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Resident Curmudgeon
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Discussion Starter · #1 ·
I'm looking at a 72 1900 that I am told runs great at higher RPMs, but does poorly at lower ones. It sounds like it was set up more for racing than driving. I would like to use it for casual driving, not racing. Any suggestions on how to tame this thing? Would going back to a "stock" Weber help? Any ideas at all?? The current owner provided the following details of the work done:

Long Block work
Bored from 3.6912 to 3.862 (.020) oversized, piston to wall clearance of .005 - (2.0 ltr)
Surfaced engine block, cleaned and mag tested
Clean and mag test head
Polished crank
New cam gear and timing chain
High Compression Piston and Rings
Forged Piston Rods
Solid Lifters
Polished and refaced valves
Cleaned head and 3 angle cut valve seats
Pressure tested head after assembly
Surface step flywheel and balance pressure plate
CAM – CAM installed came with vehicle when purchased. Not sure of the specs, it came with the vehicle. IT was located in zip lock style bag in the trunk with some other misc. parts when car arrived ‘solid racing cam for Opel’ . Not sure of the specs or details. And this is the puzzle that has stalled me since the rebuild. Car runs great at higher RPMs but low RPM driving takes effort - car chokes on gas and after gas logged – it drives sluggish (power band is difficult to achieve from low speed). But if you drive aggressive and can keep the RPMs up (even at low speed – driving in 1st gear with engine revved ) she’s a beast.

Fuel System:
2 Italian made DCOE 45s
Side draft manifolds
 

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Can Opeler
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3,570 Posts
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!
 

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Über Genius
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9,490 Posts
A stock cam and weber 32/36 will tame it. Otherwise, there's nothing special about that motor.
 
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Super Moderator
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I'm looking at a 72 1900 that I am told runs great at higher RPMs, but does poorly at lower ones. It sounds like it was set up more for racing than driving. I would like to use it for casual driving, not racing. Any suggestions on how to tame this thing? Would going back to a "stock" Weber help? Any ideas at all?? The current owner provided the following details of the work done:

Long Block work
Bored from 3.6912 to 3.862 (.020) oversized, piston to wall clearance of .005 - (2.0 ltr)

High Compression Piston and Rings
Hopefully this isn’t accurate. Stock 1.9 bore is 93 mm, or 3.661”.

A bore of 3.862” (98.09 mm) is an increase of .201”, not .020”!

When you say high compression…do you just mean flat-top pistons or aftermarket domed pistons? If they are domed then you may need to run a big cam to bleed off some of the cylinder pressures.

All this said, without specific camshaft specs it’s really hard to nail down the driveability issues.

Chances are it’s a combination of too-big a carburetor (45’s are kind of big if the head has stock valve dimensions), incorrect jetting, and most likely an unmodified distributor.

Any camshaft considered a ‘race cam’ will need a vacuum advance deletion and modified advance curve or it will do EXACTLY as you say…it won’t run worth a damn at lower rpms and will foul the plugs from a too-rich mixture.

A high energy ignition requirement is a given as well.
 

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Just Some Dude in Jersey
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15,557 Posts
Hopefully this isn’t accurate. Stock 1.9 bore is 93 mm, or 3.661”.

A bore of 3.862” (98.09 mm) is an increase of .201”, not .020”!

When you say high compression…do you just mean flat-top pistons or aftermarket domed pistons? If they are domed then you may need to run a big cam to bleed off some of the cylinder pressures.

All this said, without specific camshaft specs it’s really hard to nail down the driveability issues.

Chances are it’s a combination of too-big a carburetor (45’s are kind of big if the head has stock valve dimensions), incorrect jetting, and most likely an unmodified distributor.

Any camshaft considered a ‘race cam’ will need a vacuum advance deletion and modified advance curve or it will do EXACTLY as you say…it won’t run worth a damn at lower rpms and will foul the plugs from a too-rich mixture.

A high energy ignition requirement is a given as well.


Yeah, all that stuff he said.

:)
 

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Resident Curmudgeon
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1,460 Posts
Discussion Starter · #6 ·
Hopefully this isn’t accurate. Stock 1.9 bore is 93 mm, or 3.661”.

A bore of 3.862” (98.09 mm) is an increase of .201”, not .020”!

When you say high compression…do you just mean flat-top pistons or aftermarket domed pistons? If they are domed then you may need to run a big cam to bleed off some of the cylinder pressures.

All this said, without specific camshaft specs it’s really hard to nail down the driveability issues.

Chances are it’s a combination of too-big a carburetor (45’s are kind of big if the head has stock valve dimensions), incorrect jetting, and most likely an unmodified distributor.

Any camshaft considered a ‘race cam’ will need a vacuum advance deletion and modified advance curve or it will do EXACTLY as you say…it won’t run worth a damn at lower rpms and will foul the plugs from a too-rich mixture.

A high energy ignition requirement is a given as well.
It has an MSD Electronic Ignition System – coil, distributor, and wires

For what it's worth, here's a picture of the pistons that were installed - not sure if you can tell much from it.

