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Discussion Starter · #1 ·
I have just fitted a new Isky combo cam (OGTS p/n 6059) but I am still a few months away from running the motor and road testing. Anyone out there have any tips on specific adjustments needed when running this cam or it a case of start and run - have fitted the oil dam, new hyd lifters and will use break in oil. Also, what kind of power increase does this give. Any insights are appreciated.
 

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Power increase from this cam is depended on your engine specification, what intake / exhaust systems you are utilizing , and overall state of tune.

Without more information it's hard one to answer
 

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Discussion Starter · #3 ·
Hi Vincent, it,s a stock 19L from 1973. Not planning to do anymore on it as the rest of the motor is good. A couple of the lifters were seized so replaced all and decided to go new cam as well. Other than that, fitted Weber 32/36 along with OGTS short header and sport SS Exhaust.
 

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Stock low compression pistons? Not much use for a power improvement but who knows...
 

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Hi Vincent, it,s a stock 19L from 1973. Not planning to do anymore on it as the rest of the motor is good. A couple of the lifters were seized so replaced all and decided to go new cam as well. Other than that, fitted Weber 32/36 along with OGTS short header and sport SS Exhaust.
Generally most who use the isky combination cams ( me including) use them in engines with flat top pistons and larger valves. ..

I would think a combo cam in stock 73 low compression engine would take away alot of low end torque.
 

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I am running the hydraulic OGTS/Isky Combo cam (w/ 4 degrees advance using a Comp Cams offset bushing) with stock valves, but I have bored it 30 thou and have flat top pistons. I also tented and ported the intake quite massively, installed a Sprint exhaust header, a 38DGAS, and tuned it all with an AEM Air/Fuel-Ratio sensor. I believe my engine puts out ~100 HP compared to the stock 78 HP. With my lightened flywheel (19.6 lbs vs 23.6 lbs), it is very lively, and surprisingly torque-y

I might guess that the Combo cam in your case will bump the output ~10 HP (so 88 vs 78). But the low end torque won't be better I am afraid, and maybe a touch worse.

The biggest improvement I can suggest (aside from bigger valves, which will happen on Version 2 on my engine) is the offset cam gear bushing. Advancing the cam timing loses a bit of top end HP, but sure seems to have improved low and middle rpm torque. It is a bit complicated to do (requires a bit of machining of the gear), and aside from the bushings, there isn't an "off the shelf" (short of a very expensive Kent vernier cam gear) way to do this.

HTH
 

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I just noticed that you are in France, n'est pas? If this is a Euro GT, it might already have flat top pistons. If so, add 10 HP to my numbers.
 
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I just noticed that you are in France, n'est pas? If this is a Euro GT, it might already have flat top pistons. If so, add 10 HP to my numbers.
Good point, he may indeed already have flat top pistons
 

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Discussion Starter · #9 ·
I just noticed that you are in France, n'est pas? If this is a Euro GT, it might already have flat top pistons. If so, add 10 HP to my numbers.
Kwilford..yes I am en France! The GT is euro and although I'm not sure on the exact difference, the pistons certainly look flat tops with half round valve cutouts. Thanks for the info, I'll just have to wait and see when its street ready again.
 

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I'm thinking the biggest difference will be in the Idle. It'll be alittle loppy. Maybe a bit more hp but not alot. You need to increase Flo via the heads to really take advantage of the combo cam. A hotter ignition as well perks it right up.
 

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Discussion Starter · #11 ·
I'm thinking the biggest difference will be in the Idle. It'll be alittle loppy. Maybe a bit more hp but not alot. You need to increase Flo via the heads to really take advantage of the combo cam. A hotter ignition as well perks it right up.
Thanks Dale. Was expecting lumpier idle but will see how it goes and if there's any concern I'll put the stock cam back in. I do have the ignition upgrade to fit as well in the next month or so. This engine is new ground for me so I'm quite excited to see what can be easily tweaked without forfeiting reliability.
 

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That cam will respond well to a modified distributor. Vacuum advance is essentially useless on it with a low-vacuum camshaft.

I would lock-out the vacuum advance mechanism, and restrict the mechanical advance. 8 degrees of timing advance at idle, 36 degrees total. Use two of the ‘light tension’ mechanical advance springs, as the original heavy spring will not keep the idle low enough due to the lack of initial tension.

A modified distributor will make the engine start easier, will improve the low end torque, and will reduce the lopey idle.
 

