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Discussion Starter · #1 ·
I am looking for info on engine set-up/tuning for my upgraded GT engine. I recently completed the stock engine upgrade from 1971 - 1.9L to 2.0L that Opel GT Source advertises. The basic components include.

- 2.0L bore with the flat high compression pistons
- larger valves (42mm intake 36mm Exhaust)
- Hotter CAM ( .420 cam lift / 268 duration)
- Crain 700 fireball ignition
- Stock distributor
- Ported intake manifold with Weber 38/38

For those of you who have done this upgrade but not the carb. I strongly recommend it, what a difference.

So what I am looking for is what other owners have done to tune this set -up..

- What octane fuel have you found to run the best?

- What total timing have you found to run the best? (I will probable stay with running a vacuum advance.) I currently time to 36 dig. btdc total at 3200 RPM with vacuum disconnected. This timing seemed to be OK with 93 octane but the fuel around hear has alcohol in it. To run non alcohol fuel I can only get 91 octane which gives me a bit of knock under load.

- what type of vacuum are you seeing with this hotter CAM at 1000rpm idle. ( I am getting about 13.5)

- If you have switched over to the 38/38 weber can you give me some jetting info that you found to work best.. (i.e. mains, emulsion tubes, Air correctors and idle jet... If you have venture and accelerator port sizes that would be a bonus)

I know there is a lot here but someone out there must have gone through all this and could give me a better starting point with all this...

Thanks for any info

Thadman

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Just Some Dude in Jersey
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I had a factory 2.0 with a 38, a split profile cam that was halfway between a Combo and a Max Comp cam, deleted vacuum advance, a dizzy with locked plates and mechanical advance restricted to I think 20, maybe less. And I removed 3 loops of the accelerator pump spring because I had very low vacuum of 11-12 which causes the accel pump to dump gas while idling and also causes the "stumble". This was a very worn out engine and the cam was weird, so take my settings with a big grain of salt.

Original Weber jets
32m venturis
F-66 emulsions
155 Mains
180 Airs
50 Idles

I ran my car with:
140 Mains
170 Airs
50 Idles
Timed to approx. 15* BTDC

RallyBob suggests:
145 or less Mains
55 Idles


38's are kind of big for our 2.0 engines and that makes the adjustment window VERY narrow. I found it very difficult to find the sweet spot of reliable starting and good mid and high rpm power/no pinging. I always set my carbs and diz timing by ear and performance. I've had no luck with timing lights. My parameters are: Reliable starting/idling and no pinging at high rpm. That's it, that's all I've ever demanded from 35 years of Opel driving. My original 2.0 with a 32/36, acquired 35 years ago, gave me 225K trouble free miles and was running like a kitten when I sold it, so I guess my simple method worked.
 

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Can Opeler
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Just a small correction to Gordon’s post. Don’t trim the accelerator pump return spring. The accelerator pump is activated by throttle.

Gordo is talking about trimming the power valve spring. The power valve is activated by vacuum. It is designed to let some fuel in when vacuum dips below say 15 or 14inHg. People with large cams often have less than this which means it will dump fuel more than it should. I believe they make power valves for specific vacuum levels, but what Gordon is suggesting is to trim the loops off of the power valve 1/2 loop at a time to drop the activation vacuum lower with your existing power valve.

Note this power valve is located right in the middle of the cover near the float.
 

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Discussion Starter · #5 ·
I had a factory 2.0 with a 38, a split profile cam that was halfway between a Combo and a Max Comp cam, deleted vacuum advance, a dizzy with locked plates and mechanical advance restricted to I think 20, maybe less. And I removed 3 loops of the accelerator pump spring because I had very low vacuum of 11-12 which causes the accel pump to dump gas while idling and also causes the "stumble". This was a very worn out engine and the cam was weird, so take my settings with a big grain of salt.

Original Weber jets
32m venturis
F-66 emulsions
155 Mains
180 Airs
50 Idles

I ran my car with:
140 Mains
170 Airs
50 Idles
Timed to approx. 15* BTDC

RallyBob suggests:
145 or less Mains
55 Idles


38's are kind of big for our 2.0 engines and that makes the adjustment window VERY narrow. I found it very difficult to find the sweet spot of reliable starting and good mid and high rpm power/no pinging. I always set my carbs and diz timing by ear and performance. I've had no luck with timing lights. My parameters are: Reliable starting/idling and no pinging at high rpm. That's it, that's all I've ever demanded from 35 years of Opel driving. My original 2.0 with a 32/36, acquired 35 years ago, gave me 225K trouble free miles and was running like a kitten when I sold it, so I guess my simple method worked.


Thanks for the Info,,, Not sure how your CAM compares to the .430 lift,,, it sounds a bit hotter than mine. What octane fuel do you run normally in this set up if I may ask..

