6-71 blower tuning - Chevelle Tech
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  #1  
Old Mar 21st, 10, 8:55 AM
69 camaro 69 camaro is offline
salman
 
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Wink 6-71 blower tuning

Dears I recently build 496cu 8.5 cr on 114cc iron head with 6-71 long nose supercharger, dual Holley carburetors 750cfm hp,6AL MSD,coil MSD BLAST3 .
Since this the first time I deal with blower .how I can did the timing for this? It is the same like regular engine? Or different.
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  #2  
Old Mar 21st, 10, 12:11 PM
rtanner rtanner is offline
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ron
 
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Default Re: 6-71 blower tuning

Same, run no vacum advance, 10-12 degrees initial, 32-36 total depending on octane used.
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  #3  
Old Mar 21st, 10, 4:45 PM
69 camaro 69 camaro is offline
salman
 
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Default Re: 6-71 blower tuning

well actually I am using 93 octane. And when I check the pulleys the top one is 40 teeth’s and the crank pulley is 36 teeth.
so I think it is under drive but I don't know how many PSI in this pulleys numbers?
How can I know this……..?
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  #4  
Old Mar 21st, 10, 4:59 PM
Mike Mike is offline
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Default Re: 6-71 blower tuning

40t top w/36t bottom is a 10% underdrive.
Theres no PSI value determined from the pulleys ,it the backpressue from the manifold and heads.
You'll need to put a gauge on the manifold to find the actual boost pressure.
https://blowerdriveservice.com/techcharts.php

BTW ,you have boost referenced the Holley carbs?
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  #5  
Old Mar 21st, 10, 7:37 PM
ironhead ironhead is offline
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Default Re: 6-71 blower tuning

Blown big blocks on the street like high initial but do not require a ton of total.
I would shoot for 20* initial and a total of 32-34* all in by 2500 rpm.
You can run more total if you install a boost retard type ignition.Say 38* at no load cruise..but pulls out a degree of advance for every 1lb of boost.
For example..if this combo could muster up 5 lbs of boost..timing would lay back from 38* to 33* with spark retard.
As for the pulley combo..how well the engine moves air thru it will dictate stacked up pressure in the manifold.You will need a vac/boost gauge installed below the blower and monitor it at wot/max rpm.
As big as that 6-71 is..its not ideal atop a free breathing 496.The 8 series would be better suited..buts lets work with what you have.
If the underdriven 6-71 suits your needs..dial in the tune up and enjoy the few lbs of boost she offers.When that gets old,flip the pulleys and run 10 over.Boost pressure will not be the issue..intake charge temp will be.
if you can stay out of detonation on pump swill,fine.If not..water/meth injection is an option as well as an e-85 conversion.
And yes..boost referanced primary power valves is a wise choice for a blown street unit.There are times when the the engine requires additional enrichment to the main well..but the blower is still pulling x# of inches of vacuum on the carb base.External referancing allows the power valves to operate as per design.
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8-71 blown 461 Rat on E-85
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  #6  
Old Mar 22nd, 10, 3:02 AM
69 camaro 69 camaro is offline
salman
 
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Default Re: 6-71 blower tuning

Really this is a lot information which i don't know about.but today i am going to install autometar boost gauge and I'll set up the timing as per your recommendation and i will give you the feed back.
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  #7  
Old Mar 22nd, 10, 1:55 PM
69 camaro 69 camaro is offline
salman
 
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Default Re: 6-71 blower tuning

I installed the boost gauge and I set up the timing starting from 32 to 36 and I test the car every change of timing but it doesn’t show much different only the sound of the blower are increased and the gauge boost doesn’t move at all the RPM times and the car test like any car with stroke it look like that the blower not working at all because there is no that much power like any car with blower.
I really don't know what the reasons ,but I am thinking of the pulleys teeth numbers.
And how about if I want 8 PSI for example what is the pulleys teeth# I have to install? Or there is other than that part I have to change.
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  #8  
Old Mar 22nd, 10, 3:51 PM
Mike Mike is offline
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Default Re: 6-71 blower tuning

Where did you plumb the gauge to ? And what did it read ?
Which drive setup are you using ? Gilmer , V ???
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  #9  
Old Mar 22nd, 10, 4:35 PM
69 camaro 69 camaro is offline
salman
 
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Default Re: 6-71 blower tuning

I plumb the auto meter boost gauge fitting to the intake and it doesn’t read (zero) ,i am using it for racing and it is Gilmer.
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  #10  
Old Mar 22nd, 10, 6:41 PM
Mike Mike is offline
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Default Re: 6-71 blower tuning

Stick a vacuum gauge in the port and see what you get.
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  #11  
Old Mar 22nd, 10, 7:42 PM
Tokyo Torquer Tokyo Torquer is offline
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Default Re: 6-71 blower tuning

