high compression??

[AdamB]

Hi, I purchased my used '85 21' Wellcraft 2 years ago. Previous owner said at the time of purchase it had approx 50 hrs on rebuilt chevy 350. It ran great.

Anyhow, 1/2 way thru this season, I installed a new MPFI intake manifold and now seem to have developed a blow-by oil leak problem.

I at first thought maybe the added hp may have done something to piston rings or???? Anyhow checked the compression and got higher than normal (I think) #'s

1= 165, 2= 155, 3=165, 4=160, 5=160, 6=170, 7=160, 8=160.

Now I know about the 30% difference and I am far better than that. However this link says approx 150 psi is normal or is that just example?

Basically since I don't know what the previous owner did to the heads or??? Maybe my compression is too high? I do run premium gas and don't get knock but wtf?

www.boatfix.com/merc/Bullet/97/97_25.pdf

 

[bruceb58]

Re: high compression??

Those numbers sound fine.

How many compression strokes did you do your test
with?

Please explain what you mean by a blow by oil leak. Do you mean that you have excessive crankcase pressure? If so, do your rocker covers have vent hoses still that go up to the spark arrestor?

 

[AdamB]

Re: high compression??

I did the test until the needle stopped moving. Maybe between 4-6 strokes?

Yeah, I get leaking oil out the exhaust side of valve cover, and out the starboard side vent hose between valve cover and spark arrestor (it pushes oil all the way out to the throttle body)

 

[bruceb58]

Re: high compression??

When you do your compression test, you need to be consistant with the number of strokes when you do your test...if not...the delta between cylinders is not significant anymore.

I assume that before you put on the fuel injection you had two hoses that went up to the spark arestor. Did you have the same problem then and do you still have those hoses now.

Which fuel injection did you put on this?

 

[AdamB]

Re: high compression??

I put on a affordable fuel injection sytem, it uses a holley intake and all gm ecu's etc.

Never had the blow by problem (oil out the vent hoses), but did have leaking valve covers. I removed them and replaced the gaskets at the same time as the intake manifold.

The company I bought the system from just emailed an answer to my question. They said possibly they sent me wrong intake gaskets... they said I am not the only one with the problem. They said it is possible the gaskets they sent don't effectively cover the egr ports and thus may cause blow-by... sound legit?

 

[bruceb58]

Re: high compression??

I guess.

Is this a marine system we are talking about here? You mention GM ECU which prompts my question.

If you take the oil cap off what do you feel out of it?

 

[AdamB]

Re: high compression??

The GM Corvette ECU has been reprogrammed to run a marine type program, VSS and O2 sensors removed etc. Uses all stock hardware like spark arrestor etc.

I will check the oil cap when it stops raining, but I would expect it to huff air since it pumps oil out at high rpms. At low rpms nothing much happens.

 

[bruceb58]

Re: high compression??

You have a picture of this set up?

I take it this is not a USCG approved system that you are running?

 

[Reel Poor]

Re: high compression??

Excessive crankcase pressure is caused by piston damage or rings not sealing properly. Wrong intake gaskets would not be the culprit.

Edit: If the gasket does not cover the EGR ports between the head and the intake manifold, and allows exhaust to be expelled into the lifter valley, it could be a possibility. You would have to remove the intake to verify.

 

[AdamB]

Re: high compression??

yeah, I'll have to pull the intake manifold to verify. I am going to install new heads while I'm at it. Going to go for some dart aftermarket iron heads I believe. See my other threads...

Oh, I did post some pics of it on this forum too (my intake set up that is). Funny, GM programmed my ecu, and gm programmed the mercruiser ecu's too (I believe). My electronic fuel pump turns off when engine not running, is mounted within 12" of engine and everything else the USCG requires. I have approved fuel lines, and the boat runs great (except for the oil thing). Is there a USGC approved sticker, no. But I could add one I'm sure LOL!!

I purchased this system as a marine system. Take it up with affordable fuel injection specialties...

 

[AdamB]

Re: high compression??

I did remove the oil fill but didn't really get much pressure out of it. This was on muffs so was pretty much at an idle. I bought new heads, so when they come will redo the intake gaskets after replacing the heads with new Dart Iron Eagle 2.02/1.6 stainless steel valves... hopefully will add some hp and fix my oil leak problem at the same time.

Thanks for all your help.

 

[Reel Poor]

Re: high compression??

I hope not,,,,,but I believe your going to be disappointed in the heads performance gains if there is any. Those heads breath to well for the rpm range on your engine. Usually what happens in this case is the engine is a dog on the low end.

I believe for you application the GM vortec heads would have been a better choice, and a little cheaper too.

I hope you will let us know what happens.

 

[Bondo]

Re: high compression??

I hope not,,,,,but I believe your going to be disappointed in the heads performance gains if there is any. Those heads breath to well for the rpm range on your engine. Usually what happens in this case is the engine is a dog on the low end.

