Ok folks,

We just finished rebuilding the motor...94mm pistons and cylinders to match...71mm stroke...but old 1.7 case...CC'd the heads and come up with 44 cc's per cylinder...

Do the calculations and we come out with 1971 cc's...Great !!!

But, The problem is the compression ratio is now 10.64 to 1...

The question of the day:
Should I take the cylinders and heads back off and shim them to get a little relief...Probably not going to get much...Might knock it down to 10 or 9.75 (if I'm lucky)...

DO NOT want this thing to clatter and diesel on me when I get it back together...

OK, let me have it...What are your thoughts ???

2-OH!

Way, way to high. You willl need some big honking shims under the cylinders. CR is dependent on the cam. What cam are you running? What does the cam manufacturer recommend?

-Aaron

Only if you plan on running jet fuel.... But seriously.... 10.64 is on the high side... and the cam that you are using will either benefit from higher or lower compression. I just built my 2056 with a Raby cam... and set the compression to 9.3 to 1. And some people I talked with said THAT was high.

I personally would not be comfortable past 9.5:1. Jake might be, but he is building to a much higher precision than I did. I say shim it...

slight highjack:
Educate me - how does the cam get involved in the compression ratio? Not being argumentative - just want to understand.

should have thought about it more - has to do with where the piston is when the intake valve closes - right?

Long story short...

A high duration cam bleeds off compression due to overlap between the intake and exhaust valves so the CR is effectively lower. The higher the duration the cam is the higer the static CR can be. There are lots of "buts" with this...

Again, the cam manufacturer has a CR in mind when they build it...

-Aaron

Using a Web Cam 73 Grind...Still running D-Jet...

Good Idea, I will contact WEB and see what they think...See what the 73 was built for...

2-OH!

My guess would be 8:1 on that cam. What did you heads cc at? What's your deck height? Pistons have a dish/notch in them? If so what does it cc at?

Just trying to get you to double check your math.

-Aaron

Ok, that compression is definitely too high for D-jet. I think Aaron is right; if that cam is Djet friendly it probably will like near stock static compression.

The cam bleeding off compression spoken of above is referred to as dynamic compression. In your case webcam will probably give you the desired compression in static terms. This website has a good dynamic compression calculator.

http://www.kb-silvolite.com/calc.php?action=comp

For TIV's I have read that the dynamic compression should be around 7 to 7.5:1, but that spec is for rather high performance builds I believe, so not totally applicable to yours with stock FI.

Anyways, good luck

I agree with Aaron above...

Somebody check my math...

Can someone give me a formula for determining the compression ratio...Here is what I used without my formula so I can get an unbiased opinion...

Heads cc = 44cc
Stroke = 71 mm = Height
Cyl. Dia = 94 mm = divide by two for Radius
Formula ???

mm to cm conversion... 1mm = .1cm

Pistons do hve a very slight dish, but are really almost flat...

2-OH!

Whats your deck height?

I.E. From top of piston to top of cylinder.
(Piston and cylinder installed, then torqued down a bit and measure for volume)

Theres a bit of volume there that you need to include into your calculations.

Or have you already included that volume into your calcs?

Clayton

Thanks Clayton...

The way I measured it was with the cylinder hand tight using a spacer and nut to hold it in place...

Calipers, using the depth gauge end...71.77mm, BDC... .55 TDC...Leaving a balance of 71.22mm...

Actually, Looking at my notes, I'm not sure about that...That could be the problem in the math...

In short, is there anyway to check the CR without disassembling at least one head ???

My calcs:

Cyl vol: 492.7 cc
head vol: 44 cc
deck ht (guess 1mm min.) vol: 7cc

CR= (492.7 + 44 + 7)/ (44+7) = 10.66!!!

Add 1 mm shim....deck ht vol doubles to 14cc

CR = (492.7 + 44 + 14) / (44+14) = 9.49 !!


Are you sure the head vol is 44cc? Seems pretty low.

I would think you want to get inn the low 9's at least.

WEB thinks that cam works with D-jet, that's what they think. It has certain, shall we say, drivability issues? Monster HCs (that's unburned fuel) at idle, poor off throttle response, requires serious rethinking of how the MPS is set up. their theory and reality don't agree all that much. There are worse cams, but not by much. The Cap'n

Toss the Djet, buy a nice cam Web 163/86b, or similar variant. Put some carbs on there with a nice exhaust and you will have a very good street engine. Yes you will have to run premium, but watch your timing and you will be fine.

