir, I measured it. Yup, I was getting 2.03psi at 4000rpm, full throttle. So I changed mufflers and got it down to 0.28psi at 4000rpm and full throttle. The difference in power was not huge but enough to notice with a seat of the pants dyno.

I can't imagine the power loss if it had been 23psi back pressure... or 29psi! That's a potato jammed up the tail pipe with a 3/8" hole in it! And if you think about it... and look at the nozzle on the turbine housing... that is exactly what you are looking at!

All I am saying is no matter how you make boost it take power to compress air!

Wed Apr 27, 2022 7:13 pm

Them superchargers are nice! Looks like fabrication city mounting one on the VW aircooled.

The perfect specimen be Type IV engine for a supercharger. The intake manifolds are already positioned nicely.

Type I application is gonna be cluster-fuck looking coz of the fan housing.

Waiting on my plasma cutter - I may take on something like this. My TIG will feel right at home w/ this project.

Wed Apr 27, 2022 7:56 pm

oprn wrote: clonebug wrote: My turbo engine has a 1.13:1 back pressure ratio. In turbo speak it is a non issue. That was testing to 26 lbs boost.
I do not doubt that those are good numbers. I have not calculated turbo back pressure ratio so does that mean that at 26psi on the intake your exhaust system back pressure is 29psi, or 23psi?
clonebug wrote: A N/A engine usually has backpressure too so it isn’t worth worrying about as far as power loss through a turbo.
I just went through this issue recently and asked on this forum at what pressure does one consider to be excessive back pressure on a N/A engine. Guess what? Nobody knows! The best answer I could get out of all the experts on this site was "It should be next to nothing".

Well sir, I measured it. Yup, I was getting 2.03psi at 4000rpm, full throttle. So I changed mufflers and got it down to 0.28psi at 4000rpm and full throttle. The difference in power was not huge but enough to notice with a seat of the pants dyno.

I can't imagine the power loss if it had been 23psi back pressure... or 29psi! That's a potato jammed up the tail pipe with a 3/8" hole in it! And if you think about it... and look at the nozzle on the turbine housing... that is exactly what you are looking at!

All I am saying is no matter how you make boost it take power to compress air!

Yes, except that with a turbo vs n/a, the pistons are being forced down by boost pressure, as much or just a little less than they are being held down on the exhaust stroke (function of back pressure.) Equal pressures mostly cancelling each other out. Blowers don't add back pressure to the exhaust other than an increase in the exhaust volume in the pipe.

Wed Apr 27, 2022 8:14 pm

Oh! I am not arguing that blowers are better, it's been proven over and over that turbos do the job more efficiently. It just bothers my OCD when people say turbos are free power given to you by the exhaust that is just leaving anyway.

Well sir those "free" mints that you picked up at the counter by the restaurant cash register on the way out? Ya! You paid for them too!