How badly did I increase my compression ratio?

[SchoolBoy]

When I rebuilt the svo motor 7 years ago I had .020" oversized pistions put in and the head was surfaced twice due to the machine shop screwing up the first cut. I believe the head was cut .010" both times for a total of .020" but untill I pull the head I won't be sure.

Can anyone point me to the calculations needed to figure how big a bump in compression I'm facing? My plan is to pull the head an compensate this bump with a thicker head gasket but I need to know how big to go.

[MikeFleming]

Nothing serious though, so not ot worry.

Call Esslinger and ask them how much chamber volume was reduces by milling a stock d-port iron turbo head 0.020". THey used to hafve some data in their catalog, didn't find it just now. So call them.

Then plug in the numbers into this calculator:

http://www.csgnetwork.com/compcalc.html

+0.020" bore = 3.800"
2.3L stroke = 3.126"
Compressed stock head gasket = 0.040" - 0.045"
Head gasket bore = 3.810"
Combustion chamber = (62cc stock)
Piston deck clearance = -0.010-0.015" (stock)
Piston dish volume = (iirc it's +14cc - check this)


The folks on www.turboford.net will probably have those numbers in their heads.

[SchoolBoy]

Mike I searched for the piston dish volume and did not come up with anything so I worked backwards using the stock bore camber size. -10cc was the magic number to get 8.0ish compression ratio. Esslinger did not have the numbers for the head cc, but I did find a thread where boport states that the stock head with a .020" deck produces a 57cc camber. So if I plug that info into the calculator with your numbers above I get 8.611xxx.1 Now if my head was cut .030" I am going to assume the camber gets close to 55cc making my compression ratio 8.815xxx.1 This would probably explain why I can't run more than 14psi without it knocking.

Now to correct this I would have two options? Find a uncut/cracked head and swap it on, or buy cometic mls head gasket with a thickness of .070" like this one http://www.summitracing.com/parts/cgt-c5369-070/overview/year/1986 to get back to 8.078ish CR?

Is it ok to run a head gasket that thick safely to 18-20psi range?

[Raven855]

Sorry, just saw this. http://www.merkurencyclopedia.com/Motor/CompRatio21.gif . Look at the chart, it should answer your question.

[SchoolBoy]

Thank you Tony, that helps a lot.

[Raven855]

If you are knocking with good flesh fuel and a good tuneup, I would probably have the injectors checked and flowed before I pulled the head.

[SchoolBoy]

I had the brown top injectors cleaned by wichhunter performance when I swapped the pe in 6 years ago. Could they have gone bad that fast? Also last time I had her dyno tested I had done a full tune up and even with a good afr she was detonating then to at 15psi. I the major change between then and now is the addition of the fmic and that didn't help.

I'm tempted to put a few gallons of race fuel in next time I run low and see it that helps?

[Bob Holmes]

Pull a couple of degrees of timing.

[Bob Holmes]

You may induce detonation if you use a .070 gasket. There is quite a bit of discussion about proper piston to head clearance. Most conventional wisdom is that you should be no more than .045; with anything over .60 encouraging detonation.

Pull some timing, cool the intake charge, add water/ally etc (obviously not all of those together) and leave it alone.

Our roadracing engine was 9/1, our LSR engine will be 12/1 with race gas.

[MikeFleming]

My Prius is 13.8:1 static and runs on the recommended 87 octane.

[SchoolBoy]

Bob if I move away from the stock 10* of timing will that mess up the PE computer?

Also how does using a .070 head gasket induce detonation when its mearly replacing the material thats been shaved off the head?

[MikeFleming]

Bob if I move away from the stock 10* of timing will that mess up the PE computer? No.


Also how does using a .070 head gasket induce detonation when its merely replacing the material that's been shaved off the head? You're thinking volume of the "hole in the gasket" plus the "volume of the hole in the head" (aka chamber). You need to consider the distance between the top of the piston and the flat portion (not the hole - aka chamber) of the head. THAT clearance is critical for proper "squish" - where the charge is pushed away from the cylinder walls into the chamber for burning.

While using a thicker gasket will increase the total volume, it's adding it to the wrong place. There's a critical relationship between the top of the piston and the bottom (flat) part of the head for proper squish configuration as Bob stated above.

Alternately you can have a good head porter increase the chamber volume with some coordinated grinding and polishing, smoothing of edges, etc., if you're particularly worried about the CR - while keeping the chamber shape and sizes the same. Smoothing the chamber shape will help with detonation issues by making the engine less octane sensitive.

[Raven855]

Bob if I move away from the stock 10* of timing will that mess up the PE computer?

Also how does using a .070 head gasket induce detonation when its mearly replacing the material thats been shaved off the head?