I believe for you application the GM vortec heads would have been a better choice, and a little cheaper too.

I hope you will let us know what happens.

Ayuh,........ I Agree.........

An Engine is a Balancing act,...
Adding More Air, ei; an Improved Induction Usually will Kill a Boat Motor,......

Your trying to Pump in More Air,+ it's got Nowhere to Go.......
You're going to be Fighting the Exhaust system......
The Only Way you'll see Any Improvement is with Aftermarket, True Headers.........
Which of course are Ungodly Expen$ive...............

Even Thru-Hull Exhaust will Not overcome the Exhaust Restrictions inherent in Marine Exhaust Systems............

 

[AdamB]

Re: high compression??

these heads I got have 67 cc chambers, that and the longer runner design of my intake manifold should do well. I am running a 21 pitch prop and the boat still jumps out of the water now. 'Course she'll rev until about 52-5400 rpms depending upon load if I'll let her.

 

[AdamB]

Re: high compression??

Oh, I know about the proper rpms, but these heads will rev better and I've never had an issue in the past. A 25 year old engine and she still likes to breath LOL.

I'll have to get a higher pitch prop for every day running around.

 

[Don S]

Re: high compression??

You really don't understand the principals and physics of a marine engine, do you?

 

[AdamB]

Re: high compression??

Well, for not being a mechanic I think I have a pretty good grasp on the mechanics of an engine. I realize that a marine engine is required to work a lot harder than an auto engine (higher revs for sustained periods, etc) I also know that with better heads, valves and springs I definitely won't gett valve float with the new heads if I didn't get it with the old 20 year old heads.....I want my engine to breath better (both my intake and heads have larger runners), the fuel system will provide proper fuel, and I'll end with higher hp to turn a higher pitch prop...at WOT. When I switched to the MPFI injection system, I gained low end torque due to the larger/longer runner design and the boat almost jumps on plane. Impressive for a 21 year old heavy deep v wellcraft.

Don S, I value your opinions or I wouldn't be on this site with almost 200 posts (mostly all questions) myself. My Uncle (cousin) actually owns a marina and his thoughts are alot different than mine and some of the thoughts on this board. Starting with spark plugs, he took out my AC43T and put in the dreaded and hated Champions...

I only run the prop that put me into the mid 5000 rpm range when pulling skiiers, I know I'll need to get a higher pitch prop for everyday use. I don't run her at over 5000 rpms except for a few seconds at a shot. I normally cruise around 4000 rpms, or less when on the ocean. This boat also spends 90% of it's time on fresh water lakes or I wouldn't have put on an aluminum intake manifold. I did have it powder coated to resist the salt for the few times when I do the ocean trips, and I flush her out right after every trip.

Oh, and for understanding engines, I managed to get my 302 Ford Mustang over 500 hp, dyno proven.

Edit: I was going to build a 383 stroker engine for the boat, gobs of torque and could lower the revs and still get increased hp. My Uncle (cousin) said it's much better to work a 350 hard, then to stroke a marine engine. Said the longevity wouldn't be there with the marine 383...Don S what are your thoughts on this?

 

[Bondo]

Re: high compression??

"Edit: I was going to build a 383 stroker engine for the boat, gobs of torque and could lower the revs and still get increased hp. My Uncle (cousin) said it's much better to work a 350 hard, then to stroke a marine engine. Said the longevity wouldn't be there with the marine 383...Don S what are your thoughts on this?"

"There's No Replacement for Displacement in a Marine Motor,...... Period"

That's an old Marine Mechanic slogan,+ it's True.............

A Properly Built, Stoked Motor will Always Outperform a motor of lesser Displacement.........

The 377cid, 6.2l Mercruisers are nothing but a 350cid, 5.7l Block Stroked out to 4, 3/4" stroke.......
You get to 383cid with the Usual .030" overbore when rebuilding a 350.......

You really don't understand the principals and physics of a marine engine, do you?

Ayuh,........
Adam seems to understand Exactly What He Wants to Hear..............

 

[AdamB]

Re: high compression??

Bondo,

that's what I thought too... Well if I was going to have to tear into the motor for the ring repair, I was going to do a .030 over with the stroker kit. But, since my compression test revealed that my rings are fine, I'll probably wait until I beat the 350 some more LOL. I am really curious what my top speed/ rpms will be after adding the new heads. I'll have higher compression, larger runners, larger flowing valves...

Question, how much hp are the center riser exhaust manifolds good for I wonder???

 

[Bondo]

Re: high compression??

"Question, how much hp are the center riser exhaust manifolds good for I wonder"

They flow Marginally Better than what you Have,........
But,.........
All this Extra Flow you're putting into the Motor,.......
Will do you No Good till you address the Exhaust Issue......
And,.......
I've already given you That Answer.........