Compression ratio and deck height

[runningmonkey]

Just wondering if someone can put my mind at ease?

Iv just had a new 2332 engine built by my regular engine builder, He's never let me down before & I trust his ability and quality, but he is very old school and I know that this is the biggest CC motor he ever built. Now long story short I told him that I was going turbo with this motor and after doing a fare bit of research and talking to other folk we settled on a 8.4:1 compression ratio.

Now after I picked my engine the engine builder confessed to me that he never really dealt with working out compression ratio that much and he had to look on line on how to get my compression ratio to 8.4:1 and that he was 90% sure that it was about this? 

Now at the time this didn't worry me, as I said before I do trust him and he knows a lot more than me, He said he had to shim the barrels to achieve this, I just wanted to check and to put my mind at rest is this a normal thing to do? I checked the shims with a feeler gauge and they seems to be 2 x 0.80 shims. This is correct? Sorry for what seems a very dumb question 

 IMG_20171202_101058 by John Mills, on Flickr


full spec is as follows -

Auto Linea aluminium Super race crankcase,
Scat 84mm type 1 mains, chevy rod journal crank
Scat 5.5 H beam con rod with clevite rod bearings
Engle FK 87 Cam
AA 94 MM Barrel and pistons
Scat Straight cut cam gears
Scat Pro Street Heads 44mm x 37mm wedge ported
Scat 1.4 Rocker arms 
1.5 Liter extended CB oil sump
Kennedy Stage 2 clutch with Super Dalken plate
Complete CB performance turbo kit
CB performance Magnaspark Crank Trigger Kit
Charge cooler kit

Cheers in advance John

[leec]

Now I'm no expert, but you need to know deck height and cc in the cylinder head chamber (and if the pistons are dished what cc are in them)

Are you worried he has created your desired compression ratio by shimming a lot and creating a really huge deck height?

[neil68]

I just built a 2332 cc with Auto Linea aluminum case and it required 0.080” shim to produce zero deck height.  If your machinist used another 0.080” shim for DH and your Scat heads have a 65 cc chamber then that would provide an 8.4:1 CR.  Perhaps you can find out from Scat what the wedge pro head chamber volume was?

[runningmonkey]

Are you worried he has created your desired compression ratio by shimming a lot and creating a really huge deck height?

Yes basically, but also if the compression ratio is incorrect should I be worried?

[leec]

If its still a long block, could you pull one head off?

[runningmonkey]

If its still a long block, could you pull one head off?

Yeah still a long block so I could take a head off. What would I be looking for? I just been on YouTube and watched a few how to videos on checking deck height. So I could buy a tool and check it?

[leec]

Call the builder Monday, he must have measured deck height surely?

[PPRMicke]

Are you worried he has created your desired compression ratio by shimming a lot and creating a really huge deck height?

Yes basically, but also if the compression ratio is incorrect should I be worried?

No 
 Here in sweden
 CR 9-10 on pump gas
/// Micke

[Martin S.]

Just wondering if someone can put my mind at ease?

Iv just had a new 2332 engine built by my regular engine builder, He's never let me down before & I trust his ability and quality, but he is very old school and I know that this is the biggest CC motor he ever built. Now long story short I told him that I was going turbo with this motor and after doing a fare bit of research and talking to other folk we settled on a 8.4:1 compression ratio.

Now after I picked my engine the engine builder confessed to me that he never really dealt with working out compression ratio that much and he had to look on line on how to get my compression ratio to 8.4:1 and that he was 90% sure that it was about this? 

Now at the time this didn't worry me, as I said before I do trust him and he knows a lot more than me, He said he had to shim the barrels to achieve this, I just wanted to check and to put my mind at rest is this a normal thing to do? I checked the shims with a feeler gauge and they seems to be 2 x 0.80 shims. This is correct? Sorry for what seems a very dumb question 

 IMG_20171202_101058 by John Mills, on Flickr


full spec is as follows -

Auto Linea aluminium Super race crankcase,
Scat 84mm type 1 mains, chevy rod journal crank
Scat 5.5 H beam con rod with clevite rod bearings
Engle FK 87 Cam
AA 94 MM Barrel and pistons
Scat Straight cut cam gears
Scat Pro Street Heads 44mm x 37mm wedge ported
Scat 1.4 Rocker arms 
1.5 Liter extended CB oil sump
Kennedy Stage 2 clutch with Super Dalken plate
Complete CB performance turbo kit
CB performance Magnaspark Crank Trigger Kit
Charge cooler kit

Cheers in advance John

Shimming is the ghetto way to get your 8.4:1 for turbo on a 2332. If you read some of this thread about dishing pistons, it would help you realize that:
http://cal-look.no/lounge/index.php/topic,27525.0.html

[Chip]

I don't know that i would call it ghetto. You shim to get the appropriate deck height, unless cutting barrels to length. I can see pocketing the piston as a countereasure to a chamber that has been cut too plunged too deep for a low compression engine. Basically turning a purpose built NA engine into a turbo setup, dramatically changing cc without swapping heads.
I buy my heads with big chambers so i can run a tight deck. I don't screw with my piston tops.

