HP increase with M90

I could have swore that I read that with carbed engines that the positive displacement blowers needed to be draw thru. I may be on crack because I couldn't find it anywheres.

The picture you saw in MM, is a centrifugal blower.
 
yeah, I know it was different, I just thought the set up looked real nice, easy as well. I figure if there was any way to do that set up it would be real nice, but oh well, if you find anything saying it is only draw thru, let me know. I know what your saying tho, most blowers like that I have seen have the carb mounted on top or somethin similar. I just would like to do otherwise.
Matt
 
It's theoretically possible to build a positive displacement as a blow-through. The carb re-work would be the same as for a centrifugal. the blower seals would have to be for dry flow, the same as on an EFI engine. The problem areas would be:

Mounting it, since positive displacement blowers typically bolt to something solid, like the top of an intake manifold.

Fabricating the discharge tube from the blower to the carb and the air intake tube. This would be a bit more complicated than on a centrifugal but not insurmountable by any means.

It would be SO much easier to bolt an adaptor plate right to the top of the manifold, bolt on a Whipple and be done with it, although hood clearance would probably become a problem.
 
With an Eaton M90 (like off a T-bird or GM 3800) you gotta use a blow through setup. M90's came with a bypass valve, either externally or, if you have a later model M90, it will have an integral bypass valve. Don't get rid of the external bypass system, it works like a turbo pop-off valve, except it recirculates intake air from the pressure side back to the draw side under low vacuum conditions like at idle or cruise. The effect of this is that your supercharger is then freewheeling, and not using up any horsepower (and they use a LOT), when you don't need it.
Build a pressure box for your carb, use an advance/retard unit, and try to keep your boost around 6 psi. Eaton's start to really heat up the air above 6.5 - 7 psi (you could use an intercoller w/ blow through). Draw through roots type supercharger systems suck for normal driving. The gas falls out of suspension, you always get puddling, and just one backfire...
Rickwrench
 
awesome, THATS what I wanted to hear, I was planning on building a pressure box, then running through the stock or similar small intercooler to get a little more boost, then runing some sort of BOV or pressure valve to get rid of boost pressure when not needed. I am gonna stick to stock pistons and run a hotter cam with this set up along with hopefully an MSD timing retard when under boost. Any other considerations I oughta look into?
Matt
 
Check the compression ratio of your engine. Mainly check you head. YOu want as low a compression as possible. A late model 250 head should have the largest combustion chambers available, so long as you don't get a milled one. It should only be milled to be true, not to increase compression ratio. The higher initial compression ratio, the lower boost.

Even with a low 8:1 compression ratio, you can still only run about 7-8 psi on pump gas before detonation. An intercooler may help to delay it a little, but not by very much.

Look here...some more really great information:

http://www.holley.com/HiOctn/TechServ/T ... CTech.html

Slade
 
that is a great link, I appreciate it! What are some good ways to lower my compression ratio??? If I ran an intercooler and a spray kit to cool that cooler, then an MSD timing retard would I be able to run higher boost at my compresion ratio or would I still have to run smaller boost. My main deal is that I want to get into the 200+ Hp range, what is it going to take?? I will get a new cam, roller rockers moley pushrods, lifters etc from Ford Six Parts.com, then I will get the MSD box and intercooler as well. Will this help me get closer to 200, what else would I need to do. Like I said, that guy in Mustang Monthly got into the 200's with a stock exhaust manifold!!!!
Matt
 
In theory...here is what boost pressure will do in an ideal circumstance:

14.7 PSI (1 bar) will result in a 100% power increase. This is because in theory you are putting 100% more air/fuel into the cylinders then normail atmospheric pressure can do. That is theoretical.

To lower compression ratio, look for a late 70s 250 head (if you want to stick with the log head). Also, do not run the nice steel gaskets that Mike sells, they raise the compression ratio. GO with the stock Felpro gaskets that don't compress as much.

Also, consider enlarging the valves. This will allow air to flow easier into the cylinders. ALso, when you do this, you'll need to enlarge the compression chamber so the valves have proper clearance. Enlarging the combustion chamber will lower compression (just don't widen too much).

Also, make sure you don't have flat top pistons. Get some dished pistons, make some 8cc ones from ACL. we talked about them on another post not too long ago.

Can you dish your own pistons? Anyone know?

Hope that helps.

Slade
 
yeah, I was wondering about that too, can you disht he stock pistons??? I looked into those ACL pistons, will prolly have to wait on that one. Im thinking Ill just run mild boost till I get enough time and money (money being key) then I will lower my compression as much as possible and add more boost. I still wonder what its gonna take to get to 200 hp safely tho, I wish Mustang Monthly had talked a bit more on all that was done like they do with the countless V8 buildups. Oh well, maybe someone around here knows. Anyways, thatnx for the advice, all this is awesome and really is helping me get ready for this next project.
Matt
 
Why the fous on 200 HP? It's just a number. Because of how they make boost, a positive displacement blower that gives 180HP at peak may give you more performance than a centrifugal that makes 200.

If you really want the big number for bragging rights, a turbo takes about 25 HP less to drive than either belt driven blower. Less drive losses = more HP to the wheels.
 
well, I was lookin into a turbo but I just bought a dual out header and sold my stock manifold already. I dont feel like trying to get it back and then having to loose money on my brand new header. Unless I can run a Y pipe from the dual header to the turbo, than back out from the Turbo into another Y to my new duals, I think the supercharger is the way Im gonna go. In all reality, I wasnt plannin on boosting until well after I got the header or else I woulda either stuck with the stock manifold or got a single out header. The 200 hp mark is just a number, but I saw it done on a car with stock exhaust etc and wondered how it was done, thats all. I want to have a car that is fun to drive and has respectable performance as well. If making a Y pipe from the header is a good idea, I might look into it, but it sounds too cluttered and like a little too much work if you ask me, maybe Im wrong, anyone think that might work??? Turbo, Y pipe from dual header to turbo, then back down to another Y pipe to duals???? Im doin this cause Ive already spent the money, might as well keep what I have
Matt
 
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