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Opel Rallier since 1977
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It sounds like you’re right on it.
I drove around with the vacuum advance to manifold for all the positive reasons that you read about but the engine seemed too have much advancement on higher rpm deceleration (throttle plates closed)with no backing off from the advancement, I just didn’t like that so I moved it back to the carburetor.
I’ve since tuned out the off idle stumbles, I found that getting the mixture screw to 1.5 turns out from bottom enriching my idle AFR to 12.5 or close took care of the little lean spot off idle. Back when I had trouble with that was another reason for trying the manifold vacuum advance.
All this discussion about vacuum advance, and I’m out of my depth here on the 2.4, I thought Opel did away with the vacuum advance in 75’ ? Or was that just on the FI 1.9’s?
The numbers for ignition advance on all other engines form this era are similar. So there is not any real 'out of my depth' on this matter. And yes, the '75 US FI Opels only had a vacuum retard. But, IIRC without looking it up, it is only at idle.low RPM, so really is a form of ported vacuum advance.
 

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Discussion Starter · #42 ·
ok. just wanted to be shure, that my carburation experiments are not the cause of my new very saddening problem
 

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Discussion Starter · #45 · (Edited)
there is smoke from the exhaust, even in idle. and when take the hose off the valvecover, there are stong puffs coming out .
this is a new built engine, less than 1000km old
my friend at the engine shop suspects a broken ring land in the piston, due to kocking.

could cry.....
 

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The numbers for ignition advance on all other engines form this era are similar. So there is not any real 'out of my depth' on this matter. And yes, the '75 US FI Opels only had a vacuum retard. But, IIRC without looking it up, it is only at idle.low RPM, so really is a form of ported vacuum advance.
I was quite surprised when reading the posts for the 2.4 on the forum that it doesn’t except the 34-36° total that I’m using on my 2.0 and most engines that you read about. Prellbock seems to have it close to where I’ve read it should be on the forum.

Curious that you mentioned the burn can look fine on the air fuel ratio gauge while you may be leaving unburn’t fuel in the combustion chamber, I’ve learned in past days of over jetting using the gauge and even occasional spark plug reading that there must be some truth to that.
I still have an old oil sample from the old days of gas boiling and generous (lower) afr numbers. I haven’t sent that out yet 🙈 to have it analyzed from those days. Now I’m getting more curious to compare that to how it looks now.

I’m very sorry to hear about your piston ring issues Prellbock, who would have thought, it sounded like a strong engine. Hope you’re not going to be up against too much and you will keep us in the loop.
 

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Opel Rallier since 1977
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Curious that you mentioned the burn can look fine on the air fuel ratio gauge while you may be leaving unburn’t fuel in the combustion chamber, I’ve learned in past days of over jetting using the gauge and even occasional spark plug reading that there must be some truth to that.
I still have an old oil sample from the old days of gas boiling and generous (lower) afr numbers. I haven’t sent that out yet 🙈 to have it analyzed from those days. Now I’m getting more curious to compare that to how it looks now.
I'd like to hear that analysis, Tom. Could be interesting. How long was that oil run?

As for the AFR readings, the O2 sensor is just that.... and O2 senors. It is not a hydrocarbon or CO2 or CO or NOx sensor. It can only read free oxygen, and, with the assumption of standard 'complete' combustion is taking place, use that free oxygen level to infer the AFR. Here is a good graph (with the same curves I ahve seen several places) of the different combustion products and their percentages with varying AFR ratios. At stochiometric, the free oxygen on just above 0.5%....not a lot. It is amazing they work as well as they do IMHO.

 

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I'd like to hear that analysis, Tom. Could be interesting. How long was that oil run?

As for the AFR readings, the O2 sensor is just that.... and O2 senors. It is not a hydrocarbon or CO2 or CO or NOx sensor. It can only read free oxygen, and, with the assumption of standard 'complete' combustion is taking place, use that free oxygen level to infer the AFR. Here is a good graph (with the same curves I ahve seen several places) of the different combustion products and their percentages with varying AFR ratios. At stochiometric, the free oxygen on just above 0.5%....not a lot. It is amazing they work as well as they do IMHO.

Thanks for the article, interesting how things fall off once you get the afr’s into the 12:1’s. Makes sense. There’s some posts on the site that mentioned MAP sensors, maybe it was tuning dual side drafts but in that case you ideally had 4 (I think) and that requires a header. I’m going by my faulty memory LOL, hopefully I remember that right. That, of course with the air fuel ratio gauge would be a big help for tuning any carburetor.

