Yep a buddy of mine with a black one. he doesn't post here. I'm not sure how much of a shot, but believe it was a small one. He's running the 91 tune from InMotion. So far 11.9's with spray in the best DA in AZ. LOL.

 

Ive got 104 octane so I should be alright.

 

The more boost the ECU sees the less the timing it will advance. The higher the Charge Air Temp the less timing it will advance. Both work conterproductivly with a larger pully from a factory tune perspective. Yes the car makes more boost and yes it will make more power (good rule of thumb would be 7-12hp per psi boost) but at the same time your going to lose power by running less timing. So in the case of a factory tune I could see where the power lost by the reduced timing is larger then the power gained by the increased manifold pressure.

The trick is to win in both worlds.

 

So it seems to me that the seemingly missing performance of the 185 pulleys is not necessarily due to increased heat, but more due to tuning and lack of fuel.

I remember reading here somewhere that with a pulley (any size), CAI, and intake manifolds, you're at or very near the limits of the fuel delivery of the stock fuel system. No more fuel = no more power.

 

Tuning fuel is more to be safe then to make power. The difference between 10.5 and 11.5 AFR's really is so marginal power wise. But being to rich and getting spark blow out on the other hand can destroy your power.

and saying your near the limits of the stock fuel isn't exactly true, yes you may me near the limits of the fuel the ECU or your tuner has provided. But I highly doubt your at the limits of your injectors Duty Cycle or your Pumps flow capacity. If you can run a 150+ wet shot, then thats proof alone the fuel pump can keep up to the bolt on parts you listed flow wise. As far as injectors I really havent seen much posted, nor have i hunted around to see if anyone has had the ability to monitor Injector pulse with or micro sec/bit.

 

At what point does the ECU begin to pull timing? Boost levels, IAT, ECT, etc..

It's one thing to talk about it - another thing to know....

Remember, the 185mm only overdrives the SC 4% more then a 178 at any engine RPM. (see post #6) So these claims don't really add up.

I do agree that increased IAT (and ECT) will cause the ECU to pull timing - but that can happen to a factory setup on a hot day. (or pump failure, clogged/leaking HE or IC....)

I found that separating the coolant systems, installing a larger HE and adding a larger flow tank for the IC coolant reduced my IAT with the 185 pulley below what I was logging when stock.

 

didn't notice the no more fuel= no more power part... Did you edit that in?


Anyway again this goes back to spark advance being your main source of power through tuning. Typically advancing your timing will not eat up much for. Case in hand...

On the SRT-4's Mopar "Factory" Stage 3R kit they offered a option called "toys" with that option came a little red buttom called "High Octane Mode" (HOM). The intent was you put 100 octane in the car, hit the button and BAM, 40+ hp instantly. All the button did was switch the ECU into a super agressive timing map that was built to support race gas. Typically the car would see about 5-7 degrees more timing through the power band. All that without changing your AFR's but maybe 1/2 a point.

 

Your 100% correct, almost all info out right now for this platform is speculation when it comes to specific details. It's standard tuning practice that as manifold pressure increases, timing decreases. Typically till you hit the engines VE at which point you can level it off. But how much is left to be unknown at this point. But considering this car only runs 15ish psi factory and we are talking timing levels that are 5+psi above factory levels I would figure it's "safe" to say at that high a level Mercedes slams the timing to the basement to protect there motor. I wish I had AEM installed on this computer so I could make a quick timing table and post it to give an idea... but anyway in words I would venture to say beyond the factory boost levels the timing slowly tailors off, maybe 1-2 degrees per psi, but at some point before there factory map ends I'm sure they plunge it (drop 2-4 degrees). And for all we know that point could be right there between a 181 and 185's boost levels. Who knows...

Temps kill timing. On factory cars a huge portion of that has to do with emissions. If I recall someone, probably woody posted 92 degrees or so was the Magic IAT that the car started yanking timing back.

Good news is IAT's are simple to control, as you posted along with ECT's Add to that simple Water/meth injection kits, or heck even a super, super, super small wet/dry shot.

