Air fuel ratio for direct drive

keys2pines · Post by **keys2pines** » Sat Mar 23, 2019 10:17 am

I come from a drag racing background so I decided to put a wideband setup on my boat to fine tune. Once warmed up, my AFR is 13.6 from idle all the way through WOT (2800rpm). I'm thinking I can go leaner on idle and cruise, maybe 14.0-14.7, but I'm worried about my WOT. I'm used to being around 12.5-13 naturally aspirated WOT. My question is, is it safe to run this type of AFR WOT since I'm only turning 2800 rpm, or should I get more fuel in it to protect the engine under the high load? I'm thinking I need more fuel on top end, but new to airboat tuning.

CarMotorBarge · Post by **CarMotorBarge** » Sun Mar 24, 2019 7:35 am

I would recommend experimenting with the AFR and see how the engine responds. Also make sure you read the plugs while doing this looking for signs of detonation. Going a little richer at 2800 is definitely safer and might help you turn a little more prop.

SWAMPHUNTER45 · Post by **SWAMPHUNTER45** » Mon Mar 25, 2019 8:09 am

CarMotorBarge wrote:I would recommend experimenting with the AFR and see how the engine responds. Also make sure you read the plugs while doing this looking for signs of detonation. Going a little richer at 2800 is definitely safer and might help you turn a little more prop.

Agree

What carb you running and is the AFR stable at 2800 or does it jump around?

John Fenner · Post by **John Fenner** » Mon Mar 25, 2019 10:02 am

Knowing what powerplant you are running will help, along with carb size and your total advance, what heads, intake etc.

John Fenner · Post by **John Fenner** » Mon Mar 25, 2019 10:08 am

Ok, by your signature line it is a 383, I would hope it has only a 450 cm with rear metering plate with 72 jets, 68 primaries, if larger carb you aren't getting the low end snap you deserve.
Cam profile?
Heads?

keys2pines · Post by **keys2pines** » Sat Mar 30, 2019 12:25 pm

SWAMPHUNTER45 wrote:
CarMotorBarge wrote:I would recommend experimenting with the AFR and see how the engine responds. Also make sure you read the plugs while doing this looking for signs of detonation. Going a little richer at 2800 is definitely safer and might help you turn a little more prop.
Agree

What carb you running and is the AFR stable at 2800 or does it jump around?

Sorry for the late response, I've been without internet for a week. It's a Holley 450cfm with mechanical secondary. The AFR is dead stable.

John Fenner wrote:Ok, by your signature line it is a 383, I would hope it has only a 450 cm with rear metering plate with 72 jets, 68 primaries, if larger carb you aren't getting the low end snap you deserve.
Cam profile?
Heads?

Yea, it's a Holley 450cfm. I don't know anything about the cam, and the heads are Edelbrock E-street aluminum. I'm not sure what jets are in it, as I didn't want to take it apart unless necessary. The previous owner found me on Facebook after I posted the video running the new prop, so I just sent him a message to get the engine details.

John Fenner · Post by **John Fenner** » Sun Mar 31, 2019 7:25 am

Look to see if it has a secondary metering plate, it will look same as the primary bowl, plate to air horn body, if secondary bowl is right up to air horn body then there is no metering plate conversion.
Does it idle smooth or have a cadence as a performance cam would idle?
If it has a cadence, I'd suggest an RV cam or better yet a mellings CS-711 flat tappet cam, a set of 882 gm heads and a stock gm aluminum 4 bbl intake modified to fit the Holley. You will like the snap.

keys2pines · Post by **keys2pines** » Sun Mar 31, 2019 10:43 am

John Fenner wrote:Look to see if it has a secondary metering plate, it will look same as the primary bowl, plate to air horn body, if secondary bowl is right up to air horn body then there is no metering plate conversion.
Does it idle smooth or have a cadence as a performance cam would idle?
If it has a cadence, I'd suggest an RV cam or better yet a mellings CS-711 flat tappet cam, a set of 882 gm heads and a stock gm aluminum 4 bbl intake modified to fit the Holley. You will like the snap.

This is the carb. https://www.jegs.com/i/Holley/510/0-9776/10002/-1 I'm new to carbs, but I think I have the basics down. It idles smooth, and definitely doesn't chop like a large duration low LSA cam. I forgot to answer your timing question, it's 18 at idle, 36 degrees WOT. I definitely think the setup is very good, I just want to make sure it's safe. The previous owner told me he took the 5-blade razor off before he sold the boat and put it on a O-540 without adjusting the pitch and it was perfect.

