thanks to rich at gotham racing



bye bye 12psi, hellooooo 17

 

Hmmmm, yummy. Let me know how the install goes.

 

17 PSI on what?

 

stock twins, all bolt ones, haltech, half bridge

 

i thought the efficiency on the stock twins dropped like a rock after 15...?

 

do you believe everything you hear?

how much boost was john running when he pulled a 10.98?

think for yourself, try new things

and efficiency has a lot to do with flow and a little to do with pressure, i doubt my motors flows with the same characteristics as a stock/street port

 

The key to running a lot of boost with the stockers is to have a IC with very low pressure drop.

BTW - going from 12psi to 17psi is going to be like.......well I dont know how to even put it into words. Lets just say this....the first time you step on it your going to have a grin from ear to ear lol


STEPHEN

 

yeah, pretty much. i believe everything i see on TV, too.


who is john? actually, never mind, i don't care.

why should i think when you can tell me everything?


basically, it was a simple question, just looking to see if there was something I was missing. Obviously, given your smartass response, i wasn't really missing anything.

as for the flow of your engine (since motors are not power by gas, and you want to be "technical" about things), i guess you forgot that the exhaust is "flowing" through your STOCK turbos.

from the LIAWOT site:

All turbochargers present compromises between flow capacity and turbo lag. The larger the turbo, the slower it is to spool, but the more air it can flow when up to speed. The FD's units were sized for maximum response while meeting the flow requirements of the engine at the targeted power level. Each compressor has an area of greatest efficiency (adiabatic), in which it can compress/flow a given volume of air per unit time without introducing excessive heat in the process. This is defined graphically by a compressor map, and is primarily a function of compressor design, size, and rotation speed. Increase flow to obtain more power on the FD by adding intake, exhaust, intercooler, etc.and you will rapidly find yourself outside the stock turbocharger's efficiency sweetspot, since the compressor must spin faster to maintain the same intake pressure. The main detriment in the 11-13 psi range is that the compressor outlet temps become extremely hot, on the order of 300F, which places additional thermal stress on the engine, and may increase detonation risk. Also, in sequential twin-turbo cars, the secondary unit is accelerated to a high speed in a closed circuit chamber (surge) to prevent a drop in compressor speed and flow at the switchover point when the compressor comes under load, which would cause a dip in power and torque (the famous dip we all notice in the dyno plots). This power dip, already slightly noticeable in stock cars, becomes much worse in modded cars, since the turbo is already operating at its pre-spin speed just to maintain a given level of boost, and becomes extremely resistant to overspeeding.


"Over 14 psi on sequential twin cars with fully open intake and exhaust, the stock turbos actually cause a restriction in the intake path which limit the effective power you can make. Can you upgrade to larger compressor wheels? Sure, but shaft failures often accompany this mod, because the stock shaft was not sized for that weight wheel. You can also clip the turbine wheels for better flow at high speed, but low speed response may be impacted. The switchover problem does not go away. "

There are three things that trade off against each other with a turbo. Lag, airflow (measured in CFM), and boost. You can improve any of these but the other two suffer. If you want to improve all three, then your turbo must work harder, which reduces its efficiency. This translates into increased temperature and more "effort" expended to produce a given amount of boost. Turbos have an efficiency range in which they work very well within certain boost and CFM parameters, but rapidly become very inefficient outside those parameters. Typically, a bigger turbo will have an efficiency range better suited to high boost, high flow.

 

if i can run and make power up to 15 with the stock ic then im sure with an upgraded ic 17 should be no problem.

 

oh yeah, please write a thread reviewing the aem after install

 

And what does the CDI have to do with running 17 psi !? And for gods sake I hope not on Pump Gas...

 

stock ignition starts to break up after 15psi, well at least mine does anyways

 

Good luck.. btw is that ignition setup just pnp?

 

Okay, but that's usually not untill 4-5K rpm... Given that it has to do with it, but from the post it looks like THE SOLE REASON for the 17psi, is the CDI... and that's not going to do it, I hope no one here tries to put in a CDI and crank it to 17... cause it won't work and I have serious doubts that 17 PSI is attainable even on 98 Oct. gas... it'd have to be 100+ since the heat at 14-15 is barely what pump gas can support... and id say every lb after that increases pre-detonation exponentially...

 

With the stock IC running 15psi at the manifold is about 19-20 at the turbos. That is basically RIGHT at the limit before they start SUPER heating the air.

If you make a 4th gear pull and your air temps raise more than a few degrees C then your out of the eff range.

You need to check those air temps in 4th gear and make sure they arent rising to much. Based on experience I'd say they are probably raising around 5C with a 4th gear pull, and that would be too much

BTW - This is why having a good IC with low pressure drop is so important with running high boost on the twins.

STEPHEN

 

I think that we can see 17 psi on 93 octane, i mean damn ive run subys to 20psi without detonation on pump.

my car has been running fine at 14.5psi on the stock ic with no det on sunoco 94. Im probably pushing my turbos the same as he would at 17 with an upgraded ic.

 

I am very aware of all this, and have checked the temps.. I HAVE run 15psi with no problems. and done days of it with high boost and high ambient temperatures. However i made the decision to not push them past 12 on stock ic anymore cause i cant afford a rebuild atm.

 

Well I guess ambient air is a lot colder in MD than here in cali and 93 can't hurt over 91 either... good luck... you'll need it...

 

so are you saying that c16 gas doesnt come from a pump. Does it just get poored into gas tanks and containers from big jugs? just kidding, i know what you mean. On another note, i ran 19 psi on 93 octane with absolutely no sign of detonation. I am going to be running 20+ psi on pump gas when my car gets tuned again by KDR. We are thinking 22 psi on 94 octane gas. Skips anti detonation device definately does the job of allowing to run high boost settings without the detonation. For anyone going to Rotary Revolution, you guys will be able to witness me running 20+ psi on pump with a T78.

Adam

 

Right !! T78 bigger turbine, lower intake temps... that makes sense... I thought we were talking about Stock Twins... .... Oh wait, we ARE !!!

 

I do have to say that i agree with DCrosby, about running 100+ octane if you plan on running 17psi. Unless you get the KDR/Skips anti det device.

 

ha, yeah - i figured someone should let all the guys in the "single turbo" section know that they've been wasting money upgrading to singles to run higher boost....

 

I hope your joking! There is a huge difference from running 17 psi on the stock twins to running 17 psi on a bigger turbo. Its all in how much air the turbo flows.

 

You gotta realize the whole "lower intake temps" is blown way out of proportion as the difference in compressor efficiency is like 10% max. 17 psi on a T-78 vs 17 psi on stock twins is like a 30-40F difference at the compressor outlet and even less of a difference after it goes through a good IC. Most of the gains come from eliminating exhaust restrictions.

Of course you have the benefits of much better reliability with a slower spinning single (1 turbo spinning at 100k rpm vs 2 at 160k rpm)

 

Definetly interested to see the results with the AEM also! I was running 16psi's consistently on a stock fuel system but with an upgraded ecu, and large smic. Felt awesome, now I have an untuned PFC and don't want to go past 12psi, I miss those extra 4psi.
Off topic.....fastcarfreak, was that your T-78 at kd getting tuned a couple weeks back? Looked and sounded nice while Dave was gettin into it!