What I have so far on my set up with the 38 is
Main Jets 145
Emulsion tubes F-66
Air corrector 185
Idle 60

It appears I am a bit bigger than RallyBob suggestion in the idle mixture jet.. however, to stay as close to the 38 factory "set up recommendations" ( i.e. 1 turn out on the idle mixture and only 1/2 turn on idle speed. the 60 worked best (7/8 turns out mixture and 1/2 in on speed for 1000 to 1100 rpm)).. the 55 was within limits, but just,, ( was at about 1 1/2 turns out which is max high end ). I definitely know the 45 and 50 idle mixture jet is to small for my 2.0L set-up.

My carb set-up was based on a Total time of 36 btdc which gives me around 6 to 7 btdc at 1000 rpm idle.. I have no gas dripping in the carb at idle and with 93 octane fuel it pulls good with little load knock.. switching to 91 octane however does give me a bit more knock, I dropped the timing to 34 total but took a 1/4 more turn in on speed setting, still no fuel dripping,, knock is a bit better.

Thadman


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Just Some Dude in Jersey
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I'm pretty sure that you should NOT have ANY knock or pinging with any grade of gas with your set up, if properly timed.

If you are getting knock, then in my opinion, you are too far advanced.

I have NEVER had one of my GT's various engine set ups develop an engine knock or pinging due to the octane of the gas I put in it. If I did get knock it was always because I had the timing too far advanced. All my GT engines have been perfectly happy with any kind of gas. You don't have excessive compression, do you?

It's a very common scenario that people advance their timing for more power, but then get pinging.
 

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Can Opeler
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I agree with Gordo. I was accidentally running 50° total advance on my GT with no pinging on premium. I had only mechanical advance. Most Opel distributors have about 34° total mechanical advance. Add that to 10° initial and you are about 8° too far advanced for a car without a cam. Some cammed engines need more like 25-30° max advance.
 

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Discussion Starter · #8 ·
I agree with Gordo. I was accidentally running 50° total advance on my GT with no pinging on premium. I had only mechanical advance. Most Opel distributors have about 34° total mechanical advance. Add that to 10° initial and you are about 8° too far advanced for a car without a cam. Some cammed engines need more like 25-30° max advance.
Well, this is all good info thank you.

As indicated in my initial note, I am running the flat top high compression pistons I do not know however, what the compression ratio would be. Also as part of the upgrade, I am running the hotter .420 lift CAM. I also don't know how this compairs with the "Stock" 2.0L engine CAM. As far as timing goes, my timing light is adjustable,, so total timing is pretty straight forward. I follow the asperated Engine guidelines indicating all engines like about 34 to 36 Deg. btdc with full mechanical advance engaged. I set my light to 36 Deg. , disconnect the vac. advance, run the engine RPM up till the disturber mechanical advance is fully engaged and then rotate distributor to set the mark dead on. At idle (1000 rpm) I am getting around 7 Deg advanced doing it this way. I then reconnect the Vac. adv.. Doing it in this fashion the mechanical total cannot be more than 36, but, when cruising the Vac. will add an additional 8 to 10 on top of the 36. I'm starting to think my Vac. advance may be a little sluggish. In other words, under engine load/ acceleration, the vac. advance should drop out and it should be going back to total mechanical,, which is set at 36....

Maybe this is all for naught,,, next summer I plan to take it in to a local shop that specializes in older , asperated car engines and have them jet the carb and set final timeing, using scopes and air/fuel sensors...
 

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I don't have any input on the tune up questions, but that's a damn nice looking GT you have there. Love the color!

If you don't mind, what did it cost to upgrade to the 2.0? It's something I want to do in the future along with the 5 speed and wanted to get a ballpark figure.
 

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...the mechanical total cannot be more than 36, but, when cruising the Vac. will add an additional 8 to 10 on top of the 36. I'm starting to think my Vac. advance may be a little sluggish. In other words, under engine load/ acceleration, the vac. advance should drop out and it should be going back to total mechanical,, which is set at 36....
While full vacuum AND mechanical advance may not actually happen simultaneously, the combined advance is likely going to exceed 36 degrees, which could certainly create detonation and actually reduce power. I like vacuum advance to some extent, although many delete or disconnect it. In fact, there is no vacuum advance on the '75 distributor, only vacuum retard (which is typically disconnected). The solution to excessive combined advance is to modify the breaker plates to limit total advance to 36 degrees, using a set screw. I haven't done one yet (on my list) but there are several threads with photos here that show ways of doing that.
 

