idle relief holes...

[Phil Cartier]

Today i just remove my cylinder heads on my Evinrude XP300 1988. They're going to be shaved at 48cc this week...My concern is about the idle relief holes, how to plug them correctly...I think to drill and tap and install 1/4-20 "set screw" to plug them. Is it correct to do that? Somebody have a better idea? The holes are drill at 450 and easy to reach, but is that correct?

A picture for you guys:


http://i864.photobucket.com/albums/ab208/PhilCartier/IMGP0423_zps7c63bf46.jpg

[davemvegas]

drill and tap. i use allen head set screws with locktite. i get set screws at lowes i dont recall the size but it is a fine thread metric that is in between 1/4 and 5/16. i do not drill all the way thru so the set screw can bottom out. there is not a lot of room for error. not deep enough and set screw will catch rings and a little deeper it will drill thru and you have to rely on locktite to hold set screw. i feel better when it can be bottomed out and tighten good.

[phil blomquist]

Id fill them with marine tex use acetone to clean it up smooth no shavings to worry about

[NosBoss]

Id fill them with marine tex use acetone to clean it up smooth no shavings to worry about

I agree.

[frederick55]

Tap them, and then use marine tex. The threads will hold the epoxy better.

[NosBoss]

Wait a second! That's an 86-87 Bridgeport block. Why does it have idle relief holes???

[Phil Cartier]

Wait a second! That's an 86-87 Bridgeport block. Why does it have idle relief holes???

It's a 1988 4.0L, first year with 4.0L instead of the 3.6L...

[Phil Cartier]

Ok, thanks guys for the advises...:thumbsup:

[Phil Cartier]

You guys who haved plug those holes do you see a difference when you start the the engine? Is it harder to crank the engine? Is the idle become very rought after that? I'd like to know what kind of difference i'm supposed to see...

By the way, pardon my bad english...I'm a frenchy from Quebec...:D

[phil blomquist]

Maybe a little on the start, but idles fine ,The main thing would be to jet up at least 2 sizes on the mains you should gain about 10 psi on compression filling idle reliefs plus you mentioned shaving the heads so you might want to retard your timing 2 degrees to be safe

[davemvegas]

You guys who haved plug those holes do you see a difference when you start the the engine? Is it harder to crank the engine? Is the idle become very rought after that? I'd like to know what kind of difference i'm supposed to see...

By the way, pardon my bad english...I'm a frenchy from Quebec...:D

i have done 4 motors in the last 6 months all were v6 motors. no change in starting hot or cold. no change in idle rpm or smoothness. noticeable takeoff and midrange power increase.but did not gain any top speed mph. but i feel like the increase in low and mid range is well worth the little time and cost to plug them.

yon need to start with the basics. check compression and spark on all cyls. if good then go to fuel system.

[Phil Cartier]

i have done 4 motors in the last 6 months all were v6 motors. no change in starting hot or cold. no change in idle rpm or smoothness. noticeable takeoff and midrange power increase.but did not gain any top speed mph. but i feel like the increase in low and mid range is well worth the little time and cost to plug them.

yon need to start with the basics. check compression and spark on all cyls. if good then go to fuel system.

Thanks Dave!!!

[Phil Cartier]

This afternoon i just mesure my cylinders heads and i was surprise a little bit...The heads are already been shaved to 48cc!!! But the question i have...With the heads already shaved but the idle relief holes not plugged, could this make no difference in the compression? for the moment i've got 110-112 psi on each cylinder. I already heard if you shave the heads and don't plug the relief holes, the compression will not change...In my case i thinks i would have to plug de relief hole and the job will be done...
I take few pics to show you the cylinder heads with 48cc of fluids. The fluid came flush to the edge...

http://i864.photobucket.com/albums/ab208/PhilCartier/IMGP0424_zpsc3fa033b.jpg
http://i864.photobucket.com/albums/ab208/PhilCartier/IMGP0425_zps539b2971.jpg

[davemvegas]

i have cut heads and not plugged idle relief holes and it does gain compression. on a v6 plugging reliefs will gain 10 to 15 psi. cutting heads .050 and not plugging reliefs will also gain about the same. the difference is 115 psi on motor with reliefs plugged will not gain anymore psi as rpms increase. a 115 psi motor with reliefs open could be 125 or a little more at higher rpms. the reliefs do as the are named. at idle and up to about 3500 rpm compression escapes out relief hole. by about 4000 rpm and up piston speed is fast enough that little compression as time to escape.

[Phil Cartier]

i have cut heads and not plugged idle relief holes and it does gain compression. on a v6 plugging reliefs will gain 10 to 15 psi. cutting heads .050 and not plugging reliefs will also gain about the same. the difference is 115 psi on motor with reliefs plugged will not gain anymore psi as rpms increase. a 115 psi motor with reliefs open could be 125 or a little more at higher rpms. the reliefs do as the are named. at idle and up to about 3500 rpm compression escapes out relief hole. by about 4000 rpm and up piston speed is fast enough that little compression as time to escape.

Do you take the compression when the engine is cold or hot? I always take it when then engine is cold...If the compression is 110-112 psi (standard compression for 4.0L V8) when the engine is cold with relief open, what can i expect for compression with relief plugged and a warm motor? 120-125 psi...?

[davemvegas]

i have only done v6 motors. i run mine on hose a few mins before i do compression test.

[Phil Cartier]

i have only done v6 motors. i run mine on hose a few mins before i do compression test.

Ok...I will do like you this spring with relief plugged...Thanks for the infos...