Do not throw a shim under the heads. Decreasing the compression by increasing the deck height is an awful way to accomplish the goal. Your 9.5 engine will ping worse than your 10.5 engine will. Just put more cam in and lower the dynamic compression ratio. Or open the chambers up and decrease the compressed volume.

If you would go with a programmable fuel injection system you could probably go a little higher and still run it on pump gas.

What was the deck height measurement?

CCC

yeah, what is it again?

Thanks for the help guys...

Looking at my notes, I'm not sure of the deck height...Guess I'll be removing at least one head this weekend instead of building it up...

2-OH!

rick, was your case 0 decked during the machining process?

k

Ok, How the hell did you get a 44cc chamber?? Are these 1.7 heads? To take a 2.0 head, or a 1.8 to 44cc requires a ton of flycut, on a 2.0 head you'll break through the exhaust stud holes closest to the chambers at less than 51cc most of the time!

Now, if the heads have been machined this deep you have bigger issues as the va;ve deck has been dropped so far that you'll more than likely collide valves into pistons!

How did you determine that you had 44cc? Do you have pics of the chambers?

BTW_ adding a gross amount of shim to lower the CR has negative effects on the quench... This also lowers the engine's efficiency mandating a ton of extra timing advance to be used. I have seen engines have bigger issues with detonation and tempewrature with a ton of deck and lower CR than they did at much higher CR and better quench. Quench= efficiency and efficiency is the name of the game.

ONCE AGAIN, HOW THE HELL DID YOU END UP WITH A 44CC CHAMBER?
If you do have this chamber volume pull off the heads and sell them to a racer, or have them partially hemi cut to add some volume which would also be a half assed way of completing the task..

Chamber volume can only be calculated by measuring the fluid volume capacity of the chamber. You can't calculate it by measuring the chamber dimensionally. So double check your chamber volume and deck height.

Rick,

I just now read this thread. I too question the measured head volume. (And) I f this is truely accurate, then there's sure to be piston/valve clearance issues. Did you clay the valves? Yes, what's the deck? All of what Jake posted..........

If your motor is on an engine stand, rotate it so that the spark plug is at the highest point on cylinder 1 and you're close to TDC. Fill with trans oil from a Burette tube through the plug hole but not quite all the way. Very slightly rotate the crank in both directions to find where the oil is at its highest point, then complete the fill untill it is even with the top of the spark plug hole. Record the amount of oil and subtract 1.8cc. This will now be your trapped volume. This method works best if you first grease the piston/wall and then install the head. If you want to sort cut it without removing the head(s), avoid working slowly as the oil will leak down past the rings; you can first squirt a small amount of 50WT oil into the cylinder and rotate the crank a few times to help seal off the rings.

Keep us informed of what you find. I think there may be some fundamentals that were overlooked somewhere.

Andys

Thanks Andy, good great idea...I would like to figure it without removing the head and that would be a perfect way to do it...

My Burdette (spelling) tube is at the cleaners and I do not have a spare laying around, but I do have a syringe marked with cc's...I will try your method and record the info...Then we can just add the stroke into the formula...

See ya at GAF...

Thanks...

Bring both of your heads to GAF.
I have a burrete and a plastic plate. Add a little grease... Voila. We will have your exact CCs......

WE can do this at Mr. Crusty's or Mike Zs table if they lets us......

Clayton

Clayton,

What a great offer, many thanks...Let me see if I can work it first and come up with the answer...I will get back to you on this thread before Sunday...

The tubes are too delicate to haul around and I would hate for it to get accidently broken...

Be sure to check this thread before you go...

Many thanks...

2-OH!

You can also use a graduated horse serum syringe (120CC) and a piece of plastic with a hole drilled through it.
Just put some grease around the head to seal the plastic plate to the head and some grease around the valves to keep em from possible leakage.

I use a water thin cutting fluid/kerosene mix for my CCing of heads. I used to use alcohol. But I kept drinking it after every chamber reading. Man those were the good old days...... Lol.....

That will get ya within a half a cc.

You are probably doing it this way anyway.

By the way... Give us a pic of your combustion chamber. As you NEED to yank those heads anyway.

I might have a spare set of 1.8 and 1.7 heads that haven't been decked floating around.

Hell I have 4 spare engines. I probably have what you need.

