I was wondering if anybody local had decent experience with the Megasquirt ECU? It might be handy for someone with more experience than us look over the maps and let me know what you think. We are very close, but running the car a bit "fat" and with less advance than possible for safety sake.

The car runs really well, but I can't help but feel that we are leaving something on the table regarding power. Last fall, we were able to run with a Super Touring CTCC BMW for a few laps until we started to detonate again. This year, we are using race plugs to elimante this, but it may help to have somebody double check the settings to make sure we aren't missing something.

Let me know if you are interested and your level of experience. By the way, for those who don't know, we are running a 4 throat ITB setup on the car.

Regards,

Eric

 

I've done a little Megasquirt here and there. I could take a look but there is often little that can be told from a map without the datalogs to go along with it. It's hard to tune by remote.

 

If you want to bring your car down for a couple of days here to London, you can keep it at my shop for a couple of days if you'd like.

 

How much timing are you running and what AFR? I'm assuming this is a PPort? If its detonating, you need to back off no? Race plugs isn't going to eliminate detonation, only help a little bit. Maybe the temp corrections aren't setup right?

thewird

 

We are running between 18 and 20 degrees total and its locked at that setting. AFR's are between 12.0 and 12.5 and the car is a 1/2 bridge. We thought about the temp corrections, but they seem to work. The car will run at full throttle for about 30-40 minutes with no issues before it starts to detonate just slightly going into Turn 8 at Mosport. It never detonates at Shannonville or other shorter tracks. It starts detonating at Mosport harrder first going up Andretti straight pulling hard in fourth, then it will start doing the same thing pulling hard in 3rd going into 3. Soon it will start detonating at more places around the track. If I start to limit the load on the car (not rpm related issue) I can use more throttle again for a while until it starts all up again.

After I pull in for a refuel and the car heatsoaks for a minute, the detonation gets worse and grows steadily worse until I am limited to 1/2 throttle for most of the lap. I can send the data downloads from the last race and the settings to anyone who wants to see them.

It seems to me that the Megasquirt setup isn't far out and that the stock plugs start to turn into glow plugs after a while, but I am not sure. Also, the car flat out flys when the air temps are cooler and slows down a fair bit when the air temps rise above 25 degrees.

Eric

 

That timing and AFR is fairly conservative so that's not the issue. Have you verified the timing with a timing light? Do you have an onboard wideband to monitor? It almost sounds like the problem takes a while to appear and/or happens under certain conditions on the track (corners or loads). How about a fuel pressure gauge? Your fuel pump wiring may be overheating or the pump itself even which would be easily determined by a fuel pressure gauge (onboard).

So your running stock 9's for plugs? Yah, definitely change that to 10's at least or 10/10.5 combo. Some might even suggest 11's but I think that's overkill (never hurts though as long as you don't spend much time idling). You can get R7420's from sparkplugs.com for ~$34 each + shipping USPS. Search for "R7420-10" (10 being the heat range)

Last thing, are you running zero split timing?

thewird

 

Great questions. We have verified the timing with a timing light, so I think that it isn't an issue unless there can be something wacky with the timing marks. I also have a wideband in the car and a gauge right in eyesight. I watch it and on the straight it never climbs above 12.5. Most of the time we are in the high 11's until everything stabilizes. I do not have an onboard fuel pressure gauge, but I am running a new 255 lph Walbro at full flow wired in with pretty big wiring. The AFR's never change over the course of the race and seem detached from the detonation issue. The injectors have been cleaned and also work fine.

We are running (I believe) 5 degrees of split. Great questions and I am going to run the NGK BUE's in the car next race as they have had a pretty strong build up in the NA Section and they are available locally for single digits.

Great questions and advice though and it has me thinking a bit.

Eric

 

One thing to check is a log of the IAT during these long sessions. If the temperature is gradually rising until the point of detonation, you've found the problem.

Also, are you running any kind of underdrive pulley on the water pump? It may be cavitating, causing hot spots.

 

Does your megasquirt map compensate for high AIT's for ignition? I guess next would be to post your megasquirt map and a log of a full run if you have one. Or you can e-mail me @yahoo.com if you don't want to post it.

thewird

 

Is your 02 sensor working properly? What does it read with the engine off ?

 

whats the heat rating on the spark plugs you're running?
there's MAT based timing retard

 

Guys, thanks a ton. These are fantastic things to look at. Just some answers to your questions, The WB O2 is working fine. It reads 0 with the car shut off and reacts correctly to air fuel changes. We do run an underdrive C/S pulley and a stock W/P pulley. I am looking to get an underdrive W/P pulley as that may contribute to the problem.

We do compensate for AIT's, but being a 4 throat ITB setup there are strong differences to the air temps each throat reads. When we had the intake bells fully enclosed in an airbox, things were better and more consistent, but we had to take the airbox off as we kept melting fibreglass ones and I haven't had time to fab up a metal one. We are basing the AIT off the last intake bell as it consistently showed the hottest temps.

We are running stock plugs. I think that they get too hot and start causing pre-ignition. When we drop the air fuels to the 10.5 to 11.5 range things are better, but it only delays the onset of the detonation and doesn't get rid of it.

So, based on the above, this is what I am going to do before the next race;

1) Run the car on premium Shell V-Power (need to run Shell as they are helping me out this year)
2) Put in NGK BUE plugs. very cold and very good pricing
3)Check the maps to ensure that we have an appropriate amount of temperature correction What would be a correct richening amount or timing reduction? We have seen underhood temps as high as 450 degrees F after pitstops!!!!!!!
4) Purchase and install underdrive Water Pump Pulley
5) Fab and install cold airbox again. This will be in metal as it needs to have a built in heat shield.

You guys are great! Lots of great ideas and they all fit with what I am seeing and areas where we need to step up the program. I know the basic map is great for power when things are cold. I just need to keep it cold, LOL.

Thanks again,

Eric

 

i think the MAT fuel correction, takes fuel away, to keep heat soaked cars from flooding, im not 100% sure tho