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Pedal Smasher
1973 Opel GT
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If you don’t own it yet, I’d say buy it. Try to setup the carb and if it still isn’t enough, then work on the pistons and cam. De-tuning an engine is cheaper than building an engine for more power.
 

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Super Moderator
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Step one is figure out the cam. If it’s too crazy then budget-in a tamer cam. You can put 32-34 mm venturies into 45 Weber’s, mill a little off the pistons, and you’re all set. After that it’s just jetting and ignition timing.
 
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Resident Curmudgeon
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1,459 Posts
Discussion Starter · #23 ·
Step one is figure out the cam. If it’s too crazy then budget-in a tamer cam. You can put 32-34 mm venturies into 45 Weber’s, mill a little off the pistons, and you’re all set. After that it’s just jetting and ignition timing.
As I said, I'm a rookie at engine work, so pardon the simple questions. Do the pistons have to be removed to mill them?
 

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As I said, I'm a rookie at engine work, so pardon the simple questions.
No need to apologize Opemel If you've read any of my Q's you'll feel much better lol
Don't know what there asking but if it's reasonable and you like it I'd go for it
 

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As I said, I'm a rookie at engine work, so pardon the simple questions. Do the pistons have to be removed to mill them?
Yes.
 

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Resident Curmudgeon
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Discussion Starter · #26 ·
Choke those DCOEs down by 2-4mm off of the existing choke size. You’ll have to completely retune the mains, air, correctors, and idle jets, but that should get you what you want.

I would also happily send you a running 1.9L with a single DCOE and a sprint manifold as a trade lol!
Bump yours to 2 liter and we may have something!
 

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Opeler
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Not that you’re asking, but my thoughts are:

If the car is in good shape (and it looks like it might be from brief shots in pictures)…
And….
If the price is right…
And…
The only thing giving you pause is the motor being too strong….the good people of this forum can help you rectify that “problem” and you’ll be set!

I’m looking forward to seeing how this plays out!

Eric
 

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Pedal Smasher
1973 Opel GT
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2,698 Posts
I wouldn't get rid of the engine. Sounds like a lot of work has been done to it and it probably cost a few grand to do it. Buy the GT and follow Bob's advice on how to proceed with de-tuning the engine so it has street manners. While you might not have a lot of engine experience, the Opel CIH engine is pretty basic so it's a good engine to start learning with. Also, parts are pretty cheap.
 

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Über Genius
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9,490 Posts
After seeing the pistons, I retract my original statement.

It will be very difficult to get that engine streetable.
 
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Pedal Smasher
1973 Opel GT
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2,698 Posts
It will be very difficult to get that engine streetable.
Do you think an aftermarket EFI, like micro squirt, would have enough control without VVT to make it streetable? I've been wondering that, as I think it's the only way to avoid replacing or machining the pistons. Even if you could make the engine streetable by just tuning the Webers, it's probably still a good idea to lower the compression ratio with a change to the pistons and cam. A better torque curve could be had with these changes.
 

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Strictly speaking, there’s no down side to high compression.

Throttle response improves. Fuel economy improves. Horsepower increases, and torque increases. Driveability does not degrade just because of a compression increase.

Yes, NOX emissions typically go up too.

The only real down side to high compression is the need to temper detonation. And detonation will be an issue because of the design of the engine. The combustion chamber design, the spark plug location, the cylinder head material, the dome design…these things are not optimally designed to be detonation resistant.

With an older engine you’ll either need very high octane fuel, or a bigger camshaft with increased overlap to reduce cylinder pressures.
It’s the bigger camshaft that hurts the driveability.

So maybe a compromise…slightly smaller cam, and slightly lower compression ratio will compliment each other and retain better manners without the need to run racing fuel or a total loss of performance.
 

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Resident Curmudgeon
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Discussion Starter · #32 ·
But how do you get the slightly lower compression without tearing the engine apart?
 

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Can Opeler
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Bump yours to 2 liter and we may have something!
No if I rebuild one I’ll build it closer to your engine’s specs. Something about the 1.9L makes it have much more low end torque than my 2.0L despite having identical upgrades and carb tuning.
1.9L to 2.0 isn’t really worth it IMO. The OGTS pistons are really only 1.98L anyway

A 1.9E and 2.0E make 105HP and 110HP respectively. It pains me that I paid $2k plus for 5 extra horses in my other car. The single SSD gained me nearly 20HP for less money.
 