 

Brian puts up some important info here as does the last poster (totomacher). Lots of variables affect the final performance:

1.) Boost Pressure - more usually means more power

2.) SC'er drive parasitic losses. The SC is matched to the speeds and flow requirements. As we overdrive it the SC performance is moved out of the sweetspot. This causes parasitic losses to drive the compressor to go up at a near exponential rate. A 185 pulley causes that loss to be up to nearly 60hp off of the crank hp the engine is making. What it means is that while the 185 makes more boost and thus more power, proportionately less is getting to the rear wheels. That don't mean it makes less rwhp only that the law of diminishing returns is starting to kick in. While the 185 may only increase the overdrive of the SC by 4% compared to the 178 pulley or the C3P unit, the increase in parasitic losse increases at a rate higher than 4%. I am not going to quote the actual SC loss as I do not have the charts in front of me but it is out there for those who want it. If I remember right, I think it is about 45-50hp for the 178/CP3 option?? guessing on this. Maybe someboday has it? Bottomline is more overdrive means more power but less of it is useable power to the wheels with a SC'ed engine using the same supercharger.

3.) IAT - will be different everyday and at every altitude but all things being equal, it will goe up with boost pressure. Unless measures are taken to improve the cooling of the intake air (intercooler, IC pump, cold air to filter, etc) then more heat robs some of the benefits from the higher pressure.

4.) Mean effective pressure - this is the combination of Intake pressue and compression ratio. The engine cares little where it comes from. Lower altitude=more pressure, as does higher compression pistons or more boost from SC'er or Turbocharger, etc. Each time you double the mean effective pressure, you double the torque output at the crank as long as you don't do something dumb like run out of fuel flow to compensate for the extra O2 and then go too lean causing preignition (knock) and then causeing the ECU to pull timing.

5.) DA (Density Altitude) and formal way to express atmospheric pressure and air temperature in pilot terms. Basics are more atmospheric pressure and lower air temps = more horsepower all things being equal. If your run the same car at Englishtown in NJ and then run it at Mile High in Denver with same temps at both, I guarantee that it will be slower in Denver.

6.) Fuel injector, pump and fuel rail flow limits. This is a big ??? with our cars. At some effective flow level, we will hit the wall on this without making changes. All the turbo car tuners know this. That is one of the reasons why the 185 pulley piggybacked to the Code3 pulley failed to put up more power.

7.) Octane limits of the combustion chamber design. Our cars run a 3 valve two plug system. That is a trade-off that give good low end torque, decent efficiency and fair resistance to knock at high compression ratios. It is usually not as good as a 4-valve cosworth style combustion chamber with a single plug in the center or a 5 valve Yamaha style design. No matter what type is used at some combo of fuel air ratio and mean effective pressure and at a given octane (say 93) you hit the wall. We cannot alter the design of the engine. We can only increase the FAR so much and without going to higher octane you are done.

8.) Octane limits of the fuel - Assuming that all fuels are equal is wrong. the USA 93 octane fuel is a chemical soup of so many hydrocarbons and additives that even on a given day from the same retailer and from the same refinery, it will vary all over the place. Winter vs Summer blends also vary. If the guy running the 181 pulley happens to have better gas and the guy with the 185 gets a tank full of crap and starts pulling timing, then the other fellow will post a better time. Not saying that the 185 won't be faster all things being equal, but the 185 pulley is closer to the ragged edge of the limits and so is more likely to be adversely affected by any of the variables such as fuel quality, IAT, DA, and boost pressure.

I personnally think that the 185 pulley is knocking (pun intended, lol) in the limits of the engine's fuel flow, ECU compensation range, octane limits at a given IAT and thus is giving some drivers erratic results sometimes. Your results may vary depending on where you live, the altitude, typical ambiaent temps and the quality of your local gas. I think that the guys who are in hot and/or higher altitude places will be able to run the higher boost with fewer issues than say guys in places where the DA is lower most of the time. Just my 2 cents...

Irish

PS. Look at our ole buddy jturkle from the C32 world. His 185 pulley is working for him. But being in the Phoenix area, the altitude is about 1100 ft above sea level and I hear that it does get fairly warm there sometimes which further increases the DA making it possible to overdrive the SC'er slightly more without over boosting the engine. Keep in mind that the engine does not know where it is or high high up. It only responds to the mean effective pressure and that will be less at higher alts and higher temps. Now take a guy at sea level in Miami, FL or worse, Long Island, NY, he could see issues sooner unless a custom ECU tune is applied to compensate for the conditions.

