how much timing to run w small roots blower?

[Scotthatch]

The water methanol injection is what allows you to spin the blower faster than "12,000 rpm"
as it cools the air charge and cools the blower too.
The blower no longer hot soaks. (gets too hot to make power)
The power is consistent,repeatable and more reliable (detonation is suppressed)
Roots blowers love intercooling. Especially when you spin them faster.
In this case 2.28:1++ ratio.
(8" crank 3.48" top pulley set.)

Very well put ... I totally agree

[rewguy]

Ok....after the block and heads were resurfaced, the final compression comes out to 10.04-1 static.
It will have to run on 92 for now. So getting this straight.....I lock out the distributor, set timing at 26. I was told to plug in the vac. advance below the blower......but if the timing is locked, it will be ineffective, no? So, my base timing is 26....locked. I will probably buy the boost/timing box I suppose.

[rewguy]

?

[rewguy]

hmmm...lol

[Scotthatch]

I'm surprised too...

The mechanical moves the reluctor wheel and the vacuum can moves the pickup so it's two different things


You locked out the mechanical advance only I am assuming

[cjperformance]

Locking the timing at the mechanical advance mechanism does not affect the vac advance.
Locking the mech adv and having the vac adv connected under the blower will give you (per your timing spec of 26*) 26 deg fixed timing plus whatever your vac can pulls, lets say 10 deg more for the sake of this. Its a basic but once set effective way to get it going.
So base idle in neutral you can get 36 deg, as vac reduces so does the vac advance figure until you end up back at 26 fixed. Dependent on your combo this may be too much or may not be enough.
One trouble you can have from this is an inconsistent idle, as the idle vac figure is affected by load , say with an auto dropping it into drive OR with M/T at idle or very light throttle loading up the clutch, the vac advance reduced timing and the rpm drops. This is where an adjustable vac can helps, you can adjust it to a light enough vac requirement that low load vac changes wont affect timing so you do not feel this effect. Of course once any significant throttle load or boost is seen the vac can releases anyhow and you are back at your 26deg.
In addition, Even a basic manual timing control that allows you some adjustment either side if your base setting will be a benefit for you to allow you to alter the timing from the chair.

[F-BIRD'88]

With a true 10:1 compression ratio you will need to go real easy on the boost (3 to 4psi max tops) or get a water methanol injection system for this car. The cr is just too high for non intercooled supercharging on 92 octane pump gas.

What is the blower drive ratio? Back it down. (switch to a larger top pulley)

[F-BIRD'88]

This engine should have been built with a deep dish piston to get a compression ratio of between 7.5:1 and 8.5:1 for supercharging on 92 octane gas.
This supercharged engine's performance will be very limited by this basic mistake when on 92 octane gas.

A water methanol injections system can make it a whole much better deal, both in terms of power/boost and reliability and blower performance. These lil roots blowers really love water methanol injection intercooling effect. Allows you to really get busy with the boost and power
and run to run repeatability (blower hot soak).

Other wise it will soon get hammered to death.

[Scotthatch]

This engine should have been built with a deep dish piston to get a compression ratio of between 7.5:1 and 8.5:1 for supercharging on 92 octane gas.
This supercharged engine's performance will be very limited by this basic mistake when on 92 octane gas.

A water methanol injections system can make it a whole much better deal, both in terms of power/boost and reliability and blower performance. These lil roots blowers really love water methanol injection intercooling effect. Allows you to really get busy with the boost and power
and run to run repeatability (blower hot soak).

Other wise it will soon get hammered to death.

Though I agree with you and that even simple methanol water injection does good things I kinda feel you are pushing the issue to far back the other way ... I have gotten away with more then that ...

[Scotthatch]

Rather then the vacuum advance on the distributor being hooked up a better option is to run a boost timing retard box and a little more initial timing ..... it will give you a more balanced timing across different throttle conditions ... I normally even run a short curve in the centrifugal advance with boost retard.....

[rewguy]

Well, I have him talked into mixing in some 110 octane at 2-1. (2 gallons of 92 to 1 of 110). This should allow me to run the 26-30 degrees and full 6 lbs, correct?

[rewguy]

Ok, Im going to use his old msd distributor (with locked out mechanical), eliminate the vac. advance totally. Add the msd 6btm box, which has the dial w the 4 settings. The octane after the fuel mix should be about 97. Static compression is still 10.04-1. So at this point should I start with say.....33 degrees of timing, and use setting number one on the dial, for 1 degree of timing out for each lb. of boost........giving me 27 total with the full 6 lbs? Sound reasonable with the new octane?

[rewguy]

and what spark plug would you reccomend? is an ngk 7 too cold? or will it foul while cruising?

[Frankshaft]

Buy a quick fuel e85 blower carb. Done. And don't worry about it. The water/meth systems do work too. Or, run a 50/50 av gas and 92, and for good measure, throw in some Lucas octane boost. It actually does work.

[Scotthatch]

and what spark plug would you reccomend? is an ngk 7 too cold? or will it foul while cruising?

That will be fine