I dunno... Pics would be best right now. That will at least tell us by looking at the last cooling fin. If the heads are decked TOO MUCH.

That would help us even if you don't measure the Combustion chamber.

Cheers,
Clayton

We now know the problem.

And we have a possible solution.

2-OH. Check your PMs.
Then PM me with your phone number or call me on my cell. (check PM for number)

I have some DAM GOOD NEWS FOR YOU.

Claytonovich, East of Krackatoa

How many ccs were they???? A hemi cut might be in order.

Clayton:
I would say from seeing this motor and the heads that the Heads are decked way to much for any stock configuration. Many assumption where made to the quality of the first Eng build and we are not even sure if the barrels have been cut in anyway????. If the shims are simply placed under the barrels and the cam requires a certain CR Rick will have other problem. I watched the injection of oil for the CC test that was preformed and would say the reading of 44cc is correct for what that head was cut to.
I should also mention that the crank had some Major work done on it from what you will see in the pic. So we have a ? crank, cam 73 grind what CR. piston no real notch for valves, barrels maybe cut, heads cut to much, To many ????. My feeling is all parts should be spec’d and calculated by a competent machine shop, JMHO.

Great info and feedback to this problem This is the root of the 914world,

Lets see the aforementioned heads.

I'm curious what the heel is going on with them.

Feel free to send me the parts if you want... do the job once.

Sorry I dont have any pic of heads. At pic time had no real reason to take a pic. But yes thay are cut to much.

I gotta tell you, after spending time at the GAF with several folks, cussin' and discussing this problem, reading through this thread and learning all the stuff I encounted these last few days (and let me tell you, there is no way to absorb it all), There is just no way to express my thanks to everyone involved...Leamon, Clayton, Steve, etc...

Looks like I will be selling a pair of 1.7 heads that have been completely re-worked and flycut too much for a daily driver but some racer type will love...

Brer, and all those interested in seeing how not to cut heads, I will take some photos and post over the next day or so...Maybe Jake can chime in and point out some of the more interesting aspects...

Thanks everyone...

2-OH!

A butt ugly person from NARP has volunteered a complete 1.8 engine to 2-OH so we can yank the 1.8 heads off of it and get then reworked for his engine. His existing heads are boat anchors. Hopefully he can then sell the 1.8 long block (minus heads) to get the money to have the 1.8 heads gone through.

I can do the heads as well as Leamans machinist. Done right and done cheap for our friend.

This will allow us to get a proper deck height and get the job done right first time.

Now there is a secondary problem. 2-OH has a bone stock 1.7 injection system that is on his engine. The system has been gone through and works perfectly.
AND he is running a 2.0 crank and P&Cs.
With these new to him 1.8 heads and heat exchangers.

I don't know much about stock injection. But I am sniffing a 2.0 with a mild FI cam might run lean with those smaller runners and 1.7 injectors.

Who knows about this? As I don't want to help build something that won't work.

Lastly. Those small chambered heads that this thread started with were 1.7 castings that had been surfaced a bunch.
Thats based on what Leamon told me at GAF. He saw them before assembly. He and Ahdoman said the surfacing was cut way into the last cooling fin. Hence the CC issue. Especially on a 1.7 head.
The heads are still on the engine. We won't be using those in this build.
Accordong to 2-OH the valves are now barely touching the pistons.

Jake... If I had my way. We could send you the whole assembly. But that probably isn't gunna happen. We are trying to get this engine finished for basicly free. And it's not that hard to do either.

Thats why we are all stepping up to help.
2-OH has spent so much time on his car. And it is drop dead nice by all accounts. countless hours have been spent on this car.

He has had this engine built twice and had issues both times.
He doesn't have the funds to buy 2.0 heads and go through them. The money simply isn't there.

Me think it's time for the fellas to step up and help.
Leamon is a great guy who steps up all the time for people.
I am going to do the same. Slits is volunteering a complete engine so we can get a set of 1.8 heads off of it.
And sell the rest for money to help pay for the head work.

I am still worried about that injection question. I don't want to do squat until that question is answered.
Hopefully 2-OH will contact Bleysing and get his thoughts on the injection.

Cheers,

Clayton

Agreed, the 2-OH car is beautiful and deserves a decent power plant!

Andys

If you ever come down this way bring those boat anchors and I'll show you how we can add cc's to them. Maybe someone can set them up on a high compression build after that. I have 2 chamber shapes we can try out.