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Resident Curmudgeon
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Discussion Starter · #34 ·
No. Something about the 1.9L makes it have much more low end torque than my 2.0L despite having identical upgrades and carb tuning.
1.9L to 2.0 isn’t really worth it IMO. The OGTS pistons are really only 1.98L anyway

A 1.9E and 2.0E make 105HP and 110HP respectively. It pains me that I paid $2k plus for 5 extra horses in my other car. The single SSD gained me nearly 20HP for less money.
And what does the "E" mean?
 

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Opeler
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110 Posts
you need more gearing and / or smaller carbs.
 

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Can Opeler
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And what does the "E" mean?
Fuel injected. These make the closest power to my tunes on my 1.9S and 2.0E engines with side draft carbs.
 

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Über Genius
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Do you think an aftermarket EFI, like micro squirt, would have enough control without VVT to make it streetable? I've been wondering that, as I think it's the only way to avoid replacing or machining the pistons. Even if you could make the engine streetable by just tuning the Webers, it's probably still a good idea to lower the compression ratio with a change to the pistons and cam. A better torque curve could be had with these changes.
I don't have enough experience in aftermarket controllers to say but I was thinking the same thing. Maybe a tunable EFI system could handle it. Getting the right marriage of components might be tough because, I'd think, at idle the air pressures could be a little blippy.
 
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Pedal Smasher
1973 Opel GT
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2,698 Posts
But how do you get the slightly lower compression without tearing the engine apart?
You can't. You have to change either the pistons, the clearances between the piston and the cylinder head, or the cam / cam timing. I highly doubt a thicker head gasket would provide enough additional volume to decrease your compression ratio enough, so a different cam could be used. So, that means different pistons. You're kinda stuck having to rebuild the engine because racing pistons and a racing cam were used. The engine was designed and intended to be ran at higher RPMs. There is only so much tuning a carb can do. It's worth trying to see if a proper carb setup can make the engine streetable because that is the cheapest and fastest thing to try and you're pretty much going to need to deal with the carb anyways. I was wondering if an aftermarket EFI system would be capable of taming a racing engine, without the use of variable valve timing. If you had VVT, problem solved but that was never incorporated into the CIH.

Even though you'll likely need to rebuild the engine to solve this problem, I'd say it's worth it. That engine sounds like a lot of work went into it, to make a reliable racing engine out of it. You could trade with Kyler and I'm sure his engine would be just fine on the street in your car. Kyler likes to autocross, so I wouldn't be surprised if that is why he wants your engine.
 

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Celtic Lady
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Since I'm much closer to 70 than 20, this looks like it's boiling down to a complete engine rebuild or taking Kyler up on his offer!
Take Kyler offer.

I did something not so extreme in a 73 Manta. Flat top pistons-60 over, 2) 40 DCOE Webbers. I did have to rejet the Webber's. which on a DCOE is easy. Ported head, not a standard cam. I can't remember the specs. I have slept since them. I have them somewhere. I have moved 3 times so that could be a real treasure hunt. And a recurved stock distributer.
Its been running fine for 30 years on the road. Still got 20mpg. It ran real nice when I could still get Shell 110 oct and the Dino340. I tried AV gas for a while but it was a hassle to get after the local general airport closed. Where I could drive right up to the pump.
It runs on reg but its not the same.
 

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Just Some Dude in Jersey
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15,553 Posts
As cool and potentially fun, there would be a whole bunch of fuss and bother needed to make it reasonably streetable. The guys here who are suggesting that yes you can tune it to drivability are heavily into engine stuff and think it would actually be fun to make that dragon roar. But are YOU willing, at your point in life, to go dragon riding? It appears that the guy had enough knowledge to go pretty far with the project, with a custom dizzy, but then said he couldn't tune it for low speed driving. Are you willing to school yourself up enough to out do him?

How much money for this whole car and engine is a factor. Are you really just wanting to buy a nice 1900, but don't really want a fussy engine car, no matter how fast it is? If you're more comfortable with street designed Opel engines and just want an engine that works, take Kyler up on his offer. If the dollars work out.
 
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