1:2.0 gear case vs. 1:1.187

[Malcolm2010]

I have a carbureted 1982 Mercury outboard 150hp v6. It ran great with a 23 pitch prop. It ran about 6000 with the stock 1:2.0 gear case. Recently my lower end had a problem. Some parts couldn't be purchased anymore (drive shaft). While I was working on this project. I decided to mill the heads. Stock pressure was 125 all cylinders. The pressure went to 140. I added a Bobs Tuner, Boysen Reeds. I set the timing to 23. I took it to the lake yesterday and opened the jets from .064 (stock) to .070. Ran good but the RPM was down to 5000. I went to the shop today where the old parts are and figured out the new gear case is 1:1.87 not 1:2.0 I understand that makes the prop move slightly faster than the 1:2.0 gear set. Which is why my RPM is down. My question is: Will a lower pitch prop on the 1:187 gear case give me the same performance as the 1:2.0 gear case with a larger pitch. In my mind it could be balanced. I was wondering if anyone could give me some advise. The boat ran almost the exact same speed with the new setup and lower RPM on the 23 prop. I know I will have more adjusting to do. I was hoping to go a little faster than before I made the changes. 45 MPH.. I hope I can figure this out with your help.

[TEXAS20225]

gear ratios all the old 150's had a 2:1 gearing only the 200 had the 1:87 if you wound up with that it would be slower out of the hole but would not reduce your rpms by 1000 your needing a pin style driveshaft??? it would invloved chaging the whole gear-set to get the 1:87 ratio

[wired247]

You are probably just running too rich. Thats a lot of jetting change for not having checked your mixture.

[Malcolm2010]

Thank you for your reply. I have an Air Fuel gage that I pulled out of my car. With the jet change I'm running around 13:8 AFR and My EGT shows about 820 degrees at full throttle. I modified the plate between the power head and the mid section to accept the gages. The jet change is because of the modifications to the motor ie compression, exhaust tuner and reeds.

[Malcolm2010]

Yes it did have the pin drive shaft originally. I purchased a complete lower end from one of the members of this forum. It is a 200 gear case with the 1:1.875. I'm also wondering if the original tach was not reading correctly. The original tach was maxed out at 6000. I'm taking a tach that reads off the plug wire out to confirm the accuracy of the new tach. 1000 RPM does sound like allot.

[wired247]

Thank you for your reply. I have an Air Fuel gage that I pulled out of my car. With the jet change I'm running around 13:8 AFR and My EGT shows about 820 degrees at full throttle. I modified the plate between the power head and the mid section to accept the gages. The jet change is because of the modifications to the motor ie compression, exhaust tuner and reeds.

820 is pig rich. You're AF readings with a lambda sensor are going to be meaningless unless its tuned for it and even then its a few minute run until its fouled in a 2 stroke.

[Malcolm2010]

You miss understood what I said. The air fuel ratio is 13.8..... The exahust temp is 820 degrees F. The AFR Gage is an Inovate. I contacted the Tech Support at Innovate. They said the sensor wouldn't last as long in the 2 stroke but it should be good for a while. Seems to be working. I started with a set of .074 jets. The AFR was about 12.5. The .070 brought it back to 13.8.

[wired247]

You miss understood what I said. The air fuel ratio is 13.8..... The exahust temp is 820 degrees F.


No. I didnt misunderstand you. 820 degrees EGT indicates a very rich mixture. Lambda O2 sensors don't work worth a flip on 2 strokes so that 13.8:1 number is meaningless.

Read the plugs and/or the piston top.

[Malcolm2010]

Thank you. I also put the .064 jets in (stock). It ran very poorly. What do you think the EGT should be reading? I thought 820 was pretty cold also. Do you have any recommendations on an AFR Gage that will work in a 2 stroke?

[wired247]

Try reading the plugs and piston tops and when you find a good insulator color and wash pattern on the pistons use that as a baseline for your EGT. You're probably going to be running best above 1100 degrees. How much timing? What sort of boat is this on?

[Malcolm2010]

23 is the timing. Its an 1982 18 foot Seaswirl with an open bow. I will check the plugs for sure. I will back the jets down .001 at a time to get that EGT up. I think I was over sized on the prop before (23"). I'm sure the extra ratio in the gear case makes this worse. I'm going to try a 19 and a 17 prop. I will confirm the tach accuracy first. I don't want to over rev. I was hoping after raising the compression, Changing the tuner and reeds. I might get a little more speed. Funny thing is the boat runs exactly the same speed as it did stock (gps) The boat speedo is surprisingly accurate.

