help reading compressor maps?

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Apr 26, 2009 | 07:14 PM

Nimitz87

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From: Cooper City, FL

help reading compressor maps?

looking around here, forcedinductions.com and turbomustangs.com to try and learn me some stuff about turbos

looking to run a 370 LQ9 truck block, 317 heads, 233/233 .585 116 +4 gives me an overlap of 1

9:1 SCR

6.60:1 DCR

turbo would be a T6 GT-47 88 .96 A/R 3" charge pipe, 4" downpipe, 10lb's or so for the street and trying to figure out what rpm I would be at that boost level

here is the air consumption for a 370 ls1

http://www.forcedinductions.com/consumption370.htm

and the T88 compressor map...

http://forcedinductions.com/_derived...tm_txt_t88.gif

PR = 1.68

using

(CID × RPM) ÷3456 = CFM

370x4200 / 3456 = 450 CFM

then multiply for VE
× 0.85 = 445.7 CFM

= 382 CFM turn that into by X 0.69 = 26lb/min

think I'm definitely doing something wrong...that says I'll only be making 4lb's of boost @ 4200rpm?

someone please help the math challenged?

edit: 3.30 rear gear.

Chad

Last edited by Nimitz87; Apr 26, 2009 at 07:38 PM.

Apr 26, 2009 | 08:14 PM

topend

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take your 26lb/min and multiply by 1.68 PR = 43lb/min

looking at the map its close to surging but that depends on the turbine u use.only realworld testing will tell u.

Apr 26, 2009 | 08:35 PM

Nimitz87

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Quote:

Originally Posted by topend

take your 26lb/min and multiply by 1.68 PR = 43lb/min

looking at the map its close to surging but that depends on the turbine u use.only realworld testing will tell u.

thanks, I knew I was missing something.

so how/why would it be surging at 10psi, how would I "fix" that?

Chad

Apr 26, 2009 | 09:31 PM

topend

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Quote:

Originally Posted by Nimitz87

thanks, I knew I was missing something.

so how/why would it be surging at 10psi, how would I "fix" that?

Chad

if u were to hit 10 psi at 4200 rpm or sooner u would be close to surging .But thats a big if... most likely u would hit the 10 psi alittle later than 4200 rpm.

Apr 26, 2009 | 11:19 PM

Nimitz87

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From: Cooper City, FL

Quote:

Originally Posted by topend

if u were to hit 10 psi at 4200 rpm or sooner u would be close to surging .But thats a big if... most likely u would hit the 10 psi alittle later than 4200 rpm.

I don't understand why its so close to surging on the map at pretty much any boost level, here at 15psi

370x5500/ 3456 = 590CFM

x.85 = 501

x .069 = 34 x2.02 = 70lb/min

so looking at the map at a 2.02 PR and 70lb min I'll be at 15lb of boost at 5700rpm but right at the "surge limit" according to the T88 map

unless I'm all screwed up...I thought the 370 and 88mm turbo's were good/common setups?

Chad

Apr 27, 2009 | 09:04 AM

ModularTurbo

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From: Homestead, FL

1st find cfm unboosted (CFMU):

(C.I.D/1726) X (maxRPM/2)= CFMU

2nd find Pressure Ratio (Pr):

(14.7+Desired boost) / 14.7=Pr

3rd find CFM boosted (CFMB):

CFMU X Pr= CFMB

4th convert CFMB to LB/min:

CFMB X .07= (required LB/min)

5th look at the comp map and use your required LB/min and Pr to place yourself on the map, trying to be in the lower right hand corner of the efficiency islands.

I hope this helps,
Rob@modularturbo