A squish distance between 0.060 and 0.120" is to be avoided because it makes the charge detonate easier. .040 is typically used as the optimum distance for squish and quench. Quench and squish are different but result from the same thing. If combustion happens in the quench area more heat is introduced into the whole chamber resulting in increased temperature for the intake charge, cooling system and chamber.

Your compression is fine. Your challenge is figuring out the detonation issue. Reading your spark plugs, checking the coil voltages, eliminating any noise being introduced into the computer, the O2 sensor and circuit, do you have an oiling issue, poor grounds, and a host of other issues could be contributing to the problem. You changed to a front mount intercooler but how effective is it at lowering the intake charge? Did it lower or actually raise the tempurature? How accurate is your boost gage? The PE computer has allot of advance built into it. Retarding the igition a few degrees will not mess with the computer. That is one of the reasons the LA3 is so popular, it has less total advance.

[SchoolBoy]

Ok guy's I had to read that a few times but I think I finally understand the squish problem.

I can pull the plugs and take pics for you guys.

How would I test coil voltage?

Not sure how to test for noise?

O2 sensor was replace few years ago?

Grounds were addressed when I was hunting the wandering idle last year.

I need to install my air temp gauge to find out how effective the fmic is.

I have two boost gauges, one analog autometer, and one digital built into the ebc. They seam to be very close on boost and 1 point different at vacuum. I trust the autometer more....

[Raven855]

Looking at the plugs will give some indication of spark. For the rest make sure the plug wires are in good shape, no carbon tracking in the cap, grounds are good for the coil and engine. Check your voltage at the coil for 12V. That will cover allot of it. Check the coloration of the plugs for heat range, fuel and burn. Check the grounding of the alternator and voltage there. That will usually find the main source of noise. Check the O2 for the signal return, the wire that grounds on the turbo.

When you installed the PE, what did you do about the knock sensor?

[SchoolBoy]

Ok hopefully this friday saturday I can dig into this and get you some feed back. Plug wires, cap and rotor are probably due for replacement now that I'm at 35k on the motor. But I'll take some pictures.

The knock sensor is plugged in. I tried driving without it and the car did not like that at all.

If more and more signs start to point to the pe being too aggressive I do have my sds sitting in the closet.

[MikeFleming]

The knock sensor is plugged in. I tried driving without it and the car did not like that at all. What was it doing? Hmmm ... was it pinging too much?

Did you test where indicated TDC actually is on the crank pulley/timing cover related to the actual #1 piston location in the bore?

[Raven855]

87058706


Nelson, I found these charts showing a comparison of the LA3 and PE computer timing. I don't exactly remember where I got them. I remember seeing them on TF along time ago and Caroth probably has them as well. I believe the LA3 and regular SVO computer had similiar curves. The PE has quite abit of timing in it.

[SchoolBoy]

What was it doing? Hmmm ... was it pinging too much?

Did you test where indicated TDC actually is on the crank pulley/timing cover related to the actual #1 piston location in the bore?

It took me a bit to find the pictures from the build, but yes we verified TDC against the timing cover.

As for pulling the knock sensor, yes it pinged a lot.



Tony, those tables are interesting, any info for the pe in regular mode?

[MikeFleming]

Tony, those tables are interesting, any info for the pe in regular mode?

PE Unleaded (aka Regular) mode is Premium minus 6 degrees. There aren't to separate tables with individual settings like the LA2/3series. Just one table and an offset.

[SchoolBoy]

Ok well I'm going to try running the car in regular mode for a bit and see it that helps.

[SchoolBoy]

So did a full tune up on the car this weekend. "oil, filter, cap, rotor, wires, pcv valve but left the ngk plugs in."
As promised, here are the pictures of the spark plugs Starting at #4 working to 1. They were close on gap but a few were kind open so I regapped them them to 0.032".

87178718871987208721


The car seams to run smoother and everything was fine except my idle started to hunt a bit from 900-1100rpm so I figured it was tps acting up again. I drove it to work sunday and it ran fin, idle stayed at 1100rpms and pulled 15inches vacuum. Boost was down from 13ps to 12ish. The drive to work this morning was more of the same with a bit of hunting idle even after raising the boost back up to 13psi. So I figured ok cool everything seams to be working the way its supposed to, so I upped the ebc to what I hopped would be 14psi for the drive home. I started the motor and it went to fast warm up idle of 1500rpm and 15inHg, after a very short time it dropped down to 1100rpm and started to run kinda odd, so blipped the throttle. Idle became erratic from 900-1100rpm and vacuum dropped to 10inHg. I figured the damn thing was just being snotty so I drove it the 6 miles home. On the way out of parking lot I gave it a short WOT kick which it responded really well to. The idle stablized at 1100rpm again and vacuum went to 18inHg "which is kinda odd, 15inHg is normal." On the way home I got give it a good 2nd gear pull of WOT and boost was right at 14psi it pulled well no nocking. But the very erratic idle was back and she was running really ruff with vacuum at 13inHg the last mile to the house. When I got home I popped the hood to see if anything was out of place..... The dipstick was sticking way up and that hole side of the engine bay was covered in fresh oil..... I explored the dictionary for a bit then hosed her off before putting her away.