[wired247]

Simi Valley huh. My son graduated Royal high. Where do you boat?

Thats too much prop for one thing. What carbs are you running? FWIW that pic in my signature was running 62 at 6800 with a 19 pitch prop, 2:1 lower and a 2.0/150.

[Dave Strong]

All things being the same other than the ratio change you only should have lost around 300rpm, that's why its best to only change one thing at a time.

Dave

[rev.ronnie]

Exhaust temps should not exceed 1250 degrees. Now, where you are getting your readings could make them really vary, so the advice to read piston tops and plugs is very sound.

[Malcolm2010]

Yes the guys at the shop gave me a 19 aluminum prop and a 17 SS. I would love to just run 55 MPH.. The carbs are the stock carbs that came on the boat. The s#6221144. If that helps. Yea.. :) I'm in Simi Valley.. I graduated Royal also in 1980. Simi is still a small place. I probably know your son. :) I've been taking the boat to Pyramid for the testing and my favorite spot is Lake Nacimento. Love that place. The fishing is great. I'm not a big fisherman. When I'm catching fish every 10 minutes. It gets me more interested.

[Malcolm2010]

Ok, That makes me feel there is a tach problem either with the old or the new tach. Nice boat.. Love your ending comment. So true. :)

[Malcolm2010]

I'm reading the temp right under the power head. There is a plate between the tuner and the power head. I can't get any closer. Thanks for the temp advise. I will keep slowly leaning it out to get the temps up. I will also keep a close eye on the plugs.

[wired247]

Yes the guys at the shop gave me a 19 aluminum prop and a 17 SS. I would love to just run 55 MPH.. The carbs are the stock carbs that came on the boat. The s#6221144. If that helps. Yea.. :) I'm in Simi Valley.. I graduated Royal also in 1980. Simi is still a small place. I probably know your son. :) I've been taking the boat to Pyramid for the testing and my favorite spot is Lake Nacimento. Love that place. The fishing is great. I'm not a big fisherman. When I'm catching fish every 10 minutes. It gets me more interested.

Ive spent a lot of time on Nacimiento. Choppier than hell out there.

[Wayne Cammidge]

21P prop at just over 6000 should give around 55. Should be doable
19"P"prop pushed to 6700 should give around 55.
If you get a good SS prop, you maybe able to raise the motor a little to get it to free up.

[6Killer]

Your compression increase only required 1 jet size up.(Been there done that, lots of times). The 2.0 does not make the torque of the 2.4 or 2.5's. (Make the torque with the gear not the motor) If you can trade the case for a 2.0 you will be much happier! The Changes you made if done on the same day, with the same lower are good for 2 to 3 increase in mph. (Again, been there done that, lots of times) The Boysens, dont do anything other than make it a little snappier out of the hole. Modify the reed cages to flow more air and then the boysens become of value. (if you modify the cages, add another size to the jet)

[Malcolm2010]

Are you thinking a 19 SS would work best on my application? I have a 1982 Seaswirl open bow. What brand of prop do you think? I notice the Mercury props are very expensive. There are all kinds of after market props at about half the price. I don't have a problem if the Mercury prop is worth it. I just cant imagine the after market companies are that much different.

[Malcolm2010]

Great info.. I'm thinking I have to run the fat jet because the prop is so big. I'm going with a 17 and a 19 next week. Anybody know if I can get the gaskets for the Jet fittings or do I have to make them? A couple jet changes and they get worn out.. I haven't heard about modifying the reed cages. What would be done to the reed cages to improve flow? Are there aftermarket reed cages? I was worried about the gear ratio. I'll see how it goes with the prop change. I just had this gear case torn apart, inspected and resealed. Its like new. There is a website that sells aftermarket gear cases http://www.obparts.com/. They sell gear cases for just under $900. I bought this gear case for $800 with the ride. What do you think of the aftermarket gear cases? Do you think I will get my money back on this gear case?

[6Killer]

Your giving up torque trying to twist that tall gear....

Look at the reed cage and then look at the reeds, use your head. They are best modified on a mill, but I have seen some hand cut.

[wired247]

Don't overthink this gear ratio thing. You are 7% off on the case ratio. Its not quite insignificant but its close. You make it up with propping. I have one of the aftermarket SEI gear cases. Actually Ive had a few in different motors over the years and have never had a problem other than where I dragged one through the mud once and broke the prop shaft and they replaced it for free AND gave me a new prop. Figure you'll get three years worth of service out of it and anything past the warranty is a bonus.


