Rev limiter & heads

[redman12]

I'm runnung a 95 2003 hull with a 225 super mag. 25 tempist prop 1/4
below the pad heavy load ( two men tackel ect) running 80 gps at about
6400 rpm my question is on outboard how do you tell when they are hitting the limiter the other question is how much in thousants can you shave the stock heads and run pump gas with no problems?

Thanks in advance for any and all responses.


Redman

 

[John Richied]

With a 225 ProMax/Super Magnum (same engine) it calls for 91-92 octane with the stock heads, per Mercury.

However if you have 91-92 octane you can have the heads shaved to 35 cc’s and be safe on 91-92 octane. If you have 92-93 octane then 34 cc is the most you want to go and not have to splash race fuel. This will bring the compression from 135ish compression to 145-150 lbs. depending on what head gaskets you use.

You can buy head gaskets in three different thickness .075mm, 1.0mm and 1.25mm. I prefer the 1mm-head gaskets.

When your engine is hitting the rev limiter you will feel and hear a surging. What is happening is the engine is going to full rich.

I doubt you are hitting your rev limiter at 6400, it should be 6750 Rpm’s…
Oh yeah, if you are going to have your heads cced, Jay Smith (JSRE) does a great job.

 

[chad202]

On 1999 promax, I never felt the limiter. I turned it 7100. Now, I'm sure it was dumping the fuel and I just didn't feel it. We have 93oct and I had Jay shave mine to 34cc(33cc on my 260) and my promax compression was 140 across the board. Shaved heads on a motor is awesome. JMO, have the limiter raised, bump up compression, slap a 25 B&B trophy on there and go fishing.

 

[redman12]

Thanks John for the reply, if I just change the gasket to a thinner one what would this give me ond which one do I use? enjoy reading all the post and it seems that you may know what you are talking aboute>>

 

[hack02]

Seems like Jay Smith posted about this once. I think for every ten thousands off equals .7cc or something like that. Which would mean thirty thousands would be 2.1cc's so if you did that it would go from lets say 37cc's to 34.9cc's. And that would be approximate without actually ccing the head, which should be done. Don't go on my memory though. Probably the best way would be to send them to Jay or someone that does this type of thing. Some of us are do it yourselfers though. I'm guilty.

 

[fishnfireman]

There are some who will dispute this however, I have done it and talked to several more who have also.

With the older promax's and my 280 bass------I could never feel anything. very seldom could you tell anything was happening......it would just go to 6700-6800 on the promax and that's as far as it would go.

Several times when conditions were right-- a light load and a big eared prop..It only did it with chopper or cleaver style props on my rig...it would turn up to 7000 and even 7100.. Some might say it was a bad tack. But the speeds would come up accordingly.
After talking to others including Darris who have seen this.
It is my opinion-- that even tho it was dumping fuel, which most times will limit your RPMs (and burn a lot of fuel) --- when everything is clicking just right it will go ahead and turn up some more Rss


Jay can and will do you a great job with your heads.. He is fast and priced right. !-!

 

[brotherxb03]

I have a 98 model 2003 with a 2.5 carb with milled promax heads,stacks,blueprinted exaust,bosen reeds and with a fishing olad by myself it will run my 25 tempast to 7 grand quick in cool weather and that ain't streched out. That's why I run a 27.

 

[redman12]

the motor is bone stock. it don't seem like it has ever run like I read on these post. I hardly ever run wide open, I'm moving on toward those senior citz. discounts. know what I mean? but I have a young son 35 or so that dont care to air it out. have the sporsmaster at J.C."s getting it woked now and hope to go to hygraulic stirring soon

 

[John Richied]

When my 1996 225 ProMax was bone stock I could feel it hit the rev limiter when I had a 30 ET on … a soft bump, bump or a 25 Trophy. With the 25 pitched Trophy if I remember right it would only run around 80-mph top speed and when it hit the rev limiter I kid you not it felt like you hit a wall…

Give Jay Smith a call on the heads, he can tell you everything you need to know. Just let him know what the highest octane you have in your area is so there is a margin for low quality gas.

 

[JR]

I talked with the guys at Diamond Marine last spring about bumping up my compression/limiter and they said I should not do it without adding more fuel... That is why I was interested in the ACU.
They were very helpful.
JR

 

[redman12]

thanks all. That's kind of what I have been thinking about. Have been there with the hot rods, had 468 big blouck 67 SS chevelle more compression most of the times means more air,more gas, more exaust,more trouble, may just run it and enjoy it. thanks again for all the input!! I am thinking aboute one of the drag4 props anyone running one on 2003 with a 225 what pitch if so??

 

[redman12]

ok, here I go again. just got my boat back from the shop having my motor checked out. everything ckecked out good by a good certified merc. mech. seems like my problem on the rpms is that everything I see says that max rpms for this motor is 6200-6500 r's (98 225 supermag) that is what the tag on the mid section says. I thought it was 6750 where did we all come up with this (6750) from. Has A32 box is this where the difference comes in? If so what box could Irun and be on the safe side?