Now its my understanding that the dipstick only blows out if the pcv valve is shot. Did I get a DOA pcv unit or do I have a bigger problem?

I am going to put my old pcv valve back in the car tonight and see just how much oil I lost...

[MikeFleming]

The dipstick (usually followed by cam cover, then oil pan gasket, then rear main seal, ...) blow out like that when crankcase pressure is too high. The crankcase can pressurize for several reasons:

Reverse leaking PCV valve. ALWAYS test new ones to make sure there is ZERO back flow. Should pass enough air to breathe through (at a low exercise level) in one direction and ZERO flow in the other direction.

- Leaking compression past rings (usually) and not enough breathing room to vent that pressure. When the manifold is under pressure, the air exit path is through the vent on he top, rear of the cam cover. It's a relatively small hole that connects to a 3/8" tube (~5/16" inside diameter) that goes to a smaller restrictor (~0.16") in the turbo compressor inlet. The smallest restriction needs to be lat least 3/8", 1/2 inch is more better. Make sure this is not plugged or severely restricted.

- Hole in piston or missing sections of piston and top ring. Replace broken parts, as needed.

- Leaking head gasket - compression into oil drain back hole. The are more serious issues here than just the dipstick rising. Fix them.

[SchoolBoy]

The new pcv valve checked out, as did the old one so I put the old one on for now as a test.

The line from the valve cover to the turbo intake elbow did seam to be a bit plugged the first time I hit it with compressed air, the second time seamed to clear it.

The compression on the number 1 cylinder was 10 psi less than cylinders 2-4. Also all cylinders built 70% of the final psi number on the first stroke.

Oil is clean as is the coolent no milkshake yet.

Could the valve stem seals be shot with 40k miles?

[Raven855]

Yes your seals could be shot, but first show us a picture of what your new plugs look like. The plugs you have shown are worn and new plugs will give a better picture of what is happening.

[SchoolBoy]

Tony, the ngk plugs I took pictures of have been in the motor for 10k miles. After talking to you last week I put them back in the car during the tune up.

Should I still change them out?

[Raven855]

With a new set of plugs it is a lot easier to tell what is happening in the chamber. For instance if you look at the porcelain you see specs. They could be from splashing or detonation or from a car that has been sitting and the carbon is simply loosening after being run. Looking at the strap there is too much buildup to tell if the plug is truly running hot or cold. Change them out, run them a few miles and take some pics.

[MikeFleming]

... to tell if the plug is truly running hot or cold. Change them out, run them a few miles and take some pics. If we're interested in seeing if the plug(s) is/are hot/cold (aka chamber temps), that "few miles" needs to include at least one full-throttle, full-load accumulation of at least 20 seconds under full load, at full op temp. Otherwise all plugs kinda look cold when idling.

[SchoolBoy]

I will do that and report back.

Mike I've been thinking about welding a bigger port on the back of the head so I can increase the size of the line going to the turbo snout. Would 1/2" be to big or small?

[MikeFleming]

You mean the cam cover? Plumb it for 1/2 tube/hose - factory is 3/8 with some smaller restrictions at each end. Then work a way to blend it into the turbo inlet (keeping it closed, type 4 PCV system) without disturbing the cone-shaped airflow of the turbo inlet before (in the hoses between the turbo inlet and the air filter).

[SchoolBoy]

If I remove the angled distribution bock at the turbo inlet and replace it with the largest thread in vacume nipple I could find, (not sure what size it is). Then weld a matching sized nipple on the cam cover with a bent metal tube connecting them for a closed system, would that help or hurt me?

[svslow]

I'm having the same issue. I pulled the car out of storage and run it. Got home the dip stick was pushed out. I can smell some oil burning on the manifold. and it intermittently idles like garbage.

[Raven855]

The canister at the top of the manifold helps control the amount of oil that reaches the intake tract. You can drill out that compression fitting at the elbow for increased flow.

[Raven855]

I'm having the same issue. I pulled the car out of storage and run it. Got home the dip stick was pushed out. I can smell some oil burning on the manifold. and it intermittently idles like garbage.
Oil on the manifold and intermittent idle could be a result of a leaking valve cover gasket. The cork gaskets will deteriorate and most people seem to over tighten the cover. The Ford part number for the rubber gasket is F57Z-6584A. The torque is 62-97 inch pounds not foot pounds! Check the simple stuff first.

[SchoolBoy]

Raven & svslow, I am currently running that ford rubber valve cover gasket and it works! The blue felpro I had on the car was totally shreaded after 25k miles.