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Just Some Dude in Jersey
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If you don't mind, what did it cost to upgrade to the 2.0? It's something I want to do in the future along with the 5 speed and wanted to get a ballpark figure.
The best aspect of a 2.0 upgrade(Meaning: 2.0 displacement and big valves/hardened exhaust seats in the head) is the head. When I got my first one 30 years ago, I bought the head first. It was a HUGE improvement over the power of the stock 1.9 1970 high comp engine I had. A year later I bought a 2.0 short block to put under the head. Only a little improvement in power.

OGTS sells 2.0 heads for about $1000. I'm pretty sure the short block would also be around $1000. You'll end up doing a lot of parts swapping over from your present 1.9. Timing chains, gears, guides often need replacing. Don't forget the $100 for the gasket set.

Many will tell you that it's much cheaper, like 1/3 the price, to buy the parts yourself and have your local machine shop do the work. We have seen many, many, guys on this site go this route and a VERY high percentage end in disaster. You can't trust your local machine shop to do Opel heads correctly.

I suggest contacting member Charles Goin, who recently has been importing 2.4 liter engines for us, and has schooled up his local shop on how to do Opel engines correctly. That's where my engine came from. He could probably make you a rebuilt 2.0, mostly assembled, for $1500. Even OGTS suggests that some people use him as an engine source. They did with me.

:veryhappy
 

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Discussion Starter · #12 ·
While full vacuum AND mechanical advance may not actually happen simultaneously, the combined advance is likely going to exceed 36 degrees, which could certainly create detonation and actually reduce power. I like vacuum advance to some extent, although many delete or disconnect it. In fact, there is no vacuum advance on the '75 distributor, only vacuum retard (which is typically disconnected). The solution to excessive combined advance is to modify the breaker plates to limit total advance to 36 degrees, using a set screw. I haven't done one yet (on my list) but there are several threads with photos here that show ways of doing that.
Thanks again Keith,, but I am not sure why you would need to "Set Screw" the plate,, can't you just disconnect the advance and cap the ports? I suppose there is always a chance of a little wobble just leaving it and that is what the set screw is trying to eliminate.
 

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Can Opeler
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Thanks again Keith,, but I am not sure why you would need to "Set Screw" the plate,, can't you just disconnect the advance and cap the ports? I suppose there is always a chance of a little wobble just leaving it and that is what the set screw is trying to eliminate.
Keith misspoke a little bit. You can either weld or rivet the plates then you install a set screw on the stops for the mech advance weights. Or if you are lazy like me you just bend those stops inward until you get the advance you want.
 

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Discussion Starter · #14 ·
I don't have any input on the tune up questions, but that's a damn nice looking GT you have there. Love the color!

If you don't mind, what did it cost to upgrade to the 2.0? It's something I want to do in the future along with the 5 speed and wanted to get a ballpark figure.
Gordo has some great advice if you are looking into this.

My car is a hobby,,, I have had it for over 35 years, so, I did a lot of the work myself,, to a degree. I stripped the block down to a short block leaving the pistons and crank all attached when I turned it over the engine shop. I was living in the Lansing MI area at the time and there is a great shop call Engine Technology that did the block work, he does all the local dirt track engines and was familiar with the Opel block. As it turns out my original 1.9L head was cracked so I purchased a full upgrade head from Opel GT Source,, minus the CAM and lifters, The shop did the bore work and main bearings and returned a rebuilt 2.0L block to me... setting the lifters and CAM and reassembly I did myself. (NOTE: If you pull the radiator, head and other engine accessories, you can separate it from the Bell Housing and lift it up and out through the top. This will work better if you block the car up off the ground about 8" or more, support the engine from the top and remove the engine mount bracket also, this allows a little more flexibility in shifting the engine around inside the compartment.)

With the block work, rebuilt Head, performance CAM (.420 lift), new lifters, gaskets and Weber 38/38 (I ported the intake)… I was into this for about $3000.00. When I did this I hadn't driven the car in over 10 years, so it was hard to tell what improvement in power their was. I drove this new engine for about the first 1000 miles with Weber 32/36 that was on the 1.9 block. This was good enough but I felt the engine was asking for more, so, I recently installed the 38/38 and man, what a difference. Much faster throttle response and so on... the 38/38 would defiantly be to big for the 1.9L, but it's a must in my opinion on the 2.0 with Com. CAM.

So there you have it,,, good luck.
 

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Über Genius
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Re: the 38

My son and I have identical engines other than I have an aluminum flywheel.
We both, now, have 38's.
We both have the same compression. We have the same pistons, the same cam grind.

His car drives like his gas pedal is an on/off switch and gets 29(ish) mpg on the highway.
I get about 22 on a good day.
We did the test on the same day, same drive, same speed.

Our carbs are jetted the same.

My car, when it's warm, doesn't want to turn over as if it's advanced too far. His just spins right up.
I've had to retard my dizzy just to get it started when it's warm.

My throttle response is lackluster.

