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Opeler
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Discussion Starter · #1 ·
I have a small problem with light spark knock around the 1500-2500 rpm range when I stomp on the gas ever sence I built my 2.0L engine (OGTS pistons), DCOE side drafts and perfomance cam.....I have 165-168 pounds compressionand I run 92 octaine, anything less and the car runs like crap.
I've tried varying deg's of timing, and rejetting the carb with no luck :confused:
The car runs and goes great ... ConreroGT can confirm that :) .
Anyone have any idea's ??

steve
 

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Im just brainstorming- but have you ever tried octainboost with the 92 octaine fuel? Any difference? :confused:
 

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Opeler
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97 Posts
Discussion Starter · #3 ·
Spark Knock

Yes.. not much of a change.
I wonder if the brand of octane booster macks a diff. ????
 

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Crusher said:
I have a small problem with light spark knock around the 1500-2500 rpm range when I stomp on the gas ever sence I built my 2.0L engine (OGTS pistons), DCOE side drafts and perfomance cam.....I have 165-168 pounds compressionand I run 92 octaine, anything less and the car runs like crap.
I've tried varying deg's of timing, and rejetting the carb with no luck :confused:
The car runs and goes great ... ConreroGT can confirm that :) .
Anyone have any idea's ??

steve
Which distributor are you using and what are your current timing settings? Vacuum advance used? Believe this is a timing advance issue . . . advancing too quickly from off-idle.

Have another distributor that you can use for parts? Take the 'light' mechanical advance spring out of parts distributor and use it to replace the 'heavy' advance spring in 2.0 distributor.

The 'heavy' advance spring effectively does nothing below ~3000 RPM anyway, so all you're doing is slowing the RATE of advance in the RPM range in which you're having your 'pre-ignition' problem by using that second 'light' spring, it's always active.
 

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Opeler
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97 Posts
Discussion Starter · #5 ·
Spark Knock

Your probably right ... I'm using a mechanical advaced distributor.
I've been playing around with my timing so much latley that I don't remember what its at right now.
The car has good acceleration at low rpm's if I dont stomp on it and doesn't ping either ...but surges slightly when I let off the gas if I'm on full throtle under 3000.
 

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Old Opeler
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5,564 Posts
Knock, knock ......

Does this happen in first gear or only when in top gear? If in top gear then you need to change down before "stomping on it".
Sounds like too much compression with not enough octane. Have you tried a higher octane fuel ( racing gas - 100 octane?). The classic "RB" method of eliminating this problem is to use a longer duration cam so the overlap "bleeds away" cylinder pressure till the engine reaches a higer rev range and the cam begins to work. Audible knock will destroy the motor eventually - break ring lands and/or burn holes in a piston so it has to be eliminated.
 

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Opeler
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97 Posts
Discussion Starter · #7 ·
Thats why I don't get on it too often at lower RPM's in any gear... I usually wait until I get up over 3000... If do get the urge, I keep the engine above 3000.. its smooth and no pinging that I can tell and it really jumps out of 1st, and 2nd gear.
I've tried octane booster but it only helps a little.
 

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I had a definite knock in my rebuilt engine. The rebuild was approx 10 years old but it only had maybe one hour on it. Some carbon attached itself to the piston and created a hot spot which caused the knocking.

I used a product called "seafoam" from NAPA. You slowly(very slowly) add this to the throat of the carb while the engine is running. It will cause the engine to stall if you pour too much in. This will steam clean the cylinders, pistons and head. It worked. I heard the piece of carbon go out the exhaust pipe and the knock was gone.

I have heard of people using just plain water in a mister bottle and doing the same procedure.

HTH

Jeff
 

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Opeler
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Discussion Starter · #9 ·
Spark Knock

Can't hurt...I'll give it a try tonight along with a couple more of the suggestions.... Thanx

Steve
 

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Opeler
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71 Posts
Knocking!

You definately have a distibutor issue.Either your vacuum advance is bad or the internal parts(springs and weights ) are incorrect for your application.You have two choices here . You can get a electronic spark control(petronix,ect.) which has a "dial up" advance/retard capabilites which are adjustable.Or you can change the advance/retard capabilities of your existing distributor by changing the weight/springs of the internals.I would surmise that you have a lean running situation where the advance is not enough at 1500-2000 which could be fixed by snipping 1 coil of each advance spring or getting competition ones.I would get a spare distibutor's springs and cut them and install in yours to test for proper advance(ie road test).Another more expensive way to fix your problem is a competition degree wheel for your cam.Where to find them??Good luck! ps.you want your distibutor to advance at a faster rate not slower. I have seen this trick used on early turbo cars with full mechanical distributors!
 

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Hi Crusher, I agree with Jack, you have a timing problem. Or you got some really bad gasoline. Be sure your vacuum advance is connected to proper vacuum for the distributor, sometimes, people change parts around and get the wrong vacuum to the distributor for proper advance.

Also, check the distributor out, make sure that is all OK, no rusty parts in there!

In general, for timing our older engines, get it out on the road, if it pings, retard it a bit, till it stops pinging/knocking. Or get better gas and see if that helps.

PJ Martin
 
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