Digital dash boost gauge...

MA70-3.0GT · 12-03-2009, 05:02 PM

Anyone one here got the digital dash on their car? If so, where does your boost gauge go up to? Just had a thought, I noticed when I drove my car home that when you floor it & the turbo spooled up (I just HAD to do it once!!!) the gauge flew straight up to 3.5+ & I don't know how the hell mm/hg equate to PSI, there's no reference in the TSRM, only to kg/cm, kpa & psi...

EDIT-: I'm getting something mixed up here, I was sure the gauge said mm/hg but 3.5 mm/hg is 0.06psi, 3.5 in/hg is 1.72psi and if I misread it & it meant 35 then we're talking either 0.68psi for mm/hg or 17.7psi for in/hg...

Think I need to do a little checking of my dash 'cause there was definitely more than 1psi & no fuel cut to suggest 17psi, although the latter figure would certainly explain the BHG!!!

Anyway, I'll check that site again once I've found the proper unit of measurement & find out for sure. For anyone else, here's a link to what I think is quite a useful site for conversions...

http://www.engineeringtoolbox.com/pr...ter-d_569.html

The only thing that comes close to a 3.5 units when converted from 4.8psi (the low boost figure for an AT car) is metres of water "m/H2o" & I can't see why Toyota would use such an obscure unit of measurement in their cars so there's definitely something amiss!

cre · 12-03-2009, 11:51 PM

I can't remember what unit was used on those dashes (they're a JDM only item, so they're not commonly talked about). The unit of measurement was an odd one from what I recall though.

On a stock CT-26 I sure hope you're not pushing 17psi... it's efficient limit is between 13 and 14psi... at that point the air begins heating way too much for the IC to help much with and you're looking a power loss due to detonation.

The stock boost sensors in most cars aren't terribly reliable anyway and as old as the sensor in that car is, I wouldn't trust it either. Stick in a mechanical boost gauge (if you can, just borrow one and run the vacuum line out of the hood and in through the driver's side window... now go check how much boost you are REALLY making and compare.

MA70-3.0GT · 12-04-2009, 04:27 PM

Right I've sorted it. The units are mm/hg x100 so 3.5+ would be 6.7psi+. I've got the turbo off now & tested the wastegate & actuator which are fine.

Can't do too much comparing at the mo as the engine's in bits (the boost going to the top of the stock gauge on the way home was just something I remembered the other night) but I'm adding a "proper" boost gauge to the shopping list once the HG's all sorted... I've updated my other thread on the stripdown & will hopefully be adding some pics tomorrow sometime.

cre · 12-04-2009, 07:32 PM

So it's cm/Hg then?

An accurate boost gauge is a great for tuning and fine diagnosis or problems, but as you've already got a meter I'd hold off on an aftermarket gauge if there are other things where the money would be better spent.

12-03-2009, 05:02 PM	#1
MA70-3.0GT 12psi boost Join Date: Oct 2009 Location: Crewe, England Posts: 356	Digital dash boost gauge... Anyone one here got the digital dash on their car? If so, where does your boost gauge go up to? Just had a thought, I noticed when I drove my car home that when you floor it & the turbo spooled up (I just HAD to do it once!!!) the gauge flew straight up to 3.5+ & I don't know how the hell mm/hg equate to PSI, there's no reference in the TSRM, only to kg/cm, kpa & psi... EDIT-: I'm getting something mixed up here, I was sure the gauge said mm/hg but 3.5 mm/hg is 0.06psi, 3.5 in/hg is 1.72psi and if I misread it & it meant 35 then we're talking either 0.68psi for mm/hg or 17.7psi for in/hg... Think I need to do a little checking of my dash 'cause there was definitely more than 1psi & no fuel cut to suggest 17psi, although the latter figure would certainly explain the BHG!!! Anyway, I'll check that site again once I've found the proper unit of measurement & find out for sure. For anyone else, here's a link to what I think is quite a useful site for conversions... http://www.engineeringtoolbox.com/pr...ter-d_569.html The only thing that comes close to a 3.5 units when converted from 4.8psi (the low boost figure for an AT car) is metres of water "m/H2o" & I can't see why Toyota would use such an obscure unit of measurement in their cars so there's definitely something amiss! __________________ '89 MA70 Supra GT aero 3.0turbo JDM, Rebuilt motor, K&N intake, 3" stainless turbo-back. New turbo and braided line kit... '89 Honda NC27 400, NC23 cams, open pipe, PC36a shock & possibly Showa USD forks... '83 Yamaha 29R XJ750E-II, number 69 off the line, only runner in the country? Original except Koni shocks '95 Honda PC26 CB500R, Winter hack, hateful, trying to sell it I'm not paranoid, they really ARE after me!!! Last edited by MA70-3.0GT; 12-03-2009 at 05:22 PM.

12-04-2009, 04:27 PM	#3
MA70-3.0GT 12psi boost Join Date: Oct 2009 Location: Crewe, England Posts: 356	Right I've sorted it. The units are mm/hg x100 so 3.5+ would be 6.7psi+. I've got the turbo off now & tested the wastegate & actuator which are fine. Can't do too much comparing at the mo as the engine's in bits (the boost going to the top of the stock gauge on the way home was just something I remembered the other night) but I'm adding a "proper" boost gauge to the shopping list once the HG's all sorted... I've updated my other thread on the stripdown & will hopefully be adding some pics tomorrow sometime. __________________ '89 MA70 Supra GT aero 3.0turbo JDM, Rebuilt motor, K&N intake, 3" stainless turbo-back. New turbo and braided line kit... '89 Honda NC27 400, NC23 cams, open pipe, PC36a shock & possibly Showa USD forks... '83 Yamaha 29R XJ750E-II, number 69 off the line, only runner in the country? Original except Koni shocks '95 Honda PC26 CB500R, Winter hack, hateful, trying to sell it I'm not paranoid, they really ARE after me!!! Last edited by MA70-3.0GT; 12-04-2009 at 05:51 PM.

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12-03-2009, 11:51 PM	#2
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	I can't remember what unit was used on those dashes (they're a JDM only item, so they're not commonly talked about). The unit of measurement was an odd one from what I recall though. On a stock CT-26 I sure hope you're not pushing 17psi... it's efficient limit is between 13 and 14psi... at that point the air begins heating way too much for the IC to help much with and you're looking a power loss due to detonation. The stock boost sensors in most cars aren't terribly reliable anyway and as old as the sensor in that car is, I wouldn't trust it either. Stick in a mechanical boost gauge (if you can, just borrow one and run the vacuum line out of the hood and in through the driver's side window... now go check how much boost you are REALLY making and compare.

12-04-2009, 07:32 PM	#4
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	So it's cm/Hg then? An accurate boost gauge is a great for tuning and fine diagnosis or problems, but as you've already got a meter I'd hold off on an aftermarket gauge if there are other things where the money would be better spent.