Blowers/superchargers

[smokeyco75]

I have always loved how some blower motors lurch when idling. I am curious as to what causes this to happen? I have never tinkered with one before and if I were to ever add one to my big block chevy I would like to know some things to keep in mind such as what compression ratio the engine should be, how to pick a camshaft, pulley ratios and their affect, etc. I know a good amount of folks here may have the answers. Thanks in advance!

 

[409T]

Boost referencing or rather lack of is what causes that. You can set the carbs up so there is no blower surge, although some people actually aim for that effect.

 

[hutchman]

I'm assuming you are referencing this:

Well, still can't post links.....

 

[hutchman]

We'll try again:

[youtube]

This one had me laughing out loud...worst I've ever heard!

 

[fletcherson]

We'll try again:

[youtube]

This one had me laughing out loud...worst I've ever heard!

That sure gets the heart pounding! I bet the owner of that beast knows how to put clutches in a tranny! lol I sure wouldn't want to try to drive that thing through town with the cop on duty!

 

[Golly]

I believe" blower surge" or "hunting" is an over rich condition where the motor gets a gulp of fuel /air, idle speed drops , then leans out causing idle speed to go up, , gets another load of fuel/air, etc etc . . . .
That video is an Aussie car by the way.

 

[Screaming Metal]

What Golly Said! And its really, really extremely hard on the lower end of the motor....You see with a blower, your cramming in enough fuel, air mixture into the cylinders, the motor actually thinks its 2 or 3 times its size....and it puts that much 'Hit' on the lower end. Thats why the Blower folks selling kits always say forged cranks, and steel rods w/forges pistons to put up with such high pressures on the rotating mass.
At Idle, your oil film that floates your mains and rods on a chevy sb, is pretty low, oil pressure wise, and that 'Hunting' will pratically destroy the lower end bearings.
On fuelers that idle at 1300RPM+ rpms....their idle isn't that lopey, BUT, with over 800 Horses per cylinder hitting that crank, they are pratically shot after 1 trip down the 1/4 mile.
Its not that hard to get a Blown car to idle. You can get a all out roller race cam, stick a blower on top of the motor....and it will idle pretty damn good. That is because at idle, the all out cams can't get a full gulp of air, because of the low rpms. The Blower cures that and idle fill effeciency is restored....

 

[Screaming Metal]

Not to mention the speeding up and slowing down is really hurting that blowers bearings and the rotor pinning....the clearances are so close rotor to rotor and rotor to endplate....if folks that actually rebuilt them themselves, they would not be doing that....
BUT, some folks got more money than common sense....
Can't tell them nothing until about 5 lbs of rotor pieces parts fall down on top of their intake valves....and scraped a perfectly good motor....just to hear it idle like that.

 

[smokeyco75]

That is some great info folks, I had no idea it was so hard on parts when they lurch like that. I know I would rather have everything right instead of self-destructing a power plant just to get a certain sound. I can just go to a car show to hear it from someone else's ride lol. For my initial build I plan to keep this engine completely stock. I will probably put a fresh oil pump in it and an aluminum intake and some finned aluminum valve covers. That should be plenty of flash and plenty of motivation for such a small car.

So what is the purpose of different pulley ratios on a blower? To increase or decrease boost?
Screaming Metal, so your saying typically you can run a ridiculously radical cam with a blower and it will tend to idle much better than it would without the blower? I never thought of that but it makes sense.

 

[Francis Blake]

I had a blower on my t when I first bought it, and it worked very well had some surge but it used so much gas I could not afford to drive it on a long cruse. It had an unbelievable amount of power, to the point of having to be very careful on the throttle. So my advise would be unless you want to race or really burn some tires don't get a blower. They are a lot of fun and draw LOTS of attention but have their disadvantages. But if you want and can afford it go for it.

 

[Screaming Metal]

Yes, the more overdrive you throw at a motor, the more pressure your applying, the faster the blower spins, more boost is put out, with that increase in boost means for fuel is mixed with that given amount of air.
Ideally, a street car is 5-7psi....good for about 550 horses or so....
A hot setup for the street/strip combos will run about 10-12psi....
Racing, we go as high as 24-26....

