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914World.com _ 914World Garage _ Deck Height with Euro Flat Top Pistons

Posted by: ThinAir914 Mar 30 2005, 11:09 PM

This started out as this topic: http://www.914world.com/bbs2/index.php?act=ST&f=2&t=28067

It seemed like a good idea to start a new thread with different subject.

The 2.0L engine I'm building is using stock crank & rods with stock size (94mm) Euro flat top pistons. My understanding from other topics is that when you build such an engine you get slightly higher compression than stock because of the flat top piston, but you basically don't need to change anything else.

When I put the first piston & cylinder in place I used the .007" barrel gasket that was included with the overhaul gasket set. I measured the distance from the top of the piston at TDC to the top of the cylinder at .022"

I don't have the actualy head cc measurement, but the paperwork for getting my heads done says they were cut .005". I don't know for sure if that is just this time or if the final cut is .005 including any cuts done during previous rebuilds.

Using the math formulas and various calculators mentioned in the previous topic, I figure that if I assemble the engine this way I'll end up with a compression ratio of about 1:8.2 or 1:8.4

This engine will use the stock D-jet FI. So my question is: is it ok to assemble the engine with what I have or is this compression too high? If it's too high, what should I be shooting for with Euro flat top pistons?

If I need different barrel spacers to reduce the compression, it's fine with me, but I don't want to just pick some number out of a hat or build it this way without knowing that it's ok.

Posted by: Demick Mar 30 2005, 11:29 PM

Don't waste your time trying to figure this out without CCing the heads. Small changes in chamber volume make big differences. Wait until you get your heads back and measure them. Only then can you determine what to do.

Demick

Posted by: ThinAir914 Mar 30 2005, 11:32 PM

Well I've got the heads in hand. I asked my local shop if they had a way to measure the volume of the heads, but they don't. I was thinking of putting a spark plug in the head, filling with water, then measuring the water as accurately as possible. Will that be accurate enough?

Posted by: MarkV Mar 30 2005, 11:53 PM

You need a round piece of plexiglass and a syringe or a buret. You measure the quantity of liquid as you fill the combution chamber.

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Posted by: Brett W Mar 30 2005, 11:57 PM

GO to your local veterinarian and ask for the largest syringe they have. tell them you have to kill a horse. (JK) Use the syringe to measure the CCs of the combustion chamber.

Posted by: redshift Mar 30 2005, 11:59 PM

I just fill my up with carbon.

M

Posted by: MarkV Mar 31 2005, 12:06 AM

I tried using a syringe and could not control it very well. I just bought a Titration Burette on ebay. Should be here in a couple of days, I will let you know how it works.

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Posted by: ThinAir914 Mar 31 2005, 01:08 AM

Cool! You guys are really helpful. I'm sure I can get this done.

Now the question that remains is what compression ratio am I shooting for with these pistons? I've always heard that it's "about 8", but I've never seen a precise number.

Posted by: Joe Ricard Mar 31 2005, 06:51 AM

http://users.erols.com/srweiss/calccr.htm
Go here this is the simple online calculator. Just pay attention to positive and negative when talking dome or dish. works great and you can play around with it to figure out what to change to obtain the ratio you desire.
.022 deck is pretty close by the way you could end up whacking the piston against the head at high RPM. But setting your deck to obtain 8.5 to 1 should drive you to a taller deck not to mention shaving .005 off the head you probaly lost a good bit of cc's.

Posted by: Brett W Mar 31 2005, 07:23 AM

You want as much compression as you can get. Depending on cylinder wall clearence and piston material, you can set the deck height to .035. I would go no tighter than that.

Posted by: type47 Mar 31 2005, 10:31 AM

we are at a similar point:

http://www.914world.com/bbs2/index.php?act=ST&f=2&t=27670&hl=deck+height

i bought a piece of thick plexiglas at home depot and a circle cutter for a drill press and cut my own plastic disk to cc the combustion chamber volume. luckily, i borrowed a burette from a chemistry teacher. i used auto trans fluid but someone mentioned using cooking vegetable oil. i didn't have much trouble with the process. i ordered cylinder spacers to obtain a deck height of .055" (about/recommended)

Posted by: ThinAir914 Mar 31 2005, 11:09 AM

QUOTE (type47 @ Mar 31 2005, 09:31 AM)
i ordered cylinder spacers to obtain a deck height of .055" (about/recommended)

I'm assembling the pieces today to measure the head. Where did you order your gaskets from?

