Boost Question
 

I have a 355 with 6-71 roots blower (TBS). 8.25:1 CR, aluminum heads, Cometic MLS head gaskets.

I run 8 psi boost with pump gas. Can I just change the pullies and run higher octane to run more boost? How much?

How are guys runing 15, 20, 30 PSI of boost with turbos and cintrifugal super chargers?

Thanks, Steve

Boost?
 

Steve,
1 Issue?What do ou have for a Lower END?
If its all Forged and you have Good Head Bolts,Studs.It all depends on the Ammount that you want?
I Never had any Issues w/a GM Block until I made 26-28lbs of Boost,then the Heads Studs would JUST PLAIN LEAVE there Spots in the Block!
If you have a Aftermarket Block,then It will Handle More!
A GOOD Outboard Crank Support is another way of keeping the Snout attached to the Crank!
If you are looking for 15-18lbs?
Change the Pullys,Octane and Take some Timing Away!
If You want to Make More,Then I Need some More INFO on your Motor?
Later
G 8)

X2, a stock block 355" can't hold it, case in point 1471 blown alcohol running 30lbs boost, cracked a cylinder burned down a piston and i was running the best parts available including splayed main caps and front crank support.

JMO

Zip.

Thanks for the help guys. I should have added it is a stock GM 4 bolt block with 4340 forged crank and rods. Forged aluminum pistons.

Made 615 HP on the engine dyno in January. What can I expect if I go to 12-15 pounds?

Steve

One last thing. ARP head bolts.

I would ditch the head bolts and go with studs. You'll get a better seal and less wear and tear on the bolt holes in the block.

I have run blown sbc on the street for years. I will give you some advice in a bit after i rest!!!! Just got home from a steel erection job for DPS.

ps i run up to 10-12 lb boost on with 93 octane. Proper jetting and correct timing and a good cooling system. Unless ur blower is a aftermarket it is not going to put out more than 10-14 lbs of boost max. Being in a street car it will put less strain on the engine, since you will get little traction.

Be back later

I look forward to your knowledge.

My Nova is 80% street and 20% 1/4 mile. As many do, I am chasing the big billboard.

My blower is from The Blower Shop. Th400 w/TB, Ford 9" with 4-link.

And no traction with street tires.

ssym: I know nothing about blown stuff, but I wanted to say welcome & that is a beautiful Nova... does not get much better than that... color & all!! Scooter/Rigsby

a GREAT example of my kind of street machine 8) 8) 8)

LIVELY

This is a very good question and hits home at the right time. My new motor is on the dyno all good parts Dart block, callis crank,oliver rods,everything studed,Dart pro 2 heads enderle bird catcher,its a 540 ci w/ BDS 871 stage 2 w/ air lock rotors. 8.5 compression. its 25 % overdriven and should make 20 lbs of boost and 1300 HP on 118 gas more with alcohol.
My problem is It flat lines at 11 lbs of boost at 5500 RPM. I have talked with the blower shop, BDS, Littlefield, and they told me to teflon strip the rotors will help which Im taking it apart today and doing. Or get a 1471 and that will do the trick.

Any one have any suggestions or have run into this ?

Thanks ssym for bring the topic up.

The teflon 8-71 is going to be tough on the street. It probably wont make the boost u are looking for in a 540 8.5 to 1 engine. Spinning it faster is going to make the intake air temp rise more than the boost you will get out of it. The bigger blower is better, You wont have to spin it as fast which is better for the end of that bbc crank with no support. Dont get me wrong a 14-71 is gonna be a big momma to spin, but it will make any boost resonably could want and have a lower air temp on the charge.

Back to work!!! At least its Friday

X2, an 871 is not big enough for a 540" motor, just not enough volume. Maybe a 1271 and you could run your distributor in the stock location without an offset drive.
Don't know if you guys heard or not, but Mert Littlefield passed away 2 weekends ago. I've know him for over 25 yrs, i think it was due to a heart attack.

RIP Mert.