My car pings a tiny bit sometimes. if it's hot out and I'm putting it under load on a hill.

his engine has 50K on it (though rebuit with new bearings about 5K ago)
My engine has about 10K total.

We have the same Pertronix and the same coil and the same alternator, etc.

I built both engines.

So, what's different?

We don't have the same springs in our distributors.

I don't have pictures but I am going to try to explain how the springs on the mechanical advance work.

One spring is usually weaker than the other. This spring is your initial throttle advance spring. It has a tight loop connection on both ends.
The other spring is stronger and has a slip fit on one end of the connections. This is VERY important in determining the curve of your advance.



At least that's the way it's SUPPOSED to be.


The first spring is your initial curve. It allows the mechanical advance to move at lower RPM's. Once your mechanical advance gets it's initial curve, the slack on the other spring (the slip fit loop) is taken up, the stronger spring kicks in and the curve slows down. This will get you to "total" advance if and when the RPM's are sufficient enough.

The vacuum advance is also part of the system as it adds a little advance to get the engine off the idle speed. It reacts faster than the first spring but adds to total advance.

So, when you add all the factors together, you get your curve.

Changing the tension of the distributor springs is how you "tune" the distributor. Also changing the length of the slip length spring is part of the tuning. Vacuum advance, longer stroke or shorter stroke will also tune it.

And then there's the modifications you can make to total advance and such. If you are playing with restricting total advance, you probably have other factors that have been changes. Perhaps tight loop weak springs, for example.
 
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Just Some Dude in Jersey
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So, what's different?

We don't have the same springs in our distributors.

I don't have pictures but I am going to try to explain how the springs on the mechanical advance work.

One spring is usually weaker than the other. This spring is your initial throttle advance spring. It has a tight loop connection on both ends.
The other spring is stronger and has a slip fit on one end of the connections. This is VERY important in determining the curve of your advance.



blah....blah...blah

Nice post! I never knew any of that stuff. RB did all that stuff to my dizzy, but I never knew why.

:veryhappy
 

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Keith misspoke a little bit. You can either weld or rivet the plates then you install a set screw on the stops for the mech advance weights. Or if you are lazy like me you just bend those stops inward until you get the advance you want.
Thanks for the clarification Kyler. I haven't modified a distributor yet for my engine, as I haven't decided for certain if I will be using my stock '71 dizzy, connecting only the vacuum advance and disabling the vacuum retard, or a '75 dizzy which doesn't have a vacuum advance (and similarly not connecting the vacuum retard). I thought that there was a way to install a limit set screw on the '71 dizzy that allowed for vacuum advance at high throttle & low rpm, AND mechanical advance at higher rpm, but the set screw would limit TOTAL advance (vac + mech) to a certain set amount. If not, then the '75 dizzy might be the obvious choice.

Time to dig out my distributors (I think I have several of various years, all "reconditioned") to see what I want to do.

But my point above remains that having BOTH vac and mech advance can allow total timing advance to exceed 36 degrees, thereby causing detonation and/or power loss.
 
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Discussion Starter · #20 ·
Thanks for the clarification Kyler. I haven't modified a distributor yet for my engine, as I haven't decided for certain if I will be using my stock '71 dizzy, connecting only the vacuum advance and disabling the vacuum retard, or a '75 dizzy which doesn't have a vacuum advance (and similarly not connecting the vacuum retard). I thought that there was a way to install a limit set screw on the '71 dizzy that allowed for vacuum advance at high throttle & low rpm, AND mechanical advance at higher rpm, but the set screw would limit TOTAL advance (vac + mech) to a certain set amount. If not, then the '75 dizzy might be the obvious choice.

Time to dig out my distributors (I think I have several of various years, all "reconditioned") to see what I want to do.

But my point above remains that having BOTH vac and mech advance can allow total timing advance to exceed 36 degrees, thereby causing detonation and/or power loss.

That is true, your combined vacuum and mechanical will put you up in the 40 BTDC range when cruising at steady state,,, this supposedly, at least for street driving will give you better millage and help your engine run cooler. However, when you get into the throttle, the vacuum in your engine goes to nothing and your back on just your mechanical advance,, which for my setting is 36 BTDC. My engine is strong and peppy at this setting, idles nice, but, I do have a low sounding knock, almost like banging two pieces of wood together, not bad but it's there under load. When I drop my timeing back, it idles like crap with this combo CAM, so , I'm thinking maybe my Vac advance isn't falling off quick enough, or, my mechanical is going to full advance to quick. The 1971 GT repair manual indicates full mechanical around 3600, my distributor however, is at full Mechanical advance around 2400, What I read on various distributor power curving forums, (V-8 mostly) you should be all in mechanically around 3000 to 3200 RPM... is the 2400 RPM full mechanical normal for a 1971 Distributor?? Just more to ponder I guess.
 
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