Mythbusters - engine & dyno edition

[JeffMcKC]

Jeff.... Do you run an air cleaner on your car? Does Jake?


The reason I ask is I'm wondering if in your cases you are dealing with the fuel standoff above the carbs being blown away and experiencing a lean condition at the top end, thus requiring a change in timing.

Just thinking out loud here and trying to get my learn on.


Ron

It can cause issues for sure if not done right, and there is no right answer most of us do what we have found works best for us. I will try two or three things and follow a dirrection if I have the chance. This is the fun of drag week. I was sharing my air filter set up with 2 other cars in 07 made a big difference in their cars so each day I loaned it out, it was a cut up Moroso set up.

Last year I took my air pan for jake to try the last day but the rain stopped us from trying it.

[JeffMcKC]

Launch control is never the reason I hear for why this timing retard is done. The reason I hear is "because if the engine is changing RPM rate faster, you need to ignite the mix earlier to have the peak cylinder pressure end up in the same place"

that's the myth that's been busted here. Using timing for launch and traction control is not what I was getting at, but a fun topic to discuss, so have at it!

Yep, but this is why we "over time" low gear by a couple * not take away, if the car can hook it.

[dieselgeek]

Yep, but this is why we "over time" low gear by a couple * not take away, if the car can hook it.

And that's the part the dyno data disagrees with. "over time" is wrong timing, and you can prove this by steady stating the dyno, or running it at a high sweep rate. Now, the timing at higher RPMs might want to be more or less than timing at other places in the RPOM range (check CDMBill's timing on his motor, it had a VERY specific timing map). But I am sure his engine wants that same timing map whether it's accellerating, or being held steady state, whatever it's doing at WOT.

We should put your motor on a dyno some time and test the theory again.

[TC]

Scott, I have another question. Yeah, I know... I'm full of 'em (among other things) but you have piqued my curiosity.

In the example of a pro stock engine, what do you do on the dyno to account for the pressure above the carburetors created by the large by huge scoop sitting on top of the engine at 200 mph? Would the pressure difference inside the scoop between zero mph and 200 mph dictate a change in timing?


Ron

The question is how fast is the air moving into the carb at 9000rpm with the car standing still??.......I'm guessing it's way over 200mph............


Here's some old time thinking that was told to me by a few old time racers back in the day.... It was pretty bone simple stuff when it came to Chevy's, small blocks like 36 degrees of total timing and big blocks like 38 degrees of total timing and you're going to want all your timing in by 3500rpm........ I wonder how much of that still stands true today...........

Though IMO, you run as much timing as you can get away with without detonation occurring.......

And Jeff you said something about having to back off timing on the top end, maybe you should look at gear change instead......

[JeffMcKC]

TC I think you are reading me wrong this is why I have changed the vocab to Over timing low gear. The going to what the dyno says farther down track, its also not that uncommon to use 1* less timing at the track than the dyno for max MPH to be found.

TC Search Bernoulli's theory and your air speed ideas will change with the shapes and what those hood scoops look like inside and what they are doing with the air

http://mitchellscience.com/bernoulli...iple_animation

[JeffMcKC]

.

We should put your motor on a dyno some time and test the theory again.

yup I would like to make one............................................... .................................................. .................................................. .................................................. .................................................. .......................................Hint

[squirrel]

Hiding under a rock? that's one of the biggest beliefs of "top engine builders" racers, etc.

I think I'll stay under my rock. Not much of that kind of BS penetrates it.

[dieselgeek]

I think I'll stay under my rock. Not much of that kind of BS penetrates it.

Sorry Jim, I figured you'd already heard this. My bad.

[dieselgeek]

Though IMO, you run as much timing as you can get away with without detonation occurring.......

That is perfect transition into my next Dyno Mythbuster question: the idea that Max Timing = Max Power


I notice some guys have the philosophy as TC says, run the most timing you can get away with.

Similarly I know a lot of guys who believe that running "race gas" means "you can run more timing" which means "you can make more pwoer"


One thing I know for sure is that almost every engine out there, will not make their best WOT power if you run the advance that far forward. There's a whole market for knock sensors, "Det Cans" (guys wearing headphones listening to knock-sensitive microphones under the hood), you name it. Yet I have never seen an engine who's max power timing advance was close to detonating (presuming the rest of the tune is in check). I see all the time where the timing is advanced to where the engine is making less power but not detonating. IMO you should definitely "sweep" the timing either at the track, or on either type of dyno, and make sure you know where power is made.

TC, ignition advance has less to do with "small block" and everything to do with what type of combustion chamber design you are running. Some smallblock race engines want 23 degrees advance, others want 40. Less is better IMO, engines making the most power N/A that I see are doing it (these days) on less timing, which = more efficient combustion.

[Mater]

i can already say max timing=max power is false at least in a boosted application never tryed it with a N/A car never had the chance to

my 2001 grand prix with the 9.5:1 compression, 10psi boost, 1 5/8" mid length headers, and a small .520/.536 lift 212/224 duration and .050 114 LSA with a 111 intake center line cam made 280 whp at 6300 rpm with 19* total timing i could run 25* total with out knock but it lost power so put it back at 19* witch was the factory max timing at WOT

that car i could of had more boost on it though i had a pretty large supercharger pulley relitivly speaking for my set up