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Corvette 383 Stroker Problems

12K views 17 replies 5 participants last post by  bigblockragtop 
#1 ·
Hello all. I bought a 69 Corvette that has a 383 small block stroker installed. Never been raced and has less than 6000 street miles. It has Dart Pro 1 215/64 AP heads, compression rated at 11.0 to 1, MSD6A ignition, MSD ProBillet Dist (no vacuum advance), it has a Comp Cams CS294S 10 Magnum solid lifter cam. I have an Edelbrock Performer 800 CFM Carb on an Edelbrock RPM airgap manifold. Engine builder claims this engine with this cam will run on the street with 91 octane fuel, and is rated at 538 HP new.

Dart recommends Autolite AR3933, I couldn't find them locally so I'm running Champion RC12YC plugs, I have them gapped at .45 with this MSD ignition. I have 10 degrees of initial advance and when I bring up the RPMs I'm hearing a slight bit of popping back in the Carb. I'm wondering about a proper heat range for occasional driving on the street. I've set all 16 valves @ .022.

I was told I need to have 34 degrees of total advance and they should all be in by 2500 RPMs with this cam, so I've used the lightest set of mechanical advance springs supplied by MSD in order to do so according to their chart on the instruction sheet. I don't know if this is a problem or not.

The engine was built in 2003. When I bought the car in 2003 the engine had about 1000 miles on it. Like the previous owner I have only driven the car to local car shows totaling less than 6000 miles since the purchase. I probably drive the car four times a year and lately just around the neighborhood to keep everything lubed.

The other day I had an oil change done on the car and discovered they had put 8 quarts of oil in my 7 quart oil pan, engine smoked a bit on the driver's side on the way home, a mile and a half. Not wanting to drive the car back, I took two quarts out at home and no more smoking problem. I think the excessive oil was being splashed up and onto the cylinder walls and burned in the engine. I mention this because that small bit of driving may be responsible for the fouling I see on the plugs now. This pic is typical of the plugs I've removed:



I'm noticing now a very slight pinging sound on moderate acceleration. So I have the car back in the garage wondering what to do next. New plugs, different heat range, more timing, heavier springs on the mechanical advance???

I'm new to the board and would appreciate any help. Thanks
 
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#2 ·
Just my unproffessional 2 cents but 11-1 compression on a carbed car is on the edge even with 93 octane. Hard for me to tell if that is black from fuel or oil. Have you checked your air fuel ratio. Pop through the carb could be as simple as moisture under the cap. Hopefully it is not a valve sticking. Does it go away after warm up or maybe get worse. Have you opened it up and blown all the gunk out of it(carbon etc). Not driving is sometimes worse then driving every day.
 
#3 ·
11:1 is pushing it for pump gas. You need more initial timing, start with about 16 - 18, vacuum disconnected and plugged, and maximum 38 degrees, all in by 2500 or 3k. If you have detonation pulling a load, back total timing down in 2* increments until it goes away. Have you checked all around for a vacuum leak? You're definitely running rich, 800 cfm is a lot for a street 383, but doable with a good tune. I have the same heads on my Nova, using the same plugs. I used 3933's initially, but now use RC12's as well. Short drives around the neighborhood can be a problem with fouled plugs.

Slow typing, BBR mentioned some of these points too...
 
#5 ·
I have an advance timing light. 16-18 degrees is way off the timing tab. I have to read it by turning the knob on the light until my timing marks are matched. I hope this is the right method. incidentally, should I set the total timing first at 2500 RPMs and then leave the initial timing fall where it falls? Mind telling me the gap on your plugs? I figured with MSD ignition I could use a wider gap of .045. Do you think that's too much? I have checked for vacuum leaks and found none.
 
#6 ·
I am not sure about the gap but 35 is where I used to keep mine. Oil can cause detonation too. I would try just changing the gas first. Do not forget there is also winter and summer formulas. So if you do not drive the car a lot you could have the wrong season gas in it. Also with the ethanol in gas it goes bad fast. If you don't drive it a lot put some stabilizer in it. Or what I did was used some 100 octane plane fuel. I know it is not totally recommended but if you do not drive the car a lot the plane fuel does not go bad. Drive that car letting it wit will kill it. At least get it up to temp once a month to get the contaminants out of the engine. Don't mess with the timing until you try the simple stuff first.
 
#7 ·
I've never had to use 100 plus octane fuel in the past. The engine builder claims the following:

HOWEVER, IN DESIGNING YOUR OWN HIGH PERFORMANCE ENGINE, WE ARE NOT LIMITED TO HOLDING ALL THINGS EQUAL AND CAN COMBINE PROPERLY MATCHED COMPONENTS TO REDUCE AN ENGINES OCTANE REQUIREMENT EVEN WITH HIGHER STATIC COMPRESSION.

