Porting Efficiency
05-12-2005, 11:44 PM
#61
Fabricator
Join Date: Jan 2004
Location: Central Ohio (Hebron) Zephyrhills Fla.
Posts: 1,322
[quote name='BDC' date='May 12 2005, 09:05 AM']
On the exhaust ports, I tend not to enlargen them much past their shape but I do open them slightly earlier and close them slightly later. I put alot of effort into making those as mirror finish as possible. I ultra-fine sand and polish by hand every one of those things. What are your thoughts on that, Lynn?
B
[/quote]
Your work is superb.
Drag increases at the square of velocity. So, a tiny imperfection in the (supersonic)
exhaust flow are amplified dramatically.
So, there is no such thing as too smooth in exhaust flow. Once the flow is subsonic the intake rules apply.
Lynn E. Hanover
On the exhaust ports, I tend not to enlargen them much past their shape but I do open them slightly earlier and close them slightly later. I put alot of effort into making those as mirror finish as possible. I ultra-fine sand and polish by hand every one of those things. What are your thoughts on that, Lynn?
B
[snapback]711691[/snapback]
[/quote]
Your work is superb.
Drag increases at the square of velocity. So, a tiny imperfection in the (supersonic)
exhaust flow are amplified dramatically.
So, there is no such thing as too smooth in exhaust flow. Once the flow is subsonic the intake rules apply.
Lynn E. Hanover
05-13-2005, 02:19 PM
#62
Senior Member
Join Date: Dec 2003
Location: Minneapolis,MN
Posts: 500
[quote name='1Revvin7' date='May 12 2005, 08:38 PM']This was the whole reason behind me making this thread. My port only flows 10% more than stock, sure it looks good and is big, but that doesn't mean anything..........
[/quote]
How much bigger is the hole over stock?
[snapback]712171[/snapback]
[/quote]
How much bigger is the hole over stock?
05-17-2005, 07:19 PM
#65
Senior Member
Join Date: Dec 2002
Location: Bayou-self Louisiana
Posts: 947
[quote name='Lynn E. Hanover' date='May 12 2005, 08:03 AM']In addition: Brian cannot move in with me, sorry. And your english looks better than some of these clowns born here in the good old USA.
I am up to my ears in aligators this month, first race, moving to new (old) house, moving shop, finish guest engine, fix up van to sell, fix up new purchase chevy tow vehicle and mow 5 acers.
The cross section of a runner should be kept the same cross sectional area from end to end. Any time you change the velocity of a flowing mass, you remove energy (slow it down and change its temperature) so you maintain a constant cross sectional area. Not shape, just area. So then velocity remains constant.
The common thinking is just make it bigger. And this works just fine so long as the design was a bit undersized to start with. When we rev the engine through the HP range we need to have the maximum amount of HP unser the curve as is possible, because we are nut cases and love the feel of mind numbing thrust as we pass through 100 MPH in third gear. Only in an off the road situation under controlled conditions of course.
Runner velocity kept high gives you a better bottom end in that HP curve. It gives you a car that jumps out of a turn. It gives you some power where you can use it rather than having to get to 45 MPH in first before any fun begins.
Think about how long that port is open at points along the RPM range. It starts off in thousandths of a second and gets smaller as you rev the engine. So think about low flow velocity vice high velocity. Sounds like high velocity has it every time.
For us NA guys (and gals) there is only 14.7 PSI of boost available, and only then if you race on a beach somewhere (sea level). So almost always less than 14 pounds available to push stuff into the port, and even less than that because we cannot produce a perfect vacuum inside the chamber so as to take full advantage of even that.
So at first as we go bigger on the runners from stock, things perk up a bit. So the next time we go bigger yet and that engine seems a bit soft on the bottom, so next time we go real big, bigger is after all better yes?
This time the engine is a pig. Mixture is all over the place. No power at all until after maybe 3,500 RPM. And even from there on up it really isn't pulling hard until maybe 5,500 RPM and then it seems fine. But now it sucks down low and is no fun to drive to work. You cannot even autocross it on a short course in low gear.