That white stuff you see coming out the zoomies after dark in the favorite Top Fuel rails and altereds....thats the extra oxygen in the nitro burning....nitromethane has oxygen built into it.
We look at that when diagnosing. Seen folks getting their hand and running them over the zoomies while its idling? They are making sure all cylinders are hitting. See the tuner or mechanic run his hand across the front and the back of the heads? He's feeling for head gasket leakage.

The alky FC's can run as much as 20-30% OD, theys why those blowers whistle so load when coming up to the staging lanes, and why they're so loud going down the track. But the Nitro cars will actually shake the ground during takeoff....

Look up the spec's on a TF/AA or TF/FC cam....it will shock you....

 

[Screaming Metal]

For the street 5-6 on the boost gauge is about perfect, lots of power, decent mileage, just barely hit the gas and your gone....
Build a stock heavy duty lower ended chevy 350, add a mild blower cam, and a 6-71 blower kit....500-550 horsepower thats really very mild mannered streetwise, sweet idle, starts quickly, powerful smooth powerband....

 

[T-Test]

I'd rather be BLOWN than INJECTED, but price wise and for drivability, injection is THE way to go including putting carbs on an engine that has 200hp with a 750 Dominator on it. MOST people aren't mechanics and just don't GET how things work on an internal combustion engine. I laugh at them because of all the money they spend on fuel and for the LOOKS. 10gallon fuel tank @ 3 miles per gallon means you want be going on a Power Tour anytime soon!

Just think what you could have/buy with the money you've spent on THAT B/A BLOWER MOTOR and can't reliably DRIVE it on the street for any real fun other than avoiding the cops when doing burnouts or wheelstands.

 

[PotvinGuy]

Adding a blower to a mild street motor is easy, IF you don't get CRAZY. Most of the time the blower isn't doing anything except adding heat and cutting mileage. I'd underdrive a 671 on a SBC. You can experiment with drive ratio on your BBC. If the motor is stock, I'd keep it to 5# boost max to be safe. The carbs should be "blower carbs," which have a line to the manifold so the power valve operates correctly. You can do without these, but the mixture will lean some when you step on it since the power valve never actuates. Read the plugs to see if you need to richen the jets. A blower cam isn't required, but if you're thinking of one, I'd talk with BDS or the cam companies to get a recommendation. Ignition timing...boost may require a bit less advance to avoid knocking. Be conservative.

I've run a 671 and a B&M 250 on my crate SBC with a plain old Holley 750. The 250 was overdriven 33% and is a great match for a SBC; unfortunately Holley/Weiand dropped the 250 after they bought B&M. They have a 177 for the BBC, but it is a puny looking thing.

 

[PotvinGuy]

Here's an interesting setup:
www.ebay.com/itm/Wild-B-amp-M-250-blower-system-B-B-Chevy-boat-marine-dual-Demon-blower-carburetors-/360470549240?_trksid=p2054897.l4275

You'd have the only one at the cruise.

 

[bobs66440]

This is very interesting reading. Personally, I have zero experience with blowers but my buddy has a '63 Belvedere with a beastly blown (8-71) 440. Absolute monster. It wiped a cam lobe so he went with a smaller roller cam setup. Since then it has that idle surge when it's cold especially. Not super bad, but bad enough to be annoying. We are both confused why it would start now with no other changes...

 

[Screaming Metal]

I've run a 671 and a B&M 250 on my crate SBC with a plain old Holley 750. The 250 was overdriven 33% and is a great match for a SBC; unfortunately Holley/Weiand dropped the 250 after they bought B&M. They have a 177 for the BBC, but it is a puny looking thing.

Yea PotvinGuy....thats their idea of being effecient....they're taking a beating for that one because thats one of the favorites....anything smalleer than a 250 looks funky. They make the 71 series all the way down to a 3-71 and smaller with another series....
Those things were used in all kinds of diff. apps., like blowing peanuts and insulation in mfg'ing processes to venting really big plating tanks, etc.
Theres one of the old 51 or 53 series that is wide as it is tall and long. Was really popular on bikes way back in the day....the thing is not much bigger than a bucket, kinda cute in a strange wierd kinda way after seeing the 4-71's & 6-71's.

