Cool, thanks for all of the Tech info.

 

my point is this, if the engine was properly tuned and set up, there should be NO reason why you would need to run a water/methanol mix with a measly 5psi. look at tuning issues and maybe the fact that comptech did not offer a after or intercooler. to me, as a tuner, the problem lies in tuning. if they wanted to lower iats, there are many other ways to do it. just water alone would do the trick. Fabricate a CAI, that would help.

Tuning is very important, thus why the comptech sc has so many issues.

Sounds to me like ignition timing is over advanced and those guys are running meth/water injection thinking that bringing down the iats will help. This is true, but not really needed if tuning perfect. It will not be right so long as the tuning duties are handles by a AFC map clamp piggyback. In order to believe this fact, you have to understand how the speed density ecu works and what the piggyback is doing to the map sensor voltage to alter injector duty cycles and how this directly relates to ignition timing in the ecus tables.

The reason why I started talking about this stuff is simple. You guys are blowing out your cats! Why? Tuning!!! on so many levels

CJ

 

Well...personally...mine is running just fine now supercharged. I really havent been concerned about IAT at all....been doing just fine in all regards just the way it is. But as you mentioned above...we fab'd up a special custom CAI unit that we believe it helping even things out a minor bit. With the CAI unit on it....I am running a thermoblock spacer (part of the kit anyway...some of it you cant use)....a standard comptech exhaust...other than that....stock. It runs about 5 lbs of boost MAX....(not running high boost pulley)...and IAT's are not a real issue here. I also have a custom alum rad on it thats somewhat larger than stock...but frankly...I doubt that plays any part...other than keeping the motor overall a shade cooler in high heat summers....but so far as blowing out the cats...I dont expect it to happen. It ran rich right after install for about 2 days or so...and slowly began to adjust to where it is now as I drove it...which is around the range you stated was acceptable. I think I just got lucky though...cause several people have faught high IAT temps and incorrect AFR's for a LONG time. One fellow even got several fuel pressure regs and crushed them to different depths (comptechs solution in their directions to adjust the fuel pressure to where they want it running at....even give you a tool to do it with....he just added shims in it to crush different depths and adjusted it out that way to get it to proper AFR #'s...Bernard is his SN I believe).

Anyway...I have been very happy with the operation and daily drivability of my supercharged TL.....no probs here so far. But again...as I said...I think I just got lucky with the right combination of parts and fabrications, which I had planned out in my head to a great degree from the start - but truely didnt know what I was doing - just got lucky and picked the right combination of stuff that I wanted that worked out somehow. We have tried and dyno'd different CAI setups, ect...and the one we came up with produced the best all around numbers HP wise and AFR wise with the parts I have on there. Thats when we felt we had a winning combination!

 

It should be noted, like stated earlier, methanol has a high octane and will raise the detonation threshold overall. But if the engine was properly tuned, there should be no problems running 5psi at all. There should be no need for methanol. You could even loose some power by doing so if you can't or don't advance ignition timing to be able to take advantage of the higher octane.

Lets break this down so its more understood. Say you are running 5psi on 93 octane. Using the comptec sc and piggyback. At 5psi with 93 octane your ignition timing is too advanced, your running too rich and you have high IAT's. There are three major problems, no matter what boost you are running. Now factor in the relatively high static compression ratio for this motor, being 11.0:1. Although a static cr is not a bad thing, it compounds problems and is unforgiving with anything other than perfect tunes on pump gas.

Ok, the first problem is this, @5psi ignition timing is over advanced. There are several ways to combat this issue. Either retard ignition timing correctly, raise octane which raises detonation threshold and find a way to lower IATs(colder denser air raises detonation threshold as long as fuel is richened up to compensate for the cooler IAT). You can also run the engine a little richer to help cool the intake charge. (sidenote: this only works in some situations, its a common practice for some companies to run pig rich in the 10's:1 to drown out the over advanced ignition...this is not a good thing and seldom works...there is a power loss from doing such a thing anyway)

Second issue, your running too rich! Well, if you try and lean the engine out a bit and your ignition timing is too advanced.....you will really have a problem with detonation.... So this can't be touched really until you correct the ignition timing issue.

Third issue, your IAT's are high! You can do many things to fix that, but a better solution would have been to address this issue with a aftercooler or intercooler.

Lets back up a minute, even if you were forced to accept a high IAT(which is normal with forced induction) all the other problems are combining to cause a bigger issue.

So you say, lets run a meth/water mix to help out, because you think the problems you are having are mainly due to high IAT's. Well you would be wrong. If ignition timing is over advanced for 93 octane @5psi it will most likely be underadvanced when injecting methanol. The water WILL cool the intake charge, but now you are running supper rich and have under advanced ignition timing for the octane and boost. Thus you are not taking full advantage of the higher detonation threshold of the meth. This is why I stated that the MAIN reason we run methanol/water is to run more boost than our fuel system and or fuel availabilites allow. The water is just added to help cool the intake charge, which also helps us run more timing and boost.

Now, lets take a look at high static compression and how this plays a role. There are already high temps and pressures involved with a static cr or 11:1. Factor in boost and you get what's called effective compression. @ 5 PSI of boost at an altitude of 0 feet. Your motor's static compression is 11 :1. At this boost level and altitude your effective compression ratio is 14.74:1. Now, as you can see this is high....not too high, but high(what is considered high does not really matter when everything else is considered). So, the effect of boost has raised the compression ratio. This makes tuning an engine like this very important. The engine is susceptible to detonation easily, it needs a perfect afr and high iats can make things worse. The more you add(boost) the tougher it can get. This is why tuning is so important when you have the correct equipment.

I'm not even getting into EGT's and how that is effected by all of the above! Nor does that talk about backpressue and how important that is to the above mentioned engine.

The above scenario is nothing extreme, its been done time and time again, reliably. It just require the right combination of parts and the ability to properly tune the engine for the job a hand. Again, its not extreme at all.

All the above was said for you to see that what you are doing to those cats. They should last a lot longer than a few thousand miles. Granted their location right off th head is a bad place for them due to heat involved, but then again, e shift decided to keep the stock locations instead of moving them further down the line, but I can see why they choose to keep them in the stock location.

Sorry for the book, as you can see there is a lot to this subject....I tried to keep it short! Lol

CJ