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Discussion Starter · #1 ·
Irmscher w/250 compression

I purchased an Irmscher tuned 2.4L Opel engine from OGTS. I knew it was tuned for performance, but told it should run with premium gas with the exception that it might ping on a hot day. Hot days in Seattle are rare, so I went for it...

After rebuilding the engine we could not get the hydrocarbon readings to come down. We troubleshot the whole fuel injection system and finally determined that it was detonating early. We adjusted the timing as far as we could and found that needed higher octane.

First we put 92 octane it with some octane boost that should have gotten it to 104, but that did not help.

So we thought we should check the compression and noticed that it was at 250 psi in each cylinder. I don't know the formulas for computing, but I was told that that might be 15:1 compression for the 2.4L engine.

We then drained the gas tank and put in 114 octane leaded racing fuel. After that we could set the timing to normal and the hydrocarbon ratings went down as well.

I had no intention of building a race car. I did want a fast car, but something that I could run normal fuel and drive on the street.

I believe this head is a 2.2L head with an Irmscher cam. I am not really an expert at cars so I'm not sure what my options are. Here are what I am considering...

1) Put a thicker head gasket on
2) Enlarge the combustion chamber
3) Put a 2.4L head on and forget about the Irmscher tuned head. (I assume there is an Irmscher crank too right?)
4) Sell then engine to someone who wants a race car.

Any other ideas?

Thanks,
 

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You could trade for a well built 1.9 that runs on regular gas? That Motor sounds like loads of fun to me. What are your plans for tranny and rear end? I can't imagine the horse power numbers from that thing. Seriously, have you talked to Gil. That sounds like something that needs a different set of pistons. If it was in pieces when you got it, maybe OGTS didn't know exactly what they had. With todays gas I would say you want around 10 to 1 for it to be reasonable all around on premium.

It does sound like fun. I'm just guessing maybe mid 200's for BHP. If you leave it in, as is, I would like to know how it acts. It does sound like something I would get a kick out of.
 

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Old Opeler
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Ping!

1) An extra head gasket would lower the compression ratio BUT would also remove the "quench" with a bigger gap between the piston tops and head surface. No good as that is just a recipie for more detonation.

2)Enlarging the combustion chamber is an option but if Irmscher has been at it already it is probably just about the right shape now and changes may be a bit unpredicable on power out-put.

3)Yu would have to check to see if the 2.4L cylinder head had big enough chambers to lower the compression enough and a standard head would not perform as well as an Irmscher preped 2.2L head. Though you could move valves/cam/springs etc and have the head ported by an expert......

4)That sounds like dispare - don't go there!

5) You could change pistons or "ditch" the ones you have, if they are flat tops. This means cutting an area out of them directly under the combustion chamber leaving the "quench" area alone.
This method is used by race engine builders to achieve specific compression ratios. However there MUST be enough metal in the piston tops to leave at least .200" of material in the crown thickness. Sort of like a reversed deflector bump.
If they are not flat tops the raised deflector may be able to be reduced.

Seek the advice of a local shop who does engines for the circle track boys - such horrors are usual to some of them.
 

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I would avoid the thicker head gasket, unless you have had the block and head "decked", in which case that would be a good way to "undo" the removal of too much material. It's possible that the rods are too long.

My preference would be to either enlarge the combustion chamber or to mill the pistons down. Both would need to be done at a machine shop.

I would also dig through all your documentation and compare all the crank, rod, head and cam specs to make sure that everything matches your expectations.
 

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First, I would try Water injection. An anverage kit can be bought for around $240. Basicly it acts as an 'intercooler' lowering intake temperatures and reduciing pinging buy injection water into the intake. You use wiper fluid as its a great mix of water and alcohol (50/50). Also the kits are pretty simple to install, you can make a DIY setup for considerable less if you read up on the design.

If you arent feeling that adventurous, I would opt for GTJIMS 5th option. Or....I can take it off your hands ;) Either way good luck to you.
 

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Code Goober
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I second the idea of water injection. A brief bit of research on the web has shown some amazing things. If I read correctly, not only does having water injected lower intake temperatures tremendously, but it can actually take the place of fuel in the combustion cycle (and effectively raising the octane rating - much like methanol). Neat stuff!
 

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Opeler
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With a ported 2.2L head on my 2.5L bottom end, I had to use domed pistons, dome height 6.5mm), to get 11.4:1 compression and I'm using 98 Octane Unleaded.

So, I can only think you may have a 1.9/2.0L head and domed pistons. I would be looking at opening out the combustion chambers and chopping the dome off the pistons as a start.

Do not under any circumstances install a double thickness head gasket, or your combustion efficiency will go to pot.
 

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Hey there, Geek, I'd be careful with using water injection. Here's why, it increases the density of the combustion charge and the increase in density will indeed generate more power in the cylinder, something to the tune of 1 cu. in. of water converts to 1760 cu. in. of steam. The major problem with prolonged use will eventually hammer the living daylights out of the rod bearings. Once the clearance of the rods opens up, oil pressure goes away at the rod bearing. I had two engines that had water leaks into number 3 cylinder, both engines lost the rod bearing on #3 and both combustion chambers were steam cleaned, as in no carbon buildup at all. The other cylinders had a thick coating of carbon on the heads, valves and pistons. Water injection was used in piston driven military aircraft for many years, but those engines were torn down and rebuilt every 600 hours. There's a point to ponder.

