5 Petal or 7 Petal Reeds for High RPM on Merc Drag Motor

[patchesII]

Thanks Erik. Very much appreciated. Im gonna try to keep the RPMs below 10,500. I’m using what I believe is the A13 curve in my Brucato ACU.
As you can see, the fueling on the bottom cylinders is offset above 9000 on Group 2 (middle pair) and starts at 1% above 5000 and goes to 6% on Group 3 (bottom pair).
I’ve noticed that the offset on the A13 curve is larger than on the A6 curve. I suppose that’s because the A13 was for the slider manifold drag motors?
I think my tune is the same A13 tune Mercury that used on the stock slider Drag motors? See my tune below. I’ve also flowed my injectors and used the highest flowing ones in the bottom holes and the lesser flowing ones up top, which might mitigate the need for that much offset.
I have the Brucato software/cable, so I can make adjustments, but I haven’t done anything more than tweak the rev limit (now set at 11,000) and the offsets, which if memory serves, I’ve leaned out by 1% overall, ever since I flowed and reinstalled the injectors.
I’m also currently running the overall enrichment potentiometer set at 6% rich, but I intend to gradually tweak that downwards in 1 or 2% increments and carefully read the plugs and piston tops.
Attachment 525248

I added 2-3% on top of the existing 6% already offset with the factory map. It’s a measure of safety that will not hurt performance, matter of fact I think it allows you to tune the engine closer to optimum without torching the bottom two cylinders.

[CI STV]

I added 2-3% on top of the existing 6% already offset with the factory map. It’s a measure of safety that will not hurt performance, matter of fact I think it allows you to tune the engine closer to optimum without torching the bottom two cylinders.

Thanks. I think that would bring the offsets in the A6 tune in line with the offsets on the A13.
Heres the A6 tune that I got from either Brucato or another S&F member who was kind enough to share some fuel maps that he had:

[CI STV]

If I’m not mistaken, the A6 tune is for the earlier Horn Drag motors and the A13 is for later model slider manifold Drags? That might explain the differences in offsets between the two ECUs, as no doubt the slider manifold will flow more air to the bottom cylinders which already run hotter.
I think I’m going to put the offsets back to the stock A13 settings before I do anything else.
Thanks again Erik. Most folks won’t share that kind of detail, so I’m very grateful for your advice.

[patchesII]

You’re correct about the different maps but of all the people I knew running SVS’s all but one ran an A6 based map. The A13 is really lean down low. I will sing Mercury engineers praises from the mountain tops on most of their stuff but the A13 always left me scratching my head. The A6 map with minor tweaks is really good on an SVS for racing. I added fuel to it from 3000 to 6000 and pulled a little above 10000. Added 2% to the bottom cylinders at 9000 up to where it had 3% extra (so 9% total) at 10500 and up. Won a lot of Pro Gas races like that. My Pro Drag methanol map was pretty similar

[CI STV]

Thanks a million again for sharing this.
What I’m trying to figure out is whether I actually have a stock A-6 fuel map.
If memory serves, I got both those tunes from Brucato, so maybe they were already tweaked for the SVS?
Because if you look at those two tunes that I’ve posted, one of which purports to be an A-6 and the other an A-13, the map values seem to be identical, except for percentage offsets for the bottom cylinders?
I’ve been tempted to try to tweak my fuel map, but I really don’t want to fubar my motor, because I don’t know what those numbers in the cells relate to, although it should be easy to figure out how to increase a certain area of the map by 2%, etc.
But, for the time being, I may just try playing with the potentiometer settings first.
The good thing about the Brucato is that it has the ability to adjust the acceleration compensation sensitivity and volume, so in my simple mind, I’m thinking changing those perform the same function of changing the squirters and cams on a Holley carb?
For ease of reference, I’ve attached the Brucato potentiometer tuning instructions below:

So, maybe I’ll try increasing the fuel volume on the accel-comp volume pot by 2% and see how that works. I can monitor my datalogs and try to see what that does to EGTs as well. I’m thinking that should help cover any lean spot in the midrange of a WOT, 800’ run?

I think we’ve strayed way off the topic of reeds, lol, but thanks again for sharing your experience.

[tlwjkw]

jus read this thread and WOW!.. he's tha best huh.............

[rjdubiel]

They always say set accel comp functions like this for every curve I have had.

Main: 0
Sensitivity: +4
Volume: +4
Part throttle: 0
Idle: 0

[CI STV]

They always say set accel comp functions like this for every curve I have had.

Main: 0
Sensitivity: +4
Volume: +4
Part throttle: 0
Idle: 0

Thanks. That’s very helpful. Thanks again for those fuel maps you sent me a while back too.
Here’s the settings my ACU came with, which is what I presume Diamond dynoed it with. It was pig rich though, and had a 10K rev limit.

The main was set at 12% rich and the two accel pots were both at 4% and idle and part throttle at 0%.
I have the main set at 6% now and I didn’t trouble any of the others.

[patchesII]

The map you posted is an A6 or a variation of it.

