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STV_Keith

EGT, too hot and why?

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I'm cross posting this from S&F, since some of you guys don't seem to be on there and I need as many heads on this as I can get. :)

A little background on this one. This is a bone stock 260. Stock adapter (not drystacked), stock A49 chip in the ECU, 39# regulator. Stock heads producing 136# compression at 2100' elevation. EGT being measured in the bottom two bolts of the exh divider (not adapter).

So, back in May, the last time I ran the boat, it would make around 1300*F EGT. I always thought that was hot, having tried to tune my old JSRE mota in at 1200*F WOT.

Anyway, fastforward to early December, the next time it went in the water. I go out after having changed the chip to an A48 I bought from John Marles. This is the first time I had been using a RacePak data acquistion system on the boat. EGT's were in the high 1300's, which scared me. I basically put it back on the trailer and went home. I tested FP, which seemed to be a little low (35psi WOT or engine off) while my Autometer dash gauge was still reading almost 40psi. Swapped regulators and a different one made the pressure come up about 1 psi to 36psi.

So I plugged in one of my dash pyros and went back to the A49 chip. Went out today and the EGT's were still hot. 1390*F, so I started tweaking on the fuel pot. Now I know I've been told that these pots are very sensitive, so without a DDT all I had was EGT to see what was going on. I started with 1/8 turn, then another 1/8, then a 1/4 then ANOTHER 1/4. 1/2 turn from where I started...how much extra fuel is that? In the end, EGT's dropped about 100-150*F at cruise, and almost 120*F at WOT. My WOT EGT is now at 1279*F.

See the graph below. ~7500rpm. The pink graph is RPM while the green is EGT on the second run of the day (+1/8 turn). The red graph is RPM and the yellow is the corresponding EGT at +1/2 turn. Fuel pressure on both runs were very consistent at around 35psi. My dash mounted gauge was showing 39-40 as it always did. You can see where both EGT's drop off as the motor hits the limiter. I know the limiter is supposed to be at 7800, and while my dash tach showed 7800, the RacePak only showed in the high 7500 range.

IPB Image

So next I swapped in the A48 chip, left the fuel pot alone and went back out. EGT's were about the same, so I added another +1/8 turn but it didn't seem to do much, if anything.

In the next graph, you can see where the A49 chip hits the limiter and EGT falls off (red RPM, yellow EGT) and where the A48 chip continues to pull just past 8000rpm (blue RPM, green EGT). At 8050rpm, EGT is 1286*F. As you can see, the EGT is very steady at a relatively constant RPM. This is all this stock 260 had with my 29 Mazco. Fastest the boat has ever gone...109mph.

IPB Image

Now I know EGT is supposed to be used as a reference, but this sure seems hot. I kept checking the plugs and they were getting progressively darker (as expected) when turning up the fuel. It seemed to come to a point of diminishing returns though, as that last 1/8 turn didn't produce much EGT drop. Cruise is fat, if anything, now, with EGT's sitting in the 1100*F range.

So since it didn't burn down at almost 1400*F after a few WOT passes and cruising at 1300*F, should I just take that as safe for reading for this motor with the probes where they are? As of today, the EGT is less than it has been on the past two outings, so it must be saf-er, but man that still seems high.

Any suggestions appreciated as to why the EGT's are so hot. I know with the PCU, my old motor never went over 1200*F, measured at the same place. Maybe that was too cold and a factor in why it would only run 107mph?

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WOW Keith, you NEED a 4 button tester!. If you are going to invest in a Racepak set up!.

When changing the pot on the 11350 series box, I use a little snap-on screw driver that fits the pot perfectly, 1% is normally about a blades width (the thickness of the tip of the screwdriver, meaning VERY little move). It is that sensitive!. And it is by no means linear!. If you were reading 1390.... I am guessing you were reading flame front, if you were moving the pot that much I am thinking you are now so rich that you are cooling the probes with raw unburnt fuel.

GET the 4 button tester.. not the peice of crap DTT... it only reads every 2 %, the 4 button is every 1%.

Also get your injectors flowed. Power Performance, or Kinsler. Put the stock chip in, and set it at 100. I beleive you are at elevation, I would suggest trying the box at 99 and lower till you get a baseline that proves your EGT's are working. BUT be gental...... you will burn it down....... if you go lean. This is a simple matter or making a pass. Shutting it down and reading the wash on the piston. Then look to you gauge to see where it sits.