Just put the heads on and run them. Don't worry about it. In the meantime let someone work the other set of heads up. Then decide if the compression is too high. The higher compression will give you better drivability.

The flywheel is kinda scary.

Whats wrong with the crankshaft? I don't see anything other than a counter-weighted crank.

Toss the D-jet and put some decent injection on there. Then you won't have to wonder if the stock (Crappy) injection will work.

Sometimes you just got to wonder what people are thinking when they design a motor. (Or is it lack of design).

WHY would you even bother cutting material off the flywheel if you are going to put a counterwieghted crank in there. That rotating assembly has got to be SOOOO heavy.
Was there any port work in the heads?
and then use 1.7L injection?
A pet monkey could not have mis configured a motor near that bad.

What about using some dished pistons to bring the CR back down? 2.0 bus pistons maybe? Just a thought.

-Chris

This would also kill the efficiency. There would be nearly no squish area.

Best to build it right as hard as it is to stomach the wallet is going to have to open a bit.

However Jake said "feel free to send it his way" Shoot free is good.

I dunno if I agree with that, I'm pretty sure the super-squish pistons run dishes in them that are mirrors of the combustion chamber shape. I've also read that a dish promotes a better mix than a flat top. I guess it depends on the size and shape of the dish, if the bus dishes run almost all the way out to the edges then you are probably right. It probably wouldn't take too much of a dish though to bring the CR back down to a more reasonable level . . .

Bus piston dish is pretty huge. and pretty deep. Think Diesel truck piston. Like 15 cc or something like that.

BTW my new motor will have 8cc domes.

It'll take 8-12cc of piston dish to get the CR back in check, so just use a VW Bus 029 piston thathas a 12cc dish from the factory to get the CR closer in check..

Doing the dish mod to a stock 914 spec piston will more than likely compromise the piston's integrity- thats a lot of material from a piston that wasn't designed for a dish.

Hmm, I have a set of bus pistons in a 2.0 motor just sitting around. Low miles I believe.

Its a good "Band aid" for his issue.

We need solutions. Not bagging on the previous builders and machining. Whats done is done.

And thanks Jake for the notion of the bus pistons. Hadn't thought of that. Thats another solid possibilty.

Does ANYONE know if a 2.0 with 1.7 injection and a web injection cam can be made to work properly with a factory 1.7 injection system?

(And I sniff the answer is no. In truth., I don't know)

Thats the next stumbling block.

OR if we use the pistons Jake suggests. Can the 1.7 injection be used?

This is out of my element. I try to play with stock injection as little as possible.

And we have very little bucks (ZIP) to get this done.

Thats the fun part. Do it right for nada. Just have to figure out how.

What the hell. You guys have any more ideas. Any trades? Whatch think?

And give us only solutions. We know the problems. Can't cry over spilled milk. That will get us nowhere.

We need solutions...!!!!!!!!!!!!!!!!!!!!!!

I haven't seen this engine yet to measure anything. That should be interesting as well.

Lets see what we can do fellas. Apparently pictures to follow as soon as the heads come off.

I'll be gone for few days. I am going up on a hill with a thousand men and having a little BBQ with my friends.
Gunna be cooking wild game from all over the world. And I have to make sure it goes off impeccably.
Catch ya Saturday....
Regards,
Clayton

What's the deck height? You can't do it right for cheap.

Bus pistons are probably your best bet if dropping the compression is what you want to do. But you are still trying to run used pistons of unknown quality.

OK...

Lets assume for a moment that we are using good 1.8 heads. And I can fit larger valves in the heads for no more money if it will be to any advantage.

In essence. A 2.0 block, crank, and P&Cs with a WEB 73 cam.
Lets also assume about 30 thou deck height. And a basically stock 1.8 pair of heads, with valve train Geo and 911 adjusters.

I am guessing that is what 2-OH will end up with.

You guys see any problems with that build?

If so. What should we look for?

Lets also assume factory injection. If so. Will we need to run 2.0 injection? Or will a tweaked 1.8 injection work as well?

Note: Exhaust will be factory HEs and a Bursch.

NOTE: Carbs are probably not an option because of cost. (else we would be done right now...LOl..)

What else ya need as far as ball park data?

Clayton

I think (sometimes not very well) that we can make the injection run well enought for long drives and canyon runs. Maybe play with injectors and the MPS. also a little more gas flow and we should be OK I have a sniffer so we can run test before we send it out.