John Fenner · Post by **John Fenner** » Mon Apr 01, 2019 9:00 am

Get an air fuel ratio gauge, weld a bung in a header collector, and go that route, you might just gain a bit of power, and fuel efficiency once fine tuned.

keys2pines · Post by **keys2pines** » Mon Apr 01, 2019 10:48 am

John Fenner wrote:Get an air fuel ratio gauge, weld a bung in a header collector, and go that route, you might just gain a bit of power, and fuel efficiency once fine tuned.

I did that already, I'm getting 13.6 AFR from idle to WOT. I was asking if that was a safe number at WOT, I'm used to being 12.5-13 at WOT when dealing with race cars, but not at such a low rpm as with a direct drive. I was thinking I can lean the cruise out a little, and richen up the WOT a little.

SWAMPHUNTER45 · Post by **SWAMPHUNTER45** » Mon Apr 01, 2019 5:48 pm

How do the plugs look?

keys2pines · Post by **keys2pines** » Mon Apr 01, 2019 11:14 pm

SWAMPHUNTER45 wrote:How do the plugs look?

Never checked them, figured the wideband was more accurate.

SWAMPHUNTER45 · Post by **SWAMPHUNTER45** » Mon Apr 01, 2019 11:43 pm

Well my advice would be to read the plugs.

Mr. Branch who in my humble opinion is the King of Direct Drive Auto engines would say if your concerned about your full throttle fuel ratio run the boat hard and pull up on some dry and run hard again. Then from wide open let it go to idle and immediately turn off the engine and let it cool.

Then read the plugs.

He will also wipe out the exhaust outlets and then read them after a few hard runs.

Old school

keys2pines · Post by **keys2pines** » Thu Apr 11, 2019 5:24 pm

SWAMPHUNTER45 wrote:Well my advice would be to read the plugs.

Mr. Branch who in my humble opinion is the King of Direct Drive Auto engines would say if your concerned about your full throttle fuel ratio run the boat hard and pull up on some dry and run hard again. Then from wide open let it go to idle and immediately turn off the engine and let it cool.

Then read the plugs.

He will also wipe out the exhaust outlets and then read them after a few hard runs.

Old school

I ran the engine pretty hard (2400rpm 34mph into a headwind), only idled a minute or so pulling into the ramp before I shut down. The first 4 pictures are of cylinder number 1. 7 of the plugs look like this, the last 3 pictures are of cylinder number 7. They all seem to have little white specs. I'm not extremely confident in my plug reading abilities, but it seems like it's lean.

Prototype · Post by **Prototype** » Thu Apr 11, 2019 10:15 pm

Check your fire on these. That's a broad range of plug identifiers and could be a spark jump on the latter pictures.
Unknown on a DD but i'm running 14.2 to 14.5 depending on climate overall. Haven't got into the low rpm factors so maybe new ground.
I did have a set of D1 champions last 12 years if that's worth anything?

CarMotorBarge · Post by **CarMotorBarge** » Fri Apr 12, 2019 6:32 am

keys2pines wrote:
SWAMPHUNTER45 wrote:Well my advice would be to read the plugs.

Mr. Branch who in my humble opinion is the King of Direct Drive Auto engines would say if your concerned about your full throttle fuel ratio run the boat hard and pull up on some dry and run hard again. Then from wide open let it go to idle and immediately turn off the engine and let it cool.

Then read the plugs.

He will also wipe out the exhaust outlets and then read them after a few hard runs.

Old school
I ran the engine pretty hard (2400rpm 34mph into a headwind), only idled a minute or so pulling into the ramp before I shut down. The first 4 pictures are of cylinder number 1. 7 of the plugs look like this, the last 3 pictures are of cylinder number 7. They all seem to have little white specs. I'm not extremely confident in my plug reading abilities, but it seems like it's lean.

The coloring on the insulator tip only shows the AFR at idle. You have to use a magnify glass and look inside the plug to determine the AFR at 2400 RPMs. Also how many hours were on these plugs? Is there anyway you can run the boat on the trailer and look at the plugs? This will create a more controlled environment to analyze the plugs.

keys2pines · Post by **keys2pines** » Fri Apr 12, 2019 7:27 am

CarMotorBarge wrote: The coloring on the insulator tip only shows the AFR at idle. You have to use a magnify glass and look inside the plug to determine the AFR at 2400 RPMs. Also how many hours were on these plugs? Is there anyway you can run the boat on the trailer and look at the plugs? This will create a more controlled environment to analyze the plugs.

