My car has been NA since labor day when I pulled the blower kit off to change the water pump and timing chain tensioner. I left the kit off because I got a Pathfinder throttle body and I'm having an adaptor plate made, and I thought it would be easier if I put the blower back on when I was ready to install the TB. But I couldn't stand being NA any longer, especially after a cocky M3 owner badly needed a lesson in humility yesterday, and there was nothing I could do about it.

So, when I got home yesterday I threw the kit back on. Of course, it started raining when I was done, so no test run last night, and this morning going to work I could feel the power was back, but I was not able to really wind it out.

So today at lunch I did a little cruising. I haven't take it up to redline yet cuz I'm carefully monitoring EGT's, but I'm happy to report the 3" pulley really feels good, even more powerful than I expected. I know that the past couple of weeks being NA may have caused me to lose some of the feel of the car when it had the 3.25" pulley, but the increase in power feels greater than the 8% decrease in pulley size should have given it. The explanation I think lies in that I have been using an 8:1 fmu, which was too rich for the 3.25 pulley, but may be just right for the 3 incher.


I'm getting about 2-3 psi at 3000 rpm, and I saw 8 psi at 5300 rpm when the MEVI actuation light came on. I haven't pushed any higher than that yet. I'm a little apprehensive about taking it to 7200 rpm when my JWT ecu comes in, since I'm not intercooled. I think I'll save that for a dyno session.

I tried to set up a baseline dyno run before I changed the pulley, but Protech wanted me to drop the car off and let them dyno at their leisure, and I said no thank you.

 

congrats on the install, Stephen....good to hear that you like the power of the small pulley It is not only adding the peak boost, but it makes the car boost much faster than your old pulley. That's what I've noticed on my change from 3.33 to 2.87.

about the 8:1....I think you are running even more rich than before now because you are adding more boost to the FMU.

 

What you say raises a question I haven't really thought about before.

It is true that I am running higher fuel pressure at a particular rpm, because of the higher boost, but the higher boost translates into more air delivered into the engine, too. The question then is did my fuel delivery increase more than the air, or air more than fuel, or did they both increase the same amount?

If increased boost pressure causes fuel delivery to increase faster than air delivery for a particular fmu disk, then why do people go to higher fmu ratios when they go to smaller pullies? (Or do they? Maybe I'm mistaken about that.)

Let's do a thought experiment. The air forced into an engine is proportional to the pressure ratio developed by the blower. So for instance, a blower developing 9 psi with a PR of 1.61 is delivering 14% more air than a blower developing 6 psi.

But the fuel delivery is going to be proportional to the square root of the increase in fuel pressure. So let's say both systems use an 8:1 fmu, with a base fuel pressure of 34 psi, and let's use the equation fuel pressure = (8 x boost pressure) + (base pressure)/2

So the 6 psi system is going to produce 65 psi of fuel pressure. The 9 psi system is going to produce 89 psi. SQRT(89/65) = 1.17, so there is a 17% increase in fuel to correspond to a 14% increase in air. Well, I'll be. So for this example, increasing boost results in a richer afr.

 

I think it is just a straight line between the fuel pressure and boost pressure. Even though higher boost means more air, but the fuel increase along with the amount of boost. You fuel delivery increase proportionally to the amount of air increase. supposedly, you should increase 8psi of fuel per 1 psi of boost.....but that's not what I see on my fuel p. gauge....I see 80psi of fuel @ 6psi of boost.


very interesting.....I think this also explained why you need a higher ratio of FMU for higher boost.

I tried your experiement with a 6:1 and turned out that I got a 15.7% increase of fuel when adjusting boost from 6 to 9 psi.

I tried it again with increasing boost from 9psi to 13psi on both discs and I got:

16% for 8:1

and

15.6% for 6:1

therefore, the smaller ratio disc will lean out the car at higher boost..but I dunno if 0.1% makes any differences......

We havent put the injectors into our little test. I believe that the reason that I am running very rich is because 2k-2k1 injectors are slightly larger than that of the 4th gen. I think 2k-2k1 are 255cc compared to 240cc of the 4th gens. Maybe I can live with a 6:1.....but I will let the dyno to tell me.


good luck on your dyno run, let us know how it goes~

 

Stephen,

What kind of tuning parts do you have? FPR? S-AFC? FMU? I am running the 3.125" on my V1 w/8:1 Vortech Disc and am hoping to pick up 30+hp from dyno tuning across the board.

My instinct tells me I will be picking up 50tq under the boost curve.

 

Craig,

I have an Apexi s-afc. I was planning on using it (along with a Vortech s-fmu) for tuning when I dyno-tune after installing Z-32 injectors. Instead of the s-fmu I have instead bought a Z-32 maf and sent my ecu to JWT for programming. That way I can run an airflow referenced system (instead of boost referenced) with the Z-32 maf (good to 420 hp) and with a very safe 43 psi fuel pressure on the Z-32 injectors, and I don't need to do any dyno-tuning. Just plug and play. I sent the ecu to JWT 4 weeks ago, only 4-6 weeks of waiting left.

So, 30 hp and 50 tq, eh? I'll be sure to use those numbers next time I buy a lottery ticket.

 

Sounds like fun Steve. Can't wait to hear the results with the Z32 stuff and ECU!

Still stock injectors for now?

 

Yep, still have the 240's in until the ecu comes back from JWT.

This morning was fairly cool because of a cold front that moved through overnight, so I boosted to 6400 rpm in 3rd, saw boost past 10, maybe 11 psi.

 

s-fmu = Vortech Super FMU?

If so, can't you adjust the slope of fuel increase to lower it to say 7:1 or 6.5:1 and adjust the min/max to compensate for the boost reference increase at lower RPM?

JWT may take 4evAr, but it is worth it IMO.

 

Yes, Vortech Super FMU. I never got it because while I was shopping around for one I changed my mind to go with the JWT. But if I was going to stay with a boost referenced tuning system, I would definitely get a s-fmu due to the multiple capabilities it has to adjust base fuel pressure, max fuel pressure and rising rate slope.

 

Ok...that makes sense. You're currently running the regular FMU.