Posted by: MarkV Mar 31 2005, 11:14 AM

Near the bottom of the page:

http://www.aircooled.net/new-bin/catsearch.php?categoryid=EPS&cmd=list&parent2=E&perpage=

Posted by: MarkV Mar 31 2005, 11:25 AM

Read through this page for info on measuring combustion chamber. about half way down the page, it's a Corvair but same concept.

http://home.hiwaay.net/~langford/corvair/valvejob.html

Posted by: Dave_Darling Mar 31 2005, 11:31 AM

QUOTE (ErnieDV @ Mar 30 2005, 09:32 PM)
I asked my local shop if they had a way to measure the volume of the heads, but they don't.

Get a new machine shop!! Any competent one will be able to CC the heads for you.

The compression ratio that you want will vary depending on a whole raft of things. For a stock engine, with a stock cam, running stock fuel injection, I would say that somwhere between 8.0:1 and 8.5:1 should work just fine. You'll probably want to run mid-grade fuel if your CR is 8:1, and premium-grade (CA's 91 is fine) for 8.5:1.

You definitely want the CR to be even across all four cylinders, so make sure you CC all four combustion chambers!!

--DD

Posted by: type47 Mar 31 2005, 11:32 AM

i got part numbers for the spacers:

021.101.341.30 for a .030" spacer
" " .20 .020
" " .40 .040

and checked around. i ended up ordering from bus depot mostly because they are close in location to me and i've bought stuff from them before. aircoolednet looks good too.

Posted by: MarkV Mar 31 2005, 11:51 AM

Before you measure your deck height make sure the gasket surface on the block & cylinders are spotless clean. I was getting measurement varied from cylinder to cylinder by .008. I cleaned the registers and they are within .002.

Here some info on measuing deck height form the same Corvair site. About 2/3 of the way down the page:http://home.hiwaay.net/~langford/corvair/trial_assy.html

Posted by: Jake Raby Mar 31 2005, 12:00 PM

I am almost finished with my head cc kit for the TIV engine.... I'll add them to the store ASAP. They are very nice.

Head ccs being measured accurately is important. There is no "standard" and no margin for error.

Heads can vary in ccs so each chamber must be check and they may need to be balanced if you really want to do it right.

I have all the cylinder shims, even very odd sizes.

Posted by: ThinAir914 Mar 31 2005, 12:34 PM

QUOTE (Dave_Darling @ Mar 31 2005, 10:31 AM)
You'll probably want to run mid-grade fuel if your CR is 8:1, and premium-grade (CA's 91 is fine) for 8.5:1.

Thanks Dave! That's exactly the kind of info I was looking for. I want to stay with regular fuel so I'll be aiming to stay below 8:1.

Posted by: ThinAir914 Apr 4 2005, 09:08 PM

This weekend I got a syringe and made myself a plexiglass disk with a hole in it like MarkV's picture shows. I carefully measured each cylinder and they all came out with a volume of 59cc. Since 60cc had been mentioned as an approximate figure in one of the formulas and since the machine shop notes say it was cut .005", I figured this seemed about right.

Since my deck height was at .022 with the .007 shim in place, I calculated that the height without the shim was .015. Using the AirCooled.net calculator I figured out that I needed a deck height of .065 to achieve 8:1 compression so that means I need a .050 shim.

When I called Jake today to order the shims, he seemed amazed that the volume would be over 57cc. He stated that he'd usually seen these kind of numbers only on engines where the heads had been worked over to create a larger chamber. We reviewed my procedures and calculations and he seemed satisfied that I was asking for the right shims, but then we got to talking about what using .050 shims is going to do the the rocker arm geometry and now I'm worried.

From everything I'd heard, using the Euro Pistons was a simple "bolt in" that would yield a compression of 8:1 instead of 7.6:1 with no other changes to the engine. With everything that I'm going through to get this right I'm beginning to wonder if I just had the wrong impression or if I've missed something.

I really respect Jake's experience and the opinions he has based upon his experience so I want to make sure I haven't missed something. Does this head look like it's been enlarged? Does this description look like I've missed something?

P.S. - When I measured the volume, I used ATF so it would be easy to see when I had all the air out. I held the plexiglass down well. The result looked just like MarkV's picture.

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Posted by: Jake Raby Apr 4 2005, 09:21 PM

Ernie,
The chamber looks unaltered..

They may be indeed 59ccs, but if they are they will be the largest unaltered chambers I have ever heard of....... Not to say it can't happen but its not ordinary..

The "dimple" in the face of that intake valve is probably good for 1cc by it's self.....

