Centrifugal supercharger question

[plovett]

Okay.  We're on the same page, basically.

To oversimplify, you need enough head flow to not back up the port with the volume of air going through, no more.

How would you know when you have too much flow and are "backing up the port"?  And what does that mean in physical terms.  Does pressure/turbulence go up in the port as the air can't be exhausted as fast as it's coming in?  I don't know how you'd measure that or know it's happening unless it was related to a power drop off.  And then you wouldn't know it unless you compared to a different head on the dyno.  Does it happen at a specific point or gradually?  I'd venture gradually.  If so it's not like a yes/no thing.   

One other thing.  Sure with a blower the port is under pressure as opposed to vacuum, but there is really no fundamental difference.  It's the difference in pressure that we call a vacuum or boost.   A blower just creates a greater difference in pressure.   So it's not like the physics have fundamentally changed just because you have a blower.  It's still the same deal and the head has to deal with it.

As an aside:  Have you considered cutting open the "cheek scoops" on your '70 Mustang?  You could have ducting on one side leading up through the fenderwell to the intake of the supercharger, right by the shock tower.  On the other side you could have ducting leading to an air/air intercooler placed in the fenderwell.   Just a thought.   I think it'd be cool.

paulie

[plovett]

A big lazy port at 1500 rpm where there is no boost, is still a big lazy port at 1500 rpm

I think that's something I can't refute.   Are you really looking for power at that low of an rpm?  If so it seems like a larger engine or postively boosted engine might be in order.  Maybe.

paulie

[cdmbill2]

Air to air intercoolers want the largest surface area possible much like radiators so a small duct from the 70's front fake scoop would be enough until very high speed. I've been looking into water to air like the current Shelby's or the Lightning/HD trucks like the one I have. The packaging can work better as the heat exchanger can be low mounted while still leaving plenty of direct air flow to the radiator.

Better heads equal more power with less 'boost' as the pressure is a measure of restriction in the inlet tract, not a measure of how much air/fuel has been crammed into the combustion chamber. The better heads also allow for a slightly smaller cam, but an aggressive lobe will out perform a more gentle one with the same measured duration and lift.

[My427stang]

How would you know when you have too much flow and are "backing up the port"?  And what does that mean in physical terms.  Does pressure/turbulence go up in the port as the air can't be exhausted as fast as it's coming in?  I don't know how you'd measure that or know it's happening unless it was related to a power drop off.  And then you wouldn't know it unless you compared to a different head on the dyno.  Does it happen at a specific point or gradually?  I'd venture gradually.  If so it's not like a yes/no thing.   

One other thing.  Sure with a blower the port is under pressure as opposed to vacuum, but there is really no fundamental difference.  It's the difference in pressure that we call a vacuum or boost.   A blower just creates a greater difference in pressure.   So it's not like the physics have fundamentally changed just because you have a blower.  It's still the same deal and the head has to deal with it.

As an aside:  Have you considered cutting open the "cheek scoops" on your '70 Mustang?  You could have ducting on one side leading up through the fenderwell to the intake of the supercharger, right by the shock tower.  On the other side you could have ducting leading to an air/air intercooler placed in the fenderwell.   Just a thought.   I think it'd be cool.

paulie

You got it Paulie.  As far as when a port can't flow enough, I haven't done it, but I understand when boost climbs but power doesn't or only does at a small rate, it's because the port is backed up.  At that point you are building pressure in the plenum that can't get into the cylinder.

I have seen it on a SBF test in the rags, but not an expert on when that happens and still researching how to determine port CSA and overall flow for a boosted street engine

In terms of the intercooler, I haven't though too much about it, but I think I would like a larger intercooler than the cheek would allow.   So my thought now is to feed air in from the scoop area and have a big intercooler across the front, below the bumper like a modern diesel.

As far as where to make power, I don't need big power at 1500 rpm, but I do want to make sure it doesn't buck and can lump along between 1600-1800.   It does so very happily now, especially with the EFI, it was good before but not as good with the 1000 Holley and RPM intake.  The EFI was certainly magic, even with a ported Victor and less lash, it idles much lower and I can loaf along or spin 6500.  I was the blown motor to do the same

So the point of going bigger motor, heck it does it now, and I want to be able to do it with a 505. so I don't see how that will be a problem at all

[plovett]

Sounds like you have it all figured out already, Bro.  I'm sure it'll be a beast.

paulie

[My427stang]

I sure wouldn't say I have it figured out, but I do know how I want to run the pipe LOL

My guess is there will be lot of learning coming my way for blower and cam choices, not to mention EFI programming under boost.

[jayb]

I think the EFI stuff will be easy, Ross.  You'll just need a 2 bar or 3 bar MAP sensor, and big enough injectors to feed the horsepower level you are expecting to make. 

The big questions will be which blower to get, and what cam to run.  And actually, the first big question will be how much horsepower do you want to make?  That will drive a lot of the other choices.