Also keep in mind that the 2.5 LOVES fuel, so being really fat doesn't really seem to kill off top end power, but it does kill your snap and fuel economy.

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Keith,

Glad to hear you're getting your boat up to speed. I don't know if you remember. But, I've talked to you a few times and you were very happy with your PCU the last time we talked. So, I went from my A48 to a PCU. So far I really like it. I was wondering why you're running the A48 and not your PCU? I just had John completely rebuild my 260 and do all his goodies to it. Should have way more power. He told me he likes the A48's. I'm bringing my boat up to his shop this weekend. He's going to fire it up and then we're going to a local lake to break it in. I haven't even started it up since the complete rebuild. I'm really looking forward to hearing it run. Anyway, just wondering why you're not running the PCU. Did you try it compared to the A48? If so what happened. Thanks for the inpute.

Edwin

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Thanks for the info guys. FS, I'm really dreading having to keep modding/fixing just to get a STOCK fucking motor to perform like it should. This thing is ALL STOCK. All I want is a baseline that makes sense, so I can move forward with some testing. I guess I need to see where the pot is set now, before I can move anywhere. If it's at +25% or something like I"m guessing it is, then I don't know what is going on. If I had an injector problem, I'd expect it to be one or two, but not the whole set.

I know it was lean when I started. I'd hit the throttle and there was nothing there off idle. It would die coming off plane if I hit the throttle to keep the wake from breaking over the cowling. After adding 1/4 turn, it was much better down there.

Edwin, I still have the PCU and I do like it. I'm trying to get some baseline info on what a stock setup does before going to it. If a stock setup will live at 1250*F for instance, then I know it will live at that temp with the PCU too.

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The pot gives 15% +/- that is it.

I agree you need to get a baseline. Get a 4 button and set it at 100!.

RT

And you might still want to get the injectors done, when even one is going away it will cost you 3-400 rpm. At the bare minimum, pull the rail and injectors and test fire them. They should have a nice cloud of fuel... any even hints of solid fuel and you have a problem. Back flowing them with air can get you by in a pinch, but you really need to know the flow numbers to tune a motor.

RT

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Where can I get a 4-button and how much $$$ ?

I guess I could pull the injectors out of my other motor, since those only have about 20 hrs on them since Brucato went through them.

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Just curious, is there any point in investing another $1000 in a 4 button tester when he already has a PCU? Would it not make more sense to get the computer software from Brucato for the PCU so you can make infinate adjustments through your laptop? ie way more flexibility then the MERC set up?

Would Brucato have the setting to represent the same chips that Keith has?

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Brad, I have the software, but again, I'm trying to get a baseline on what these engines do with stock ECU and setup. Then I can move forward to my PCU and tuning. At this point though, I'm not confident that my motor is doing what every other stock 260 would do...and that's what I'm trying to get to.

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What I was trying to say Keith, can you not get the data from Brucato as to what the setting would be for a stock A48 chip and program them into the PCU. The motor would not know the difference between a Merc ECU with an A48 and a Brucato with an A48 program. Then you wouldn't need the $1000 4 button tester to get your base line on the Merc ECU. Just asking as I don't know if this is possible.

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What you say is probably possible, but I'm just trying to do it the simple way (yeah, right!) Heh.

I thought finding out what a stock motor does would be simple.

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What you say is probably possible, but I'm just trying to do it the simple way (yeah, right!) Heh.

I thought finding out what a stock motor does would be simple.

send your box to someone with a 4 botton tester or a ddt and have them set it at 99 witch is stock for the a48box and you will no i am sure someone you how has a ddt to set it for you that would be the easy way to do it.keys dave

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What you say is probably possible, but I'm just trying to do it the simple way (yeah, right!) Heh.

I thought finding out what a stock motor does would be simple.

send your box to someone with a 4 botton tester or a ddt and have them set it at 99 witch is stock for the a48box and you will no i am sure someone you how has a ddt to set it for you that would be the easy way to do it.keys dave

Thanks Dave. Kevin here in town just borrowed a DDT last week, so I'll get it on there soon. Also had Brucato flow both my sets of injectors...ended up throwing out 4 of the 12. Got a good set in it now, and it still is hot. Tried a different A48 box and same thing. I'll get the DDT on my A48 box, then go from there.

BTW, congrats on 135! That's FLYING!

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