Anyway, yes, you can run a stock cam, and run about 20% under, and the fuel mileage isn't bad. No, not as good as efi, but not bad. Heres one thing folks don't understand....You don't need to run 2 750 carbs on a blower, and you don't need a 6-71.
Get a 600 cfm 4bbl and a 4-71 on a stock early model chevy hi-perf. 350 with steel crank/rods and forged pistons and give me 4 hours to tune and I'll smoke most of the twin carbed 6-71's out there on the street, and get better fuel mileage doing it.
The Paxtons are better yet, more efficient, cooler running, but don't have that awesome look going for them. And will perform every bit as good as a 4-71.
The only advantage to running the big blowers, is you can run lower blower speeds and not heat up the motor while putting out boost. My old Poncho 455 SuperDuty had a 8-71 on it, you could barely turn the dist. it was so close....and I had it where she'd eat 5 lbs of boost @ 5000, ran on a single Thermoquad, with 3.43's, she got about 15 mpg. That was with a fully bodied 73 Firebird. Now mind you, you had to idle around town and look cool doing that....once you hung your foot off into her, she guzzled fuel....
But I drove it daily for 3 years, rain, shine sleet or snow....if it wasn't Too bad....put a trashbag over the blower to keep the rain and the snow off her. Pump the gas 3 times, hit the key she'd lite off, I don't care if it were 20 degrees outside.
But I did have problems popping the lower gaskets all the time. I'd have to replace them about 3 times a year....that got old fast....

 

[GT63]

How about Blown and EFI, yes it can be done and is very street friendly.

 

[fletcherson]

How about Blown and EFI, yes it can be done and is very street friendly.

How about Blown and EFI, yes it can be done and is very street friendly.

I've run a 671 and a B&M 250 on my crate SBC with a plain old Holley 750. The 250 was overdriven 33% and is a great match for a SBC; unfortunately Holley/Weiand dropped the 250 after they bought B&M. They have a 177 for the BBC, but it is a puny looking thing.

Yea PotvinGuy....thats their idea of being effecient....they're taking a beating for that one because thats one of the favorites....anything smalleer than a 250 looks funky. They make the 71 series all the way down to a 3-71 and smaller with another series....
Those things were used in all kinds of diff. apps., like blowing peanuts and insulation in mfg'ing processes to venting really big plating tanks, etc.
Theres one of the old 51 or 53 series that is wide as it is tall and long. Was really popular on bikes way back in the day....the thing is not much bigger than a bucket, kinda cute in a strange wierd kinda way after seeing the 4-71's & 6-71's.

Anyway, yes, you can run a stock cam, and run about 20% under, and the fuel mileage isn't bad. No, not as good as efi, but not bad. Heres one thing folks don't understand....You don't need to run 2 750 carbs on a blower, and you don't need a 6-71.
Get a 600 cfm 4bbl and a 4-71 on a stock early model chevy hi-perf. 350 with steel crank/rods and forged pistons and give me 4 hours to tune and I'll smoke most of the twin carbed 6-71's out there on the street, and get better fuel mileage doing it.
The Paxtons are better yet, more efficient, cooler running, but don't have that awesome look going for them. And will perform every bit as good as a 4-71.
The only advantage to running the big blowers, is you can run lower blower speeds and not heat up the motor while putting out boost. My old Poncho 455 SuperDuty had a 8-71 on it, you could barely turn the dist. it was so close....and I had it where she'd eat 5 lbs of boost @ 5000, ran on a single Thermoquad, with 3.43's, she got about 15 mpg. That was with a fully bodied 73 Firebird. Now mind you, you had to idle around town and look cool doing that....once you hung your foot off into her, she guzzled fuel....
But I drove it daily for 3 years, rain, shine sleet or snow....if it wasn't Too bad....put a trashbag over the blower to keep the rain and the snow off her. Pump the gas 3 times, hit the key she'd lite off, I don't care if it were 20 degrees outside.
But I did have problems popping the lower gaskets all the time. I'd have to replace them about 3 times a year....that got old fast....