And for the valve cover breather, I bought a spare valve cover I'm going to experiment with drilling that hole bigger. Then I plan to tie it into this seperator as my svo doesn't have one. The seperator then will be tied into the turbo inlet just factory....
http://m.summitracing.com/parts/mor-85639?seid=srese1&gclid=CJ3p2qXIwcoCFUZcfgodoWAI8g

[brsvo]

Wow that is pricey. I think I paid all of 55 bucks for mine from a speed shop. Didn't come with a bracket tho.

[svslow]

Alright guys thanks a lot. I deleted the pcv valve and did a catch can. (This is robs 4E aluminum head, larger turbo) I don't think there was enough crank case relief. The hoses were all stock size. This might help school boy too. The idle issue only happens after the blow off valve opens a lot. Maybe the tune?

[Mike S]

Alright guys thanks a lot. I deleted the pcv valve and did a catch can. (This is robs 4E aluminum head, larger turbo) I don't think there was enough crank case relief. The hoses were all stock size. This might help school boy too. The idle issue only happens after the blow off valve opens a lot. Maybe the tune?

Once you install the PIMP, you won't have the idle problem as it is a speed density system and doesn't mind a blow off valve.

[svslow]

Once you install the PIMP, you won't have the idle problem as it is a speed density system and doesn't mind a blow off valve.
I've gotta put the pimp in. I just don't have enough time when I go back to Florida. It seems like it's going to be easy enough. But everything is easy until you're in the middle of it.

[SchoolBoy]

So today we did the leak down test and this is what it showed...
#1 @ 50%
#2 @ 15%
#3 @ 15%
#4 @ 15%

Number 1 & 4 both could be heard very well in the dip stick tube. Thinking about it these were the 2 cylinders that the head gasket let go on when the motor was only 300 miles old. Below are the pics of that....
8851

8852

So the game plan now is to pull the motor and autopsy it in a month or so. Gotta do some other fleet maintenance first.

[MikeFleming]

... the leak down test and this is what it showed...
#1 @ 50%
#2 @ 15%
#3 @ 15%
#4 @ 15%

Cold engine or stinking hot just after a 10+ mile spirited drive? How much pressure applied by the leakdown tester? If it was cold, and you used less than 100 PSIG to the rings, those are expected numbers. #1 is a bit high , while the others are a bit low. These low drag rings need LOTS of pressure to seal.

On my 84 I did LD and CR tests every few hundred then thousand miles since new. I NEVER got LD less than 10% at any point. In contrast the 88 Honda CR-X I had showed 4% at 100 miles, and was les than 3% for the next 20K miles.

[SchoolBoy]

Engine was brought to temp in the driveway till the radiator fan kicked on then shut down and tested. Pressure supplied was 120psi at the compressor and regulated to 100psi at the tester.

[Raven855]

With those numbers, it makes sense why you were blowing out the dipstick. Still would like to see the compression numbers. What did the camera show?

[SchoolBoy]

Compression numbers were....

#1 - 110
#2 - 120
#3 - 120
#4 - 120

When the motor was fresh we were in the 160 range if I remember right.

The camera didn't show much other than alot of carbon build up.

[MikeFleming]

Compression numbers were....

#1 - 110
#2 - 120
#3 - 120
#4 - 120

When the motor was fresh we were in the 160 range if I remember right. Same cam?

[SchoolBoy]

Yes Mike its same cam.

[brsvo]

How many miles ago was it fresh?

[SchoolBoy]

40k miles....

[brsvo]

Hard to believe the motor went south in 40K?

[SchoolBoy]

Update for everyone. We got the motor out saturday and the head off tonight. The head measured 3.778" so -.022". We did have a problem getting the front two arp studs on the exhaust side of the head out as they were crudded up with what looks like exhaust carbon. We did not get the pistons out yet that will happen probably tomorrow after work.

Is there anything we should be looking for or taking pics of before going any further?


89498950

[Under Pressure]

That doesn't look too bad . Since the design of the engine is to dump oil back into the intake you're always going to have excess oil in the chamber.

[SchoolBoy]

So got this all tore down and took it to the machine shop.... The block needs to bored to .030, number 2 rod was bent, the L2500F 50mm pistons are in great shape and are reusable. I have already sourced a replacement set of stock rods out of a 88 turbocoupe motor, unfortunately that block had pitted bores. I currently have a line on 2 other std bore turbo blocks for cheap, hopefully one of those pans out.

The new plan is have a fresh block bored for my .020 pistons, Total Seal CR3024-25 moly rings, resize the rods with arp 151-6002 bolts, line bore the block, arp 151-5402 main stud "do these work with the oil pick up tube?", and polish the crank, polish the aux cam snout.

Is there anything else I'm missing?