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That cam will respond well to a modified distributor. Vacuum advance is essentially useless on it with a low-vacuum camshaft.

I would lock-out the vacuum advance mechanism, and restrict the mechanical advance. 8 degrees of timing advance at idle, 36 degrees total. Use two of the ‘light tension’ mechanical advance springs, as the original heavy spring will not keep the idle low enough due to the lack of initial tension.

A modified distributor will make the engine start easier, will improve the low end torque, and will reduce the lopey idle.
Yes, exactly what Bob says! I went with a bit more initial advance (12 degrees BTDC at 1000 rpm) but I have exactly 36 degrees maximum advance at 3400 rpm, checked with my electronic timing advance-measured timing gun.

I also clipped the power valve spring one full loop. Vacuum was only 12" Hg at idle, and the power valve closed at 14" HG, so it dribbled a bit of gas at idle Took two half-loop spring clips before it stayed closed at an idle, and opened smoothly at a bit over half-throttle (~8" Hg)
 

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Yes, exactly what Bob says! I went with a bit more initial advance (12 degrees BTDC at 1000 rpm) but I have exactly 36 degrees maximum advance at 3400 rpm, checked with my electronic timing advance-measured timing gun.

I also clipped the power valve spring one full loop. Vacuum was only 12" Hg at idle, and the power valve closed at 14" HG, so it dribbled a bit of gas at idle Took two half-loop spring clips before it stayed closed at an idle, and opened smoothly at a bit over half-throttle (~8" Hg)
I went to a PS91 coil & XR3000 craincam ignition. Eliminated the Vacuum advance. Has worked almost flawlessly for many years so far. Run great except for cold startups. Once its warm its fine.
 

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Discussion Starter · #15 ·
That cam will respond well to a modified distributor. Vacuum advance is essentially useless on it with a low-vacuum camshaft.

I would lock-out the vacuum advance mechanism, and restrict the mechanical advance. 8 degrees of timing advance at idle, 36 degrees total. Use two of the ‘light tension’ mechanical advance springs, as the original heavy spring will not keep the idle low enough due to the lack of initial tension.

A modified distributor will make the engine start easier, will improve the low end torque, and will reduce the lopey idle.
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Bob, thanks all understood. I seem to have the 1975 type vacuum retard only distributor which must have been fitted by a PO. As far as the lighter tension springs go, is there a known part number for these? I am planning to refurb the dizzy anyway so it would make sense to change them at the same time.
 

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Discussion Starter · #16 ·
Bob, thanks all understood. I seem to have the 1975 type vacuum retard only distributor which must have been fitted by a PO. As far as the lighter tension springs go, is there a known part number for these? I am planning to refurb the dizzy anyway so it would make sense to change them at the same time.
I have just come across Opel club notes concerning the 1975 type distributor and conversion from earlier types. From what I've read, I should be good to go with this cam distributor combo, just a bit of a timing check and adjustment when I get the motor running. Interesting..
 

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Discussion Starter · #17 ·
I have just come across Opel club notes concerning the 1975 type distributor and conversion from earlier types. From what I've read, I should be good to go with this cam distributor combo, just a bit of a timing check and adjustment when I get the motor running. Interesting..
20201226_121108.jpg
 

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The point made about trimming the Power or Accelerator valve spring is important. That cam will almost certainly drop your vacuum at idle to the point that the Accelertion valve starts to open.. We are assuming that you are using a Weber 32/36 or a Weber 38. The low vacuum will cause the Power/accelerator valve to prematurely start to open at idle. When you step on the gas the valve will allow too much fuel into the engine as you are coming off idle and you will experience what we call The Bog. The engine will seem to slow down or hesitate. This can be very annoying. You are probably using a stick shift and not an automatic, so maybe this will not be a problem because you can rev the engine as you go into 1st gear, but I have always used automatics that you don't rev coming of idle and this problem was bad for me. I would have to flutter the pedal to get through that transition phase. I lived with this for 20 years before I learned what the problem and fix was.

The fix is as Kwilford stated: You cut off 1, 2, or even 3 loops of the spring. Cutting the 1st loop does almost nothing because it is flat and does not change the spring tension much, but try that first is your engine hesitates. If that does not fully fix the problem, then cut 1/2 of a loop at a time and drive again. Keep cutting 1/2 of a loop at a time until the problem goes away. When working properly, you should be able to squash the gas pedal at idle and instantly the engine will accelerate with no hesitation.

