conventional plugs, superchargers and dyno tune

tbird91sc

Registered User
due to the mods i have made to my engine, my research has lead me to draw the conclusion that most of my detonation problems under high boost is a timing issue (as the computer cannot catch up fast enough with the motor).
i have talked to two people about doing a dyno tune and adjust the computer accordingly and both want me to swap out the double platinum plugs and install conventional plugs one heat range colder and a gap of .035". they would not even strap the car on the dyno till i did this.
has any body done this and what plug did you use?
i am certainly no expert on this subject but was caught by suprise by this. the reason i was told to do this was because the boost could blow out the spark in the larger gap.
any thoughts, comments or experience will be greatly appreciated.
if the plugs were a piece of cake to change i would just give it a try - but thats another story
jim
 
Stay with the double platinums, you can use a different part number that has a smaller gap rating (somewhere in the .30's) There was a post on this where a guy started using this other motorcraft plug. The smaller gap works much better under very high boost. But I would not stray from the Double platinums. You might also notice a slight increase in emissions, not sure if that is a problem for you.
 
Jim,

I've heard that "Blowing out the spark" line from every dyno operator in the country. Apparently adding a supercharger to an otherwise normally aspirated engine causes problems.

Since our cars were supercharged from the factory they are designed to work fine with the stock plugs. If this person knows enough to dyno tune your SC (I doubt they do) they should know better. Unless these poeple can burn a custom chip your not going to get a real dyno tune. BTW, There is no way to adjust your timing without a chip or an EEC tuner.

Talk to these guys if you want someone who knows how to tune an SC.

http://www.apten-us.com/

David
 
i kinda had that same feeling about the plug situation. the one guy does a bunch of mustangs so i am sure he is going by his experience with them (and he admitted to not doing that many scs) and he can burn new chips to deal with the timing issue . my concern about apten was that i am in southern cal and therefor the dyno was out. I feel a little leary about sending off a list of the stuff i did and wait for the chip in the mail - or - am i off base.
thanks
jim
 
David I'm surprised to hear you think that. Tell you what since you spend so much time on the dyno run a set of stock SC plugs and see what happens to your stout power curve. A perfectly stock SC blows out the spark at WOT. Remember when I was the only one running lean at OKC? That's when everyone started taking my advice on plug gap to heart. Remember when David Daulk was getting detonation at WOT then tried a non-extended plug per my advice and all but eliminated the issue.

Jim, these guys understand the misfire issue but they don't fully understand Motorcraft DIS. You can't use standard plugs sucessfully for very long. The plugs fire twice as much int and ext stroke, and half the cylinders fire in reverse polarity whereas the spark jumps from the ground electrode to the center, and the voltage is extremely high at WOT, 64K+. The gap on non double platinum plugs will errode so quickly that the reverse polarity plugs will start misfiring within a month in most cases.

But they do know a crap blower plug when they see it and the stock SC plug is great for getting a low compression motor to have lower emmessions and still able to meet Ford WOT power goals for the SC. But it encourages misfires and detonation under boost. They don't want to hear from you and your lawyer if something gives on their dyno and you already have detonation. One more thing if you don't have new injectors and a fresh fuel filter have the injectors flushed (can be done on the car, I do it all the time at my shop) and install a new filter. You shouldn't have detonation unless you have a fuel issue. Is your MAF correctly calibrated?

There is a comprimise that will suit both partys. Use Motorcraft plug AWSF 34 PP. It is the standard 3.8 double platinum. It has a smaller gap at .045 that coupled with the high power of the DIS will withstand misfires. It also has a non-extended tip design (standard) that sits flush in the combustion chamber preventing a hot spot that would encourage detonation at WOT. You can run them out of the box after checking gap and condition.

I am the guy and this is the plug that was hinted to above. Since these guys are serious and from what you said actually care about getting the best time off your dyno dollar I would do this following trick at home first. It will clean up common issues that hamper SCs that for the most part go undetected. It will have to be in the next post I just got a post too long message.


Vernon C.
 
Checking for and removing boost leaks using compressed air.

