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1970 Opel Gt - Purchased July 1972 - Chartreuse - restored - 3000 miles as of 02-16, 2021 -
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Discussion Starter · #1 ·
I was wondering if someone could tell me, on average, the horse power rating of a 2.0 engine with a Weber 32/36.
The engine:
.430" lift with a solid
grind camshaft, installed with 1.72/1.50 Chevy valves,
and 2.0 (.030" OS) pistons.
Electronic ignition

Stock exhaust
  • Have not done it yet but on my project list is to remove the carb and determine the sizing of all of the jets and emulsion tubes and match them to what would be the best possible combination listed on the forum
  • When I purchased the Weber I feel sure at the time I just told the company I purchased if from that it was for a 1970 Opel GT not considering that I had an engine upgrade so it most likely was sent for a standard 1.9 - The car runs really well however with that said I have no point of reference for a perfectly tuned Weber on a 2.0
  • I plan to remove the intake/exhaust manifold and replace the gasket to ensure no vacuum leaks
  • And while the manifold is off, I have read a lot about porting of the manifold, would that be something that I should consider on a 2.0 and if so is that something a local shop could do for me, I mean would you trust a local shop for something like that - or is that something I could do
  • Thanks, Carl
 

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Can Opeler
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3,468 Posts
With the 32/36 you won’t make much more power with a 2.0L the power band will be better with your mods though. 70-80 HP on a dyno

My 2.0L with similar mods and a ported intake with a 38DGAS made 78HP on the dyno. I could have probably gotten around 85HP now that I am a much more experienced tuner.

I would estimate I have about 90-95HP now with my side draft set up.
 

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A stock 20S with a Varajet or Zenith 35/40 INAT is rated at 100hp DIN at the flywheel, so equipped with a mild sports cam and a good exhaust one should easily make around 115hp DIN even with a Weber 32/36DGV.
 

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I was wondering if someone could tell me, on average, the horse power rating of a 2.0 engine with a Weber 32/36.
The engine:
.430" lift with a solid
grind camshaft, installed with 1.72/1.50 Chevy valves,
and 2.0 (.030" OS) pistons.
Electronic ignition

Stock exhaust
  • Have not done it yet but on my project list is to remove the carb and determine the sizing of all of the jets and emulsion tubes and match them to what would be the best possible combination listed on the forum
  • When I purchased the Weber I feel sure at the time I just told the company I purchased if from that it was for a 1970 Opel GT not considering that I had an engine upgrade so it most likely was sent for a standard 1.9 - The car runs really well however with that said I have no point of reference for a perfectly tuned Weber on a 2.0
  • I plan to remove the intake/exhaust manifold and replace the gasket to ensure no vacuum leaks
  • And while the manifold is off, I have read a lot about porting of the manifold, would that be something that I should consider on a 2.0 and if so is that something a local shop could do for me, I mean would you trust a local shop for something like that - or is that something I could do
  • Thanks, Carl
Definitely port, tent and weld up your intake manifold. One of the biggest restrictions to any Opel engine is a stock down draft intake..

Also upgrade your full exhaust to a 2" system. Remember, your engine is an air pump, what goes in must come out efficiently to acheive your engine's full potential.
 

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1970 Opel Gt - Purchased July 1972 - Chartreuse - restored - 3000 miles as of 02-16, 2021 -
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Discussion Starter · #5 ·
Definitely port, tent and weld up your intake manifold. One of the biggest restrictions to any Opel engine is a stock down draft intake..

Also upgrade your full exhaust to a 2" system. Remember, your engine is an air pump, what goes in must come out efficiently to achieve your engine's full potential.
Hi Vincent, I appreciate the information. While I have gained a lot of knowledge about the GT over the past years I must confess that I have never been an engine guy so to that point I do understand porting to a point, based on what I have read on this forum, but the term to "tent and weld up your intake manifold," has no meaning to me. Can you explain in layman terms what that means/what is involved. My entire exhaust system is almost new, actually installed in 1999 or there abouts but only has 3000 miles on it - the manifold is original so that would be 51 years and somewere over 100,000 miles. Would hate to have to replace it all when I have a considerable amount tied up in the current set up - I do understand where you are coming from and that if I want what I want then I will have to pay the price. And I know that if I replace the exhaust system then the next thing you know I would be talking headers and with all that why not a 2.4 and then of course I would have to go with the 5 speed transmission. Which is something every GT needs - I mean you would not believe the number of times I reach up there to put it into 5th gear when I only have 4 but the sound of the engine tells me I should be in 5 gear.
 

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Opeler
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More Information:
 

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Discussion Starter · #7 ·
Thanks Lindsay, Lots and lots of really good information and my understanding level have moved up several notches.
 

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Just Some Dude in Jersey
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15,203 Posts
First of all, you have the economy 32/36 carb. A Weber 38 will be way faster. A single side draft and manifold will be even more way faster. The lots more expensive and difficult to set up and tune dual side draft set up will be a little bit faster than the more affordable single side draft. These last 3 choices will vastly increase your power, especially at low speeds. I've had the tented downdraft intake mod, it doesn't really improve things much until you are at the higher rpms. Mods that improve flow generally are like that. Big carbs give you more power all through the power band.
 

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I don’t think any of us can know what HP we are running without taking it to the dyno shop, already you have a wide variety of reply’s.