[Martin S.]

I'm saying ghetto (easy way out) assuming he added the shims to get the 8.4:1 for a turbo engine. Shim to get the appropriate deck height doesn't mean much unless you say what the deck height is. Dishing the pistons is the alternative to losing the squish bands and is considered the normal way to go. If the builder was searching the internet, he could easily find the old school info to shim to get the CR desired which is info from 30 to 40 years ago and very common info available on line.

That said, my old 1776 was set that way from the 90's and we put 15 psi thru it at 7:1 CR (EFI) with a ton of deck and it was a blast to drive! 

[Jim Ratto]

You can "cc" the cylinder, with piston @ TDC through plug hole with some type of graduated instrument, and compute your compression if you're concerned as to what your actual compression ratio is. This is how Porsche would check their 547/692/587 Carrera motors.

Technically, you should remove one head and apply a light bead of grease around outer perimeter of piston @ TDC to seal.

Good luck. Your builder probably didn't wrong you. Not by using shims, in any case. If the valvetrain geometry and P to V clearances are done correctly, there is nothing wrong with shimming the cylinder.


Jim

[Martin S.]

“To lower compression ratio, first Semi-Hemi cut the heads, then add spacers under the barrels.”

This is from Berg’s Blue Book. Who does that anymore?

NOBODY!! 

[modnrod]

With respect Martin, I have an experiment for you to try out if you would like.
Yes I've done it, and did the experiment on 3 different types of engines with similar results.
You might like to use a chassis dyno (maybe you might even have an engine dyno to play with?) to ensure "repeatability" and "accuracy", so........

Build a 100hp engine with about 8 or 9:1 compression, preferably big bore to show up the results better. You will need full street spec.
Put it in a car (or bolt it up to the stand), roll it up on the dyno, and play around with throttle positions and loading until it is steady at about 35HP at about 3300rpm. This will simulate the load of a Beetle pulling a small-ish caravan into a bit of a headwind at about 60-65mph. Waiting until the ambient temps are well into mid-30s Celcius would be ideal, so bring plenty of cold drinks. 

Start with the tight squish, deep chamber, flat top engine, and then time how long it takes for the oil temps and also the CHT to reach runaway meltdown, whatever temps you wish to set, but HOT.

Then change the top end out to stock chambers (which is 43cc remember, NOT 50cc......) and add spacers to get exactly the same compression ratio, and repeat the dyno test. Buggy's are good, only takes 20 mins, as are engine stands. Obviously before the test you have the same pushrod length, valve-train angles, etc, worked out to make it all a bolt-on deal. EVERYTHING else is the same.

Finally, get a stock 43cc head, flycut the crap out of it, semi hemi it, then add round dished pistons to again get exactly the same compression ratio, and repeat the test. Wide shallow chamber with a wide shallow dish.

By the way, as you can see at no point did I mention HP or torque output. These little VWs are old antique vintage steel, huge fun to play with and improve any way you can, but there definitely is not one "correct" way to do things........if you want to go fast then buy an Evo, a Skyline, or (my favourite) a Supra.

Enjoy the experiment, it's good fun, and then re-consider the Word of Berg. The "blue book" is a chapter, not the whole bible. He did experiments like this all the time..........
 

[Martin S.]

I see you had problems with CHT using one of your combos
If it does, you likely need to look at your tuning. If you change to a more modern chamber design, address the timing. It will need less advance, but quicker advance.
For CHT to be normal, the heads need to be efficient with a complete burn of the mixture.

Here is my turbo's ignition table, and notice the advance goes from 7 at idle, to 45 degrees at 3000 rpm. 

[Fiatdude]

I've got 3/8" spacer (about 10 mm) under my barrels (so I can run a long rod) and a .060 copper head gasket -- -- so it comes down to what ever you need to get the job done.......

[Martin S.]

Dude, didn’t you do a little work on the pistons too? 

[Fiatdude]

those were on my 2990 -- On the 2332 I've got now just running flat tops

[Martin S.]

JE custom pistons ($1000) or copper heads gaskets ($20)... hmmmmm 

[Chip]

JE custom pistons ($1000) or copper heads gaskets ($20)... hmmmmm 

Whats wrong with copper? I can blame them for saving my heads a few times at this point. Cracks in cylinders that go right up to the copper and stop. Change out cylinder, throw it back together and back in business. I'll never own a turbo motor without a copper gasket.