I'm working on a head program for guy here in SD. He had a similar problem I believe a member here had, and that was his chambers were too small for his 2056cc engine. (edited, he's using a 71mm crank and 96mm slugs)

Facing large barrel shimming, which he didn't want, I worked this up for him.

perfect 60cc chambers, his non 2.0L heads will now install with a .045 shim , he has a zero deck, giving (I believe) a 8.5:1 compression ratio.

This method of modifying heads results in perfectly matched chambers (and ports for him), so when he gets them back they will technically be blueprinted to within .001".

not a 2.0L head granted, but thats sometin else and this is within his budget.

Looks like that chamber would have interesting quench.. I'd bet that it would want quite a bit of timing and would give tuning characteristics similar to that of a semi-hemi chamber.

It looks like the basic shape of a 2.0/914 chamber but without the quench pads..

Would be interesting to do a back to back on..

Our cure for small chambers is not creating them... Heads that have small chambers have generally been flycut so much that the heads have lost a bunch of rigidity..

Those small chamber heads are retained for use in production engines so they can be used and disposed of :-)

I figured someone would have seen the design before. Its nothing new, just tailored a little to fit his application. The inside radius was custom made to match his valve sizes.

The heads were about 54cc I think originally.


I'm sure they are easily within your price range jake!

I consider that a perfect chamber volume for a wide range of combos.

Looks like he likes to run those grossly oversize valves.

I just thought that people who have small chamber syndrome just go out and buy a red Ferrari 308

44x38 valves.

2 revisions later, this is how they look...

...major wood..oh wait, thats metal.

i'll bring it along to your gig sean.

open them for 96's and valves next.

brer:

With that much meat removed, and the history of cracking around the spark plug holes, how do you think that configuration will hold up...Particularly if you open up the valve sizes...

Also, will that much removed, how will it effect the valve/rocker geometry...It would appear that the valve stems will clear the other side of the guide by quite a bit more...

2-OH!

Spark plug depth on these heads hasn't changed, only the angle of deviation either side of the plug hole. These 1.7L heads are not as prone to cracking due to the fact that there is more material around the plug to act as a heat sink... this head still has a large bulk of alloy, more than a 2L, around that hole.

The flat area of the chamber had less than .003" removed so your valve height will remain identical to stock... depending on the valve job you put on it of course, so rocker geometry with not change any more than a regular head rebuild which is nearly nothing.

This head gains cc's by pushing down along the lower edge (similar to the 2.0), opening up several millimeters next to each valve and bowing back at the plug. more prone to cracking than a 2.0 head? Don and I discussed that and he feels this will not alter its lifespan much in relation to its performance.

whats important is factoring the cost of a cherry set of 1.7 cores in relation to the performance gains.

Since jake mentioned it, and out of curiosity I calculated the quench pad area on this head

and found it to be 4.1 in^2 for a 96mm.

A 2L head I have here has aprox. 3.7 in^2

And the spark plugs are .100" closer to the chamber deck on the 1.7 heads compared to the 1.8....

Quench area and quench pads are two different things... The BSFC numbers back to back would illustrate it clearly.

forgive me for repeating things other people tell me.




commentary promotes thought though, and ways to waste time.
no doubt it could be made better as well with more money and time.
better plug angle, better ports, better chamber shapes and so on....

I've been playing with video and thought I'd post this of the head machining. Better than TV in person, but on video? not so sure.


After the seats were installed in these heads, and in most, there was a fairly uneven lip where the seat was proud or recessed into the chamber floor.

The initial roughing of the chamber looked nice, but still hadn't cut deep enough to totally clean the chamber floor, leaving areas of the orginal chamber showing. So after the seats where installed I zeroed the table and ran the program again on both heads one after the other.

By running both on the same talble and setup sequentially, without adjusting the height between the heads it was possible to see how different the chambers on this matched set of heads was.

One removed a good .020" more from the base of the chamber while the other just kissed it, worrying to watch!

After both chambers were finished with the final passes and all the seats were then totally flush with the chamber floors they were moved to the next station and bored and surfaced. It was only during the surfacing that it was possible to see that the chambers were no where near identical. Both heads cleaned up to exactly the same depth when surfacing while there was that frightening .020" difference in the floor of the chambers.

In the end these ended up exactly the same without a doubt, and the seats are flushed and should make an easy valve job.

sorry for the SHAKY VIDEO but the camera is the size of a pack of smokes.

...Or a Corvette...

Lol.

Your machinist. Who is he?

Hi Alpha.
I built the models, I built the heads.

I hope you're laughing at the jokes and not my crappy video!

I should give kudos to this special tool Don makes and was kind enough to let me abuse. Surfaces and clearances the fin in one go, made it super easy.
The picture is of the Type 1 Tool, the type 4 is essentially the same but with different blades and heights.

That tool is in my box too... Its made by the guys at Bugpatch..

Works well