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dimpled vs polished port job


AZGhost623

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If that's the case, I'd drop the CR down a couple points. There is power in the CR, but only if you can run the right amount of timing. This is coming from a guy who built an L28/E31 combo at around 11:1 which wouldn't run the best timing without 95 or 96 octane gas.

 

 

Yep. Chamber design, cooling, FI, etc. Everything is going to be better on a 2015 vs 1975 engine.

 

I have to agree with this. The only car I know of running 12:1 on pump (Bryan Blake) is also running ITBs and a standalone. Complete control over timing and fuel, along with the much better flow and atomization with the modern EFI, I'm sure has a lot to do with his success. (and not to forget the very tight quench he runs .022" iirc and a bigger cam than most street cars ~.590")

 

Will be great if you pull it off, general wisdom is like 10.5 on pump from most I have spoken with. Your cam will be a huge determining factor in this working or not, how is way above my general knowledge but a good cam grinder should be able to juggle cylinder pressures to help avoid detonation. Getting that engine tuned with carbs sounds like awfully long and expensive dyno session...

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FWIW, Formula 1 engines have (at least since the mid 80's) used between 240-400 grit paper finish on the ports. Most commonly around 320g- both FI and NA engines alike. A far cry from laborious dimpling process, accomplished by using a 1/8 shank ball-end burr on a pencil grinder. (They get reaaaaaaal violent when you start using them to reach far into the port). If you're going to attempt this, try your best to find a 1/8 ERICKSON collet grinder. It is much better than the "pinch" style collets, especially for extended bits.

 

From my reading/research... port size/shape/floor is where 90% of your focus should go, as F1 engines also have virtually no SSR on the intake ports, and slight SSR on the exhaust ports, which are a lot smaller than the intake ports as well. 

 

However, Larry Wildmer @ endyne (theoldone.com) has created CNC programs that leave the ripples in the ports, and his work is some of which I used to follow the most whenever there were updates. Not sure how he's doing now.

 

There are finishes that I have seen on many different engines- and everyone says theirs is the best for <insert reason here>, but I tend to look at F1 as a good place to begin- and they've proven that shape is more important than finish.

 

You can achieve a good "smooth" type of paper finish using a variety of cross buffs rather than paper. 

 

tFfiGbL.jpg

 

The advantage to smoothing out the port during the porting process, regardless of final finish, is that it gives you a much better look at the port shape and unevenness or undulations as you progress, and it is a necessary porting tool, IMHO. Look at photos of cross sections of your particular port castings, and go from there. Finish is something you can worry about after, TBH.

 

Also, from the heads I've taken apart- I've noticed that two of the ones that had polished exhaust ports, as well as the ones I have on my engine stand right now on my VG33ET have soot that can be easily wiped off with a little scrubbing with one's finger (I use someone else's finger whenever possible :D ). The polishing is most likely a lot more "self cleaning" than a rough surface that gives peaks/valleys for carbon to bond to.

 

Think about it, you roughen things up to allow adhesives to bond better- why wouldn't you at least polish/320g+ your exhaust ports?

Edited by Careless
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So going to run E85, we will see what happens!

With triple DCOEs?  Don't those have brass internals (jets, etc)?  I'm generally a big fan of E85, but it doesn't play well with brass, especially if you are expecting the brass parts to do precision metering.  Can you get ethanol-resistant parts for these?

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With triple DCOEs?  Don't those have brass internals (jets, etc)?  I'm generally a big fan of E85, but it doesn't play well with brass, especially if you are expecting the brass parts to do precision metering.  Can you get ethanol-resistant parts for these?

 

Not with DCOE's. Ill be getting the 50mm OER/SK sport Injection kit to go along with the 3.2L kit I have on order.

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As my old Rupp 600 Magnum had prominently stickered on the cowling:

 

"Carburettors equipped for Methanol, Change Diaphragms after each Racing Day"

 

Gotta love anything that does 0-60mph in under 3 seconds on glare ice...

 

There is just no way to be Politically Correct with any of the old Rupp Triples, it gives Prius Owners Infarctions...

https://youtu.be/v5xYFVldpx4

 

Oh, and for the record... that's what the red sticker on the cowl says on the right side...

https://youtu.be/YEYOKT14stw

 

Man, I miss that old beast, breaking two of my fingers or not!

Edited by Tony D
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  • 2 weeks later...
  • 4 weeks later...

yeah, you really need a maxima N47 (or shaved P90/79) to run those numbers.  I ran a stock MN47 on an f54 flat top with a felpro gasket for years. (daily drove in phoenix heat too!)  Hell, it would probably still fire up if I put the intake back on!  

 

the calculated cr on that is about ~11.5:1.  it ran on pump premium with a total adavance somewhere in the high 20s.  with a stock cam.  keep in mind that the more quench the less advance you NEED, as the flame front doesnt need to travel as far.  

 

Having MS&Se helps a lot as well. 

 

 

EDIT:  to throw in some experience that pertains to the original content of this post, before I installed the head I gave it a very mild port job that was basically limited to cleaning the casting lines and blending the step right above the valve seat  into the bowl.  I also port matched the gasket and the intake as best I could.  All was done with just burrs and a dremel.  no polishing.  When I pulled the intake off, the ports looked fairly clean. FWIW, but anecdotal at best.  

Edited by Mack
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  • 5 years later...

It works, if its done right and perfecktly:

 

https://www.researchgate.net/publication/328589753_To_Determine_the_Effect_of_Dimpled_Poppet_Valve_on_the_Flow_in_Engine_Cylinder_by_Port_Flow_Simulation

 

greatings from western germany,

 

Sash Moet

 

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