I think I’m my case having just the air fuel ratio gauge and periodic spark plug checks I’ve learned to tune on the lean side these days as long as acceleration is good, driving is smooth, there’s no hesitation or flat spots.

I’ll definitely post the results for the oil analysis on a separate thread, fortunately I have all my jetting selections recorded, and dated along with the oil I had in mind to send in. The changes are done every 3,000 miles oil & filter. I have the container that was sent out to me from the analysis company, all I have to do is send it in. See if I can get around to it this weekend. It’s actually a very healthy habit to get into on a regular basis for anyone interested in prolonging the life of their engine.
 

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Discussion Starter · #53 ·
My experience with my 2.0 was a huge boost in low end torque with the change from the 32/36 to a 38DGAS. It did come at a price, though, I had to suffer with much more power everywhere..
what valve sizes does your 2.0 have?
 

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Detritus Maximus
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I have a stock rebuilt euro 2.0E. Probably '81-ish for its year.
It is 'as purchased' from GT Source in 2000. Nothing 'performance' at all on the inside.
I have a 75 distributor with Pertronix coil and pick up. About 10 degrees initial and 34 total. 75 exhaust manifold (and to my shame, a stock GT head pipe and muffler, no resonator).
It was strong with the 32/36 DGAV, but really changed character with the 38 DGAS.

Currently has a 32/36 on it, but I have no idea what jets are in it. I'd have to open it to check.

From your questions, I don't think my jetting is what you are looking for, since I don't have the cam and additional work.
 

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Good deal on the 38 DGAS. Did it improve performace all through the RPM range, or just in certain parts of the RPM range?
 

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Detritus Maximus
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All of it. The power improvement was noticeable all thru the rpm range.
It actually made the car easier to drive as it needed less rpm to take off from a stop due to the extra torque.
I saw no down sides.

The only issue I can think of is what has been mentioned before about the fuel bowl draining too fast on a serious run thru the gears. I never experienced it. I think the solution suggested was enlarging the fuel line from the tank to the carb, including the fitting at the tank.
 
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The only issue I can think of is what has been mentioned before about the fuel bowl draining too fast on a serious run thru the gears. I never experienced it. I think the solution suggested was enlarging the fuel line from the tank to the carb, including the fitting at the tank.
Really not an issue until you’re making at least 135-140 hp. And even then, it only happened to me at the track, running at around 6500 rpms in top gear.
 

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All of it. The power improvement was noticeable all thru the rpm range.
It actually made the car easier to drive as it needed less rpm to take off from a stop due to the extra torque.
I saw no down sides.

The only issue I can think of is what has been mentioned before about the fuel bowl draining too fast on a serious run thru the gears. I never experienced it. I think the solution suggested was enlarging the fuel line from the tank to the carb, including the fitting at the tank.
If you ever drain your fuel bowl while accelerating hard in 3rd gear, this would be an indicator that your carb floats need adjustment.
 
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Discussion Starter · #59 ·
hello folks,
long time no see.
time for a little update:
i disassembled the whole engine, only to notice that really nothing was wrong with it.
except that a little aluminum plug in the head popped out, causing an oil spill, which floated the whole head area, so that a lot of oil made it through both inlet and outlet valve guides.
fixed that and put everything back together. just to decide right after assembling to get a proper cylinder head. so i bought a X24 head (thats the one, which came originally on the C24NE). overhauled that one made some mild modifications. modified the manifold as well to fit on this head. bla bla bla and so on.
i even got me a new carb. an 38 DGAS, like u guys recommended. overhauled that one too.

good news is: DAMN, this car makes fun now. holy smoke, i love it!

bad news: i have the same issues with wrong mixture at the wrong time.
(crusing is very rich, light accelleration is to lean)

so it must be an engine related problem.
than i had an idea: my car does not have an crankcase ventilation into the manifold like normal cars have.
as i see it, this ventilation causes a little air leak, changing vaccum in the manifold. carbs are made adapted for that. since my engine doesn't have that, noting matches.
could this be the reason or is this complete BS?
 

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Discussion Starter · #60 ·
ok, this theory is BS.
changed crank case ventilation back to original - made no difference. cruising is still in the 11's and light acceleation is lean in the 15's or 16's. with bogging when opening the trottle from cruising. WOT is somehow ok. could be improved with simple rejetting, i belive (high 12's).

so i'm back to my camshaft theory- that it produces too much vaccum. when that is true - there must be a possibility to change the carbs general behavior somehow.
any ideas for that or is this BS as well?
 
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