Deck Height with Euro Flat Top Pistons, Was: Engine Assembly Questions Options

[ThinAir]

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.

[Demick]

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

[ThinAir]

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?

[MarkV]

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.

[Brett W]

GO to your local veterinarian and ask for the largest syringe they have. tell them you have to kill a horse. (JK) (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif) Use the syringe to measure the CCs of the combustion chamber.

[redshift]

I just fill my up with carbon.


M

[MarkV]

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.

[ThinAir]

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.

[Joe Ricard]

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.

[Brett W]

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.

[type47]

we are at a similar point:

http://www.914world.com/bbs2/index.php?act=...&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)

[ThinAir]

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?

[MarkV]

Near the bottom of the page:

Cylinder spacers

[MarkV]

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

[Dave_Darling]

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

[type47]

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.

[MarkV]

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/t...trial_assy.html

[Jake Raby]

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.

[ThinAir]

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.

[ThinAir]

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.