Supercharger question

How do you guys protect from overboost with a draw through setup?

 

blow off valve, as you would with an injected system to my knowledge

 

You determine boost when you are designing the system... and you can adjust boost via pulley size.

You DO install a backfire valve but a Roots-type blower will not "overboost" as you call it.

 

Is a Eaton M90 a roots type blower?

 

Yep...

 

It's real neat to drive something with a roots blower in the winter, the boost goes up!

 

I absolutely love roots type blowers!! I put one on an 85 Volvo 240 and it turned into a burnout machine. Man I miss that car. It was SO fun.

http://www.youtube.com/watch?v=C3UzMk2ViY0

 

I thought Overboost had to do with Turbo's not Blowers.
( that is where I've heard the term, anyway...)

Are you still trying to figure out what to do with your '94 vehicle?

 

One easy way to limit boost is by using a smaller throttle body or carb. If it can't get in it can't get compressed

 

Yes I am.

 

I'm just setting up my first blown engine now (671 sbc in non HAMB freindly car) so have been reading all I can and been talking to guys that have done it to learn what I can. I though you would be able to produce more boost than you may want by spinning your blower faster and thus creating to much compression leading to detonation and other issues. I've also been told that if your exhaust diameter is too small, you won't produce boost properly as the air needs to get out. Heres a chart showing boost in realtion to compression ratios.
http://www.blowerdriveservice.com/techcharts.php

 

A '94 anything is not Trad.


http://www.jalopyjournal.com/forum/showthread.php?t=44274

 

The engine I'm thinking of supercharging is 134 cu in 4 banger.
I'd like to get 5-6 psi outta it, but 7-8 would be better.
If I remember right 6psi should get me around 170 WHP...

Edit: I come here because I can get information I can't get anywhere else.
Nobody does carb conversions or anything like that. I like it here..
But.. I guess I'm not supposed to be here.

 

The M90 is a screw compressor. The difference is that in a roots blower, compression does not occur in the blower, but in the manifold from the volume of air moved by the blower. In a screw compressor the air is compressed within the cavities of the screws. The result is a vast improvement in efficiency.

 

Oh, and "overboost" is a physical impossibility with a positive displacement blower, and a highly unlikely condition with a centrifugal blower. Its a turbo thing....

You do need protection from backfires though, in the form of a burst panel or spring loaded pop off.

 

5-6 seems very high for a 4 banger motor .I would start low and walk my way up (pulleys).A Lot of your over boost problems will be resolved with timing.If you run 7-8 psi your boost problems will be work out when stuff flies out the bottom of your pan .My 2 cents

 

I'm just going on what the turbo guys are doing with these engines.
They say 8 psi is the most they'd run on a stock engine.
Its an OHV pushrod 4 cylinder...

 

I built my BBC for boost it is under driven my motor is just under 8 to 1 boost puts it close to 12 to one.Maybe way different monster I was told in the past 4 bangers with lots of boost had to be overhauled every 10 thousand miles .I am just saying walk it up slow you will be surprised .My 2 cents

 

Gearstix, create your own tradition.
Under or direct drive is plenty for street if you keep temp/ stresses down with appropriate fuel- air mix/ ratio and efficient exhaust ( starting @ cam timing, down thru port/ valve character and so on. You have to mathematically arrive at the spec. that suits the intended use.
Read/ talk all you can . Use careful assemb. +good oil/ gaskets/coolant/ filter. 2c from someone who knows not a lot.

 

The guy or gal asked a question .Do you have a answer for him or is this your answer .My 2 cents

 

Depends on the belt. On GILMORE drives (the cogged tooth pullies) you need a pop off valve or burst panel, if it is serpintiene or v belt, you dont because in case of a backfire the belt can slit. If you notice the baby B&M and Bbaby Weiands dont have pop valves.

 

True the smaller blowers all have smooth pulleys I ran one on a sbc and a sbf never a issue (back fire)never thought about why .871s have ribbed pulleys and pop off valves .My 2 cents

 

The ABS brake on my 2002 Mitsu Montero is chirping under the dash, and my GF is LOL at me. Can you tell me what color would look good on it? Can i fit a straight axel under it GASSERRRRRSTYYYYLLLEEEEE??

 

This is what the pulley looks like on most of these.


What i don't understand about the Ford style M90s, is where is the inlet?
Is it still the top?

 

The inlet is that plate with 3.8 on it.

 

I think it is in the back m90

 

fyi i ran 14 psi of boost on my totally stock vw 2.0 for a very long time with no parts exiting the pan or block. yes motherfuckers, i said vw. deal with it.

look dude, i appreciate your eagerness to do something with this motor you've got but it's pretty obvious that you're kinda clueless which is okay. we all gotta start somewhere. my biggest advice is to do INDEPENDENT RESEARCH. get some books. find some web sites. use the search tool on this site.

it wouldn't kill you if your questions were a little more "focused". last week it was a turbo and efi and then a carb and now it's an m90. you've been a member on this site for less than a month and you have more posts than i do.

not trying to flame... just trying to help you grow from a clueless newb to a certified car guy that actually knows something.

 

Thought that is the blower "outlet"

 

That time of the month come early?

 

I understand what your saying. I just can't make up my mind.
I have some engine building DVDs and crap here, was going to watch them...

But if I do anything with my four cylinder, I don't want to keep the stock FI. the computer is not tuneable and is a major PITA, plus the injectors are at almost 100% duty cycle.