Johnson 40 hp mods

[Kevodaniel]

I have a 99 40 hp johnson converting it to a 50 if I put a 50 hp head on it will it raise or lower the compression or do I need to have the head milled to sst 45 spec what's y'all opinions thanks for you help

[LittleCharger]

I have a 99 40 hp johnson converting it to a 50 if I put a 50 hp head on it will it raise or lower the compression or do I need to have the head milled to sst 45 spec what's y'all opinions thanks for you help

Look at post #60 of this thread

http://www.boatracingfacts.com/forums/showthread.php?10179-Set-Up-Help-11-Tunnel&p=98945&highlight=#post98945

[Kevodaniel]

Look at post #60 of this thread

http://www.boatracingfacts.com/forums/showthread.php?10179-Set-Up-Help-11-Tunnel&p=98945&highlight=#post98945

Is there any way to adjust the timming accurately I'm assuming it would be better to mill the head to sst 45 spec thanks for the help

[LittleCharger]

Is there any way to adjust the timming accurately I'm assuming it would be better to mill the head to sst 45 spec thanks for the help

Timing light for timing is the only way

might as well go to 45 spec so long as milling a 50hp head

[Kevodaniel]

Ok do you know sst 45 spec

[Kevodaniel]

What's sst45 spec

[LittleCharger]

What's sst45 spec

http://www.apba.org/sites/all/files/documents/2013_SST45_TECHNICAL_SPECIFICATION041013.pdf

[Kevodaniel]

Thanks for your help I'm trying to get a little more speed out of it I'm running 41 mph on a 16/48 welbuilt mod v aluminum boat I'm trying to get 45 mph out of it gonna have the head milled and lighten the flywheel I'm on the rev limiter with 11 3/4x19p prop I have 4in of set back off the transom and raised 6in off the transom just trying to get the most out of a twin without porting and balancing the internals anything else that I could improve on I'm wanting to keep the rev limiter till I decide to port and balance it

[LittleCharger]

Thanks for your help I'm trying to get a little more speed out of it I'm running 41 mph on a 16/48 welbuilt mod v aluminum boat I'm trying to get 45 mph out of it gonna have the head milled and lighten the flywheel I'm on the rev limiter with 11 3/4x19p prop I have 4in of set back off the transom and raised 6in off the transom just trying to get the most out of a twin without porting and balancing the internals anything else that I could improve on I'm wanting to keep the rev limiter till I decide to port and balance it

2 banger balancing waste of money, lightening flywheel not worth the money for your application unless you like the look, build your motor to the 45 specs and that will get you a strong motor, alot of times the ports heights are within spec and will be good enough for your application.

Change out the powerpack and get a powerpack without a limiter, we spin ours over 7K without issue all the time.... no porting or balancing your not gonna hurt the motor

Before spending to much money on the motor make sure you have exhausted all the set up and prop variables, there is always more mph in set up and props then building more power. It takes alot of hp increases to gain a mph.

If you really want to hit 45 it might be easier to just move up to the 3 cylinder.

Cheers,

[Kevodaniel]

I'm runnin 150 psi compression with a 40hp head and I'm putting a 50 hp head on it if I have it milled to 45 sst spec will I be running too much compression

[LittleCharger]

I'm runnin 150 psi compression with a 40hp head and I'm putting a 50 hp head on it if I have it milled to 45 sst spec will I be running too much compression

Did you deck your block, if so to what spec.

Compression won't be a problem, you may have to upgrade to a higher octane fuel

[Kevodaniel]

I did not deck the block I was told with my motor having 150psi if I had the head milled it would have too much compression I can not find the spec on the 50 hp head to compare 45 sst head too I don't want to run over 93 pump gas

[LittleCharger]

I did not deck the block I was told with my motor having 150psi if I had the head milled it would have too much compression I can not find the spec on the 50 hp head to compare 45 sst head too I don't want to run over 93 pump gas

I guess one needs to define "too much compression"...these will run with 200 psi so I assume your definition is of "too much compression" is based on the fuel you are willing to run.

I'm surprised the compression with the 40 head is that high if your block is not decked.

If you have the 50 head measure the pocket depth versus the sst45 spec to get a rough idea of the difference.