As some know I have upgraded the SC pulley to run a little more boost. But as reported there is a slight knock issue which was mostly addressed by bumping up the fuel pressure but not completely.

The problem occurs at the VTEC change over and lasts until just after 5500 revs. This mainly occurs in 3rd+ gears but has been seen in 2nd on a rare occasion. Also, it is mostly present when cooler out and diminishes as the temperature rises.

All of this revolves around a change in airflow rates when the hot cam profile is selected causing the engine to lean out enough to promote knock. Comptech is working on the piggy-back computer to allow more fuel to be added where needed but this is some time away.

So in the mean time I needed to find a solution or just go back to the other pulley and run the lower boost. But as with any mods, it is always difficult to go back. I almost reserved myself to going to the lower boost pulley but decided to try something first.

I am running a lower temp stat and fan switch which helps keep the ECT around the 180 range. This has also proven to help keep from loosing power on the order of about 6 - 7 HP and the same in torque. The assumption is that at the normal operating temps (about 200 F) the ECU pulls some timing. Whereas with the temps in the 175 - 180 range you get a few degrees more timing and the added power (or rather the reduction of the loss of power).

With that being the case I decided to fool the ECU into thinking the ECT is warmer than it really is. There were two methods I thought of, using the ECU output for the VTEC solenoid and triggering a relay to switch the ECT signal. Or use a pressure switch. I choose the pressure switch route.

I purchased a Hobbs pressure switch from ATR (a GN/T-Type/Sy/TY tuner) as I knew they used them in their double pumper fuel kits for the Typhoon. I set it up to switch at 3 PSI boost. Since the ECT is a simple temperature dependant resistor I could fool the ECU into think it was warmer by determining the appropriate value to run in parallel. After trial and error I found that a 300 ohm resistor worked well.

The 300 ohm resistor in parallel would cause the ECU to see ECT temps about forty five degrees warmer. So with an actual ECT reading of 180F the ECU would see 225F when the boost went above 3 PSI. I used one of our pressure calibration systems to set the pressure switch setpoint.

The results have been good so far. I have not encountered any knock as of the last couple of days nor had any problems. Since the ECU reads the actual ECT value most of the time the normal driving is not affected and part throttle romps are no different. But when I floor it the boost will go to about 5+ PSI which triggers the switch to close causing the ECU to see 220+ temps and hopefully pulls back timing enough to keep knock suppressed.

I had considered putting back in the stock T-Stat and fan switch. But after pondering this idea I decided that I wanted to retain the lower engine temps to help keep hot spots minimized. But also I like the part throttle power which would have been affected. This way timing is reduced only when I get on it. Now I wonder what the power difference is. I'm guessing the pulley upgrade could have increased the power 20 - 25 HP. But with the reduction of timing the power gains would also be reduced; I'm guessing about 8 - 10 HP. So the expected gains of 10 - 15 HP with the new pulley are probably right. But the increased torque across the entire power band is what I like, not the peak power.

I made a quick sketch of the setup. I know there are few who would be doing this now as the kits are new. But just for future reference until Comptech releases the computer.

 

All the more reason Comptech needs to get that upgraded ECU to market.

 

Very goog work steve!

 

Scalbert: Ever thought of doing the opposite by fooling the ECU to think the car is running 'cooler' than usual and hence advance timing a bit? Of course, preventative measures such as high-octane fuel etc. need to be used. But for a track day... good results!

 

You could but with the lower temp stat and fan switch you are at about the lower limit you would care to run. I haven't seen any real timing difference with going cooler than 160F.

 

Scalbert, As always, nice work! Over a year ago Shad at CT emailed me that if I brought in my car they would conduct research and install "Unichip" from Racer's Group of Sear's Point.
CT certainly has the R&D capabilities to handle this but has never developed further. Have you ever gone to the Racer Group internet site?! Claims of up to 60hp. on Porches! We should encourage CT to do this!

 

This could be what they are employing.

They have a system running on the S2000 and once that testing is done it will be put on the CL. Based on what I have heard is sounds similar to the Unichip package leading me to beleive they might be using it.

 

Aren't those gains from increasing the turbo boost?

 

Both.

But they did acheive decent gains on an AV6 through just fuel tuning and no ignition adjustments.

 

scalbert,


simply amazing! Could you tell me more about switching to a different pulley, or with the problem of knocking adherent, would just changing my T-stat and fan switch give me any noticable gains? You always take us into the unknown, thanks.

 

Very cool,..... or hot! Nice job!

 

 

Scalbert...a lady by the screenname of acurafreak on the "other" acura site has the unichip tuned and running on her TL-S. There are dynos also.

 

i hope i didnt read 3 pages worth of bullshitt...for you to refer what we are talking about here to that story over at A W ...please tell me there's an acctual dyno?

 

Comptech will have a pulley out, for the alternator, which will turn the blower faster which will obviously generate more boost. But due to the knock issue they have been slow to release it. I believe they want to hold back until the piggy back computer is ready; more for their protection I assume (and agree with). The knock is very slight to where you have to listen for it and only occurs at high load.

Considering your location I would certainly get the T-Stat and fan switch. I cannot say there would be gains on a blown vehicle but there were on an NA vehicle. Actually I should say gains from the stat and fan switch, you just don't lose as much as the engine warms.

 

Thanks for the info, I'll try and look that up.

I will be contacting the local Unichip distributors in the Atlanta area to see what the costs are. But I did see they have the AV6 application listed so it does work with a similar system and controls.

Do you know where the dynos are??