Fluid Automotive tire Gas Auto part Automotive lighting


Also, a shot of the engine compartment. I'll try to find out more about the pistons and valves, but right now this is all that I have to go on.

Hood Automotive fuel system Motor vehicle Automotive exterior Automotive design
 

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Opeler
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1,318 Posts
It has an MSD Electronic Ignition System – coil, distributor, and wires

For what it's worth, here's a picture of the pistons that were installed - not sure if you can tell much from it.

View attachment 438447

Also, a shot of the engine compartment. I'll try to find out more about the pistons and valves, but right now this is all that I have to go on.

View attachment 438448
The pistons definitely looked domed to me, at least from the picture.
 

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Super Moderator
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The pistons look like Venolia forged pistons. I’d say at least 11:1 compression ratio, so yea…you HAVE to run a big cam or else you’re stuck running 110 octane fuel.

MSD never made distributors for Opels, so that part is still an unknown. It has to be recurved with a big cam and compression like that.
 

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Super Moderator
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That almost looks like a high-port head too in the last pic. If so it already has bigger valves than the 1.9.
 

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Resident Curmudgeon
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1,460 Posts
Discussion Starter · #10 ·
Here's a better shot of the engine:
Hood Car Vehicle Automotive tire Motor vehicle


I have pulled and replaced engines in Kadetts and a GT, but my experience in actually working on the internals of an engine is of the "drink beer and stare at it" variety. Am I getting in over my head here in trying to tame this beast?
 

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Super Moderator
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13,985 Posts
Here's a better shot of the engine:
View attachment 438449

I have pulled and replaced engines in Kadetts and a GT, but my experience in actually working on the internals of an engine is of the "drink beer and stare at it" variety. Am I getting in over my head here in trying to tame this beast?
I apologize, judging by the photo somebody has adapted what seems to be an aftermarket (MSD?) distributor to that engine. I’m sure that cost a pretty penny. Definitely not off the shelf.

As long as you understand the principles of tuning a high performance engine, it can be made very driveable. However streetability by description is a matter of taste and tolerance. What is streetable to a 20 year old may be downright intolerable to a 60 year old.

If that engine is in fact ‘high strung’, it may be made worse by factory gearing (transmission and rear axle ratios). More highly strung engines respond better to closer transmission ratios and steeper final drives.
 

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Pedal Smasher
1973 Opel GT
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2,700 Posts
I think the biggest issue is the domed pistons. This choice in pistons necessitates a racing cam. So the engine is designed for higher RPM use. I don’t know if changing the carb specs would make much of a difference. Bob has tons of experience with these engines so if he says it can still work, he would know. I think the piston and cam might need to be changed so the engine is designed for lower RPM use. A piston meant for racing is compromising its low end manners.
 

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Resident Curmudgeon
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Discussion Starter · #13 ·
I apologize, judging by the photo somebody has adapted what seems to be an aftermarket (MSD?) distributor to that engine. I’m sure that cost a pretty penny. Definitely not off the shelf.

As long as you understand the principles of tuning a high performance engine, it can be made very driveable. However streetability by description is a matter of taste and tolerance. What is streetable to a 20 year old may be downright intolerable to a 60 year old.

If that engine is in fact ‘high strung’, it may be made worse by factory gearing (transmission and rear axle ratios). More highly strung engines respond better to closer transmission ratios and steeper final drives.
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!
 

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Detritus Maximus
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Bob,
If those pistons are what you think they are, could the domes be machined down to reduce compression?
 

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Super Moderator
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Bob,
If those pistons are what you think they are, could the domes be machined down to reduce compression?
Yes, unless they are hollow domes (machined underside), you can mill off what you want to get to the desired compression ratio.
 
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Super Moderator
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Maybe some one local to you can spec out the camshaft you have. Very easy to establish valve lift, and with a mock-up cylinder head and a dial indicator, duration can be established too.
 
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Resident Curmudgeon
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Discussion Starter · #18 ·
I don't own it yet. What I'm trying to figure out is what it would take to get it to where I'd be happy with it. Although knowing the cam numbers would be helpful, I'm not sure that those pistons will be able to be "tamed" to a reasonable degree.
 

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Detritus Maximus
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Yes, unless they are hollow domes (machined underside), you can mill off what you want to get to the desired compression ratio.
Yeah, that's what I was wondering about. Mill the pistons, different cam and some carb work (or Weber 40s) could make a fun, steerable motor.
 

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I think the biggest issue is the domed pistons. This choice in pistons necessitates a racing cam. So the engine is designed for higher RPM use. I don’t know if changing the carb specs would make much of a difference. Bob has tons of experience with these engines so if he says it can still work, he would know. I think the piston and cam might need to be changed so the engine is designed for lower RPM use. A piston meant for racing is compromising its low end manners.
It's definitely over carbureted with those 45's. They need smaller chokes like Kyler said.
 
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