Yea I was doing a lot of research on plug reading after I posted this. I have no idea on the hours of the plugs I'm going to buy new plugs today, run it on the trailer WOT and shut down. I will post the results later. Thanks!

keys2pines · Post by **keys2pines** » Fri Apr 12, 2019 7:40 am

Prototype wrote:Check your fire on these. That's a broad range of plug identifiers and could be a spark jump on the latter pictures.
Unknown on a DD but i'm running 14.2 to 14.5 depending on climate overall. Haven't got into the low rpm factors so maybe new ground.
I did have a set of D1 champions last 12 years if that's worth anything?

I just replaced the plug wires, a lot of them were cracking, but these plugs have been used for at least 30 hours by me, and no idea on previous owner. Getting new plugs today to test.

keys2pines · Post by **keys2pines** » Fri Apr 12, 2019 12:47 pm

These are brand new plugs, I changed them after I let the engine warm up. Ran it up to max 2600rpm on the trailer for 10-15 seconds then shut it off. Too lean?

CarMotorBarge · Post by **CarMotorBarge** » Fri Apr 12, 2019 3:33 pm

keys2pines wrote:These are brand new plugs, I changed them after I let the engine warm up. Ran it up to max 2600rpm on the trailer for 10-15 seconds then shut it off. Too lean?

You need to look inside of the plug using a magnify glass to determine if it is too lean. This is the only way to see the color at the base of the insulator. Running at 2600 burns off most of the color on the insulator tip that you can see without a magnify glass. Google reading spark plugs and you will see what I am talking about.

Post by **kwanjangnihm** » Sat Apr 13, 2019 6:51 am

A spark plug magnifier is an inexpensive tool to have at the track. They are lighted and have a typical 10x magnification that allows you to look closely for the slightest bit of coloring on the insulator and to easily inspect heat patterns.

https://www.enginelabs.com/engine-tech/ ... selection/

keys2pines · Post by **keys2pines** » Sat Apr 13, 2019 12:49 pm

kwanjangnihm wrote:A spark plug magnifier is an inexpensive tool to have at the track. They are lighted and have a typical 10x magnification that allows you to look closely for the slightest bit of coloring on the insulator and to easily inspect heat patterns.

https://www.enginelabs.com/engine-tech/ ... selection/

Got it! Thanks!

OneBFC · Post by **OneBFC** » Sat Apr 13, 2019 1:40 pm

Heat range appears good. Can tell by the color change on the ground strap. Once you get used to reading plugs you will gain a lot of confidence in tuning your engine.

I think you are on the right track.

CarMotorBarge · Post by **CarMotorBarge** » Sat Apr 13, 2019 3:18 pm

keys2pines wrote:
kwanjangnihm wrote:A spark plug magnifier is an inexpensive tool to have at the track. They are lighted and have a typical 10x magnification that allows you to look closely for the slightest bit of coloring on the insulator and to easily inspect heat patterns.

https://www.enginelabs.com/engine-tech/ ... selection/
Got it! Thanks!

http://www.jetsrus.com/FAQs/FAQ_spark_plugs.htm

Here is another link. You need to look at the picture that shows where you read different parts on the insulator to determine rich/lean at idle, mid range, and WOT.

You need a magnify glass to look inside the threads to read the rich/lean on the insulator for WOT or you need to chop a couple of plugs. The white insulator in the pictures above gives you no info about rich/lean at WOT.

keys2pines · Post by **keys2pines** » Wed Apr 17, 2019 6:44 pm

OneBFC wrote:Heat range appears good. Can tell by the color change on the ground strap. Once you get used to reading plugs you will gain a lot of confidence in tuning your engine.

I think you are on the right track.

Thanks! I was confident when I had my turbo camaro, airboat has me second guessing myself because of the low rpm. After doing more reading, the AFR at WOT is just way too lean because of the load on the engine. The AFR should be 12.3-12.8 or 13 max under full load, which at 3000rpm I'm at full load. I was emailing holley to see about tuning this carb, and basically I'm stuck to changing main jets only. The rear metering plate is not able to be changed, and can't be converted to a metering block. This carb was meant to be on a two-carb setup, not used alone. If I change the main jet, then I'm going to be richer all around, and my mpg is going to go down. I honestly think I'm going to convert to EFI and be done with it. I can play with the AFR instantly and see how the boat responds and I won't have to second guess myseslf.

CarMotorBarge wrote: http://www.jetsrus.com/FAQs/FAQ_spark_plugs.htm

Here is another link. You need to look at the picture that shows where you read different parts on the insulator to determine rich/lean at idle, mid range, and WOT.

You need a magnify glass to look inside the threads to read the rich/lean on the insulator for WOT or you need to chop a couple of plugs. The white insulator in the pictures above gives you no info about rich/lean at WOT.

Thanks, I ran across another similar article when I was reading. I'll still end up reading the plugs again, but I'm going to follow the wideband and see what happens.