Hey all... I've been doing some creative brainstorming lately... and I think I've come up with a plan to run a 2.8" or smaller pulley with 42lb injectors and stay under 100% duty cycle on the injectors.

What I need to know is this... at what RPM are y'all hitting ~15PSI in 2nd-5th gears? I'm hoping it's gonna be roughly the same throughout each gear... but there's only one way to know for sure.

Thanks in advance!

 

about 5800

 

Thats weird....

I hit 15psi at right around 4200, and full boost by 5500. Every gear.

 

Do you have different size pulleys?

 

what are you thinking? a boost controller?

 

2.8"

 

Well then! haha???? Weird can your tune affect that?

 

Well the stock gauge is a little off, and exhaust modifications lower boost.

 

ahhh, true.

 

Stage 2 tune, cat back exhaust.

Willing to bet my elavation(Beach = 2 minutes from my house) plays a huge role.

 

what were you thinking. im sure i can let you know if it will work or not

 

Not entirely... but the concept should work the same.

HP Tuners has the ability to limit boost in all 5 gears based on a table... X% of max boost at Y RPM.

If I were to adjust the limits based on a curve as RPM increased I should be able to hold 15-16PSI throughout the RPM range in every gear. The only thing a smaller pulley would do then is allow the 15-16PSI to be reached at a lower RPM. Once the desired amount of boost is reached it would bleed any excess and I wouldn't have to worry about outrunning the injectors ability to provide fuel. Basicly I would be making the same amount of power at redline, but the power curve would be much flatter and should lead to better performance without having to utilize more boost than a conservative 15-16PSI.

This is all in theory ofcourse... and would take considerable tweaking... probably a nice dyno tuning session with A/F and all the appropriate readings. But it should work.

 

Your basically using the overspin effect that the vette guys use on their prochargers. (which i plan on doing as well).

 

https://www.cobaltss.net/forums/showthread.php?t=61804

I already thought about it also and I think it will work well !

 

The thread says it is possible... I don't think anyone has actually done it before.

 

It is a good idea. Just bear in mind that you are still spinning the blower more than you have to to obtain your 15-16psi at high rpms, thereby unnecessarily adding heat to your charge. Consider meth. injection and/or a 2nd heat exchanger and/or dual-pass aftercooler conversion -- then you can safely tune in some extra timing up top.

While you're at it, limit boost in 1st gear to even lower than 15 (maybe 11-12ish) for traction purposes.

Then get yourself a 4-2-1 ex. header w/ 3" DP/high-flow cat and full 3" cat-back exhaust to make it as free-flowing as possible. Your "over-spinning" concept will prevent free-flowing exhausts from robbing low-end power (lower back-pressure, intake charge PSI drop) by a simple tune.

 

PM denny he is running that setup )

 

or instead of worrying about overworking your injectors simply buy 60#'s and call it a day. seems like you willl get more performance if you get 60#'s. more fuel and air equals more performance. why half ass it when you can hit 15psi in the lower rpms and 20psi in the higher rpms.

 

Simply b/c I don't want to run anything higher than 16PSI or so. This car is about speed and reliability... and good gas mileage. I've seen what the 60's do to the mileage. I also want the ability to easily return the car to GM stock if anything breaks.

As far as the extra heat generated by "overspinning" the blower... that is true... a Cobra HE is already in the works... I should have that taken care of in the next few weeks.

And yes... I do plan on limiting boost in 1st gear to 8-10PSI... for traction's sake.

 

For the most part, every time someone runs say a 2.6 with 60s, number 4 goes.

 

Precisely... I've seen a lot of threads about stuff blowing up... and apparently anything under a 2.8 is detrimental to your ride's health unless you plan on spending some major money.

 

that is simply tuning it right and getting better cooling mods such as meth/water injection. its all personal preference. as long as you keep your tune a tad rich through the upper rpms you should be fine. with it running rich you will be running cooler so there for lower temperatures. look at the turbo kit i think tag produced. 330whp i believe it is and no number 4 has blown on them. tuning is the key.

 

No, HEAT is the key. Blown-4Banger had his ride tuned to the max and he popped #4.

Tune plays a major roll, but IMO heat is what kills.

 

exactly thats why i was saying get meth injection. anybody who puts a smaller pulley should already be thinking about getting a cobra heat exchanger. with a cobra heat exchanger, dual pass kit, ported blower which i hear results in lower temps also and water/meth injection the heat should be taken down quite a bit. i was thinking today, maybe we could hook a tranny cooler up in our car and instead of using it for the tranny fluid which we dont have, use it as an extra heat exchanger because most tranny coolers have fans on them which could help reduce the heat even more. just a thought but could work.

 

he just exceeded the pistons capability to hold the cylinder pressures.

now, you can run full boost with the 2.8 on 42's IF, you know what you're doing. most people don't, hence why it is not advisable.

in hptuners, you can limit the boost to what ever you want too. if you have a header back exhaust, this will change what peak boost is. mine is 17.5

if 17.5 is 100% it's just simple math from there

90% = 15.75
80% = 14.00

just a rough estimate. could be wrong, which wouldn't suprise me, i suck at math.