Question for two stroke experts regarding port height and jetting

[Mr. Demeanor]

Just when I thought things coudnt get weirder.....Chaz comes along

[FMP]

Just an after thought, did you ever measure the distance from ex ports to the divider base and to the tuner end ? When do ports open in degrees and how many degrees did you raise or is that all secret ???

[dwilfong]

well there you go..........bet that little bad boy moved out........
Would it be legal to drag race with...............unlimited class any one?????????????
3960 HP.....YA BABY.....................the truth is always stranger than fiction...................

[Chaz]

Just when I thought things coudnt get weirder.....Chaz comes along

Translation = Cool water products will be offering twin sponson mounted set-ups by the end of next month ...

As a youngster my folks took me to Harris field to watch the solid rocket test burn ... now that's burnin rubber ..

www.youtube.com/watch?v=rmtzFNy1t3U

The casing is still in the silo to this day ...

www.youtube.com/watch?v=3ZfziiXYPrU

[Mark75H]

I JUST have chime in after reading your posts about making power mods very impressive ! i never hear anything about rod ratio for any one unfamilar this is the ratio of stroke vs rod length changing rod lgth changes rotating geometry in several ways. a longer rod allows piston to remain at bdc longer while crank is moving several * this gives more time for cyl filling also piston stays at tdc longer taking advantage of slower flame front of high octane race fuel also piston accelerates faster away from tdc with the longer rod only neg is its heavier which a lighter wrist pin can offset custom piston would be used with ccorrect compression height wrist pin moved up. anybody consider this mod top engine builders should know it well rember old z28 302 short stroke long rod would turn 8200 comments welcome

If you like I can dig up the SAE papers that say this is not true. Might be in Ricardo's book too, but it might take a month to find the page to quote.

[Mr. Demeanor]

Just an after thought, did you ever measure the distance from ex ports to the divider base and to the tuner end ? When do ports open in degrees and how many degrees did you raise or is that all secret ???

Actually I raised them to specs John at Hydrotec shared with me. He said that was the highest he would go and I went for it. Its all in the build thread somewhere....old height vs new.

[Mr. Demeanor]

I think this thread need sub-threads LOL

[FMP]

I felt like doing the pulse number figures before close , need the distances port to divider base and tuner and height in degrees or stroke and distance from deck.

[Chaz]

I JUST have chime in after reading your posts about making power mods very impressive ! i never hear anything about rod ratio for any one unfamilar this is the ratio of stroke vs rod length changing rod lgth changes rotating geometry in several ways. a longer rod allows piston to remain at bdc longer while crank is moving several * this gives more time for cyl filling also piston stays at tdc longer taking advantage of slower flame front of high octane race fuel also piston accelerates faster away from tdc with the longer rod only neg is its heavier which a lighter wrist pin can offset custom piston would be used with ccorrect compression height wrist pin moved up. anybody consider this mod top engine builders should know it well rember old z28 302 short stroke long rod would turn 8200 comments welcome

Outboards already have a long rod by today's standards. And has an overly long piston for that ratio .
3.0L Merc has a 6.5" rod and a 3" stroke = 2.16 rod ratio
The 302 smallblock you mentioned 5.7" rod 3" stroke = 1.9

A good friend who races comp eliminator runs right around 300 " with a 6.125 as his go to rod for 3" stroke stuff. Not so much for the 2.04 ratio as much as it makes for a very short piston that put the pin way up into the oil ring.

And yes it's true the longer the rod , the longer the piston will dwell at TDC and BDC . However , you cant have it both ways. If it dwell's longer , it moves away slower all the way to 90* where they even out and then starts out the same for the bottom half.

Short rods pull away quicker , starting a strong signal early in a four stroke , but put more load on the thrust face of the piston.
The 706 ci motor I ran used a 7.7" rod with a 5.300" stroke = 1.45 ratio . Which works well with nitrous motors . The piston goes up , does it's job and gets away quick before it get's hurt . Some of the latest 900ci motors with 5 stages on them have a ratio down in the 1.20 range .

Anymore , guys just measure the deck of the block and how much stroke they want to run and just fill it with what fits. I looked into changing the rod length in the 3.0L Mercs . Custom pistons come in sets of 36 or 48 minimum to do a run , and rods ... well that's even worse .

Here is a calculator you can play with to see what different rods do to piston position ...

http://torqsoft.net/piston-position.html


Mr. D ....
The Biel really looks good with the new red paint job ...

[Magcat 62]

If you like I can dig up the SAE papers that say this is not true. Might be in Ricardo's book too, but it might take a month to find the page to quote.

y info from how to build horsepower books i used those basic guidelines to build a s\p 10 sec nova s/b all motor no juice single 4 bbl . didnt know outboards used such high rod ratio i guess every combo is different thanks for your response ART

[dwilfong]

Rod to stroke ratio mean a lot in a two stroke eng. Thy determine port timed area.
How much time a port area is open and where it is opened has a lot to do with how that port flows.
Holding it open at the bottom with a large R/S ratio has a advantage but remember it comes off bottom quicker. The piston speed changes as it moves up and down at different points in the cyl. R/S ratio has a lot to do with where the piston speed is at a particular point in the cyl. So timing is not the whole story as R/S ratio is a veritable.
Now when stuck with a R/S ratio with a particular eng this is a none variable that has to be worked around.
On car eng there are lots of choices available. But not with a outboard eng....................

[Chaz]

I'm somewhat sad @ the moment .. >>> I just knew TorqueXrpm would come along with a non asymmetrical transfer system to make better use of crankcase pumping pressure from port opening to BDC and ex scavenging from BDC to the new closing number .
My guess is we will be stuck with the same opening and closing numbers for a while longer ....

Well at least until till I debut one like dis-heea ...

[FMP]

well there you go..........bet that little bad boy moved out........
Would it be legal to drag race with...............unlimited class any one?????????????
3960 HP.....YA BABY.....................the truth is always stranger than fiction...................

I can't stop looking at his thing, it's like an old friend I haven't seen in years.

[FMP]

I'm somewhat sad @ the moment .. >>> I just knew TorqueXrpm would come along with a non asymmetrical transfer system to make better use of crankcase pumping pressure from port opening to BDC and ex scavenging from BDC to the new closing number .
My guess is we will be stuck with the same opening and closing numbers for a while longer ....

Well at least until till I debut one like dis-heea ...

This I talked with someone about, just can't remember who it was. Said it ran pretty good.

[dwilfong]

Have you seen the guy in Sweden I think it is. With the OMC v8 with tune pipes in his drag car.