A Weber 38 is a nice performance increase, a Weber 32/36 is for fuel economy. The 38's have a very narrow sweet spot of adjustment because they are bigger, almost a little too big for a stock engine. 38's open both throttles at the same time, 32/36's first open one throttle and then the other one. 32/36's are easy to tune. Most of us hate the Solex carbs, they use more gas and give less power.

The Combo cam performs as the name says: It gives a little bit more torque at low rpm some more power at higher rpm. It shifts optimal power range 500 rpm or so higher. So, for example, if your stock engine's cam makes it's best power between 2500 and 4000rpm, the Combo cam will shift this higher to 3000-4500 rpm. I am just making these numbers up to give you an idea of what I am talking about. I don't know what the best power range is of a stock engine. It is often hard to tune an engine with a Combo cam at idle below 1000 rpm(You should aim for 700-800rpm) because of the lope and you should not have your engine idle at 1000 or higher, this makes the Accelerator valve open even more.
 

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Discussion Starter · #19 ·
The point made about trimming the Power or Accelerator valve spring is important. That cam will almost certainly drop your vacuum at idle to the point that the Accelertion valve starts to open.. We are assuming that you are using a Weber 32/36 or a Weber 38. The low vacuum will cause the Power/accelerator valve to prematurely start to open at idle. When you step on the gas the valve will allow too much fuel into the engine as you are coming off idle and you will experience what we call The Bog. The engine will seem to slow down or hesitate. This can be very annoying. You are probably using a stick shift and not an automatic, so maybe this will not be a problem because you can rev the engine as you go into 1st gear, but I have always used automatics that you don't rev coming of idle and this problem was bad for me. I would have to flutter the pedal to get through that transition phase. I lived with this for 20 years before I learned what the problem and fix was.

The fix is as Kwilford stated: You cut off 1, 2, or even 3 loops of the spring. Cutting the 1st loop does almost nothing because it is flat and does not change the spring tension much, but try that first is your engine hesitates. If that does not fully fix the problem, then cut 1/2 of a loop at a time and drive again. Keep cutting 1/2 of a loop at a time until the problem goes away. When working properly, you should be able to squash the gas pedal at idle and instantly the engine will accelerate with no hesitation.

A Weber 38 is a nice performance increase, a Weber 32/36 is for fuel economy. The 38's have a very narrow sweet spot of adjustment because they are bigger, almost a little too big for a stock engine. 38's open both throttles at the same time, 32/36's first open one throttle and then the other one. 32/36's are easy to tune. Most of us hate the Solex carbs, they use more gas and give less power.

The Combo cam performs as the name says: It gives a little bit more torque at low rpm some more power at higher rpm. It shifts optimal power range 500 rpm or so higher. So, for example, if your stock engine's cam makes it's best power between 2500 and 4000rpm, the Combo cam will shift this higher to 3000-4500 rpm. I am just making these numbers up to give you an idea of what I am talking about. I don't know what the best power range is of a stock engine. It is often hard to tune an engine with a Combo cam at idle below 1000 rpm(You should aim for 700-800rpm) because of the lope and you should not have your engine idle at 1000 or higher, this makes the Accelerator valve open even more.
Scifi guy, thanks! Great info from all you guys. Have been working on engines and machinery all my professional life and before but my career has pushed me more over to the big diesel side so just getting my head back into pre electronic gas motors.
The car is stick shift with a new 32/36 ready to fit once the motor goes back in. All understood about the power valve spring trimming, will give it a go when the time comes.
Once again. Thanks!
 

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I went to a PS91 coil & XR3000 craincam ignition. Eliminated the Vacuum advance. Has worked almost flawlessly for many years so far. Run great except for cold startups. Once its warm its fine.
Dale, I am not very familiar with the Crane XR3000 ignition. IIRC it uses an optical sensor, and a box that converts the optical signal to an electronically created coil "ground", and a somewhat variable coil dwell angle. But it don't believe it in any way offers variable ignition timing, as in no rpm-related advance.

Removing the vacuum advance makes that complication go away (although it can be argued that "some" vacuum advance is a good thing). I assume you locked the distributor plates together?

What did you do for altering the mechanical (aka centrifugal) advance? Did you alter the advance springs, and/or create an advance limit system? Do you know what your initial timing is set at, and what the maximum advance is, at what rpm?

I just re-read your thread:


Clearly a good outcome, even 8 years later!
 
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