I am building a new 357ci small block for next summer and the thought of forced induction has crossed my mind.

Are those short type roots blowers made by weiand and holley any good?
I was looking at the weiand 177 roots blower or the weiand 142. I think holley makes similiar units.

What kind of compression and motor do I need for one of these blowers? how much boost can I ran? Are they hard to install? Sorry, I know nothing about superchargers.

I have all the parts for the motor except pistons so I can pick whatever compression I need.

 

Here is what I have for the motor so far:

pro topline heads (200cc, 64, 2.02)
Comp cam SOLID 274/280 236/242 .535/.545 110LSA
750cfm speed demon carb. mech sec
Harland sharp roller rockers

short block

forged crank
pink rods
.040 block
I was going to get forged .125" domed pistons for ~10:5.1 compression(with a NA setup)



I have a big cowl hood so I wonder if the blower will fit under. Don't want to cut a hole in the hood.

 

This is what I'm talking about. This is from a S10 truck, the kid who owns it made 405rwhp with it on his 350ci. He has a 383 stroker with it now.

 

I did some research

I would need 8.1- 8:5.1 compression
Blower cam with widder LSA (113-114)
Bigger carb that is setup for a blower



Has anyone here done this??

 

some one will chime in,,,,

 

On a street motor shoot for 9to1 comp ,it will give you more bottom end without spinning the supercharger so fast.Those little blowers work well with a single carb,so do 114 cams.8lbs of boost should be a good place to strive for.Keep timing at 32 max and start with the best gas you can get.It will be close with that hood. You will need to make some measurements.

 

I have the tallest hood Eckler had. I might have kept it all under the hood with a thinner air filter but the point of the blower is to move air so I cut a hole and added a scoop. Anyway, here is a pic of the 144 cu B&M blower that Holly bought the rights to produce. Hope this helps. I'm using a 400cu pully to pick up the boost to 7psi. 5 psi is about all you get with the 350 cu pully that comes in the kit. Your Dad has helped me a lot, if you need special pics or help...let me know.

Jim

 

I can't say I've had personal experience with the 142 c.i. blowers you're talking about, but I've heard a lot of great things... The smaller blowers are overdriven by ratios of (up to) 2:1. They have tight tolerances, and boost comes in very quickly, in a very linear fashion... I think, going this route, you will be VERY happy with the results.

As for the pistons, IMHO, go for a static C.R. of 8-8.5:1. (I would say higher, if it's for mild driving, lower if you want more boost and overall HP).

I made the mistake of going with a cam that's a little too large, for my 427 BBC.... If I had to do it over again (and may, in the near future), I'd go with one of the "blower" cams.

There are a LOT of guys that'll tell you to go with a monster carb for this application, but I would submit that your 750 is likely to be perfectly sufficient for your combination.

A quote from the book "Street Supercharging," (SA Design, Part No: SA17 ISBN 1-884089-29-1, www.cartechbooks.com) is as follows:

(referring to Mike Jones, a carb expert on forced induction systems)

 

I took the advise of B&M and went with 7.5:1 forged TRW pistons and a "blower" cam they manufactured. The exhaust profile of the cam was designed to get the spent gases out. I have the cam specs at home. I wish I had 8.5:1 instead as I feel that their advice was fine for cast iron heads but alum. heads will handle the detonation better. A 750cm quad worked well, I now have a 900cfm EFI throttle body.
Jim

 

You should not exceed about 12 or 12.5 effective compression on the street. That said working backwards at 8 psi of boost your compression should be 8.0 to 1
If you infact go to 9 to 1 your limiting your boost to 5 psi/6 maximum.
You get a snappier engine by running low compression and higher boost.
For a carb you need a boost referenced holley. The carb has it's power valve referenced off the boost side of the blower. Not the sucking side.
I run dual boost gages. ONe on the intake side and one on the outlet side of the blower and while the output can be at a good boost level the carb side is also reading a good vacuum level. If the carb is referenced off the carb side the power valve remains closed.
DO NOT run without a power valve. I run fairly lean, about 15-1 on normal driving and when the boost level crosses Zero and power valves are blown open and the ratio drops to 13-1.
This works. With dual 850 double pumps on the blown bigblock I can pull down a easy 15 mpg. The motor is snappy, runs very cool on the open road and never never fouls plugs.
Blower like about 112 lobe serperation angle on the cam and I do run alot of timing. Actually 43 degrees with a boost retart computer.