Have you picked out a blower?

[My427stang]

I have not yet Jay, looking for something that will mount on the pass side and fit a low mount alternator.

That will let me keep PS and A/C on the other side.   I think I am going to have to do some work on the radiator support to make some room, I am pretty much out of room with a shroud and cant imagine fitting a big belt in there

[plovett]

Air to air intercoolers want the largest surface area possible much like radiators so a small duct from the 70's front fake scoop would be enough until very high speed. I've been looking into water to air like the current Shelby's or the Lightning/HD trucks like the one I have. The packaging can work better as the heat exchanger can be low mounted while still leaving plenty of direct air flow to the radiator.

Better heads equal more power with less 'boost' as the pressure is a measure of restriction in the inlet tract, not a measure of how much air/fuel has been crammed into the combustion chamber. The better heads also allow for a slightly smaller cam, but an aggressive lobe will out perform a more gentle one with the same measured duration and lift.

I agree the fenderwell is not the ideal location in terms of large space and airflow.   I try not to mount heat exchangers if front of my radiator though.  Still, in front of the radiator is probably just about the only space for a large air/air intercooler.   ATI makes some intercoolers that are 9"x4.5"x11" that would fit in my fender.   You'd have to make some ductwork and maybe a shield to protect from it road debris.    And whether it has enough cooling capacity would be a question that depends on the build particulars.

paulie

[sumfoo1]

i have a 482 stroker pond block setup with pond heads at 9.5 to 1 forged crank oliver rodded bottom end. i was thinking about turboing her at some point  but i'm pretty sure my 112 lsa 262@.050 cam may be a little much.

its gonna be in a 61 galaxie so i have plenty of room for a giant air to air intercooler

its an efi engine using the victor efi setup.

i'd like to run 6-9 psi on pump and twice that on some kind of race gas or e85.

sound feasible or?? overzealous?

[jayb]

I think you might have too much compression to run that much boost, but you might be able to get away with it using EFI and timing control. If the engine is already together you can certainly give it a try, and the intercooler and maybe a boost cooler setup will help.  If you just can't get to the boost level you want, you can always change pistons.

Why do you think your cam is too big?  The only thing I would say about the cam is that it could use a little more lobe separation, maybe 114 instead of 112.  I ran 17 psi in my 489" FE with a Vortech supercharger, and my cam was bigger than yours (272@.050" I think?).  Compression ratio was 8.75:1.  Made a little over 1000 HP on race gas with a carb; probably would have done better with EFI like your setup...

[sumfoo1]

question... thicker head gaskets a bad idea... i think going from .030 to .080 on the head gasket (doing something like SCE pro copper or something) can get me down to 8.72/1 CR but is it a bad way to do it because i'm effing up quench? or is it really not going to affect it much?

My issue is all my tuning efi experience is on a Subaru lol  so i'm a little used to some help with knock sensors but usually my ears can pick out an unhappy engine before the knock sensor does. I will have timing control too  i'm pretty sure it goes similar to the subie...  lots down low tapering to barely any advance when she first hits full boost and then start feeding it back in. 

[jayb]

The thicker head gaskets are kind of a double edged sword, in my opinion.  Lowering the compression ratio for your application is good; increasing the quench distance is not good.  On the other hand, some engines (like the SOHC) don't have any quench at all.  If you can change the head gaskets when you go to the turbos, I think I would opt to go to thicker head gaskets.  You might look at getting some thick Cometics rather than copper gaskets; they'll last longer, and I believe that they are available in multiple thicknesses for the FE.

When you get around to doing this, I would STRONGLY suggest you set the engine up and tune it on a dyno.  You can sneak up on the tune that way and avoid potentially damaging scenarios.  You can blow a supercharged or turbocharged engine real quick with the wrong timing or air/fuel ratio...

[sumfoo1]

yeah... it will be tuned by a local shop that tunes for a couple ford x275 cars.

I did my own with the subie (23psi @ 10.8-11.2 afr & 373whp 405ft-lbs on a 2.5liter with crazy amount of drivetrain loss [awd] and more impressively 40k miles on a stock bottom end with this tune) but this engine just costs too much money not to let a pro do it.

the pump tune will be WAY mild and i'll tweak it to fill in gaps/hole  myself but the race gas tune will be on someone who knows how to trim out the fat safely

i mean i know i can the heads to do the turbo setup i guess i could just as easily pull the pistons as change head gasket.. i'm just one of those people who lets everything snowball so i'm trying to keep round 2 reasonable.

i was going to do a mild refresh on my 352 when i ended up with the solid roller 482 with 4 bolt aluminum block yadda yadda yadda
its a disease i swear.

[jayb]

i was going to do a mild refresh on my 352 when i ended up with the solid roller 482 with 4 bolt aluminum block yadda yadda yadda its a disease i swear.

Sounds familiar