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-   -   weiand 6-71 blower questions (http://www.hotrodders.com/forum/weiand-6-71-blower-questions-162865.html)

uplateagain 08-05-2009 08:13 PM

weiand 6-71 blower questions
 
Hello everyone, iam new here and hope someone can help me out.
I just recently got an 82 camaro with a 30 over 350, afr heads, 6-71 blower and dual holley 600's. The rear is a moser 9" with 456's and is a mini spool. I need all the help i can get on blower engines as i have never had one before.
I don't really have any specs as what the c/r is, or cam specs, what boost its pushing etc.
Iam looking for info on how to figure out what boost iam putting out, or ways to change the boost for more power. The only thing the previous owner told me was it was running 13% underdriven, and is detuned for cruising on the streets, which is meaningless to me as i have no clue what it means.
My major problem right now is, i just don't think the engine is performing at low rpm like it should be, especially with the 456 gear ratio. Iam not getting much power until over 3000 rpm.
Sorry this post is so vage, but iam looking for a tutor in blower engines, as iam new to them.
Thanks in advance for any help anyone can shed onto me.
Daryl

BORTI 08-05-2009 08:51 PM

Blower Motor
 
Theres a lot to learn about blower motors, I recently built one myself. Theres plenty of very knowledgable guys on this forum. I would recommend reading books on tuning supercharged engines, and doing research online. I would visit the Blower Drive Service website,The Blower Shop site, Mooneyham, and Don Hampton Blowers. One thing is very crucial, and thats your timing curve. I blew a headgasket in the learning process. The fuel curve is also very critical, I recently had a similar issue with low rpm power. Turned out the air bleeds were too large in the high speed circuit. Theres plenty of stuff to learn, take your time and have fun. Do your research and you'll learn fast........Borti

motorhead454 08-05-2009 10:09 PM

sounds like you have a start to a very nice little setup. there is most definetly alot to blower motors. to answer your question on the underdrive that means that you are basically not using the full potential of the blower.And how you do this is by changing pully ratios like that of a bicycle sprockets and gears. to be 13% under driven you are likely running lower boost and would result in less lower end. with it being under driven that means the blower is spinning slower. but you better know that bottom end before you start cranking up the boost. and be ready to run race gas. :thumbup:

Jeff The Ruler 08-06-2009 12:56 AM

If this is your first motor, you have alot more things to worry about than how many pounds boost it has...Your time would be better spent on other areas of tuning the motor. Seems to me theres alot of people that get real caught up about boost numbers.

Pull the motor out, put it on a motor stand and pull the oil pan off. Someone earlier said you should get to know the rotating assembly and make sure nothing is awry or out of clearance, and thats a real good point IMO.

uplateagain 08-06-2009 05:40 AM

Thanks for the info everyone. I will be looking into the websites mentioned.
I knew i would be having to pull the engine to check how the bottom end of the engine was built, The guy said it was built for the blower, but i take that with a grain of salt as its just someones word with no paper work to back it up. but just not ready to do that yet. Just picked the car up last week, so i thought i would run it until winter, then pull the engine over the winter an give it a go through.
Just trying to get as much info as i can on blower engines, and tuning them.
Is there a way i can measure my pullies, and check which size are on the car so i have an idea where iam with that? Are the pullies measures in standard inches, millimeters, or?
Thanks again for everyones help on this.
Daryl

T-bucket23 08-06-2009 06:49 AM

Quote:

Originally Posted by uplateagain
Hello everyone, iam new here and hope someone can help me out.
I just recently got an 82 camaro with a 30 over 350, afr heads, 6-71 blower and dual holley 600's. The rear is a moser 9" with 456's and is a mini spool. I need all the help i can get on blower engines as i have never had one before.
I don't really have any specs as what the c/r is, or cam specs, what boost its pushing etc.
Iam looking for info on how to figure out what boost iam putting out, or ways to change the boost for more power. The only thing the previous owner told me was it was running 13% underdriven, and is detuned for cruising on the streets, which is meaningless to me as i have no clue what it means.
My major problem right now is, i just don't think the engine is performing at low rpm like it should be, especially with the 456 gear ratio. Iam not getting much power until over 3000 rpm.
Sorry this post is so vage, but iam looking for a tutor in blower engines, as iam new to them.
Thanks in advance for any help anyone can shed onto me.
Daryl

