how much timing to run w small roots blower?

rewguy · Post by **rewguy** » Mon May 07, 2018 3:59 pm

small blower....looks to be a 144ci older B&M blower. Engine is a 9.8-1 compression 4vr flat top sealed power 2256 .040. 357 cube small chevy. Edelbrock rpm heads. Stock bottom end w good rod bolts. How much timing (and any ideas on timing curve) with this on 92 PUMP GAS? Apparently makes about 6 lbs. Not sure where prior owner had timing, as the top rod bearing shells were to copper. Car is 3600 lbs, 3000 converter, 4.10 gear. Any hints? Don't know anything about the blower deals.
Thankyou !!!!

ProPower engines · Post by **ProPower engines** » Mon May 07, 2018 5:16 pm

What LSA on the cam??
The amount of over lap has an effect on cyl. pressure and if you are just blowing the extra boost out the tail pipes then its hard to say where to start.but a safe bet would be start at 30 total and go from there.You may need less if you can get to full boost depending on the pulley set up.

F-BIRD'88 · Post by **F-BIRD'88** » Mon May 07, 2018 6:29 pm

Start at 26 to 28deg BTDC locked out. Ideally you want a Spark retard box to knock back timing under boost as boost comes in but this will get you by.

26 to 28 deg locked and then connect the vacuum advance to the intake manifold UNDER the blower,,, not on the carb. Use a slightly colder spark plug Do not use big spark plug gaps.

What carb? Be sure the carbs power valve sill not be pulled shut at high rpm WOT.
Be sure the WOT jetting is plenty fat at WOT. 10.5:1 ish AFR

you may then be able to sneak up on a bit more spark advance under boost
30-31-32deg... Don't get carried away.

Water/methanol injection will really allow you to unleash the hounds
More boost/drive pulley ratio and max timing under boost.

F-BIRD'88 · Post by **F-BIRD'88** » Mon May 07, 2018 6:40 pm

What is the current blower pulley ratio?
The key to higher boost is to use a BIGGER crank pulley as opposed to a smaller blower top Pulley. (better belt grip) There is a generic 8" diameter crank pulley that only requires a custom pulley spacer to use with the lil B/M blowers.
Again water methanol allows you to really kick up the boost and power ( and increase reliability too.
2.33:1 +++ drive ratio.

grant6395 · Post by **grant6395** » Mon May 07, 2018 8:42 pm

I've had good success with 30 degrees. Locked out distributor.similar combo. Don't get carried away at first with it. But you should be safe with 28-30 for sure. I get daves point about the cam timing events making a difference, butimsure this is not a " blower specific " cam. Carry on and don't overthink it. Grant.

oldhead · Post by **oldhead** » Tue May 08, 2018 9:50 pm

I had a B&M 162 on my SBC-400 for many years wirh 8# of boost. i used 32 locked. Even used a 250 hp shot with 24 degrees..The carb was a 3310 with stock jets, I tried a 850 holley.. Which B&M said the 850 was worth only 10 hp and I saw no difference from the 750. There no power above 6000 Oldhead

rewguy · Post by **rewguy** » Wed May 09, 2018 1:14 pm

Camshaft is apparently the Edelbrock perf rpm camshaft #7102
234/244 @ .050, .488/.510 on a 112. Sounds decent enough for the intended usage.

It must be an old lazy slow grind.......lol. The advertised duration is 308/318. I read that it is exactly the same cam as the elgin #1067P...not sure if thats true.

rewguy · Post by **rewguy** » Wed May 09, 2018 1:16 pm

oldhead wrote: ↑Tue May 08, 2018 9:50 pm I had a B&M 162 on my SBC-400 for many years wirh 8# of boost. i used 32 locked. Even used a 250 hp shot with 24 degrees..The carb was a 3310 with stock jets, I tried a 850 holley.. Which B&M said the 850 was worth only 10 hp and I saw no difference from the 750. There no power above 6000 Oldhead

what was your static compression? and was pump gas enough without the nitrous?

rewguy · Post by **rewguy** » Wed May 09, 2018 1:25 pm

How much more power to be found in a similar (except for lift) hyd roller? say, 232/244 .565/.540 on a 112?
25-35?

Scotthatch · Post by **Scotthatch** » Wed May 09, 2018 9:16 pm

15233805177111.jpg

Don't think you are giving up HP by backing off on timing .... as the charge density goes up you will need less timing to get the burn to peak where you need it as the burn rate will go up ....

Dyno runs above are a big block with 174 mini blower and is rear wheel on good pump gas

F-BIRD'88 · Post by **F-BIRD'88** » Wed May 09, 2018 11:35 pm

The cam yu got is fine for this.

F-BIRD'88 · Post by **F-BIRD'88** » Wed May 09, 2018 11:47 pm

Your 9.8:1cr is a bit high for this on pump gas so don't get carried away on boost or timing with pump gas. If you are rebuilding this motor (and want improved reliability) change to a dished piston to lower the cr.
8.5:1 or less. Otherwise water methanol injection will stop detonation and the coppered rod bearings. And allow that 9.8:1cr supercharged motor to sing. (more boost+ more timing too)

oldhead · Post by **oldhead** » Thu May 10, 2018 6:40 am

rewguy wrote: ↑Wed May 09, 2018 1:16 pm
oldhead wrote: ↑Tue May 08, 2018 9:50 pm I had a B&M 162 on my SBC-400 for many years wirh 8# of boost. i used 32 locked. Even used a 250 hp shot with 24 degrees..The carb was a 3310 with stock jets, I tried a 850 holley.. Which B&M said the 850 was worth only 10 hp and I saw no difference from the 750. There no power above 6000 Oldhead
what was your static compression? and was pump gas enough without the nitrous?

The year was 1992 to 1996 he comp. ratio was about 8.1 to 8.5...I used 100,150 and 250 shot.using 50/50 93/c16.....I have a B&M book somewhere showing VERY MANY dyno pulls. they tried alot of cams,different CLs up to 116 and up to 20 degrees more on exhaust. they picked two to sell 216/226 and a 234/244 (Hyd).I had both and not much power difference between them (20 hp)They sold 4 pulleys for the top, they gave something like 20 hp more at low end ans the same at top end.....Spining the 144, 162 & 250 blowers above 12,000 the air got too hot and power fell off.....I have a "Like new" 144 case between and rotors that are like new that I would almost give away..Out of all the blowers (471,671,871 B&M 144,162,250) that I have had,
and Vortech YSI the 144 &162 were the most fun

oldhead · Post by **oldhead** » Thu May 10, 2018 6:52 am

Scotthatch wrote: ↑Wed May 09, 2018 9:16 pm 15233805177111.jpg

Don't think you are giving up HP by backing off on timing .... as the charge density goes up you will need less timing to get the burn to peak where you need it as the burn rate will go up ....

Dyno runs above are a big block with 174 mini blower and is rear wheel on good pump gas

on my Vortech YSI Timing at 26 went to 29 picked up 35 hp at 32, 17 more...Tried at 16,19 and 22# of boost, I would bet 7-8 hp more at 34.....C16 used

F-BIRD'88 · Post by **F-BIRD'88** » Thu May 10, 2018 11:24 am

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.)

Don Terrill’s Speed-Talk

how much timing to run w small roots blower?

how much timing to run w small roots blower?

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