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Curses curses curses!!! <img src="/forums/images/graemlins/angry.gif" alt="" /> <img src="/forums/images/graemlins/angry.gif" alt="" /> <img src="/forums/images/graemlins/angry.gif" alt="" />

I've been screwing around with this for 40 minutes and the best I can do is put thumbnails up-and that was on accident!!! I wanted the full size images. Oh well. If you want to see them, PM me and I'll email them to you.

And this is an email response from Ted. Actually, this is one of probably a dozen email responses from Ted. If you are buying parts, buy them from Engnbldr. NOBODY has ever gone to this length for me. I can't express enough my appreciation for all of his help. He and Tod have gone WAY over and above the expectations of even the most picky customer.

Read on...

"K....time for some engine theory.

The piston goes down and up. On the way down the intake valve comes open well before the piston even starts to move which gives some lead time for fuel/air to be pushed in due to the difference in atmospheric pressure. (It doesn't get "sucked" in, it actually is more like being pushed.)

Note at the drag strip modern racers carry barometric pressure gauges because a serious PSI change dictates a jetting change, otherwise "El pistone' esta no bueno!"...

The dyno reports you give me tell me that your engine REALLY likes cool wet weather, bet I am right on that one.

When the piston arrives at the bottom and starts back up, velocity keeps the mix moving in for quite some time so the cylinder continues to fill even as the piston is rising. (Same thing that causes the wind to blow, the greater the difference in pressure, the harder it blows. Since the surrounding air mass is at a fixed pressure, the sudden drop in cylinder pressure simply creates a hole for it to run into.)

Then as the piston begins to squeeze the mix the valves both close to allow that or it will get pushed right back out. Actually, some of that does happen, it's called "reversion." The now squeezed mix gets ignited and it burns in layers, as the temperature rises, more fuel vaporizes and that layer burns. This is called a flame front. It isn't an explosion, because if it did all explode at once the cylinder head ends up alongside the road, or the piston goes through the oil pan. (This had me cracking up-Jason)

The technical engineering term for this situation is the "loud noise and big cloud of smoke.".....:)

The piston is forced down by expansion as the fuel burns, which means we spent all the effort of three complete engine cycles to use just one to drive the wheels. *Kinda sloppy and inefficient but it's what we have.

Then the exhaust valve opens up and the piston having been forced to move keeps right on going, using some of the ignition force to shove the burned up gasses out what is basically a hole. Since the outlet hole has restrictions and the gas has mass and still has pressure struggling to not move, we do everything we can to make that easier to do, getting "free power" if we get that close to just right.

Bigger exhaust pipes, nice smooth turns, straight as possible, free flowing Cat and muffler. A nice clean pipe with no muffler would be best but the neighbors get irritated.

A longer duration camshaft keeps the valves open longer, so there is less time for the piston to compress. Less time to compress means less pressure, even with higher compression engines.

This is because everything is moving so slowly. There is no real way to recover that pressure, except by going faster. So a tight duration camshaft lobe, opened early (just right early I mean) makes really nice slow speed power. That is cool and feels good but we sacrifice high speed power to do that.

Balance/balance/balance...That is the key. We can sacrifice what we seldom use to improve the area we use the most, or vice versa.

Now an extremely high compression engine with an extremely long duration camshaft will have much lower crank speed compression, our 13.5 to one 355" NASCAR powerplants pumped as little as 105#. This sounds odd, I remember taking the engine in my 1961 Corvette back apart trying to figure out what the he** was wrong with it. Turned out nothing was....if I kept her above 3000 RPM.

So we lose on "squeeze" TIME and gain on the AMOUNT of "squeeze" simply because the valve is open longer while the piston is in motion in that situation.

We gain power from the increased compression through added flow and velocity, and to make the latter situation work, we then rotate the engine at a much faster speed. Thus we have a 355" powerplant that runs well at 6000-9000 RPM, but if we drop down to below 3000 RPM and she doesn't make enough power to pull herself, we have to shift gears and bring RPM up.

(There will be a test at the end...*LOL**)

So in your situation, when out chasing rabbits or rattlesnakes you are likely working the engine harder and typically in lower gears. On the highway you are cruising along at a steady pace and typically lower RPM, so she drops into that lean mode. It takes time to recover so she feels soft. The solution is to shift down to pull the hill or pass. The trick is to be ahead of the hill, not in the middle of it.

One thing to remember is these tiny little engines look up and see a hill coming, and begin to slow down in anticipation...*LOL**.

It doesn't help on calculating actual mileage that a combination of gears/tire size throws the odometer off. So we test at sustained throttle, measuring actual fuel flow in GPM (Grams per mile).

A long series of dyno runs showed none of our cams made any difference at all in GPM tests. Math says the same thing, there is a given amount of power in a given amount of gasoline which will move a fixed amount of load a given distance, assuming stoichiometric. (This is the point where all of the fuel and all of the air is consumed in one given cycle.) This is so hard to actually accomplish in the real world that we use a computer to calculate it. Then add in that different cam lobes do the best at different RPM ranges and I get the email that says "YOUR camshaft only gets xxx MPG!"

Does not.

Does too!

*LOL**...

Mileage/economy falls when the engine is operated at some point other than just under torque peak. Response also falls when the engine is operated below torque peak.

Your numbers were excellent, so my personal opinion is you are chasing a ghost. I would keep testing with the slightly cooler plugs, and note I said slightly. A little is a lot, go too far and she will start to miss under load. Those dyno numbers were excellent and matched some of our better dyno pulls, you will beat 75% of all the other rigs just like yours in a drag race.

*I dare you to cut and paste this and post it at 4X4wire......you should be able to post those dyno sheets that way, too.

Hope this helps,

Ted"

Dare? It's posted! I have installed a set of plugs that are one step colder. We'll see how they work.

Thanks so much for your help Ted. I'm positive that a lot of people will find your imput helpful.

Jason

>>>*LOL**..I knew you would post that...the dyno sheets can be clicked on and brought up...sorta.

*I am not sure what is up with the rabbit, though...*LOL**...*EB

Rabbit?

>>>*Yea, I clicked the dyno sheet and it took me to a web host site, posted the dyno chart and a pic of a cute wittle wabbit....*Said it wanted me to twitter it whatever the he** that is....*EB

That sounds dirty, EB... Do you want to be alone with the rabbit for a while? <img src="/forums/images/graemlins/butwiggle.gif" alt="" />

75 hp 110lb-ft torque? Lol.
AFR looks a little lean then gets better near the end. I bet if you rev'd up to 5750 your hp would hit 90 or 95, maybe even 100. Not bad considering they had 110hp at the crank stock...

HP is just shy of 90 at 4479 at the wheels. That's a heck of a lot better than stock.

Why it is a dog on road remains a mystery because the numbers sure look good.

Not yet sure what to do about the lean condition. I'm tempted to adjust through the AFM but not just yet...

>>>*Those are ground numbers, not flywheel numbers. Add in oversize tires, and figure in typical drag numbers and they are very good. I have seen quite a few bone stock dyno runs, even figuring in that every single one of them has different numbers totals, normal is around 60/90 with stock size tires. Baseline anyway. Best used for tuning and ignore the numbers.

Yep, lean early, then she hits stoich and fades off too rich, odd fuel curve....*EB

I'm shooting for 250-300 at the wheels with the 3.4 s/c'd i'm building right now <img src="/forums/images/graemlins/lol.gif" alt="" />

Well, in those dyno runs it's in open loop, maybe you are having issues with closed loop? remember, all they are doing there is flooring it, not part throttle cruise/w/e. It's closed loop where you are having an issue.
Are you running an NGK/denso o2 sensor?