Deck Height, How much is Too Much

Lees73Super · Post by **Lees73Super** » Wed Apr 10, 2002 11:50 am

I am rebuilding my lower end and I need quite a bit of deck height to reach my desired compression of around 8-8.5:1.

Here is what I came up with:

82mm stroke
90.5
mofoco 050 heads with 51.9-52.9cc chambers
42x37.5 valves
en120 cam

With those heads my deck will have to be between 110-130 to acheive the desired compression. Is this too much. Should I have the heads flycut? What problems can too much deck cause.

Finally, is that a decent compression ratio. We have 94 octane here in Kentucky.

Thanks for the info.

Lee

------------------
One of these days ill get this stuff right!

73 Super, 2110, 120 cam, 2x 44 IDFs Hyfire CDI and some more fun stuff.

Muffler Mike · Post by **Muffler Mike** » Wed Apr 10, 2002 1:27 pm

i think its kind of a catch 22. run big deck and loose. cut the heads down and loose the combustion chamber.
id say run the big deck, and hope the turbulance of whats left of the side squish outweighs lack of combustion chamber.
shoot, i run .150" deck in my motor for as long as i can remember, id say my motor runs fairly good.

------------------
Muffler Mike
www.MufflerMike.com

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Wed Apr 10, 2002 8:58 pm

Anything more than .065 is too much for me, unless it in a bus, I like .040 to .o50 according to chambers and etc.

------------------
Jake Raby
Raby's Aircooled Technology
www.aircooledtechnology.com

Marty · Post by **Marty** » Wed Apr 10, 2002 9:04 pm

I run zero deck plus a .060 copper head shim so I end up with .060 deck really. With my heads, this gives me 9 to 1 compression. This is plenty for a turbo motor.

------------------
Marty Staggs
www.staggsracing.com

James2 · Post by **James2** » Thu Apr 11, 2002 3:19 am

IMHO, I would run .065 deck and let the CR fall where it may. The loose deck can cause loss of squish and cause the VERY same problems your trying to avoid with the low CR. ie. pinging, over heating

James2 · Post by **James2** » Thu Apr 11, 2002 3:24 am

I know you can get the heads out to 55-56 cc by just laying the area around the chamber back a little. that with .065 deck makes it 8.9-1. Running just the 0.065 deck like I posted above would put you at 9.3, which is a little high for the 120 cam.

Why is the chambers so small? heads been fly cut?

[This message has been edited by James2 (edited 04-11-2002).]

[This message has been edited by James2 (edited 04-11-2002).]

Lees73Super · Post by **Lees73Super** » Thu Apr 11, 2002 5:28 am

I'm not sure why they are so small. I called Mofoco before I bought the heads (New) and asked the chamber size. They said between 51.9 and 52.9 cc. I might have to just get a good set of 044 to avoid having to cut the heads even more. If I did I wouldn't have much cumbustion chamber left.

Lee

James2 · Post by **James2** » Thu Apr 11, 2002 6:12 am

If you have not bought the heads yet, then I would get the 044s, the chamber is about 58cc after all the port work is done, which is right in your ballpark.

JohnConnolly · Post by **JohnConnolly** » Thu Apr 11, 2002 9:39 am

I won't run over .070" deck, I build them as close as .030".

John
Aircooled.Net Inc.

Greg Ward · Post by **Greg Ward** » Fri Apr 12, 2002 2:56 am

I'm not real clear whether you have those heads or not, but since you say you called them before you bought them I assume you then did buy them?.......

If you have them, CC them properly yourself. Lots of heads are not the same CC between cyls straight out of the box. I've seen engines running 9:1 on one side of the engine and 8:1 on the other!!
A discrepancy of .5cc is too much for me.

Anyway, we always run 0.060- 0.065" deck and I'd say you've got plenty of cc's in your chambers, mine are 38cc,:-) same size valves.

No shims at all I think are best, just like the factory intended, and if you really have 94 octane, then James's 9.3 cr should work fine, and it will scream.

Just ask Eric Draynor (edraynor) on the CLF, I've had many discussions with him over the last year, and his 2110? after we discussed it a lot ,was changed to a tight deck, more cr situation and there was no pinging and Heaps more grunt...

I reckon you can have your cake and eat it too.
If it doesn't like it and you can't stop detonation, then the worst is you take the heads off and stick a nasty little shim in there.

My advice to you is the same as to him, what's the harm in trying it as it is?
I think you'll like it.....

[This message has been edited by Greg Ward (edited 04-12-2002).]

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Fri Apr 12, 2002 10:28 am

From what my dyno has told me, loose deck (more than .065) is the same as semi hemi, it sucks and requires more advance, even with higher CR.

heres an example:
8.2:1 engine, running .100 deck, really wanted 36 degrees full advance to cool, and use the fuel, normally 8.5:1 likes 28 degrees, no more than..

------------------
Jake Raby
Raby's Aircooled Technology
www.aircooledtechnology.com

Lees73Super · Post by **Lees73Super** » Fri Apr 12, 2002 10:56 am

I guess the first post was a little misleading. I don't have the mofoco 050s yet. I was going to order them but didn't want to run too high of compression or too much deck height. I have decided on a pair of cb's super mag 044s. I have been told they have a 55 cc combustion chamber. According to a few folks I can get away with 9:1 comp with my en120. my only concern is cooling. I think I'll kick my deck down to .080 and run with a 8.8:1 comp. Will this run reasonably cool?

I run a 36 HP shroud W/O flaps (I read all the flap posts so no flames pls) and a 72 plate mesa cooler with a thermostatically controlled fan for oil cooling.

Lee

------------------
One of these days ill get this stuff right!

73 Super, 2110, 120 cam, 2x 44 IDFs Hyfire CDI and some more fun stuff.