 

Not correct on a blown motor, a low compression high boost engine is very lazy on the bottom end while a higher comp motor with less boost will be more responsive down low, It is better to have more compression than more boost on a street motor.Timing should not exceed 32-34 degrees ,most air fuel ratios are 11.5 for best power ,that gives a little cooling of the heated inlet charge. Norval lets see an up to date pic of your engine/car its been a while since something new.Spinning your blower faster will give it snappier feel if it is lacking in bottom end power but it is only masking a weak engine.You can get away with it if you never go to full throttle for very long, otherwise you will detonate with lean condition and or too low an octane gas.

 

Kid, what course is that you're studying in RI??

 

My opionion; I would stay on the conservative side, build something that's hard to blow up. I prefer to drive my stuff rather than fix it.
The 177 is a great little blower. It's about the same price as the 142, you dont need to spin it as fast, and it can even support a 454.
Stay conservative on the compression. I ran 8:1 on my 454 with 7 psi, never a problem even with questionable gas. Sooner or later, that 92 octane at the pump is going to be slopped out with thier extra 89 octane. And with the lower compression, the 177 has enough volume to increase your boost by just changing your pulley.
Like 632 said, stay a little conservative on the timing, 10-15 initial gives good idle and 32 total shouldn't melt stuff. Holley website has good info on this.

 

Norval, last time I saw you post this I thought it was a typo...but now you post the same number again. That can't be right, especially w/ iron heads and a blower running 15 over like you say and those lean mixtures...how on earth can you run that much advance w/ the cyl. pressures you must be creating and not run into serious detonation and overheating issues????? Do you have the quench real tight...what's the trick here???

 

Mike that motor picture was from last winter. That motor is now apart and the heads sold off of it.
I have also run this combination for 4 or 5 years on the street and when I pulled the heads a few weeks ago the pistons are in like new condition, what little dicoloration or carbon came right off, no burned spots and I do run 15-1, my plugs are lean, I do run 43 degrees of timing while under light load, I do not need a fan while running on the open road, I never foul a plug ever and I can get 15 mpg.
As for snappy off the line performance 10 pounds of boost right off idle gurantees that snap.
Mine is not a race motor like yours but on the street as a daily driver or even long distance cross country it would put a race motor to shame.
As for high intial compression and lower boost levels that is not true.
This is not a pissing contest MIke. I have a combination that works and am sticking with it.

 

That is not typo Marck. I have in car timing control. I dial what the motor likes while driving down the road. I calibrated my distributor which has a fixed curve or no curve at all. I set the distributor at 30 degrees fixed. I then have 15 degree of electronic timing that I can adjust in the car. While driving I can make changes and I found without looking at anything that the car seemed to run the best at a certain setting, it is not hard to play with but when you look at the dial reading it is showing 13 degrees.
So adding the 30 built into the distributer with the 13 degree electronic and I did check it again with a timing light I am running 43 degrees total at 3000.
Marck I don't pretend to know all the theory but I do ask my engine with timing and boost and carb jetting what it likes and it tells me.
I do many many testing sessions until I get it worked out, forget theory, do the tests. Watch what the motor is telling you.

 

Norval,
How much boost is showing at 3000rpm? I'm assuming highway cruise.
And how much does the computer retard the spark?

 

You can get any number of centrifugal chargers to fit under your hood, or if you want to go with fuel injection, a SC like mine will fit under there...

http://temp.corvetteforum.net/c3/zma...ginepage01.htm

 

Oh, under light load, what do you run under full boost?? It's kind of confusing, one time you're talking about how much boost you run and how rich & lean under conditions and then you mention 43 degrees of advance, I was assuming this was the max. timing under full load because you said 43deg w/ timing retard computer...so I was assuming this was w/ full retard.

 

Sorry Marck. I do run a Vortex timing computer. It too can be dialed in for retard under boost. I have it set a 1 1/2 degrees retart per pound of boost.
For running down the road under light load and the boost in the intake actually in vacuum I am running that straight ignition setting of 43 degrees at 3000 like anyone else would set a car up. I have a MSD timming computer for the ignition curve.
When the boost level crosses zero the power valves are blown off their seats bringing the mixture to 13-1.
As boost climbs the boost timing computer pulls 1 1/2 degrees per pound out of the total.
Off a light I often see 9 or 10 pounds of boost so using math and starting at 43 if I was in fact reving 3000 minus say 1.5 time 10 pounds I would be at that point running 43-15 or 28 degrees.
Marck all timing is set by a curve, you always specify maximum advance. I hope I did not mislead anyone by saying 43 degrees because that is what is dialed into the distributer if you use a timing light. At 3000 you get 43 degrees.
I would not run a blower motor without a boost retart system nor would I ever consider running without power valves or even romotely consider running 11.5 fuel ratio in any street motor.

This is a street motor. It is not a race motor. I do cruise at 100 mph plus.