Zip.

I have a 47 bottom pulley and a 55 top pully or 14.5% underdriven. Pump Gas and 33* timing. It makes 8 psi at WOT.

I am thinking of going to a 50 top pulley, C16, 30* timing.

Any thoughts before I volunteerily grenade my engine?

What king of performance can I expext?

According to the charts that BDS has in there book you will be around 10 lbs of boost and your final compression ratio will be close to 13.5 to 1.

Must have good parts in the rest of the motor. Like rod bolts for starters

Make sure the belt has some slack in it. A lot of people like to snug a blower belt, You want about 1/2-3/4 flop side to side. The crank will pull the slack out of the pull side. What pulleys are you running? 8mm.

Remember how often are you going to be at wot on the street? Not long at all. 99 percent of your driving is going to be slow quick burst of tire shredding. what ignition system are you running and does the dist have any adavnce oris it locked out?

#1 make sure you are on the fat side of your jetting when you first start playing out on the town. Unless you have a monitor your going to have to read the plugs. do you have a pressure relief valve on ur intake? or blow off plate?

kwkracing:

Your experience is of great value to me.

I keep the belt good and slack. Blower whine means nothing to me.

I just spent a good part of the day enjoying 400 ft/lbs of torque at 3000 rpm. The timing is locked out with a MSD Digital 6. I do not under stand boost retard or when you need it. I don't have it.

I do have an air/fuel gauge with O2 sensor in the right collector. runs between 12.5 - 13.5 to 1. Closer to 12 at WOT.

Pressure relief is on the back of the intake. Couple springs and I don't even know if its ever been used.

Thanks for the help and knowledge.

Steve

Yes, 8mm belt and pullies.

Do you have any trouble keeping the cooling system cool after you have been hot rodding around? Whats the average temp? If you can keep the temp down to under 180 or so you should have no problem running a 93 octane in a aluminum headed sbc with 8 to 1 static compression. Your timing is about right, if the engine is built with nice forged pistons, rods and good head gaskets, you should have no problem. Make sure you have a good tranny cooler and maybe even a trans temp gauge. You are toying alot of torque around on the street and ur convertor is doing alot of slippage, making heat. I run a tad more timing, up to about 35-36 but no more. Your limit is your 6-71 blower. it wont make much more usable boost that 12 lbs and if your tune is safe, engine is cool, you will be fine

[quote="kwkracing"]The teflon 8-71 is going to be tough on the street. It probably wont make the boost u are looking for in a 540 8.5 to 1 engine. Spinning it faster is going to make the intake air temp rise more than the boost you will get out of it. The bigger blower is better, You wont have to spin it as fast which is better for the end of that bbc crank with no support. Dont get me wrong a 14-71 is gonna be a big momma to spin, but it will make any boost resonably could want and have a lower air temp on the charge

Telflon stripping my 871 how much more boost can I expect ? race only motor. Another question my intake air temp is 170 degrees. can I spin the blower faster to get more boost ? if so what is the high end of the intake air temp ? I no the bigger blower is better but $$$$ I can only use what I have. Thanks

BOOOOOST
 

I Have Made in Access of 25LBs w/a 8/71.With 433"s.
Just Sell me the 8 and SHAKE a Tree,them 14's will Fall out EVERYWHERE!
Let me know,a Good 8 is worth about a Grand or so?
Later
G 8)

Re: BOOOOOST
 

[quote="bbchevy"]I Have Made in Access of 25LBs w/a 8/71.With 433"s.
Just Sell me the 8 and SHAKE a Tree,them 14's will Fall out EVERYWHERE!
Let me know,a Good 8 is worth about a Grand or so?
Later
G 8)[/quote


I went out and shook all my trees and wore my hard hat. nothing came out, I guess I'm stuck with this 871. I must live in the wrong part of MI. North of me is where all the cash is :lol:

some good info and prices

http://www.superchargerusa.com/blowers.htm

Thanks kwkracing, Great Info.