So runner velocity as high as is possible at any RPM. The runners in my Drummond built 245 HP 12As is the same as the stock gasket. They are smooth as silk. Not shiny just smooth. My closing line is radiused and polished like chrome. Although he is not supposed to be below about 8,000 RPM, the engines still have over 212HP at 7500. So the runners don't need to be enlarged very much at all. I must add here that the 12A center iron has good sized ports in stock trim should you want to build up a special street engine.
This power is from a 48 IDA with 36MM chokes.
You are not that limited with any stock Mazda induction system.
Let me try that picture again.
Lynn E. Hanover
[/quote]
Speaking of flow..this after noon I was at Leonard Hughes house picking up a video cam.( he was the CANDIES & HUGHES ,Smoking Joe Camel funnycar, owner and manager)We were talking about motor stuff.A local drag guy (car dealorship owner) was talking about how his motor (certain cylinders) run rich at the bottom and lean at the top end but cant tune it out and ask Hughes what he thought because these were extreme high dollar race heads. Hughes said put some epoxy humps in these two runners (the ones that were off) and see how that works on the bench. Then weld that design in. At the end of the season this owner gets a custom head set that addressed the problem....with humps in a hogged out runner! He called Leonard and said he was right and should have done it earlier himself.Mr. Hughs is always preaching velocity over the bigger is better stuff and we talked about the the inside turn verses outside (low pressure and high) Lynn is on it!This coming from some one who is still consulting about 7,000 HP motors. Coooool
I am up to my ears in aligators this month, first race, moving to new (old) house, moving shop, finish guest engine, fix up van to sell, fix up new purchase chevy tow vehicle and mow 5 acers.
The cross section of a runner should be kept the same cross sectional area from end to end. Any time you change the velocity of a flowing mass, you remove energy (slow it down and change its temperature) so you maintain a constant cross sectional area. Not shape, just area. So then velocity remains constant.
The common thinking is just make it bigger. And this works just fine so long as the design was a bit undersized to start with. When we rev the engine through the HP range we need to have the maximum amount of HP unser the curve as is possible, because we are nut cases and love the feel of mind numbing thrust as we pass through 100 MPH in third gear. Only in an off the road situation under controlled conditions of course.
Runner velocity kept high gives you a better bottom end in that HP curve. It gives you a car that jumps out of a turn. It gives you some power where you can use it rather than having to get to 45 MPH in first before any fun begins.
Think about how long that port is open at points along the RPM range. It starts off in thousandths of a second and gets smaller as you rev the engine. So think about low flow velocity vice high velocity. Sounds like high velocity has it every time.
For us NA guys (and gals) there is only 14.7 PSI of boost available, and only then if you race on a beach somewhere (sea level). So almost always less than 14 pounds available to push stuff into the port, and even less than that because we cannot produce a perfect vacuum inside the chamber so as to take full advantage of even that.
So at first as we go bigger on the runners from stock, things perk up a bit. So the next time we go bigger yet and that engine seems a bit soft on the bottom, so next time we go real big, bigger is after all better yes?
This time the engine is a pig. Mixture is all over the place. No power at all until after maybe 3,500 RPM. And even from there on up it really isn't pulling hard until maybe 5,500 RPM and then it seems fine. But now it sucks down low and is no fun to drive to work. You cannot even autocross it on a short course in low gear.
So runner velocity as high as is possible at any RPM. The runners in my Drummond built 245 HP 12As is the same as the stock gasket. They are smooth as silk. Not shiny just smooth. My closing line is radiused and polished like chrome. Although he is not supposed to be below about 8,000 RPM, the engines still have over 212HP at 7500. So the runners don't need to be enlarged very much at all. I must add here that the 12A center iron has good sized ports in stock trim should you want to build up a special street engine.
This power is from a 48 IDA with 36MM chokes.
You are not that limited with any stock Mazda induction system.
Let me try that picture again.
Lynn E. Hanover
[snapback]711615[/snapback]
[/quote]
Speaking of flow..this after noon I was at Leonard Hughes house picking up a video cam.( he was the CANDIES & HUGHES ,Smoking Joe Camel funnycar, owner and manager)We were talking about motor stuff.A local drag guy (car dealorship owner) was talking about how his motor (certain cylinders) run rich at the bottom and lean at the top end but cant tune it out and ask Hughes what he thought because these were extreme high dollar race heads. Hughes said put some epoxy humps in these two runners (the ones that were off) and see how that works on the bench. Then weld that design in. At the end of the season this owner gets a custom head set that addressed the problem....with humps in a hogged out runner! He called Leonard and said he was right and should have done it earlier himself.Mr. Hughs is always preaching velocity over the bigger is better stuff and we talked about the the inside turn verses outside (low pressure and high) Lynn is on it!This coming from some one who is still consulting about 7,000 HP motors. Coooool
05-18-2005, 10:52 PM
#66
Fabricator
Join Date: Jan 2004
Location: Central Ohio (Hebron) Zephyrhills Fla.
