1.8 Head cc Question? Options

[martman]

OK i am building a 2056 with carbs and the 186 webcam. The heads that I am using have been gone thru. I cc the heads to see what the deck height would be and got 44cc. This doesn't seem right to me but not sure. The heads have been rework. So my question is have the heads been decked to much to use in this case.

[type47]

I'm not sure I get this. I thought the deck height was the distance from the top of the piston to the top of the cylinder, that is, you don't want the piston to protrude out of the top of the cylinder. That makes a small volume to be included in the volume of the combustion chamber, the other part of the volume is the volume in the cylinder head. Those volumes totaled, results in DATA to calculate the compression ratio. When I cc'ed my heads, I put a plastic disk in the head where the top of the cylinder would fit and, through holes in the disk, filled the chamber under the disk with fluid that would be the volume of the head part of the combustion chamber. Now if a head is "fly-cut", done sometimes to clean up the mating surfaces, it's possible to cut too much off and give too small a head volume and mess other stuff up. I seem to remember a volume of around 55 cc for my heads, it's written down at home.

[martman]

Yes Jim I cc'd the heads and got 44cc on all 4 cylinders. It seems a low cc to me but not sure. From what I have read it looks like 49-50cc is the norm for the 1.7,1.8 heads that have not been rebuilt yet. These heads were done for a bus motor, and had about 300mi on them berfore the bus was wrecked. So I was going to use them, on the rebuild, but now I'm not sure with the low cc in the heads.
The deck height is configured to .149" / 8.1:1 which seems a lot of shims.

Engine bore 96

Engine stroke 71

CC 44

Com Ratio 8.1 = .149" deck height

or Com Ratio 8.5 = .128"

Does this seem right?


Marty

[r_towle]

What are your deck heights with no shims?

Rich

[martman]

I ran out of time to get the deck height with no shims before work.

Do you think that the cc is right for the heads.

[r_towle]

seems a bit low, take a picture of how you cc'd the heads.
If you are using dished bus pistons, a 44cc chamber is probably correct.

There are several dished pistons with different sized dishes.....so you need to CC the piston also to get an accurate number.

If you are using flat top pistons, its gonna be a high CR.

Rich

[martman]

OK had time to get the deck height, and re cc the heads, I also cc the piston head because it has valve clearance cut in them.

Here's what I got:

Engine bore 96

Engine stroke 71

Head CC 44

Cyl Head CC 3

Deck height .075 no base shims - Base Shims are .010

Head Gasket .030

If I add this up right I have a total of .115 deck height

I need to get to .128 DH for 8.5:1 CR, I then need to add .013 base shim, or .149 DH for 8.1:1 CR need to add .030 shim.

If I add the 3 cc to the head cc that would be a total 47 cc then the DH would be .138 for 8.1 CR and .117 for 8.5


Do I have this right? I would appropriate all input thanks (IMG:style_emoticons/default/smile.gif) (IMG:style_emoticons/default/smile.gif)

[banger]

A deck height of .128 sounds a bit high. I am not really an expert, but deck height can play a role in how well the combustion chamber breathes. The chamber has both squish and quench zones, if you make the deck height too big, then the squish zones arent really doing the squish they were designed to. Often the deck height is set to .030-.060 for the squish zones to do their job. Maybe someone with more knowledge can comment on this, or correct me.

OK had time to get the deck height, and re cc the heads, I also cc the piston head because it has valve clearance cut in them.

Here's what I got:

Engine bore 96

Engine stroke 71

Head CC 44

Cyl Head CC 3

Deck height .075 no base shims - Base Shims are .010

Head Gasket .030

If I add this up right I have a total of .115 deck height

I need to get to .128 DH for 8.5:1 CR, I then need to add .013 base shim, or .149 DH for 8.1:1 CR need to add .030 shim.

If I add the 3 cc to the head cc that would be a total 47 cc then the DH would be .138 for 8.1 CR and .117 for 8.5


Do I have this right? I would appropriate all input thanks (IMG:style_emoticons/default/smile.gif) (IMG:style_emoticons/default/smile.gif)

[Todd Enlund]

Even the .075 deck with no shims or head gaskets is a bit higher than optimum. I agree with Rich... those heads were built to run with dished bus pistons. I think that if you are going to use those heads, you'd be better off running bus pistons to reduce your CR than increasing your deck to get a lower CR. Too much deck is going to reduce the burn efficiency... you want combustion in the combustion chamber, not in the squish area. I think that generally accepted deck is 1mm, or .040".

What is your "Cyl Head CC 3"? Is that your piston dish volume?

[r_towle]

96mm bore
71mm stroke
47 cc chamber (head cc and valve pockets in pistons combined)

If your target CR is 8.5:1
You need
.117 deck height.
If your current deck height is .075 without shims.
You will need .032 in shims.

The deck height seems very high.
What are the pistons and cylinders you are using?
If these are AA pistons, that may be the issue, they have the pin height placed at the bus height...so thus the higher deck height number.

It will work, its just not the optimum way to go. You have moved the combustion event farther away from the plug.
Yes, it will work, but this (from what I recall) is the issue with using the AA pistons (versus a piston with the right pin height)

Someone shaved your heads, or decked them.
From what I have seen 54cc is more normal.

But, all in all, it will work and you are close to the right number, you just need a different base shim.

Rich

[HAM Inc]

If you're 1.8 chambers are actually 44cc's then someone has flycut about .075" from your heads. An OE 1.8 chamber will hold around 55cc's. A .010" flycut removes around 1.35cc's.