The following is from a post I saved describing leaks to someone who found his Supercoupe produced more power on lower octane fuel. This was obviously confusing. There is a usual cause for this with forced induction, boost leakage. This is very common on our cars, especially at their age and mileage levels nowadays but usually goes unnoticed. Here's the problem and reason it could use 89-octane fuel and actually run better with it than 93. All the air that the supercharger is pulling through the mass air meter is measured whether it gets combusted by the engine or escapes back into the atmosphere through a leak and therefore the EEC computer is adding excessive fuel to the engine because it doesn't account for any boost leaks. The oxygen sensors are ignored under wide-open throttle and the air fuel ratio is calculated for a rich mixture based mostly on the mass air readings. So what you end up with is an extremely rich full throttle mixture that not only cools the cylinder more than necessary but also generates much lower than optimum power levels and less combustion heat than normal ones. The largest factor in engine octane need is air charge heat inside the combustion chamber. Octane is not fuels power rating, rather it’s a volatility rating, or it is a measure of the fuels resistance to combusting. Actually lower octane fuel burns quicker and hotter. The higher the octane number the more stable fuel is and therefore more resistant to self-ignition. In this theory of a super rich air/fuel charge, a lower octane fuel burns faster and hotter, therefore perceptibly producing more power than fuel with higher octane. In an engine that doesn’t need higher-octane fuel you normally wouldn’t be able to tell the difference between the octane ratings. But with a properly tuned high-octane need engine lower octane fuel usually doesn't work.

Most of the time boost pressure leaks from the ends of old vacuum hoses that have gotten soft and swollen. Check the 3/8” hose connecting the intake plenum in the back, if it's easily pulled off by hand it positively leaks at 15 PSI. Under vacuum leaking fittings can pull together and seal up so it runs fine. Don’t be pacified by normal boost readings, even with some leakage the supercharger can maintain 15 PSI because the engine and some small leaks are still within the superchargers flow capabilities. Look at your tailpipes and the area around their exits; is there a heavy soot coating? My advice to you if you see excessive black soot in the rearview mirror at WOT (especially at night with someone’s headlights right behind you), soot build up around the tailpipe exits, and loose fitting vacuum lines is to take an hour to search for and eliminate any possible leaks. Give this a try as not only have I done this on quite a few Supercoupes with very impressive results, but others I have shared this method with have reported back giving thanks and having a blast with the new found power and fuel efficiency for less than $15 and an hours work.

Just so everyone understands, when you do this the entire intake will be pressurized, from the back off the throttle-body to all cylinders with an open intake valve. The idle air bypass valve will be closed with the key off so it is of no consequence for this test procedure. The IAC solenoid is spring-loaded and shuts without current. This makes the system somewhat airtight and allows pressure to build without excessive air escaping. Both sides of the bypass valve will see equal pressure so don’t tie it open. Use an inline pressure regulator like those used for air gun painting with an air compressor. Set it on 20-PSI maximum as excessive pressure could blow out seals and gaskets so act in a prudently careful manner. One regulator would work but two in series are better for pressure stability and safety. Run an air hose to the regulator hung under the hood with a wire hook. Find a hose barb fitting and a reducer fitting to thread into the regulator outlet port and clamp a section of small clear vinyl tubing onto it. Run the tubing into the intake manifold at the boost gauge nipple, as this seems the most unlikely place for a leak to develop or go unnoticed. Once the airline valve is opened the intake will pressurize to 20 PSI. A slight hissing can be heard at the throttle-body as pressurized air leaks through it. Using a plastic spray bottle filled with soapy water saturate all possible leak points. It helps to use thick film soap like laundry detergent. This is easier on a cool engine. On mine the large hose nipples at the back of the intake and the PCV line joints in the back were leaking a shocking amount. Another car I’ve sealed had a large one at the PCV valve opening itself. Be sure to check every possible point such as: fuel injector o-rings, intake gaskets, all tubing joints including the spanner nut, the vacuum tree on the firewall, etc.

If you find similar leaks and chances are you will, first replace the large engine mounted vacuum hoses and use screw type hose clamps at all large fittings to seal them permanently. Get a handful of small zip-ties to use on all the small vacuum line fitting that hold boost pressure. Installing a new Motorcraft Supercoupe specific PCV valve should be considered mandatory. It is designed to seal boost and many aftermarket PCV valves aren’t capable of this. The correct valves are rarely in stock under any brand; beware if they don’t have to order this part. Also make sure the inlet tube clamps are very tight to avoid vacuum leaks between the throttle body and the MAF.