Port matching your carburetor to intake manifold is the easiest way of achieving more HP Matching this gasket to the top of your intake manifold, I used a Dremel on my intake manifolds to get them matched up with the carburetor being used. Gil sells the stainless steel heat shield already ported to the 32/36. I like using this as my phenolic spacer , it’s port matched perfectly with the 32/36. If that’s checked off, and it may already be if you did this when you installed the Weber then you’re all set on that category.

With the Weber all jetting gets done with the carburetor on the car if needed. If you’re going to jet out the carburetor I might suggest getting an air fuel ratio gauge. It sounds like you have things tuned pretty nicely as it is.

Depending on how comfortable you feel disassembling your carburetor, you can also bore out the secondary venturi on your 32/36 to 29 or 30mm from its original 27mm and re-jet.

I’m currently running the 38/38 in my European 2.0 converted from my 1.9 with near stock 405/256 cam (less than yours). Meanwhile since I’ve seen how much better my 2.0 can do with a bit more flow currently running the 38/38 (I’m running a sprint manifold with the 2” exhaust). I’m boring the secondary on my 32/36 to 29mm. I think I’ll be happy with that. Honestly the 32/36 by itself isn’t as peppy as the 38/38 which has very smooth and effortless midrange power. I haven’t seen it yet but I’m thinking that the 29mm secondary by itself would be enough and I can go back to the progressive carburetor if I want keeping the same or better airflow. I wouldn’t get into anything there without an air fuel ratio gauge its just a suggestion for a bit more power.

What you read on the internet is true of the 38/38 it’s a PITA to get rid of the occasional off idle stumble. This has been my experience and it’s 6 months in of tuning with the AFR gauge. It’s just a different animal than the 32/36 and more difficult to get right. There wouldn’t be so many posts on the internet if it weren’t true.

Vincent is talking about the intake being tented the idea is to eliminate the sharp 90° angle that the air fuel mixture has to take coming out from the carburetor, look at Lindsay’s last RBob attachment for some really fine work on the subject. A superb suggestion, but requires a good welder used to fabricating aluminum intakes, you would then pick up a shorty header from OGTS to improve the exhaust side.

There you are, now if you have the stock size exhaust that’s now in the way and you want to open that up to 2” LOL. How far do you go?

I have no experience with the shorty header but it should bolt right in and could give you a nice bang for the buck. Finally be sure that your distributor timing is running at or close to 36° total mechanical timing that seems to be a nice spot for my 2.0.

I want to compliment you on the very good work you’re doing particularly with the interior. I just added new red carpet to my white GT and will be able to get almost everything else from OGTS with the exception of the door panels, I’ll be replacing the vinyl on a used set of red door panels and looking back on your thread as a template, you have helped give me the inspiration to take on the project 😃
 

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Just Some Dude in Jersey
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15,203 Posts
Trim the acceleration pump spring to cure the stumble.

I also had the trouble with the off idle stumble on both the 32/36 and the 38. It all boiled down to reducing the strength of the acceleration pump spring. The factory Weber setting to start opening the acceleration pump valve is set too low and is actually dumping gas at idle. By removing 2-3 loops of the spring, 1/2 loop at a time, in the carb lid, I was able to totally eliminate the stumble. I drive automatics, so I can't rev my engine before dropping the clutch nor set the idle above 800rpm, the tranny won't let the engine go faster than 800 when stopped at a red light. I got it tuned so perfectly, with a very exotic cam, that I could slam the gas as soon as the light turned green and instantly spin tires and roar off into the sunset.
 

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1970 Opel Gt - Purchased July 1972 - Chartreuse - restored - 3000 miles as of 02-16, 2021 -
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Discussion Starter · #15 ·
Pictures would be helpful to clear this up.............or diagram maybe.
 

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Just Some Dude in Jersey
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In this picture of a 32/36, the spring in question is part of #93 and is called the "Carb power valve assembly". My erroneously stated accelerator pump is #31, thank you for correcting me. I had it right the first time.:

435020
 

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Opeler
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Power valve tuning. See Post #13.
Think that 38/ 38 power valve is similar to 32/ 36.
 

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And here’s the accelerator pump.
82212CD7-AF0F-4BF8-8E92-307218A173E4.jpeg

It’s operated mechanically as you depress the gas pedal it adds a squirt of gas into the engine via the pump jet (circled in green).

287C8B59-0B78-4556-BE96-7500D155EF7C.jpeg

The red would be the main jets, purple are the main jet air correctors. All are removable without removing the carburetor and can be changed to larger or smaller sizes.
Note: the second picture was borrowed courtesy of the street source.com website.
 

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Discussion Starter · #20 ·
Thanks to everyone for the great information and visuals are always a plus. At sometime in the not to distant future I will open the top of the carb to see the hidden jets and check the float and will remove the carb to determine the porting match and at that point I will remove the Carb and the manifold again for porting possibilities but to also to install a new manifold gasket, making sure there are no vacuum leaks. And while I am at it I need to straighten out the part of my linkage that goes to the bracket mounted on the fire wall so I can install the new throttle grommet/bracket combination.Currently using a rubber grommet that is slightly larger than necessary but required because of the bent linkage section
The car has no stumble and the only noticeable issue, to me, I have low idle at first start 6 to 7 RPM's and after warmed up idle at around 13 - so something is not right. The car is running really well but since the 32/36 was right out of the box seems likely, based on what I have read, that it could use a little tweaking. Before I do anything I plan to reset the timing and adjust the carb as per factory settings and start from there.
 
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