Engines coming off of dyno’s are typically set very rich because the dyno puts such a big load on it requiring a lot of fuel. When Pete Elliot raced Pro Gas one of his best engines was a 280 from Diamond. When we got that engine the A6 was set at 113. We raced it at 103 if that tells you how rich they set them. I ran into the same thing with the OMC and the 2.5 I ran on my Pro Drag boat when they came off Dave Bush’s dyno

[CI STV]

The map you posted is an A6 or a variation of it.

Engines coming off of dyno’s are typically set very rich because the dyno puts such a big load on it requiring a lot of fuel. When Pete Elliot raced Pro Gas one of his best engines was a 280 from Diamond. When we got that engine the A6 was set at 113. We raced it at 103 if that tells you how rich they set them. I ran into the same thing with the OMC and the 2.5 I ran on my Pro Drag boat when they came off Dave Bush’s dyno

Needing a much richer mixture on the dyno makes sense to me, and is what someone else mentioned a while back on another thread.

Did you guys have a way to change the tune in the Merc A6 ECU? I didn’t even know that was possible

As you can see from the picture I posted, the main pot on my ACU was set at 12% rich. When I pulled the heads to change the pucks, the cylinders were drenched with fuel and the fuel wash mark across the top of the piston was pretty wide, so I figured it was getting a lot of fuel.

So I dialed the main pot back to 6% rich and the motor seemed to like that, even though it may still be a tad rich.

Then, to try get a reading on the plugs and pistons, I put a prop on it, cinched it down on the trailer and backed it into the water until it buried the foot end and warmed it up and then then made a WOT run and pulled the kill switch when it was under load at around 8000rpm.

Below is a picture of what one the pistons looked like (at 6% rich). This was taken with a borescope a few minutes after I shut it down at WOT:

The pistons all showed a similar fuel wash and the plugs were all soaked with fuel.

BUT, I found out after that the the Denso 27 plugs I was running might’ve been fouled (or I fouled them from loading the motor up too much?). But based on the timing mark on the ground straps, it looked like those plugs were running too cool. So I changed them out to 24s (which look physically identical to the 27s) and it ran better with those.

BTW: I only run Sunoco 112 octane (or sometimes VP C-12) and the Merc red oil mixed at 32:1. I’m running 17cc heads with ~215psi cranking compression.

[patchesII]

A lot of racers have the Mercury computer program to access the 849849 ecu’s and change anything we wanted in there. I sold my laptop with the program and all my fuel maps when I got out of racing after my crash.

Your method of doing a plug chop on the trailer with the prop buried is still gonna have you on the rich side. Nothing wrong with that, these engines have a pretty good window on the rich side to make power, it’s even bigger on methanol

[rjdubiel]

Put that dial to zero (or 3-4%) and make a trailer pull. You will not be on the gas long enough to hurt anything even if it is lean, but that will show you that you are really rich right now and still will be at the leaner setting. I am rich but finally getting some carbon on the piston top. Still a huge fuel wash on the intake side. I bet you get closer to where you will be happy. As you and others stated, being on the trailer is much more of a load than on the water, requiring more fuel on the trailer. If rich on the trailer, you will be safe on the water.

Maybe try an NGK BR9HS plug? I doubt you will notice any different but maybe then you can run a less expensive plug.

[CI STV]

Put that dial to zero (or 3-4%) and make a trailer pull. You will not be on the gas long enough to hurt anything even if it is lean, but that will show you that you are really rich right now and still will be at the leaner setting. I am rich but finally getting some carbon on the piston top. Still a huge fuel wash on the intake side. I bet you get closer to where you will be happy. As you and others stated, being on the trailer is much more of a load than on the water, requiring more fuel on the trailer. If rich on the trailer, you will be safe on the water.

Maybe try an NGK BR9HS plug? I doubt you will notice any different but maybe then you can run a less expensive plug.

Thanks. I think I’m going to dial it back by 2-3% and see what that does. I’m going to increase the offset a little on the bottom cylinders like Eric advised as well.
BTW: I get my Denso Iridium plugs from Rockauto for like $6.50 each. Hard to beat that price even on a regular NGK plug. I’m a big believer in Iridium fine wire plugs.

[CI STV]

A lot of racers have the Mercury computer program to access the 849849 ecu’s and change anything we wanted in there. I sold my laptop with the program and all my fuel maps when I got out of racing after my crash.

Your method of doing a plug chop on the trailer with the prop buried is still gonna have you on the rich side. Nothing wrong with that, these engines have a pretty good window on the rich side to make power, it’s even bigger on methanol

I read somewhere about your crash. It was due to a loose clamp on your cable steering, right? That really sucks man. After I read that, I’ve been checking mine every time before I launch my boat.

[patchesII]

I read somewhere about your crash. It was due to a loose clamp on your cable steering, right? That really sucks man. After I read that, I’ve been checking mine every time before I launch my boat.

That’s correct. I talk about it in detail in these videos. Warning! I learned from these videos that I like the word “killer” and I sound like cornbread. Lol

https://youtu.be/XAgEbU1OARU?si=zSZlDdnRz0F2CJrn

https://youtu.be/jE8wlF2Q2KE?si=8IXC8HBOStyXDe5m