Help-need to reduce power-bigger pulley or less timing?
05-07-2007, 10:57 PM
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Help-need to reduce power-bigger pulley or less timing? Well guys my last trip to the dyno resulted in 885 rwhp at 5800-the boost guage was pegged at 20psi. Do I need that much horsepower-if I had a F-body i would say yes-but since this is a C5, I don't think so. Remember I'm shutting it down early because AFR climbs up to 11.5-so when everything is sorted out-the car will be revved out to 6800. I'm currently running a 4.13 pulley and can swap over to a 4.25-problem is they don't make a belt size that will take the 4.25 properly-maybe a 4.38 but then i'll start killing off lowend torque which will help me get out of the hole without having to launch hard. Now instead of changing pullies-can I just pull out timing instead and maybe just keep fattening it up? I mean that will kill power-what do you guys think?
05-08-2007, 05:00 AM
#3
You don't want to fatten it up too much, you'll probably kill your spark plugs. I'd go with taking timing out in the upper rpm ranges.
Me, I'd shoot for 1000 rwhp... lol Bob
Me, I'd shoot for 1000 rwhp... lol Bob
05-08-2007, 07:31 AM
#5
That's not a very small pulley, doesn't that one normally only make about 9psi? If your getting up to 20psi I would think your best bet to cut down the power would be to go one size up on the pulley. I don't think messing with the tuning would be a very good way to take out power, you might start killing plugs and sensors. Plus wouldn't you eat up a lot more gas, at these prices that might be something to consider. It's too bad you don't want that much, those are some good numbers. I understand though, I'll have to do the same thing if mine makes too much.
05-08-2007, 09:13 AM
#7
Easiest and cheapest would be just restrict the intake some, best and most expensive thing to do would be to go down on blower size. It sucks to be limited by belt and pulley restrictions, thats where I am at as well..
Taking timing out will work to a point (taking too much out and EGTs will start going up), making it too rich at WOT will kill the o2 sensors. But either way you are still turning a large blower and making more heat with it so its really not the 'best' way to go. Slow it down too much and then it will drop off the map. I would fool with some restrictors first if it were me.
Taking timing out will work to a point (taking too much out and EGTs will start going up), making it too rich at WOT will kill the o2 sensors. But either way you are still turning a large blower and making more heat with it so its really not the 'best' way to go. Slow it down too much and then it will drop off the map. I would fool with some restrictors first if it were me.
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05-08-2007, 10:54 AM
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i wouldnt worry about killing low end torque... you have an automatic that will stall instantly and get you in the power band.... if your scared about the 900+hp not hooking then i'd sugest a 4.38 or bigger... because by the time you pick up that extra 8k rpms its gonna spin that thing even faster...
that is a sick problem to have... hell i say keep the pully on it and adjust your hp by where you shift it at... if you wanna go fast shift at 6700... if you wanna go slow shift at 5500... lol... i envy your problem.
that is a sick problem to have... hell i say keep the pully on it and adjust your hp by where you shift it at... if you wanna go fast shift at 6700... if you wanna go slow shift at 5500... lol... i envy your problem.
05-08-2007, 11:03 AM
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I would just keep running it but how long re these heads gonna stay planted? I'm not seeing any knock, nor is it pushing any coolant but just how much boost can a 347/stock heads take take? I could just put a restricter infront of the blower-maybe a 3.5 inlet-to see what happens.
05-08-2007, 12:19 PM
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I'd do the restrictor first Arun.
You'll maintain better area under the curve than changing the pulley. That combined with a bit of tuning should do the trick and allow you to go to 6500rpm
When are you hitting the track man?
You'll maintain better area under the curve than changing the pulley. That combined with a bit of tuning should do the trick and allow you to go to 6500rpm
When are you hitting the track man?
05-09-2007, 09:23 AM
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Originally Posted by kp
Easiest and cheapest would be just restrict the intake some, best and most expensive thing to do would be to go down on blower size. It sucks to be limited by belt and pulley restrictions, thats where I am at as well..
Taking timing out will work to a point (taking too much out and EGTs will start going up), making it too rich at WOT will kill the o2 sensors. But either way you are still turning a large blower and making more heat with it so its really not the 'best' way to go. Slow it down too much and then it will drop off the map. I would fool with some restrictors first if it were me.
Taking timing out will work to a point (taking too much out and EGTs will start going up), making it too rich at WOT will kill the o2 sensors. But either way you are still turning a large blower and making more heat with it so its really not the 'best' way to go. Slow it down too much and then it will drop off the map. I would fool with some restrictors first if it were me.
Kp-my IAT temp on a 75 degree day is 55 degrees at the top of the pull-the meth works reall good!!!!If I go to a 4.25 pulley I will need a 89.9 belt, I'm currently using a 89.7 belt with the 4.13 pulley. Gates next closest size is 90.3, Dayco makes a 90.0 in there Gold Label Polycog belts-my buddy who races in NMRA rengade swears by the belts. I think the easiest thing to do will be to just put a restricter plate on the inlet of the blower-i'm going to try a 3.75", and a 3.5". I hate to make too many changes when everything is working so well-so I figure the restricter is the easiest to change on the dyno, track etc.... I mean-it's not, knocking, not pushing any water, not lifting the heads. My fuel octane with the Torco is 105 and then with meth it's up around 116, IAT temps are low so if I can keep knock away the heads should stay put.
I just ordered up a FJO driver box and some Delphi 96lb injectors-I'll get them on this weekend and hopefully Lonnie will have my pumps done.
05-09-2007, 04:10 PM
#17
anyone ever heard of half throttle, lol jus kidding yea that seems like a logical problem to have since its probably a light car already and pretty hard to race full throttle. Well if its an auto maybe its not that hard after all. I say try the plate which is an inexpensive alternative like mentioned above...and if anything just go less boost obviously with a smaller pulley. Lingnefelter is actually selling an ASA track car restrictor plate right now which they used in their race cars to limit power on these kind of motors specifically. Its cheap its anodized blue like your car and its for sale on ebay. Look for Lingenfelter Performance and check their listing out. Or just type in ASA restrictor plate im sure it will come up somewhere...?? Hope you enjoy your problem alot of us would like to be in ur shoes lol 
05-09-2007, 04:11 PM
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Originally Posted by dixonk
How the hell did you make 20 psi with a 4.13 pulley? Man I wish I had your problems. Maybe I'll trade for my belt slip problems. LOL.
05-09-2007, 04:16 PM
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Maybe just go down on the timing some??I only have 15 degress in mine.It would at least make things a little safer for that high amount of boost.Sounds like a nice setup
05-09-2007, 04:29 PM
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It's a vette -- just program your pedal-to-throttle table to limit the max throttle opening. You can dial the power back as far as you wish, and still maintain the tune and blower setup exactly as is.
