2.0L 135 fatblock heads on 2.5L 200?

[tlwjkw]

two handed Stihl...........

[OnPad]

two handed Stihl...........

Two hands, and a foot for easier starting.

The one lung engine is cheaper to learn porting/machining vs Merc v6. Modified a few saws, but that one has the most compression.

[tlwjkw]

3/8ths two handed handle starter rope if little (use ta be) like me!!!!!!!!!!!!!!!!!!!

[blackmaxonly]

What's the difference between 18787c4 and 18488c4? I got a pair of c5 I'm looking to swap for better compression

[OnPad]

2 litre/18787c4 has less chamber diameter, cc/volume, and a larger squish band than 2.5 litre/18488c4. Otherwise the chambers are the same shape.


On a side note. I was able to get 130lb compression reading out of the 2L heads after i removed the adapter off the end of the compression tester. Doh!!

[NZ Sidewinder]

Here's my workings on this.(in metric)
2.5L engine
Bore is 8.90cm
Stroke above exhaust port is 3.9cm (some wriggle room on that)
Swept volume is 242cm3.(242cc)
Head chamber volume 30cc and squish volume is 6cm3 (6cc)
Add all those together = 278.82cc
Devide that by the chamber volume plus the squish volume.
Squish is part of the chamber volume.
278.22cc ÷ 36cc =9.27/1 ratio.
If that's wrong then someone should pipe in and say so.
9.27/1 is up there but ok for. Good gas and cool plugs/ piston imo
This also assumes 100% volumetric efficiency and 0 leakage

[David - WI]

On a side note. I was able to get 130lb compression reading out of the 2L heads after i removed the adapter off the end of the compression tester. Doh!!

Plus 8% – 9% for altitude?

Also, you really need the SnapOn type gauge... (I think) you're giving up a couple cc because the end of your hose fitting is shorter than your actual spark plug. The void in the spark plug hole isn't there whe the spark plug is installed.

[OnPad]

Plus 8% – 9% for altitude?

Also, you really need the SnapOn type gauge... (I think) you're giving up a couple cc because the end of your hose fitting is shorter than your actual spark plug. The void in the spark plug hole isn't there whe the spark plug is installed.

No compensation for altitude. All the guys at sea level could add 8-9% to my 130lbs. Your right there is some extra space under that Schrader valve that could account for a few more lbs. That puts it closer to the 150lbs at sea level that everyone else is claiming.

Here I am trying to figure out a compression gauge while NZSidewinder is posting fancy corrected compression ratio calculations. What a show off.

[NZ Sidewinder]

I've got the exact same pairs of heads in front of me right now.
I'm aiming for 160psi.
Here's the unknown.
Squish protects the edge of the piston and probably the high point of the liner from the flame front during the period of piston travel where its moving much more slowly than mid stroke.
So for 160psi, do I want to use the 2.0L head with a .040 cut or the big chamber 2.5L head with the narrower squish band and a .140 cut?
If you draw a circle around a cross section view of this squish area, it will prove to be full of secrets.

There was a comment here somewhere that people forget how long ago the 1980s were.
This is correct
I call the marine shops and automatically assume that the parts guy knows what a 2.5 merc is.
I mean what other motors are there?
But of course 2.5 mercs are almost extinct and the parts guy wasn't even born in the 80s.

[LakeFever]

All I can add to that is a fast boat guy I ran into at the launch who had a Bridgeport on a Ventura said he ran these heads on a 2.5 FF like mine and it worked amazing. I’ll cc mine when I get around to this mod. Maybe tomorrow if I can squeak the time in to do this

[OnPad]

Heres a link to a interesting article.
http://www.powercdi.com/manual/combu...squish/en.html

[NZ Sidewinder]

Just a point on cranking compression readings.
There are two types of cylinder liners that affect compression readings at cranking speed.
Standard and exhaust relief.
The exhaust relief engine will have lower cranking compression compared to a similar engine without exhaust reliefs.
This came up just today when a racing administrator suggested to me that a restricted race class could be subject to compression tests.
I pointed out that an exhaust relief engine could have cut heads yet return low compression test numbers

[tlwjkw]

Thread: 2.0L 135 fatblock heads on 2.5L 200?

how did we get this far off topic..... those have been around on tha 2.0, 2.4, 2.5 150/175's for a very long time.. its well known that crankin' comp is effected by a few lbs. with that liner...

i'm still waitin' on someone ta take bone stock "fat block" 2.0 heads and bolt 'em on a 2.5 "fat block" and come up with this mystical number?????..............................

[LakeFever]

i'm still waitin' on someone ta take bone stock "fat block" 2.0 heads and bolt 'em on a 2.5 "fat block" and come up with this mystical number?????..............................

working on it

[tlwjkw]

working on it