Another blown engine
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Joined: Nov 1999
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From: Bryan, Texas
Senior Member
Joined: Jun 2001
Posts: 999
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From: Houston, tx
a 2.8" upper is a 2lb upper for an L which would be a 4lb upper for an HD since we are over 3" Their stock is 2.93.
So... If you put a 2.8 upper on, you should stick with a 4lb lower for a total of 8 over stock... (same as an 8lb lower)
Ken
So... If you put a 2.8 upper on, you should stick with a 4lb lower for a total of 8 over stock... (same as an 8lb lower)
Ken
Blower pullys
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Joined: Jun 2001
Posts: 999
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From: Houston, tx
I would just put an 8lb lower if that is where you are headed in terms of boost. A smaller pulley lends itself to slippage as you have less surface area. I personally won't go to an 8, though. I am sticking with my 6 in hopes of not introducing my rods to the outside world. I don't think an 8 will throw one, but I personally believe (opinion here) that 8 is the absolute upper edge of safety. One false move and kaboom...
again MY opinion. Several are running 8# lowers with no issues whatsoever.
Ken
again MY opinion. Several are running 8# lowers with no issues whatsoever.
Ken
Ken 800
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Joined: Aug 2002
Posts: 56
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From: Midland, Texas
ken800,
thanks for the info. regarding the 2.8" pulley. i was told that the 2.8" would give 2.5-3.0 lbs. of boost. i have only ran the truck hard on 106 octane and in ultra-performance mode so i have not noticed any detonation or adverse problems with my setup. i ordered a boost gauge and a gauge to monitor exhaust temps, so i should be able to get the definite answer.
chgames,
the 2.8" upper has never caused any belt slipage on my truck. i also used the stock belt by removing the stop tab on the idler arm. this setup may add some tension to the belt since the idler arm is rotated higher in its stroke thus increasing sping tension. at least that's one explanation for why my belt does not slip, the other maybe luck. anyway, i have heard alot about the difficulty of installing the upper pulley and that scares some guys away from doing the task. i personally found it to be not a difficult job, but you will need a good puller and some anti-sieze and a friend to help. i think that ken800 is correct though, the easier way to 8# is on the bottom. i just did not know if 8 was going to be my limit.
thanks for the info. regarding the 2.8" pulley. i was told that the 2.8" would give 2.5-3.0 lbs. of boost. i have only ran the truck hard on 106 octane and in ultra-performance mode so i have not noticed any detonation or adverse problems with my setup. i ordered a boost gauge and a gauge to monitor exhaust temps, so i should be able to get the definite answer.
chgames,
the 2.8" upper has never caused any belt slipage on my truck. i also used the stock belt by removing the stop tab on the idler arm. this setup may add some tension to the belt since the idler arm is rotated higher in its stroke thus increasing sping tension. at least that's one explanation for why my belt does not slip, the other maybe luck. anyway, i have heard alot about the difficulty of installing the upper pulley and that scares some guys away from doing the task. i personally found it to be not a difficult job, but you will need a good puller and some anti-sieze and a friend to help. i think that ken800 is correct though, the easier way to 8# is on the bottom. i just did not know if 8 was going to be my limit.
I was also scared to see the thread thinking it was Outnumbered's HD.
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Joined: Jun 2001
Posts: 999
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From: Houston, tx
Hey guys...
I guess should have clarified actual vs. stated. The 2.8 lb pulley is "stated" as a 2lb upper pulley for the L. That would of course be a 4lb to us HD guys. The boost guage will of course not show 4lbs of increase. The important part to remember here is that you are spinning the blower faster than stock and generating a lot more heat.
Early on with the pulley changes, your net with a good guage will show what you bought -- i.e. a 6lb lower will show close to 12 on the guage. As you increase from there, it will not show what it says the pulley will do.
In the case of the blown engine, he had a 4lb upper, an 8lb lower and 6lbs of stock boost by the pulley numbers. That's 18lbs. I suspect he probably showed 15-16lbs on the guage, but that is not what is *installed*. The ratios of the pulley combinations are the ultimate deciding factor in how much the blower is wound up. the below sheet can help with the calculations, but remember, THIS IS A GUIDE.
http://www.svtlightnings.com/svt/how-to/blowerrpm.htm
FYI, for the 18lb guy, here is a the increase in blower rpm at 5200 (close to stock shift point)
12200 stock (Harley) 18600 with 2.8 upper and 8lb (10") lower.
That is spinning that blower through the roof. If your chip shifts higher (i think blown engine guy said his was 5600), you are at 20K rpms. The blower starts to rapidly lose efficiency right about 13K rpms (increasing heat at an increasing rate). Eventually the intercooler throws in the towel.
With a 6lb lower and a stock HD upper, I am in the 14.6K ish blower rpm range shifting at stock points. This puts me 1500 or so rpms over the stock L setup which shoud be fairly safe...
Anyway. Enough nonsense from me.
Good luck on your mods.
I guess should have clarified actual vs. stated. The 2.8 lb pulley is "stated" as a 2lb upper pulley for the L. That would of course be a 4lb to us HD guys. The boost guage will of course not show 4lbs of increase. The important part to remember here is that you are spinning the blower faster than stock and generating a lot more heat.
Early on with the pulley changes, your net with a good guage will show what you bought -- i.e. a 6lb lower will show close to 12 on the guage. As you increase from there, it will not show what it says the pulley will do.
In the case of the blown engine, he had a 4lb upper, an 8lb lower and 6lbs of stock boost by the pulley numbers. That's 18lbs. I suspect he probably showed 15-16lbs on the guage, but that is not what is *installed*. The ratios of the pulley combinations are the ultimate deciding factor in how much the blower is wound up. the below sheet can help with the calculations, but remember, THIS IS A GUIDE.
http://www.svtlightnings.com/svt/how-to/blowerrpm.htm
FYI, for the 18lb guy, here is a the increase in blower rpm at 5200 (close to stock shift point)
12200 stock (Harley) 18600 with 2.8 upper and 8lb (10") lower.
That is spinning that blower through the roof. If your chip shifts higher (i think blown engine guy said his was 5600), you are at 20K rpms. The blower starts to rapidly lose efficiency right about 13K rpms (increasing heat at an increasing rate). Eventually the intercooler throws in the towel.
With a 6lb lower and a stock HD upper, I am in the 14.6K ish blower rpm range shifting at stock points. This puts me 1500 or so rpms over the stock L setup which shoud be fairly safe...
Anyway. Enough nonsense from me.
Good luck on your mods.
Last edited by ken800; Oct 27, 2002 at 11:26 PM.
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Joined: Feb 2001
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From: Oak Ridge, TN, USA
I think for an everyday driver, that would be plenty. Any more and I would question the reliability of the motor at say 100k miles on it. Any more pressure than that on the blower, my personal opinion is the rods and pistons should be upgraded as well. It like all this nitrous. That pressure has to go somewhere. If the motor isn't built to withstand it, it will let go. The question is when.