Posts: 1,322
[quote name='Rub20B' date='May 12 2005, 08:20 AM']great info!
As my engine is a 20B, runners are huge from stock so just cleaning up will do..
When I have more time I'll make some plexi and enlarge the ports a little and check that the side seal kept supported and I don't create overlap.. Should I open up a bit earlier or close a bit later or both? But I won't make them much larger..
Why the pics aren't working?
[/quote]
That is a turbo engine is it not?
Turbo rotaries are only similar in construction to NA rotaries. You control the compression ratio with the throttle pedal. Think about that for a while.
Without the computer to ****** away that ignition advance when the boost comes up, most people couldn't make it to the next light without blowing the engine.
But you wanted porting info.
For just running on the street, the boost is very low if any is available at all. So until it steps up into the boost the engine with low compression rotors can be a bit of a dog. So you want to think like an NA builder with little early opening and not much late closing. If you don't mind waiting for the boost to come up before showing off, then the turboed engine suffers little at all from late closing, because the boost overcomes any reversion that would be normal in the NA engine. A bit earlier opening helps remove exhaust dilution.
The exhaust can open a bit early, and be a bit wider. A bigger intercooler with a bit of a water spray and extra fan is good. But like a good race engine, timing changes are actually modest. Better area under the curve rather than better peak HP makes a great street engine as well as a race engine. More important on the street because of the wide ratio trans you have to run.
Lynn E. Hanover
As my engine is a 20B, runners are huge from stock so just cleaning up will do..
When I have more time I'll make some plexi and enlarge the ports a little and check that the side seal kept supported and I don't create overlap.. Should I open up a bit earlier or close a bit later or both? But I won't make them much larger..
Why the pics aren't working?
[snapback]711665[/snapback]
[/quote]
That is a turbo engine is it not?
Turbo rotaries are only similar in construction to NA rotaries. You control the compression ratio with the throttle pedal. Think about that for a while.
Without the computer to ****** away that ignition advance when the boost comes up, most people couldn't make it to the next light without blowing the engine.
But you wanted porting info.
For just running on the street, the boost is very low if any is available at all. So until it steps up into the boost the engine with low compression rotors can be a bit of a dog. So you want to think like an NA builder with little early opening and not much late closing. If you don't mind waiting for the boost to come up before showing off, then the turboed engine suffers little at all from late closing, because the boost overcomes any reversion that would be normal in the NA engine. A bit earlier opening helps remove exhaust dilution.
The exhaust can open a bit early, and be a bit wider. A bigger intercooler with a bit of a water spray and extra fan is good. But like a good race engine, timing changes are actually modest. Better area under the curve rather than better peak HP makes a great street engine as well as a race engine. More important on the street because of the wide ratio trans you have to run.
Lynn E. Hanover
05-20-2005, 01:24 AM
#68
Senior Member
Join Date: Jun 2003
Location: Grand Prairie, TX
Posts: 917
[quote name='rotarygod' date='May 19 2005, 05:23 PM']Brian, I seem to remember you and I several years ago having a conversation about the importance of velocity over volume.
[/quote]
Indeed, Fred -- three years ago in August in my kitchen.
B
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[/quote]
Indeed, Fred -- three years ago in August in my kitchen.
B
05-20-2005, 08:53 PM
#70
Member
Join Date: Aug 2004
Location: Houston
Posts: 76
Wait a second. That was just the last time I was there. We did talk about this probably 6 or 7 years ago when I was there another time. It was back when I first told you about my exhaust sleeves. The first time we ever spoke about it was the first time I met you. That night we were both under your car using zip ties to hold the diff to the subframe for a race! I remember us drawing pictures of the exhaust sleeve cross section on your dry erase board in your room.