I've run a 671 and a B&M 250 on my crate SBC with a plain old Holley 750. The 250 was overdriven 33% and is a great match for a SBC; unfortunately Holley/Weiand dropped the 250 after they bought B&M. They have a 177 for the BBC, but it is a puny looking thing.

Yea PotvinGuy....thats their idea of being effecient....they're taking a beating for that one because thats one of the favorites....anything smalleer than a 250 looks funky. They make the 71 series all the way down to a 3-71 and smaller with another series....
Those things were used in all kinds of diff. apps., like blowing peanuts and insulation in mfg'ing processes to venting really big plating tanks, etc.
Theres one of the old 51 or 53 series that is wide as it is tall and long. Was really popular on bikes way back in the day....the thing is not much bigger than a bucket, kinda cute in a strange wierd kinda way after seeing the 4-71's & 6-71's.

Anyway, yes, you can run a stock cam, and run about 20% under, and the fuel mileage isn't bad. No, not as good as efi, but not bad. Heres one thing folks don't understand....You don't need to run 2 750 carbs on a blower, and you don't need a 6-71.
Get a 600 cfm 4bbl and a 4-71 on a stock early model chevy hi-perf. 350 with steel crank/rods and forged pistons and give me 4 hours to tune and I'll smoke most of the twin carbed 6-71's out there on the street, and get better fuel mileage doing it.
The Paxtons are better yet, more efficient, cooler running, but don't have that awesome look going for them. And will perform every bit as good as a 4-71.
The only advantage to running the big blowers, is you can run lower blower speeds and not heat up the motor while putting out boost. My old Poncho 455 SuperDuty had a 8-71 on it, you could barely turn the dist. it was so close....and I had it where she'd eat 5 lbs of boost @ 5000, ran on a single Thermoquad, with 3.43's, she got about 15 mpg. That was with a fully bodied 73 Firebird. Now mind you, you had to idle around town and look cool doing that....once you hung your foot off into her, she guzzled fuel....
But I drove it daily for 3 years, rain, shine sleet or snow....if it wasn't Too bad....put a trashbag over the blower to keep the rain and the snow off her. Pump the gas 3 times, hit the key she'd lite off, I don't care if it were 20 degrees outside.
But I did have problems popping the lower gaskets all the time. I'd have to replace them about 3 times a year....that got old fast....

A blown Pontiac, That's my kind of rod! Pontiacs are very timing sensitive, from my experience. I ran a 73 4 bolt main 400 with 670 heads and a tri-power in a 76 Ventura with a m-20 4 speed. I really miss that car, hard on clutches but never boring. I surprised the Hell out of a lot of Mustang's, Camaro's, etc...I have limited exposure to boosted motors. I am toying with the idea of boosting my 67 Firebird convertible when I get to that point. What do think about turbo's vs blowers? I intend to run a Edelbrock pro-flow port fuel injection with a 4 barrel type throttle body. I thought the added low end performance and timing control that the injection allows should compliment the Pontiac's rpm and torque curve. What do you think!

 

[Hot Rod Todd]

Well Ive run a 671 blower on a 454 in my bucket with a pair of 750 Edelbrocks and Ive run a 540 in my bucket with a pair of 1250 dominators.

The 454 set up was VERY streetable and dyno'd at 627 hp. Was a 2 bolt mains block, cast crank, stock rods and heavy TRW blower pistons and a set of second hand Chevy Bowtie heads, Cam was Comp cams blower/turbo/nitrous hydraulic flat tappet one and the whole deal was 13mpg on the open road. Engine cost $600 and all the shortblock parts except the heads was $1800 from Summit (shipped to NZ). Crank got a crack in it after 5000 miles and many quarter mile jaunts. Best was 10.2 @ 132.

So it was a very cheap engine, built with cheap parts and it only ran about 5-6lbs of boost. Way nicer to drive than a big cammed normally aspirated 450hp SBC that a mate had in his bucket.

He drove mine and reckoned the engine was like a late model EFI car in comparison to his. Just smooth dependable power.

I would recommend a blower on a bucket. They look great, and they can make good smooth power. Contrary to what you may hear at a cruise night, they are not all about to launch the front end 6 feet into the air, or smoke the rears if you hit the loud pedal.