Budman II

iTrader: (1)

I also found the discussion on preignition interesting. I wonder how many preignition events have been triggered by cross firing on spark plug wires, particularly on cylinders that fire successively with wires that run close together?

mike tkach

iTrader: (3)

no doubt in my mind that can,and does happen,i remember a car i had years ago,if you opened the hood at night it looked like a fireworks show.todays wires are much better.

ICDEDPPL

iTrader: (1)

Hey Mike, was it kinda like this??


http://www.youtube.com/watch?v=CMNry4PE93Y

FIXX

iTrader: (2)

Mike

Why,,only guys that don't know how to read a spark plug has no right tuning a engine..a afr gauge wont tell you timing tracks and besides what happens in a cylinder and where all the exhaust ports meet to where the afr gauge is don't tell you what EACH and individual cylinder is doing..its a combined reading between all the cylinders and dont tell you if one it a few points rich and another could be a few points lein.a egt probe rite at the exhaust port and spark plugs do..

MILD THUNDER

iTrader: (3)

Used to check for bad wires that way . In the dark, a bottle of windex, spray wires down, and watch for the spark show .

mike tkach

iTrader: (3)

to each his own,with all the good afr gages out their today it would be foolish not to put it in the tuning toolbox,but if reading plugs and egt,s is how you do it,carry on.imo,afr gage is the most important tool for proper tuning.

mike tkach

iTrader: (3)

yes,that,s it dan,LOL.

ICDEDPPL

iTrader: (1)

Theres no way you can read a plug and tell me if its 11.7 or 11.2 , I`ll agree reading individual plugs gives you a better idea when the AFR gauge gives you an average .
I Go Pro my runs to check afrs.. no need to stop 20 times to check plugs, plus it takes a while before the plug gets some color so on 2 motors that could take all weekend.. AFR takes 10 minutes.

I like turtles

MILD THUNDER

iTrader: (3)

I agree. The AFR gauge helps get you in the ball park for sure, but obviously isn't the end all to the tune. Problem with EGT gauges is they aren't practical in a boat. How does one install 16 probes in a twin engine boat and monitor them, along with 18 other gauges while out on a poker run in 4 ft'ers?

This is where things get fuzzy in my opinion regarding timing. For example, the EGT gauges on a dyno pull, might show lower temperatures with added ignition lead. However, the dyno pull is just that, a dyno pull. Nothing is heat soaked, nothing really has the time to stabilize. For example, on the dyno you might get the EGT's to 1300*. But, now, you stick the engine in the boat, and hold it WOT for for a couple minutes. You'll find the EGT's raise to a alarming point. This is probably where the tuner/builder/ has to determine from his own experience, what to give the engine for timing. Just because it didn't detonate on the dyno, there has to be a little cushion there for slightly lesser quality fuel, hot ambient air temp's, different loads, etc. The same engine going into a 30FT stepped bottom, might tolerate more timing than the engine going into a 41 apache. Its almost like a diesel. You can install a tuner, and power adders, and be totally fine punching it from 0-80mph, and EGT's look great. Now, strap a 10k lb trailer on it, and go up a long hill. Without detuning it, or backing out of the throttle, you'll surely melt it down.

I try to look at things Mercury did. While their engines may not have produced the maximum power, maybe not the best parts, one things for sure, they weren't known to melt down. Most stock untouched mercury setups, can withstand an extended amount of WOT run time, and do it weekend after weekend. They ran them Fat, and were conservative on timing, and compression. You know how much ignition lead a 800SC engine had? 28* total. a 600SC had 33*, and the 525SC had 35*. Some guys will say 28 degrees will melt the exhaust valves, and 35* will detonate in one pass. They weren't guessing at mercury on these tuneups, they couldn't afford too. Point is, every setup is different, and sometimes you just cant have it all. lots of timing, leaner air fuel ratio's, lots of boost, hot spark plugs, etc. Otherwise, your "marine endurance" engine, is no different than the engine the guy is running in his strip car. You have to be willing to give up a little, to gain longevity. Did mercury ever build a 10.5:1 aluminum headed N/A engine? Nope. So the guy who says "I can run 10.5:1 in my 502 build with 38* timing and make 100HP more than a 525", probably can. However, the question is for how long. I'd have no qualms about holding a stock 525EFI wide open on marina gas all day.

As far as AFR readings, I'd like to know what mercury supercharged engines had for AFR' readings? Like a 600SC, 800sc 575sci, 1075 etc. My guess is they aren't anywhere near mid-upper 11's at wot. I would bet they are in the 10's, probably low 10's at wot.

With that being said, Im ordering smaller blower pulleys.

Budman II

iTrader: (1)

Good post, MT, and I agree that you have to be smart about tuning these engines. The discussion in the article about combustion chamber design and timing greatly interested me. I am switching from stock GM heads to AFR 265's on my little old 489, and I am wondering how much that will affect the timing curve for the engine. Not sure if the AFR chambers are a true "fast burn" design, but they have to be more efficient than the 50-year old technology that the GM heads were sporting.

My plans for this engine are to end up in the 575 - 580 HP range with a conservative tune to help promote longevity. I like turtles too - don't want to be the hare blowing up out on the water.