At this point seriously consider changing the spark plugs, as they will already be fouled out from the rich mixtures preventing full performance. Since Supercoupe engines have a low compression ratio Ford specified emissions type spark plugs that are notorious for misfiring under boost. Their extended tip design is to place the spark kernel in the center of the charge with dished pistons but it under power it absorbs too much heat being exposed like so and promotes detonation. The extra wide gap helps to positively ignite leaner air/fuel ratios under light loads thereby preventing misfires at those loads but it produces the opposite effect under power when cylinder pressure is high. I recommend using Motorcraft AWSF-32PP plugs; these are the standard 3.8 double platinum plugs. Their smaller tip design remains flush with the chamber roof thereby remaining cooler and reducing pre-ignition. Also they have a smaller gap, about 0.047”, which greatly reduces misfiring under boost. Both are good things for any supercharged engine, proven to improve efficiency and power under boost without a significant emissions penalty. For a manufacturer who is producing thousands of cars it mattered but for your emissions testing these plugs won’t cause a failure unless your car was already on the edge of passing, in that case you have bigger concerns than normal type plugs. The most important reason to prevent misfires under boost is so you will be able to accurately judge air/fuel ratios. Rich ratios on the dyno or excessive soot in the exhaust gasses are more often from misfiring plugs than boost leaks, but most cars have both until corrected.


After sealing a leaking intake system like this you will notice an immediate difference. The increase in part throttle torque is phenomenal along with better mileage and higher power levels across the entire engine range. This higher power output is due to a more realistic air/fuel ratio and should generate the need for higher octane again with boost, but the increase in mileage and power will even out the cost. You will surely be surprised and pleased with the new character your engine develops. In my experience part throttle torque and throttle response improved about 20%. The engine felt like it got another cylinder. The throttle became very responsive and more precise. The engine runs much smoother and gets better mileage. Less carbon in the WOT exhaust. Boost, while unchanged at peak, peaked sooner and held longer. The WOT power improved as well and the car sped up but not as much as the part throttle improvement, more like 10%. With a 5-speed the car will be easier to drive away from dead stop.

The reason being is two-fold. Not only do boost leaks rob power producing pressure but all air going through the mass air is metered for fuel requirement whether it gets used as charge or blows out as leaks. Therefore, with leaks the engine always runs rich causing lower power and crappy mileage when using some boost. Because the blower can outflow the leaks and engine, boost will still peg at expected levels but the blower will be pumping a lot of air through the mass air that doesn't stay in the intake. The fix traps all air and restores factory fresh fuel ratios.

Vernon C.
 
Vernon,

I'm not saying that there are not gains to be had from changing spark plugs on some heavily modded engines.

I've had stock plugs gapped .046, 32 PPs gapped .046, NGK iriduims gapped .030, stock plugs gapped .045, NGK iridiums gapped .045 and right now another set of Autolite stock plugs gapped .045.

It seems to run the same on all of them. Since plugs are pretty easy to change, whenever there is a problem we usually start there. So far..the plugs have not been the problem.

My main point was that...almost every dyno operator that sees the supercharger will say "your spark is blowing out" if there is any kind of a problem. It has been my experince that there was always something else causing the problem, like a pegged MAF or valve float.

I'll be making a couple pulls with the stock plugs next weekend and if I lose any power I'll put the NGKs back in. For clarity when I say stock plug I mean (Motorcraft plug AWSF 34 PP or Autolite equiv.). Your response seems to indicate these are not the stock plugs, if that's the case, my bad...I've been using a special plug all along and didn't know it.

David
 
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There is a comprimise that will suit both partys. Use Motorcraft plug AWSF 34 PP. It is the standard 3.8 double platinum. It has a smaller gap at .045 that coupled with the high power of the DIS will withstand misfires. It also has a non-extended tip design (standard) that sits flush in the combustion chamber preventing a hot spot that would encourage detonation at WOT. You can run them out of the box after checking gap and condition.

Vernon:

My head is starting to hurt with this stuff I thought the AWSF 32PP plug was the shorter version and the 34PP is the stock (long tip version). Is that simply a typo in your explanation or am I off base here.
 
I made a typo on that sorry, yes use the shorter 32 in place of the 34.

David it's the gap that makes the difference in power not the tip length. The shorter tip length is just insurance against detonation for most of us. But in cases where detonation is an issue the shorter tip does help. So by running stock plugs at a smaller gap you are doing it right. The 32PP can be run right out of the box because they have a smaller gap already.

If you want to see a difference run the stock plugs at their specified gap. This is when you will see some mis fireing.

Vernon
 
I know I'm a little behind on this thread, but would a 32pp be a better bet with a stock gap than a 34pp for slightly modified motors?

I'm going to be adding some things to my motor very shortly, and I'm not sure I want to go through the headache of fussing with new plugs all the time.

I need to buy some plugs today....which way should I go?

Also, is there an autolite equivalent to the 32pp plugs?

Thanks
-Steve
 
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