You need to supply a lot more information if you want help
to start with
Cam model or specs
Compression ratio
Ignition type and timing
Head type (model)

There are people here who can help but they need info.

ericnova72 08-06-2009 02:11 PM

Pulley drive ratio is best determined by counting the number of teeth on each pulley and doing the math.

motorhead454 08-06-2009 02:34 PM

Quote:

Originally Posted by T-bucket23
You need to supply a lot more information if you want help
to start with
Cam model or specs
Compression ratio
Ignition type and timing
Head type (model)

There are people here who can help but they need info.

he bought it from a guy so I dont think he will have the specs. It doesnt sound like he gave him any info on it. I dont buy used motors especially blower motors from people. Unless you plan on tearing it down and rebuilding it. Just to much to risk. the teeth like eric said is the best way. I am not sure on the exact math but there are people here who can tell ya. If it were me I would just buy a few different pulleys and play with it. I think you can even buy them in sets. :mwink: but remember the higher the boost the higher your comp ratio will be so you depending on how high you plan on going you might have to run higher octane. have fun though. and good luck

ericnova72 08-06-2009 02:40 PM

Quote:

Originally Posted by motorhead454
he bought it from a guy so I dont think he will have the specs. It doesnt sound like he gave him any info on it. I dont buy used motors especially blower motors from people. Unless you plan on tearing it down and rebuilding it. Just to much to risk. the teeth like eric said is the best way. I am not sure on the exact math but there are people here who can tell ya. If it were me I would just buy a few different pulleys and play with it. I think you can even buy them in sets. :mwink: but remember the higher the boost the higher your comp ratio will be so you depending on how high you plan on going you might have to run higher octane. have fun though. and good luck

Have you ever purchased blower pulleys in sets to "play with"?? They ain't cheap, close to $100+ each.

motorhead454 08-06-2009 03:01 PM

Quote:

Originally Posted by ericnova72
Have you ever purchased blower pulleys in sets to "play with"?? They ain't cheap, close to $100+ each.

this is true!lol but if you got the cash why not?lol I would just cause you would always have them. My grandpa has had his for two blower motors now. but he has money though.lol. or just buy the ratio that you want? but they are damn expensive! :D

uplateagain 08-06-2009 07:19 PM

Thanks again for everyones replies.
I don't have any specs on the c/r, cam, or the bottom end. I know the heads are afr aluminum, so i can probably find a stamping on them to look up what they are.
Iam not looking to go nuts with the pullies, just get a little more low end out of the car as it doesn't produce much until after 3000 rpm. so i can change out the gears from the 456's to 373's or around there.
What is the math that needs to be done after countng the grooves in the pullies?
This is only a street car, its not going to be run down the track, so i would like to be able to stay with 93 octane.
Thanks again for all your help. I will check the pully size and get back to everyone.
Daryl

motorhead454 08-06-2009 09:48 PM

:thumbup:
Quote:

Originally Posted by uplateagain
Thanks again for everyones replies.
I don't have any specs on the c/r, cam, or the bottom end. I know the heads are afr aluminum, so i can probably find a stamping on them to look up what they are.
Iam not looking to go nuts with the pullies, just get a little more low end out of the car as it doesn't produce much until after 3000 rpm. so i can change out the gears from the 456's to 373's or around there.
What is the math that needs to be done after countng the grooves in the pullies?
This is only a street car, its not going to be run down the track, so i would like to be able to stay with 93 octane.
Thanks again for all your help. I will check the pully size and get back to everyone.
Daryl

no prob. I couldnt tell ya what the math is for the pulleys cause i do not know how either. lol. I would think with afr even the baseline would be fine for your set up. I would talk to the blower shop they could give you a ton of info. the c/r is your biggest thing to figure out. I would hope it is at around 8.5-1 to 8-1.

XNTRCI-T 08-07-2009 06:54 AM

Divide the number of teeth on the driving (crank) pulley by the number of teeth on the driven (blower snout) pulley, like this...