 

Great topic: I would love to know the RPM limit our Supercharges begin to experience diminishing returns so I could graph and plot my engine's performance to see where and if I hit a wall.

I do believe there are diminishing returns ( I understand this concept in an economic point of veiw) but diminishing returns does not mean loss of gain.

Rather then use a lot of words to explain, I made a chart that compares engine RPM with supercharger RPM for both the 178mm and 185mm pulley.

Let's say (cuz I don't really know and it's never been posted on the forum) that our SC'ers hit peak performance at 10,625 RPM's and beyond that will no longer provide the same additional gain in HP per additional increase in RPM then before.

The chart below says that, "Ceteris Paribus", or all things being equal: same driver, same track, same tires, same weather, etc... that at 10,625 SC'r RPM - - The 185 has an advantage over the 178 because it reaches "peak" SC performance about 170 engine RPM's before the 178mm pulley (not very much, but about about 4%).





The next piece of data to look at would be a dyno chart. Not to look at the peak numbers; we know that different dynos, on diifferent days, at different locations, etc....

But to look at the trend line for the HP to see if there's a dead spot where the engine no longer makes HP and find that RPM.

Here's one of my dyno pulls that was performed at the shop Code3 uses to test and report gains from their products.

Bottle_Blown_Blowup-1.jpg



It looks like the 185 makes it greatest percentage gains in HP until about 4,300 engine RPM's and then it's trend line starts to flatten out - but it is still continues to increase HP all the way up to 6,000 RPM.

Works for me...

 

Actually Brian, I think you've put into pictures what I've been kicking around in my head. Mind you this is total theory, and I am by no means an expert or even very experienced with this kind of thing.

Could one of the reasons the 178, 181 and 185 pulleys are performing so closely at the 1/4 track be shift points? As Brian mentioned, the 185 pulley reaches the supercharger's sweet spot sooner than the smaller pulleys.

Is it possible that the 185 hits that sweet spot so early in the rpm range that when the car shifts at redline, it is already past the sweet spot? Now I'm making these numbers up, so bear with me, this is just an example.

Let's say Brian's car hits the sweet spot at 4300 rpm. If he shifts at 6200 rpm, the car only drops down to about 4800 rpm after the shift, thus missing the sweet spot. Where the same car with a smaller pulley may hit their sweet spot around 5000 rpm, and thus they would hit it through every gear, instead of only in first gear.

Does that make sense?

 

You make a great point - It's something I've wondered about since running the mile. Not so much as the sweet spot for the SC'r but when is the optimal time to shift for SRT6.

Perhaps one way to find would be to run a set of dyno pulls in each gear to find that "sweet spot". Not sure. I know some drag racers use a "shift light" on their tack to alert them - I'm just not sure how they calculate when the light should to come on.. Perhaps someone with a lot of drag racing experience could add to this.

Remember - the fastest SRT6 in the 1/4 mile runs a 181mm.

MikeR just ran a 12.07 sec. 1/4 mile with the 181mm / SL55 / LET tune combo.

It wasn't but a year ago when a 12.40 run got everyone all excited.

The margins between a 181 and 185 are even closer.

There's still a lot more potential in these engines and I think 240M3SRT6 & BDJ are going to tap into it.

Hang on tight.....

 

Then all I do is tap the shifter to the right at the correct RPM and I'll always be hitting the "sweet spot" thru every gear before a 178mm...

 

Do not hold your breathe…those boys are out “chasing skirt” not working on these cars.

JK…They are a couple of cool guys and they not afraid to think outside the box!

 

MikeR ran a 12.07, nice. He also has moddified mani's.

Hopefully next mon or tues my version of integrated y-pipe/ic with moddified mani's will be complete.

And BLKFIN just becuase we chase skirt doesnt mean we slack on the srt's lol.

 

Keep up the good work guys....

 

Not sure if this is quite what you're looking for, but do you remember the S/C efficiency maps from this thread? Seems to be along the lines of what you're talking about:

https://www.crossfireforum.org/forum...ad.php?t=31186

 

Wow I like where this thread went.