C) SINCE VALVE TIMING CONTROL DYNAMIC CYLINDER PRESSURE, WE CAN USE THE CAMSHAFT TO LOWER THE OCTANE REQUIREMENT. ENGINE DAMAGING DETONATION TYPICALLY OCCURS AT LOW RPM. THIS IS BECAUSE OF THE COOLING EFFECT FROM INCREASED CYLINDER ACTIVITY ABOVE 2,800RPM. THIS IS WHY WE USE CAMS WITH 240+ DEGREES DURATION @ .050" ON 110 LOBE CENTERS WITH 2,400 TO 2,800 STALL CONVERTERS TO SUCESSFULLY RUN ENGINES ON PREMIUM PUMP FUEL AT 11.0:1 COMPRESSION.
 
#8 ·
The fouled plugs could have been from the excess oil, or from an over rich mixture, or from too cold a heat range on the plug.

You've got an awful lot of compression for that cam. I compute a Dynamic Compression Ratio (DCR) of nearly 10 to 1 assuming 6 inch rods and only 7 ccs of volume in the piston crown for valve relief plus a zero deck block with a .030 head gasket. One usually looks to hit around a DCR of 8.5 to 8.8 with aluminum heads and 91 octane unleaded. The DCR is the Static Compression Ratio, in your case 11:1, then adjusting it for the piston position in the bore which is inches of lost stroke in crankshaft degrees for when the intake closes, Comp says 71 degrees ABDC at .0015 inch lift which still isn't completely closed but pretty darn close.

This cam wants more base (static) time than 10 degrees but this may be a reasonable compromise against the high DCR. Adding base timing must have a corresponding reduction in the variable timing in order to hold the maximum where the engine will tolerate it. If 34 is the upper limit of all timing and 10 degrees is in the base then the variables have to top out at 24 degrees. If the base timing is moved to 20 degrees (for an example) then the variables have to be limited to 14 degrees.
Detonation can be managed by reducing the amount of timing advance or slowing the rate at which it comes in. It is also controllable with a richer mixture, a cooler mixture, a cooler running temp, stiffer gearing, water/alcohol injection or lowering the compression ratio.
Generally a compromise between less or slower advance to manage detonation costs more power than compromising the compression ratio enough to quell the pinging. At least this is apparent at WOT/redline; but pinging tends to be present at mid RPMs due to excess advance for the power drain on the crankshaft (“lugging” could be a term here) and at WOT where everything is hot an heavy in the combustion chambers. The former is often excess advance but can be a bit of a lean mixture (both can happen a the same time for different reasons) the latter is most often a lean drop of the carb at WOT, this can often be an emulsion air correction issue as much as fuel jetting one. The safer route is to throw more fuel sooner. Messing around with air correction takes a lot of expertise and special, not to mention expensive, tools.

I really wouldn't think an additional quart of oil would cause plug fouling at least to the extent of your picture. This makes me suspicious that the pan may not have the parts needed to separate the flying oil and put it back in the sump. At a minimum the pan on an engine of this potential needs a very good windage tray or screen, an oil stripper on the right side of the crank to catch the flying oil and direct it down into the sump and a splash guard under the oil pump to keep oil from running up under acceleration and flooding the rear counter weight of the crank and the rear seal. Without a windage tray/screen and an oil stripper; the rings, especially if they are the ultra modern low pressure and thin cross section type, are just overwhelmed by the amount of oil that gets up on the cylinder walls. I'm also not a big fan of gapless second rings which quite a few builders use and your engine might have. If you get oil contamination from the valve guides, a Positive Crankcase Vent (PCV) or a leaking intake or head gasket, the oil gets trapped in the area between the second and top ring where the second ring cannot vent this stuff into the crankcase. Same goes with excess fuel. These conditions will show up as fouled spark plugs since this gunk has to ride around with the piston till it finds a way out with the exhaust by first contaminating the mixture.

Bogie
 
#11 ·
degree wheel,,ok.22 thou is a tight lash cam,was more wondering if you had over tightened 1 or more valves.,,,
my compression is 10.75:1 and I have no pinging.I tuned my engine for 92 octane but some stations here still have 94,all with out methanol. when the car is running well,hopefully you accelerate briskly on occasion to keep things clean.I can drive at 2 000 rpm in o/drive with out issues,I use 035-040 plug gap.I run my car 1 quart low.
I run 24 degrees total advance,no vacuum,about 16 at idle,all in by 2800 rpm,,,I use a holley 950 and vic jr intake and big headers.

also of note, your valve springs may have gone soft from sitting long periods of time with out running,,,think about when you park the car at least 1 valve is wide open and how long you left it like that???
 
#12 ·
Those are all good points Vinnie and I appreciate them. I'm going to re-check valve settings and check to make sure the the right springs stop bushing are installed and not contributing to excessive timing advance. Try a set of new plugs as well and see where I am.
 
#17 ·
100LL aviation fuel is horrible gas to use straight in a car.I didnt even like using it in my cessna.A mogas STC was $150.00 for small cessnas and all you got was a sticker saying you could use mogas.Buy fuel stabiliser or octane boost or racing gas,but dont use a lot of 100LL.
 
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