Quote:
Originally Posted by ironhead View Post
Blown big blocks on the street like high initial but do not require a ton of total.
I would shoot for 20* initial and a total of 32-34* all in by 2500 rpm.
You can run more total if you install a boost retard type ignition.Say 38* at no load cruise..but pulls out a degree of advance for every 1lb of boost.
For example..if this combo could muster up 5 lbs of boost..timing would lay back from 38* to 33* with spark retard.
As for the pulley combo..how well the engine moves air thru it will dictate stacked up pressure in the manifold.You will need a vac/boost gauge installed below the blower and monitor it at wot/max rpm.
As big as that 6-71 is..its not ideal atop a free breathing 496.The 8 series would be better suited..buts lets work with what you have.
If the underdriven 6-71 suits your needs..dial in the tune up and enjoy the few lbs of boost she offers.When that gets old,flip the pulleys and run 10 over.Boost pressure will not be the issue..intake charge temp will be.
if you can stay out of detonation on pump swill,fine.If not..water/meth injection is an option as well as an e-85 conversion.
And yes..boost referanced primary power valves is a wise choice for a blown street unit.There are times when the the engine requires additional enrichment to the main well..but the blower is still pulling x# of inches of vacuum on the carb base.External referancing allows the power valves to operate as per design.

+1. George gives good advice on the timing. you are at 10% under drive which will only give you ~4.4 lbs boost with a 6-71 on a 496. Flip the pulleys around for 10% overdrive and make ~8.6 lbs boost. I wouldnt overdrive the 6-71 much more than that on pump gas. If you want more boost, than that, you should go to an 8-71 on that 496.

mike
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1973 RS Z28: 401ci Dart Little M, Littlefield 8-71 supercharger @14lbs boost, Callies Magnum crankshaft, Lunati Pro-Mod rods, JE pistons, 7.8:1 compression, AFR 227 Comp heads, T&D 1.6 shaft rockers. Reed solid FT cam (240/250@.050, .523/.542 lift, 112 LSA), QFT 750 carbs, Tremec TKO-500, Lemons headers, Moser 12 bolt, 33 spline axles & 3.42 gears
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  #12  
Old Mar 23rd, 10, 1:08 AM
69 camaro 69 camaro is offline
salman
 
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Default Re: 6-71 blower tuning

Did i should lock the distributor even if the camshaft is not solid?


Salman
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  #13  
Old Mar 23rd, 10, 5:31 AM
Tokyo Torquer Tokyo Torquer is offline
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Mike
 
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Default Re: 6-71 blower tuning

Quote:
Originally Posted by 69 camaro View Post
Did i should lock the distributor even if the camshaft is not solid?


Salman
Doesnt matter if it is a solid cam. People have different opinions about locking out the timing on a street car. You will get recommendations for doing it and for not doing it. I like a little bit of a timing curve for the street, especially since I have manual overdrive and sometimes lug the engine a little. Nevertheless, a blower engine prefers to have less of a timing curve than an NA motor, and as George points out, they really like a lot of initial timing.

mike
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1973 RS Z28: 401ci Dart Little M, Littlefield 8-71 supercharger @14lbs boost, Callies Magnum crankshaft, Lunati Pro-Mod rods, JE pistons, 7.8:1 compression, AFR 227 Comp heads, T&D 1.6 shaft rockers. Reed solid FT cam (240/250@.050, .523/.542 lift, 112 LSA), QFT 750 carbs, Tremec TKO-500, Lemons headers, Moser 12 bolt, 33 spline axles & 3.42 gears
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  #14  
Old Mar 23rd, 10, 6:38 AM
BlownYenko BlownYenko is offline
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Default Re: 6-71 blower tuning

Quote:
Originally Posted by 69 camaro View Post
well actually I am using 93 octane.
Is it safe to assume that you're not living in USA? I can hear a French accent as I read what you're writing...

Just so you are aware, octane ratings are expressed differently in different countries. For example, throughout the Oceanic countries, 98 octane is roughly equivalent to 93 octane in USA.

How that relates in Europe is something worth checking. It'd be a shame to run mid to high 30s advance only to find you don't have the quality of fuel to support it
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  #15  
Old Mar 23rd, 10, 8:29 AM
69 camaro 69 camaro is offline
salman
 
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Post Re: 6-71 blower tuning

I am living in KSA and we have fuel 91 & 95 octane which 95 Octane is equal to 93 fuel in US,
And you know I test the car by C12 fuel race it show that only faster respond of the throttle but stall the performance of the engine not that much improving.
Mike I'll flip the pulleys to be overdrive for more PSI and I’ll give you the status.

Salman
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