Ron
 

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Davidmor,

The chances of you having 15:1 compression are VERY unlikely. BTW, you can not compute the static compression ratio from cranking compression numbers. Be very cautious with people who claim otherwise. Here's a thread where this has been discussed before.

http://www.opelgt.com/forums/showthread.php?s=&threadid=1477

Rather than taking randon shots in the dark at how to solve the problem you should first verify what the problem is. If you have pictures from the rebuild process they could be compared to pictures from other engines with known compression ratios to 'ball park' the compression ratio. Beyond this, you really need to pull the head and have the combustion chamber cc'd. Combine this with the location of the piston relative to the deck and a quick mold of the top of the piston and you'll be able to calculate what the compression ratio is. Until you really know what you have, everything is just a guess.

Did you find any markings on the cam? If not, you should consider having it measured or measuring it yourself. You can pick up inexpensive dial indicators with magnetic bases off eBay or through places like Enco http://www.use-enco.com
When you had the motor rebuilt, how was the cam phased relative to the crank? Did you specify?

In your testing you mention returning the timing to 'normal' when you added the race gas. What do you mean by normal? Did the distributor come with the motor? Do you know if it had been previously used with the motor?

-Travis
 

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Discussion Starter · #10 ·
CC the combustion chamber

Well I hear about as many people tell my to put a thicker head gasket on as I hear warnings not to do it.

What I am leaning towards now is increasing the size of the combustion chamber.

For those of you curious, I can spin the tires when I am shifting even with the beefed up suspension and tires... This thing is a lot of fun to drive!
 

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Discussion Starter · #11 ·
I should add...

I should add that the pistons are flat. I know that I decked and mated the surfaces and don't know how much the previous owner did. I believe the compression was put over the top from that.
 

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When you say decked and mated the surfaces are you referring to the head and block? If so how much was removed?
 

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Re: I should add...

davidmor said:
I should add that the pistons are flat.
As DavidJ said, you need a good sized dome just to get 11.4:1 compression. If you've got flat tops your compression won't even be close to this. I think you've got another problem...

-Travis
 

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Discussion Starter · #14 ·
9.4:1 compression spec'ed

I was reading a german website where they stated the compression was spec'ed at 9.4:1. This is more of what I would expect.

I don't think the machine shop removed a whole lot from the block and head. I don't have a clue how much would have been removed by the previous owner.

Let me restate the problem... I have 250 psi compression per cylinder. I was getting a ping problem and high hydrocarbon readings with 92 and 92 + boost (supposedly) 104 octane. I retarded the dwell down to -2 advance. Once I put 114 octane fuel in, I was able to get it to run perfectly at 17 degrees.

I have flat piston heads and a completely rebuilt engine.

I have headers and a high flow exhaust system.

The fuel pressure to the injections is spec. The temp reading for the computer are right. The air intake flap appears to move properly. It runs great with 114 octane.

Do I have a compression problem with 250 psi?
What could cause it to be so high?
Is it possible that the pistons are traveling further than spec?
Could I be getting to much flow into the cylinder?
 

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Re: 9.4:1 compression spec'ed

davidmor said:

I retarded the dwell down to -2 advance.
This makes no sense to me. Could you explain what you did?


Once I put 114 octane fuel in, I was able to get it to run perfectly at 17 degrees.
[/QUOTE]

The higher octane fuel may very well be compensating for bad timing...

at 17 degress what? Initial timing? total timing? Can you provide any info on the distributor? Did it come with the motor? Has it been recurved to match the engine?
There are three things of interest in terms of timing. Initial(at idle), total(maximum possible advance) and at what RPM total tiiming is achieved. `

-Travis
 

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Discussion Starter · #16 ·
Distributor & Flywheel

The distributor did come with the engine. I did not set the timing and was repeating back what I thought I heard, so I will get more information.

There was something strange about the flywheel. I got a bigger flywheel and 9" clutch, however my mechanic could not get it to fit and did not use it. I'm wondering if the flywheel that he put back was put on wrong. I realize that they bolt pattern should prevent it, but if it was wrong I suppose that could cause problems.

Any thoughts on the high compression? Assuming the timing was correct, does anyone have experience with 250 compression and required octane?
 

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boomerang opeler
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if the fly wheel was wrong you would not be able to start it
the fly wheel is a circle if you put a bigger 1 on you can not fit the starter
if you put a smaller 1 on you can not get the starter to catch the teeth on the fly wheel so no starting
so it has to be the right one
 

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Ok if I read this right, there was metal removed from the head by you and possibly previous owner. Also from the block if I am reading correctly. If that is correct, how did you get your cam to crank timing back?
 

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Discussion Starter · #19 ·
I don't know if it ever was a significant amount that was taken off. I am trying to explain it, but I don't know what the possibilities are.
 

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Any amount taken off the head or block will effect cam timing. Until you talk to whoever did that work and get some hard numbers, I would keep that in your head about cam timing. With the motor apart you can check the block, but I have never heard of a way to check the head. I don't know if this is where your problem is coming from, but it is sure something to check out. There have been some posts on this subject, Rallybob and a few others have addressed it. I for one have never gone there and hope to never have to. It could easily be the cause of your timing issues and your compression problem. CIH motors are pretty picky about the head spacing. If I remember right an average deck of the head changes timing by 3 or 4 degrees, add anything off the block to that and I don't know what to say. I would start by talking to whoever did the work. Maybe somebody here has a good way to check and knows what the numbers should be.
 
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