Blower sizing

[Roger P.]

Does anyone have a rule of thumb for matching the displacement of a blower to the displacement of an engine?

There seems to be lots of Japanese Kei car blowers for sale on that auction site, I figured it might be an easy bolt on proposition if the size was right (500cc per revolution).

[Steve]

Pretty much one to one for displacement, but there are a few other factors to consider. One of the factors is the type of "blower". You did not mention what auction site or what type of blower, so we have to guess. Another factor is 'total airflow'. You can not use a turbo that came off a 1000cc car engine that turns up to 6000 rpm on a 1000cc bike engine that turns 9000 rpm. You also have to remember that an engine with a performance-oriented cam will flow more air than an engine with a milder cam.

We are going to need more specifics, so please provide more details.

.

[Roger P.]

Ebay, Aisin AMR500, 500cc per revolution, 16,000rpm limit, Bandit 1200 with GSXR750 slingshot cams, dot head, which will have to go for compression reasons.

I figure with 2 intake events per revolution, that's 578cc engine displacement per rev, so that's almost 1:1. A mild overdrive should get you where you need to go. The blower is a simple two-lobe Roots type.

1.6 overdrive would get you to max blower rpm at 10000rpm on the tach, although I know it's probably making more heat than boost at max revs.

http://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=aisin+amr500&_sacat=0

[Mark Harrop]

Interesting...

How were you thinking of mounting it?

[GregT]

What's that blower's original application ? In my experience of supercharging bike engines for both roadrace and speedway use, a small blower running over it's max efficiency point makes more heat than you'd want.
A big blower, run slower will give much less problems.
You're still dealing with an air cooled motor so heat is your biggest problem.

I see that blower has a polyvee belt drive. Those are excellent for blower drives as they will slip slightly on overrun - and you won't break the end off the blower shaft....

[Roger P.]

I figured in front of the engine with a pipe to a plenum for the carbs, or, back of the engine with one large suck-through. Rotation might determine which way is most feasible.

These blowers are from Asian Kei-cars, with about 600cc displacement motors. I have seen these bolted to Harleys though, so I am a bit confused as to whether they would work on a 1200cc four with a 10,000+ rpm redline. Ebay ad says up to 2.2L, while others say they are best for a motor 750cc or less.

[GregT]

I'd pick the 750 or less...last roadrace setup I did when it was still legal here, was a 750cc roots blower on a 500 twin. Driven 1:1 we started with 18lb boost but the rotor expansion was such that by the time I'd trimmed them till they didn't seize on the ends, we ended up with 15lb boost.
On alky that setup on a watercooled motor got VERY hot indeed. With alky fuel we never had hot blower/carb problems but if it had been petrol...
I realise you probably won't want more than 5 - 8 lb boost but heat is still the biggest problem.