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Calculating boost from pulleys

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Old 01-27-2019, 11:42 AM
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Calculating boost from pulleys
Got a vortech t trim i picked up. Goin on a standard sbc. Its a 72 tooth crank pulkey and 29 tooth on the charger. Anyone know the aproximate boost range that should be? I know theres othe factors. Just tryin to get an idea
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Old 01-27-2019, 01:17 PM
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Re: Calculating boost from pulleys
What diameter pulleys
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Old 01-27-2019, 01:32 PM
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Re: Calculating boost from pulleys
Originally Posted by Orr89RocZ
What diameter pulleys
Ill measure asap
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Old 01-27-2019, 02:10 PM
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Re: Calculating boost from pulleys
Lower pulley looks to be 7.00 tooth to tooth. 7.53 overall lip to lip. charger pulley measures 2.86 tooth to tooth and 3.32 total lip to lip
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Old 01-27-2019, 04:23 PM
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Re: Calculating boost from pulleys
If i did this right, that pulley ratio means 7/2.86 is 2.447. Blower pulley is moving 13461 rpm at 5500 engine speed. Vortec t trim v1 is said to have a 3.45:1 ratio gear. So thats over 46000 rpm blower speed which according to map, thats 2-2.1 pressure ratio. Thats roughly 14-15 psi
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Old 01-27-2019, 04:42 PM
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Re: Calculating boost from pulleys
Originally Posted by Orr89RocZ
If i did this right, that pulley ratio means 7/2.86 is 2.447. Blower pulley is moving 13461 rpm at 5500 engine speed. Vortec t trim v1 is said to have a 3.45:1 ratio gear. So thats over 46000 rpm blower speed which according to map, thats 2-2.1 pressure ratio. Thats roughly 14-15 psi
So intercooled at around 9.5:1 should be do able. Also the higher flowing top end probly gonna drop the boost some??
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Old 01-27-2019, 05:25 PM
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Re: Calculating boost from pulleys
Yeah you will be ok
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Old 01-27-2019, 06:13 PM
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Re: Calculating boost from pulleys
Originally Posted by Orr89RocZ
Yeah you will be ok

Any cam recomendation? Preferably to be used with my current 1.6 roller rockers. I think I’m gonna go with some afr 195 comps. Using a zz409 cam now, I’m sure there is a better stick now though.

thanks for all the help
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Old 01-27-2019, 07:06 PM
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Re: Calculating boost from pulleys
Eh thats not a bad cam to be honest. Usually with a blower i would spread the exhaust duration out some. I’ll have to see what shelf grinds are out. I know comp has that 224/236 cam for nitrous/blower
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Old 01-27-2019, 07:12 PM
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Re: Calculating boost from pulleys
Originally Posted by Orr89RocZ
Eh thats not a bad cam to be honest. Usually with a blower i would spread the exhaust duration out some. I’ll have to see what shelf grinds are out. I know comp has that 224/236 cam for nitrous/blower
im not skeered of gettin a custom grind. Im just pretty cam stupid. I am runnin short travel retro hydro rollers too if that matters. Im tryin to collect as many parts as I can before I tear it down
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Old 01-27-2019, 08:58 PM
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Re: Calculating boost from pulleys
Yeah for a peak hp around 6000, a 224/230 on a 113 would work well. The 224/236 could also work which is comps blower cam
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Old 01-27-2019, 09:18 PM
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Re: Calculating boost from pulleys
Originally Posted by Orr89RocZ
Yeah for a peak hp around 6000, a 224/230 on a 113 would work well. The 224/236 could also work which is comps blower cam
I think 224/236 to peak out closer to 6500. Hogged our super ram with a welded/ ported base to step up to the 1206 port size. It’s seen 7k on the current setup. Obviously power doesn’t go that high but pulls to 6500 nice
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Old 01-27-2019, 09:41 PM
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Re: Calculating boost from pulleys
Yeah more rpm may be more boost too lol depends on a few things but good intercooling and running rich is key. Sneak up on the rpm to see where boost goes. Thats what makes blowers nice, boost curve is predictable and repeafable
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Old 03-13-2019, 10:37 AM
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Re: Calculating boost from pulleys
I believe with cog pullies, you divide the crank pulley tooth count by the blower pulley tooth count.
72/29=2.48 (pulley ratio)
X blower ratio
X engine RPM
= impeller speed

So 2.48 (pulley ratio) x 3.45 (blower ratio) x engine RPM (5500) = 47,058 impeller RPM
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Old 03-16-2019, 08:14 PM
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Re: Calculating boost from pulleys
For some reason beyond me, the unit of measurement for cogs is metric. And to calculate impeller rpm, the same formula is used as with ribbed pulleys, except pulley diameter is not used. Instead, the number of teeth is used. The formula:

(Crank tooth #) x (engine rpm) x (blower step-up ratio) / (Blower tooth #) = Impeller rpm
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Old 03-18-2019, 04:48 PM
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Re: Calculating boost from pulleys
Originally Posted by 2slow5.0
I think 224/236 to peak out closer to 6500. Hogged our super ram with a welded/ ported base to step up to the 1206 port size. It’s seen 7k on the current setup. Obviously power doesn’t go that high but pulls to 6500 nice
HSR/stock bore& stroke/6PSI/195 blue print heads with a really conservative timing table its peaked at about 5900. I'm sure different bore/stroke and head combo will alter that. fyi
Last edited by 86CamaroDan; 03-18-2019 at 04:51 PM.
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