Popup vs Flat Top?

[Moparmyway]

You two could argue till Randys cows come home. These kinds of threads just paint both porters in a bad light. January is Randy trolling Brad, last year it was Brad trolling Randy ("Come get some threads") ....................

What trend Hedge ??

 

[old-cat]

When R&D engineers get into a controversy such as this, they resort to testing devises to find the truth. Tongue wagging is useless!

 

[Big_Wood]

Doesn't the mix need to go up into the combustion chamber anyway? If the popup is going to deflect anything, it's going to deflect it upwards.

your sense cannot be understood by all young grasshoppa. Randy's really push'n it here. his backup hasn't even arrived yet. just remember Randy. i'm so young that i know all and everything. i already have all the answers but i'll just let you guys hash this out. i'll tell you who's right on page 100 in a few hours

 

[Mastermind]

I'm not trolling anyone......

I have no need to prove anything.

I'm just trying to cut though the confusion and get to something that makes real sense.

Scott posted yesterday that he cut out to top of the transfer ports on a few saws he did to get an entrance angle that he felt made more power. If entrance angle is so important, is it a good idea to sit an obstruction directly in the flow path?

 

[Big_Wood]

When R&D engineers get into a controversy such as this, they resort to testing devises to find the truth. Tongue wagging is useless!

it's about to get all serious up in here

 

[Hedgerow]

You two could argue till Randys cows come home. These kinds of threads just paint both porters in a bad light. January is Randy trolling Brad, last year it was Brad trolling Randy ("Come get some threads") ....................

What trend Hedge ??

Those models that depend on efficient scavenging benefit the most from a flat piston and cut band.. Some models are based more on sheer volume, and will run ok with either, but the best running saws I've had in my hands have had the bands cut and a flat piston.

 

[jughead500]

Picture this in your mind......

Think about what happens to the air/fuel mixture as the piston closes the squish area, and that popup starts going up into the combustion chamber.....

Cavitation.

 

[Moparmyway]

I'm not trolling anyone......

I have no need to prove anything.

I'm just trying to cut though the confusion and get to something that makes real sense.

Scott posted yesterday that he cut out to top of the transfer ports on a few saws he did to get an entrance angle that he felt made more power. If entrance angle is so important, is it a good idea to sit an obstruction directly in the flow path?

That's a moving obstruction ......... totally different !
As the cylinder volume changes so does that obstructions effects.
Also that obstruction helps add surface area, and the more surface area you have, the more power you can transmit
Remember the Hemi (both Ford and Mopar) was the only engines to be banned from NASCAR

Randy, I like you, and I like Brad, but you are stirring this thing to a head ............. as has Bradley in the past.

Best for everyone to settle down, no need to prove any point ................ you two are going to be mucho happier when you both stop comparing how far you can each throw a peepee stream

 

[Moparmyway]

Cavitation.

What ??
Please explain to me how that works when the piston is compressing the air/fuel mix

 

[Big_Wood]

You are gunna have to stop making me spit my drink on my computer ............... if you keep this up, it might get expensive for me, I am already on my second screen

that was another member's nickname for ol'magic 044 mike. i just copied it.

 

[blsnelling]

Both Randy and Wiggs have offered to turn a squishband for me in order to test this as I outlined earlier. It would require the cost of a new piston, irreversible changes to the cylinder (which I'm ok with), about $100 in back and forth shipping charges to Chad, and two sessions on the dyno. I've simply not had the ambition to make it happen since I don't really see the need

 

[jughead500]

What ??

Looking to see who was going to say what first.

 

[fordf150]

i sent one saw to randy and when i do another one it will go there too but here is food for thought.

what do the manufacturers use? A few domed pistons and lots flat tops. with the money they invest in R&D if a pop-up made more power i think we would see more saws with one from the factory.

 

[Moparmyway]

Looking to see who was going to say what first.

 

[old-cat]

There is something other than power outcome to consider. Squish bands are usually not machined as produced and not precisely square and not completely flat all the way across. So, they really should be machined for maximum squish velocity / minimum squish gap. Therefore it is not economically sensible to machine the piston and cyl. both, plus if a piston has to be replaced in the future there's added expense.

 

[Mastermind]

i sent one saw to randy and when i do another one it will go there too but here is food for thought.

what do the manufacturers use? A few domed pistons and lots flat tops. with the money they invest in R&D if a pop-up made more power i think we would see more saws with one from the factory.

A few DOMED pistons yes.

The 028 Super is the only saw I can think of with a popup from the factory......

 

[blsnelling]

Scott posted yesterday that he cut out to top of the transfer ports on a few saws he did to get an entrance angle that he felt made more power. If entrance angle is so important, is it a good idea to sit an obstruction directly in the flow path?

I don't see that as a direct comparison. Again, were only talking about a .035" "obstruction". I don't see this tiny deflection as a problem, especially when it's deflecting the charge upwards, exactly where it needs to go. You're always going to get flow directly across the top of the piston anyway, as it moves up and down past the transfers.

 

[blsnelling]

...plus if a piston has to be replaced in the future there's added expense.

I don't really see this as a deciding factor of which method to use. How often are guys replacing pistons, especially when it wasn't a catastrophic failure? If these were race bikes where the piston was replaced regularly, that might be different. Should one of my customers need a piston, all they have to do is pay for the piston and I'll mod it for free.

 

[sunfish]

Does any of this really matter?

 

[Mastermind]

What I was driving at when I asked what happened near TDC with a popup is just this. We all agree that tightening the squish is a good thing......the more squish velocity we have, the less chance of detonation. Well the tight squish is doing what it is suppose to do.......then bam.......the popup closes off the path when it passes the squish band and protrudes into the chamber.

That's the reason you don't see any wash on top of the popup......