Ive had really good luck with the Solas Titan 4 props for all around sport boat duty . Take their pitch numbers with a grain of salt though. A 19 pitch goes well into the 60's which is physically impossible with a 2:1 case but GPS on still water doesnt lie. Ive had a 21 pitch Solas Titan 4 to 77 MPH with a 260 at 7000 which is also physically impossible.

Send your reed cases to Chris Carson and he can open them up for bigger reeds. Price is pretty good to or get yourself a set of late 2.5 4 petal rubberized reed cages. .

[Malcolm2010]

Thank you.. You've been extremely helpful.

[Dave Strong]

2.0L like 2.0: 1 gears, there is a reason they came from the factory that way. 2.4 and 2.5 most the time not as important, but some of them do work better with 2.0:1's some not much diff. They all pull harder with 2.0:1's a very few will get better top end. At least the ones we have tried.

Dave

[Malcolm2010]

Thank you.. I've investigated getting another lower end. They aren't that expensive. I'm going to try this and see what happens. Your insight is very important. Thank you again. The true fact is that my hull is probably close to maxed out. Love your boat. The reason I don't go that way is because I do like to fish and take a few people out skiing. I bet that thing moves.

[6Killer]

2.0L like 2.0: 1 gears, there is a reason they came from the factory

+1.....

[TEXAS20225]

DAVE X2 :thumbsup: 2.0 is a 2:1 gearcase motor all the hocus pocus is not going to be even close to being as good, 6killer knows a lil something about gear cases:eek: i went down to his place some years ago and he loaded me up a train load of emptys and so many loose gears and shafts it took me 3/4 years to figure out what they were all for :cheers: since then im not sure how many 100's of case i have built, coned, tricked out and of course blown :o

[Malcolm2010]

LOL Thanks... All of you guys are great..

[mrcrsr]

how did you install your 0xygen sensor? your egt is way off as said previously, and you can use the wideband on a 2stroke, the snowmobile guys do it all the time

[Malcolm2010]

There is a plate below the power head and above the tuner. I had my fabrication guy drill through the plate right into the exhaust port. We used 1/2 galvanized nipples from he hardware store. He welded an o2 bung on one and 1/8 pipe thread on the other. They were threaded into the ports. If you turn the plate upside down there is a void where the pipes traveled. The void was filled with epoxy. Making it almost look like one piece. No welding on the plate. I was afraid of warping it. The bungs are flush and look like they were put in by the factory. Yes. I will lean the motor out to get the EGT up. With the higher gear and the large prop. It was to much load. I've got a 2:1 gear case on the way. I'm hoping for better results. I felt having both gauges in the boat would give me the best information. My O2 gauge company says the o2 will work but with a much shorter life span. When it goes bad it will show an error code. I'm getting the understanding that the EGT is the best along with checking the plugs and pistons. Right now they are pretty wet. After I get the gear case installed. I will slowly lean it out to get the EGT temp up. Always better too rich than lean.

[Dave Strong]

Tune it with plug cuts and piston wash checks, then use the sensor as warning. Don't rely on the sensor to tune.

Dave

[Malcolm2010]

Tune it with plug cuts and piston wash checks, then use the sensor as warning. Don't rely on the sensor to tune.

Dave Can you explain what is piston wash? I can clearly see the piston through the spark plug hole. I know how to read spark plugs but what is plug cuts?

[Dave Strong]

Plug cut is reading the plug after a wide open run and shutting the motor off at wide open. Reading the piston at the same time with a small bore-pin light to see the carbon pattern on the piston. If you do a search you will find some good pics of what the piston should look like. Some one posted some good info not long ago.

Dave

[6Killer]

Telling people that they need to "read the plugs" or the pistons is one thing, tell them how so they can be successful.......

[Dave Strong]

http://www.screamandfly.com/attachment.php?attachmentid=283920&d=1380073117&thumb=1

Start here with the basics, but I think experience helps. I know I squeaked a few before I got it right. Stay safe and don't try to run on the edge and will spend less.

Dave

[Dave Strong]

http://www.screamandfly.com/showthread.php?273134-Good-info-on-tuning-plugs-jetting-piston-wash-etc&highlight=


OOPS, Try this.
Or this


http://www.screamandfly.com/showthread.php?274271-Piston-wash

Lots of great info on this site even pics of actual pistons, the search feature is a great thing.

Dave

[Malcolm2010]

Thank you. I never heard of it called Plug Cuts before.. I've done this in the past. Thanks...

[Malcolm2010]

LOL.. Thanks

[Malcolm2010]

That was great.. I understand. Thanks again.