More than .060" deck with low compression is a sure way to end up with a turd of an engine. Low compression AND excessive deck will make it tough to tune and you'll end up with very high EGT's that are difficult to bring down, especialy if you don't have a cam that is designed for such a screwy combo, and why would there be such a cam?
I hate to be the one to break it to you, but you need another pair of heads.

[martman]

96mm bore
71mm stroke
47 cc chamber (head cc and valve pockets in pistons combined)

If your target CR is 8.5:1
You need
.117 deck height.
If your current deck height is .075 without shims.
You will need .032 in shims.

So if I add the head gasket which is .030 then all I need is .002 shim. (IMG:style_emoticons/default/unsure.gif)

The deck height seems very high.
What are the pistons and cylinders you are using?
If these are AA pistons, that may be the issue, they have the pin height placed at the bus height...so thus the higher deck height number.

It will work, its just not the optimum way to go. You have moved the combustion event farther away from the plug.
Yes, it will work, but this (from what I recall) is the issue with using the AA pistons (versus a piston with the right pin height)

Yes they are from AA. I did not know they had that issue, they were listed for the 914 and not the bus.

So I am close? or not? or just have to start over with a different set of heads.

(IMG:style_emoticons/default/confused24.gif)

[Todd Enlund]

So I am close? or not? or just have to start over with a different set of heads.

Well, no offense to anyone else who answered, but Len (HAM) has more credence than just about anyone when it comes to the heads.

If you are set on using the heads you've got, here's what I'd look at:

44cc chambers plus 12cc bus pistons gives you 56cc. Do what you need to set your deck to .045... that will give you 9.0:1 static. I assume you mean the Web 86 grind, which is a bit more aggressive than a stock cam. Calculations, if they are to be believed, bring your dynamic CR to 8.1:1... the Web 86 should reduce your dynamic CR by almost a half point over the stock cam.

This is all just my math, you probably want validation from someone with more experience than I have (IMG:style_emoticons/default/smile.gif) Personally, I tend to agree with Len, I'd be thinking seriously about selling my heads to someone else, and going with a pair of rebuilt 2.0 heads, or a pair of Len's heads from Jake. It will cost more, but the better breathing and more efficient burn from the spark plug location should make a noticeable difference in the finished engine.

[r_towle]

man...I wrote a really nice detailed response...then the server hiccupped and its gone.

I will sum it up.
If you get the 54 CC heads, that is first.
Second.
Shave the bottom of the cylinders so you end up with .030 deck height.
That will net around 9.2:1

Rich

[jcd914]

going with a pair of rebuilt 2.0 heads, or a pair of Len's heads from Jake. It will cost more, but the better breathing and more efficient burn from the spark plug location should make a noticeable difference in the finished engine.

Maybe I am missing something but replacing the heads is not going to address the 0.075 starting deck height with the P&C's he has. If anything over 0.060 deck height is too much then he is already stuck. I know how to increase the deck height but how do you decrease your deck height?

It seems to me you will need to replace the heads (cut to far) AND replace the pistons with some with a different pin height. All then heads I have seen that were cut very far also had the first cooling fin cut to avoid it running up against the fin's on the cylinders. Do your heads show signs of the fin being cut?

Have you been back through all your measurements? I have always gone at least twice through the measurements when measuring to calculate compression ratio. If I get some thing that sounds wrong I go back a couple more times. Every time I go through it I drag out Bruce Anderson's book and use it as a guide, I have done this a bunch of times and I still get out the book.

Good Luck

Jim

[r_towle]

To fix the piston pin height issue you have two choices...pick you poison.

You take the cylinders to a machine shop...they mount them on a lathe and spin off the bottom mating edge...the part that touches the case.

OR

You take the case to the machine shop and deck both sides, removing the correct amount from either side to gain that much more stroke.

I suspect that this is why Jake sells the AA cylinders, yet he sells KB pistons, or JE pistons...
The KB and JE pistons have the right pin height.

I also think that blueprinting these old cases is not a bad idea...I am sure Jake would deck the case anyways...and you could simply take care of the issue at that time.


Rich

[martman]

I dug around and found a stock head from a 1.8, it checked out at 55 cc. I then measured the spark plug hole to the fly cut part of the head and the difference was .85 and yes the bottom fin had been cut after comparing the two. So this leaves me with rebuilding the stock heads and selling the cut heads. Bummer I thought I had it made with the newly rebuilt heads, OH well

Now next problem is I have to have the cylinders cut on the bottom to make the DH in range or I have the cases cut.

It is never easy, but at least I found this out now instead of later.

Thanks all for the help, (IMG:style_emoticons/default/pray.gif)

I would have not known about the piston having the wrong pin placement.

Well I guess I will be going to a machine shop for head and case work.

[banger]

Since you have dished pistons, another option is to remove the dish from the pistons. Essentially turn them into flat top pistons. Then you could bring the deck height to where it should be, and still keep the compression ratio in check.

[martman]

Here are some pics of the problem head, and troublesome piston.

This is the 44 cc head - noticed the fin being cut Looks like these will be for sale now


This is the 1.8 head and has 55cc big difference


the piston is flat top and not domed


Well we had a learning curve the past couple of days I hope this thread help others also. Pics of the heads comparison sure makes more since now.

[HAM Inc]

The 44cc head is a 1.7. The dirty head is a 1.8.
Good luck with your project!