Crank pulley = 45 teeth
Snout pulley = 39 teeth

45 / 39 = 1.15 or 115%

In the above example you are driving the blower at 115% of engine speed, so the blower is 15% over-driven. If you wanted to reduce boost you could swap the pullies, and then you would have...

Crank pulley = 39 teeth
Snout pulley = 45 teeth

39 / 45 = .87 or 87%

In this example you are driving the blower at 87% of engine speed, so you are 13% under-driven.

F-BIRD'88 08-07-2009 08:28 AM

Detuning a blower motor for the street refers to underdriving the blower ( ususally) to keep the max boost created under power to a reasonable modrate level. (5-7psi typical) also the spark timing is retarded a bit from the max power point by 4 to 8deg. This is all an effort to eliminate the risk of engine detonation at WOT while running on pump gas.

High octane gas (110-114) will allow more blower boost (1-1 pully ratio or overdriven pulley ratio) and more spark timing.

Running the blower pulleys "underdriven" does reduce low rpm boost responce and power below 3000.
The spark timing curve is very critial. A street blower set up wants a lot of inital timing (especially with a big cam and low mechanical compression ratio) but modest total timing under boost.
Increasing the inital timing will make the low end much more responsive.
How much depends on the cam duration. around 24 to 30 deg is good.
But you only want around 28-32deg total timing under boost on pump gas.
So, to increase the low rpm responce try locking out the mechanical spark advance and setting the now frozen timing at 28-30deg BTDC.
If this motor has a fairly big cam in it (as indicated by the poor low end responce, the increased timing at idle will make it idle much cleaner and improve the low rpm response.
Do not run excessive spark timing under boost while using pump gas.
Do not guess at the spark timing.
Get a advance type timing light and learn how to use it.
I recomend the type with the advance dial as opposed to the electronic digitial type (tend to be innacurate and unreliable).
see what the timing is now. Idle timing and max mechanical advance timing.
Does this car have a boost retard box installed? How much boost retard?
Leave the blower pulleys alone for now.
Does this car have a high stall torque converter or a "stock" torque converter?
What is the rear tire diameter?

bentwings 08-07-2009 09:14 AM

The above info is pretty good. Get the car running good and drive it around for a while before you start changing things. It has to be a fun car to drive. You will probably blow off a set of tires pretty quickly. haha BTW you can get a nasty ticket or group of tickets if you aren't carefull. :mad:

I'd take a carb off and look inside the blower. Pop the belt off too and spin the blower by hand. It should turn freely and not be scored or chewed up. If it is you will definitely be down on boost. No easy or cheap fix here. You will have to send it to one of the blower shops for a rebuild.
The things are heavy. Around 70-80 pounds.
$300 up pluss massive shipping.

You can get a vacuum/boost gage from autometer in several different styles. Get one. Install the 1/8 npt fitting in the manifold under the blower. Yes there will be vacuum in the manifold even cruising. You will only get boost when the throttle is open far enough for the blower to draw in more air than the motor can by itself. The 6-71 blower displaces 411 cu in per revolution and is quite efficient at relatively low speeds. You have to overcome vacuum before you get boost. It happens pretty quick however. Don't get too carried away with boost on the street. 5-8 psi is good for a SBC You could go to 10-11 underdrive and pick up a little but I'd be carefull. The more boost you have the more critical timing and carb tuning becomes. The first time it backfires hard will open your eyes for sure.
$60 or so

Try your converter out for stall speed. You really need about 3000 stall even with the blower in this case. I've got a 3k in mine and it really made driving it more fun.
$350 or so

The 4.56 gear are going to be a major pain on the street. I ditch them for a 3.73.
$175 +/- a little. If you install them yourself.
add another $100 minimum if you don't.

Instead of messing around with the timing light trying to figure out the advance curve just take the distributor to a good performance shop and have it run on the Sun machine. Tell them you want full advance by 2000-2200 engine rpm and about 15-16 degrees of advance. Install the dizzy and set total advance at 28-30 degrees at about 3000 rpm and let the initial fall where it might. All you need to worry about is that it doesn't kick back against the starter. It shouldn't with proper C.R. With this set up and a 3k converter you will have full advance almost anytime you step on the gass.
$50-75 about.

I put a few $$$ figures in to give you and idea of the cost of blower related items. As they say "...get used to it" :(


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