educate me on port grinding 150 to 200+

[roadkill636]

What is a stock 2.4 200ports heights?

[bobthebuilder]

Porting is high enough but on a light boat like that it will probably work for you. I have been to chool at James Perry's... he taught me how to do it right... I learned once by doing too much and had no bottom end torque.. The engine would scream like 8500 rpm but bottom suffered bad.. I like the 1.575 exhaust cut to match the aluminum of the block and chamfered heavy on top.. transfers squared on top at 2.150 and fingers at 2.140 at top of bevel keeping same bevel angle .. also left the pro max style exhaust chest alone. Worked well on a bass boat.. On a much lighter boat looking for speed you are about correct.. But fingers slightly higher helps scavenge the cylinder as it gets the flow started out the exhaust port so the flow will follow it on out. Also on your block that height below the deck should be about right but did you see how the piston was even or below or sometimes slightly above the deck before you took it apart??? This is relative to the port timing. The timing is actually at what degree the port opens related to TDC of the piston.. In other words you can adjust the figures to match the piston tops not the deck..

[bobthebuilder]

Road Kill A 2.4 is usually around 1.600 exhaust but they vary some from one block to another. I can't remember the transfers but very close to the same as a 2.5 stock motor. I have several stock 2.4 blocks in my shop if you really need to know... I plan to build one this winter while things get slow.. I have been buried in machine work boring and honing fishing motors.

[roadkill636]

This is my first marine block that im porting and just courious as to what to expect with these measurements iv cut so far. Glad that im not tooooo high already.

[bobthebuilder]

Your exh. porting is high but that is a light boat... James has a lot more experience in doing those higher rpm engines. I do know it will not work well on a heavy bass boat.. Careful to not open the exhaust too much.. The exhaust gases escaping can pull fuel in behind it as it leaves... That is sort of how high ported engines work.. The exhaust work needs to correspond to the porting and other things done to it. If you had a 200 or 225 Pro Max block to copy the exhaust chest by I think that shoudl be about correct for you.

[wrechin2]

With a light hull you can go two ways. High ports and high rpms or conservative and build lots of torque. 3030 runs in corboat racing which I sponsor the 343 boat and I have a 2L engine in that class and it does not have real high porting 1.575 exhaust compared to the others in the class but runs very strong because it has a lot of torque and so far best finish last year is 2nd just behind 3030 but the next engine will be a different story though as it is on the other spectrum..lol we are gunning for ya Mike!!!


I have taken those engines and ported them to Bridgeport specs and change the front half and on light hull they are VERY impressive.


Just my experiences........

[wrechin2]

exhaust ports at 1.520 and transfers 2.120.?

What kind of pistons do you have? With that porting it will have to spin REAL high to make power and you may not like the results if you plan on using the old stock pistons you took out. From my experiences that engine will need to spin 8K++ to make its potential power. Just my thoughts......

[bobthebuilder]

Thanks for input James.. you are no doubt the man in porting... I built 15 Mercs this year and all but 2 were bone stock fishing motors.. Everyone is very happy but they go back the same as they were.. More fun to modify them and see how different they run.. And my new engine is strong and getting stronger.. Next thing and something I am not sure about is a prop for my boat.. Seems like I never get time to mess with my own boat. LOL... Thanks again James for teaching me what I have learned so far.

[bobthebuilder]

Road Kill you might should get top pinned pistons.. If you urn it 8K+ the side pins will come loose.. I have had them come out even at 6K but only in 2 engines out of like 50 builds.. Both of those were 2.4L engines and the old style Wiseco pistons which are much better now. Wiseco finally got it corrected. I normally just use Pro V 2500 series pistons in fishing motors.

[wrechin2]

]Thanks for input James.. you are no doubt the man in porting... I built 15 Mercs this year and all but 2 were bone stock fishing motors.. Everyone is very happy but they go back the same as they were.. More fun to modify them and see how different they run.. And my new engine is strong and getting stronger.. Next thing and something I am not sure about is a prop for my boat.. Seems like I never get time to mess with my own boat. LOL... Thanks again James for teaching me what I have learned so far.[/QUOTE]

Bob you are welcome. Here is somes pics of what I do to the fat block

http://www.screamandfly.com/showthre...3-Port-Heights

[wrechin2]

What is a stock 2.4 200ports heights?

Can't believe I over looked this... The best year (83) 200 had 1.600 exhaust, 2.150 on the transfer and boost, and 2.100 on the finger ports. After 85 I have measured them at 1.600 exhaust, 2.175 on transfers and boost, and 2.150 on finger ports. But mercury was never consistent...........

[canuckr]

Not to hijack, I will be doing some grinding on a similar motor, to put on a vector in the spring. I have done a few motorcycle/atv engines with great results.
Does someone have the port timing numbers expressed in terms of degrees of crank shaft rotation? (200 specs) I'm not an expert engine builder by any stretch, but measuring port heights based on deck height instead of port duration makes my head hurt.

If not can someone tell me if I am correct in assuming that these motors are supposed to have a 0 deck height? I have not had a chance to pull my motor apart yet.


Thanks for any help

[dwilfong]

I am getting ready to port my 240SJ block now that the liners are out. I have bin running some port height measurements in my program to get a feel for the timing #. Have found that if you use the top of the piston to calculate the timing that it is WAY low compared to other 2 strokes I have worked with. Now if you run the numbers using the rings as the reference instead of the piston top.
The numbers are spot on.
What I have found testing two stroke eng is that a 30DEG difference between the ex and transfer timing gives the best overall results.
This is the blow down time. the amount of time the ex pressure releases before the transfers open.

When moving the timings you should move both the same as to keep this reference of 30Deg separation.

Have spent some time talking with James on the phone about timings and he was very helpful with his experience with out board eng.
would love to here some more on what heights work with different set up so I can get a better feel for the timings involved.

What is the relation ship to ex height and how much you can remove from the ex chest?
How much is too much say on a 1200# boat set up.

[Umassot50]

Outboards as a rule have very low ports compared to other two stokes. Calculating the port opening height at the rings is not correct. It will give you artificially high port durations. You don't want that. The port opening height is from the top edge of the piston. There is some fudge factor due to port edge chamfer though. You are right most motors need at least 30 degrees of blow down time. Without an expansion chamber to scavenge the cylinder its even higher though. Even more important is blow down time area.

[dwilfong]

that makes sense that a piped eng will not need as much blow down as the pipes front cones do scavenge the cly.
I have taken chamfer into account when calculating the timings.
None of the stock port maps I have run come near to 30deg blow down. Thy all fall short.
I have seen on here some talking about a eye brow ex port.
Making the top of the ex port as wide as possible will give more timed area before the transfers open.
This is what a bridged port ex is all about. the bridge lets you widen the ex port and still support the rings.
The only other way to get more time area and keep the same timing is to stroke the eng.
I can also do a timed area calculation with the program I use.
I have two port maps that are posted on here a lot. I will run the timing # from piston top and ring as references and post them.