My '59 Enfield /Indian 750cc Chief High Compression Build

[SPARKY]

SJ  you MOST likely be better of under driving the larger blower---it shouldn't heat the air up so much---cooler air = a happier eng.

[thefrenchowl]

Hi,

No matter what size it is, a lobe type blower does not heat air since there's no compression within. The heat comes after from the air pressure increase in the plenum chamber since it pumps against closed inlet valves 3/4 of the time. Obviously, some of the plenum heat will then transfer to the charger...

When I researched mine, I saw plenty of guys using big blowers and running them slow, then moaning about the pulses and the lack of space on a bike to fit a big plenum to smooth things out...

Solution then did appear obvious to me, run a smaller charger = more rpm = more pulses = more dampening = more equal share per cylinder...

These Ansin are good for 12,000 rpm constantly. The blurb says 16,000 rpm for short blasts is OK. and that's on fuel injected cars when the Ansin just pumps air and does not get cooled further by evaporating A/F mixture.

Patrick

[TheBaron]

Hi Patrick,

I agree about it is possible to have too large a blower that can have pulsing issues. However, a 500cc blower on a 750cc engine, when geared 1 to 1, will yield about 5 psi boost...

Sounds about right to me....

Those rpm numbers are for "new" blowers. Used units with wear and tear on them can have issues when spun up to very high speeds so be careful.

Robert

[thefrenchowl]

Agreed with you, Baron, but 5psi won't get Scottie anywhere near his 200mph target

Patrick

[Briz]

No matter what size it is, a lobe type blower does not heat air since there's no compression within. The heat comes after from the air pressure increase in the plenum chamber since it pumps against closed inlet valves 3/4 of the time. Obviously, some of the plenum heat will then transfer to the charger...

This is rather arguable Patrick!
A rootes type blower 'churns' the air quite a bit, some of it gets forced back thru the clearance between the meshing rotors. This does make some heat.

[thefrenchowl]

OK, Briz, lets just say it's not as bad as a vane type blower that does compress air as it goes through!

Patrick

[Scottie J]

I emailed KE Motorsport and he confirmed that I will need to run the AMR500 to achieve the numbers I am after.  I'm thinking of going ahead and setting up this blower to push 10 psi of boost.  A nice healthy dose of air without having to worry so much about breaking something.  It should also get me pretty close to 12.5:1 dynamic ratio.

Scottie

[DaveB]

I thought I might just comment on supercharging/turbocharging and what it does to intake temperatures. The ideal gas law, PV=nRT, describes the relationship between pressure, volume and temperature. A special version of this equation generally applies to supercharging/turbocharging. It is: T2 = T1(P2/P1)^.286 .

This relationship tells us that a 100 deg F temperature rise is easily in the realm of intake temperature increase that is due only to the compression that takes place in the supercharger/turbocharger. At high boosts, the temperature rise is even more. A second source of temperature rise is due to the heating of air as it comes in contact with the blower itself. This is quite significant since turbochargers are hot. Temperature rise is one of the reasons intercoolers are used after the blower.

A similar process (temperature rise due to compression) takes place inside cylinders as the piston comes up, but in a much more pronounced way since the compressive forces are higher. This of course is the process that many diesels use for ignition.

[Scottie J]

Dave, I have discussed that information with both my head guy and turbo guy and have a plan of attack to hook up an intercooler of some sort.  Also after speaking with my head guy today I am going to be sending my crank to him and Mondello's to have it treated with plasma nitriding and have it machined and balanced.  I still don't know much about this process but is what they use on Nascar cranks and also new Subaru STI cranks.

Scottie

[panic]

Boost does not change your compression ratio, static or dynamic.

[DaveB]

Did somebody say it did?

[Sumner]

Did somebody say it did?

They hinted at it in reply 156 above,

Sum

[Scottie J]

I should have been more clear with my words.

........It should also get me pretty close to AN EQUIVALENT 12.5:1 dynamic ratio..........

Scottie

[Sumner]

I should have been more clear with my words.

........It should also get me pretty close to AN EQUIVALENT 12.5:1 dynamic ratio..........

Scottie

If you are referring to dynamic 'compression' ratio then like Panic said being boosted won't change that.  Remember it is a 'ratio' that we are talking about not cylinder pressure or anything else.  It is just a matter of where the ratio starts and the volume there, at the bottom of the stroke or somewhere up the stroke after the intake closes compared to the volume with the piston at TDC...

http://en.wikipedia.org/wiki/Compression_ratio

Sum

[panic]

Another flaw in the comparison is that 12.5:1 DCR through boost does not share temperature change or knock sensitivity with 12.5:1 N/A.