Those sodium filled exhast valves make my teeth chatter all the way here in Aircooled Heaven....... Ouch

Posted by: MarkV Apr 4 2005, 10:36 PM

Ernie,

Mine measured 57cc's using a syringe. I sealed the Plexiglas to the head with some grease and had a hard time getting an accurate reading. I bought a titration burette to try to get a more accurate reading.

You said flat top piston but the photo you posted had a dish that you need to allow for. I think the stock 73 piston has a 5cc dish. My pistons are KB from Jake and they have no dish whatsoever.

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Posted by: MarkV Apr 4 2005, 10:49 PM

Here is a flat top piston:

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Posted by: ThinAir914 Apr 4 2005, 10:51 PM

I got my P&C set from a club member who said they were brand new Euro pistons that he didn't need because his project had changed. The part number on the side of the box is 039-198-075, which matches the Euro p&c set at PP. They are definitely "flatter" than the stock pistons that I pulled out of it - the stock pistons have rather steep sides and a flat bottom to the dish.

Posted by: Jake Raby Apr 4 2005, 10:52 PM

Yep... Those are flat tops all right!

57cc is normal for a 2 liter chamber.

I have been working on a Type 4 head cc kit and deck height tool as well to make it easier to measure those puppies..

Posted by: ThinAir914 Apr 4 2005, 11:01 PM

So if I measured incorrectly (which seems likely) and it really is 57cc, then I would need a .060" shim to achieve 8:1 compression. This seems more likely.

My measurements were done using a 10cc medicine syringe. Given that I had to do 6 refills in order to get enough fluid into the chambers, I think it is entirely possible that I'm off by 2cc. One chamber measured 58cc the first time I checked it.

Jake - maybe we should change the order or we should talk tomorrow morning (or pm me).

Posted by: Jake Raby Apr 4 2005, 11:13 PM

Ernie, You really need to get a 60-80cc syringe. It is very easy to goof up with the process if you are maxing out the syringe 6 times to get the volume you need to work with.

You can normally find one of these syrings at a tack supply store for Horses or a Vet office... Most Human medical suppliers don't carry these big daddy syringes.

Get accurate measurements and I'll hold your order till you do so.

Posted by: ThinAir914 Apr 4 2005, 11:23 PM

Sounds good. I'll recheck and let you know.

Now get some sleep! Isn't it well after midnight in GA?

Posted by: Jake Raby Apr 5 2005, 06:32 AM

Midnight and beyond is when I'm most efficient....
\
Crashed at 0315 and back at it at at 0830!

Hell, that was an early night!

Posted by: type47 Apr 5 2005, 07:48 AM

i don't mean to undercut Jake or any other vendor but this was found on a site that supplies lab equipment for public schools. there are other suppliers.

http://sargentwelch.com/product.asp_Q_pn_E_WL4707D_EA_A_Acrylic+Burets%2C+Basixs_E_

Posted by: Jake Raby Apr 5 2005, 07:54 AM

I could care less about the cost of the syringe it's self.. What makes my kit nice is the plates that are made to fit a Type IV engine in various bore sizes.

Posted by: Dave_Darling Apr 5 2005, 06:04 PM

QUOTE (ErnieDV @ Apr 4 2005, 08:51 PM)
I got my P&C set from a club member who said they were brand new Euro pistons that he didn't need because his project had changed. The part number on the side of the box is 039-198-075, which matches the Euro p&c set at PP. They are definitely "flatter" than the stock pistons that I pulled out of it - the stock pistons have rather steep sides and a flat bottom to the dish.

Note that there are two different versions of the "Euro" pistons. One of them is truly flat-topped, and one merely has a smaller dish than the US version. The "smaller-dish" version seems to be the original variant, and the flat-top is later. Both will supposedly give you an 8.0:1 compression ratio if everything else is exactly as designed from the factory. (Which it pretty much never is.) I guess the flat-topped ones are very very very slightly taller than the dished ones?

--DD

Posted by: ThinAir914 Apr 8 2005, 05:00 PM

With the help of a 60cc syringe from the local feed store, and some wheel bearing grease to stick down the plexiglass, I remeasured last night. The head for all the cylinders measures 56cc, not 59cc as previously measured.

Although I knew there could be some innacuracy due to using a 10cc syringe and refilling it 6 times, I'm amazed at how far off it was. Just to be sure, I measured them all twice.

So using the calculations, this means I need .060" barrel shims. This will give me 8.1:1 compression.

Jake - if you see this, I placed an online order for the shims. I tried calling and leaving a message, but everytime I punched in 3 as directed I just got cut off.

Thanks to everyone for their patient advice to help me figure this out. I'm gonna have an extra on behalf of the group when it's finally back on the road as a way of recognizing that I could not have done it without you all!