Flathead Porting for Dummies...?

Guys -

I enjoy porting; it's a chance to take some of my fluid dynamics background and do something tangible. Had some time to kill yesterday, so I dove into the 8BA sitting on the engine stand to see how much of a benefit shadetree port job would have on the motor...

After carving up the left side ports, it's pretty obvious there are benefits to a port job - both on the intake and the exhaust side.

Intrigued, I did a web search and found AV8 did a very detailed writeup on the subject - but his process (while as good as it gets) is a little intimidating for the first-timer. The 'quickie job' performed on the left bank last nite accomplishes about 80% of the benefit of a full port job, with about half the time. I think I spent about 2-1/2 hours on one side, total.

Soo...if y'all are interested (and I can kidnap one of the kids' high rez digicams) I can step thru the process - along with the 'why' behind it

Lemme know,

Chuck.

 

Chuck:

I'd love to see it. I agree that AV8's porting tech. post was awesome!

 

I'd love to see a tech on porting the flathead. Please take some pic's while you do the right side! Thanks!

 

Yes, please.

 

And for those who haven't seen theAV8 writeup:
http://lonestar.texas.net/~mcdaniel/porting.pdf

 

I had an old hop up book from 1957 that showed the cross section of the intake ports/p***ages. It also showed where and how much material could be removed. If I find it, I'll try to get some scans.

Flatman

 

That would be pretty cool, as there isn't much material which needs to be removed - only one area requiring material removal in the intake runners, and one significant area in the exhaust tract.

Overall, not much material needs to be removed, and a relative neophyte can have an impact on port flow taking his time with just one grinding stone.

 

Mike piece on flathead porting was one of the great flathead literary works.That and Ron Hollerman book should get you started in the right direction.If I told you more I would half to kill you.

 

Where is Bruce Lancaster when you need him!?!

I'm sure he's got some thoughts on the rough vs. smooth issue...

 

Kevin -

Current thought process endorses a semi-finished surface. Reason is the same as golf ball dimples; surface turbulence helps break up the boundary layer of air - alllowing the port to flow more, relatively speaking. While it feels good to go thru 3-4 successive steps of flap wheels, there's no real benefit.

don't want to detract from AV8's piece - it's just that it can seem rather intimidating to a noob. By focusing on a couple of areas, it's possible to achive the majority of the benefit without busting a nut standing over your block all day...

 

This is from Roger Huntington's book of 1951.


Flatman

 

I agree ,You can get 90% of results with 25% of work.I have seen many old port jobs that were worst than worthless.

 

The Huntington picture is a drawing by Ed Iskenderian run in many early catalogs and books.

 

Flatman -

Neato pic! Thanks!

however...

We know a lot more about porting since that pic was published. The short radius bend into the bowl is a major source of turbulence - and we now know that tightening the radius by removing material there increases tubulence and can actually reduce flow!

flatdog is right; well intentioned folks have mucked up many a port job. Oftentimes less is more in porting.

 

Oh, I agree. More can be accomplished by just removing the factory rough and casting steps.
What's your opinion of relieving? I've read that in flow testing, relieved blocks did not have significantly higher performance.

Flatman

 

Okay - to start this out, let's talk a little about the 'why' behind porting:

Air, given a choice, likes to move in a straight line. When we move a bunch of air at the same time in a straight line, fluid dyanmics folks call that laminar flow. Laminar flow is nirvana for port guys - it allows you to move large amounts of air with minimal resistance, or pressure drop. Since most flatmotors are normally aspirated, all we have to fill the combustion chamber is atmospheric pressure - a little less than 15 PSI for most of us (denver excluded), so it's really important to minimize the resistances ***ociated with getting air in and out of the motor.

Unfortunately, a flatmotor has more twists and turns in its overall exhaust tract than a soap opera plot, so don't expect a port job to instantly turn a flatmotor into a powerhouse capable of taking on OHV's...That train's already left the station. A port job can, however, make a big difference in throttle response, fuel economy, and yes...power.

The trick is to realize that air absolutely HATES sharp edges and sudden changes in direction - gets it all worked up. Fluid guys call this turbulence, and it's the bane of internal combustion motors, as we have to introduce turns and sharp edges to the intake and exhaust tract to package the motor under the hood and seal off the combustion chamber to optimize the bang in ****, squeeze bang, blow. While the twists and turns can't be avoided in a flatmotor, the good news is there are sharp edges that can be eliminated in the tract - and these edges are easily identified and removed with minimal effort.

Remember - sharp edges bad; smooth bends good.

Another thought to remember - since the flatmotor was last produced, we've come to understand a few things about flow in ports... one of them (and an important one at that) is that intake flow tends to follow the port floor and exhaust flow tends to follow the port roof. this can be a little confusing in a flatmotor, as the ports are upside-down; the floor of the intake is actually on top of the port, and the bottom of the exhaust port is actually the roof. The reason this is important is that many novice porters make the mistake of 'hogging' out the port - in doing so, they remove too much material from the port floor on the intake, and actually increase turbulence in the process! A smooth bend into the bowl and a high port floor will outflow a big port with a tight radius into the bowl...every time.

Novice porters need to focus on three basic areas of the flatmotor to achieve results, and they are as follows:

1) port-matching the intake manifold and the block
2) removing the 'brow' at the junction between the intake runner and intake bowl, and
3) reworking the hard turn on the exhaust outlets on each of the four corners of the block.

By focusing on these three areas, a beginning porter will achieve the majority of the benefit of a full port job without mucking up the block - or spending three days at the grinder in the process.

Next: Some pics of the tools needed - along with a motor shot or two...

 

This thread is shaping up nicely. Thanks Chuckspeed!

 

Flatman -

Didn't mean to blow off your question, just got caught up in the initial explanation of porting.

Relieved Blocks

First off, you need to know that I'm a fan of relieved blocks, as I believe a relieved block is going to have better initial flow during the initial valve opening, as there's less material around the valve to obstruct flow.

I've read a bunch of the various pros and cons, and the best rationale I've read against relieving is that the flow gains are offset by the reduction in compression ratio. If you're not taking this into account when relieving, then yes - there's no bennie to spending hours and hours carving 3/16" of material out of 8 combustion chamber areas.

Think about this, though...Both Barney Navarro and Kirby's (Motor City Flathead) high flow heads utilize big combustion chambers - allowing more area to move the combustible mix in and spent gases out of the motor. It stands to reason that relieving would provide a benefit AS LONG AS there was a plan to offset the reduction in compression ratio by going to a .400 head as opposed to a .425 head, for example.

But...this is porting for dummies. The LAST thing a shadetree porter should be doing is mucking about around the valve seat; one slip of the grinding wheel and the block is in for a seat job. As a kid, I practiced on junk SBC heads to get a feel for the work, and I STRONGLY recommend you snag a junk OHV head and smooth a few ports thataway first; while the overall job of smoothing a flattie port is easier IMHO, you're much better off bunging up a junk head - or cracked flattie block - before tackling a pristine piece of Cast Iron Charlie's finest. What's there on a stocker 8BA or 59A is tried and true, while a little carving would help (eliminating sharp edges which can initiate knocking, for example) it's not worth the risk if you're not sure of your skills.

 

Good stuff - keep it coming.

On relieving, Joe Abbin, who probably has as much time on a flow bench with a flatty as anyone, has determined that with common aftermarket heads, there's a 7-15% increase in flow (7% was with hi-flow heads like Baron).

Many will argue that flow is only improved with a relief above 2500-3000 rpm and my answer to that is, "What's your point?" If you plan to run your engine hard, I'd rather have it than not...

Joe is also a big fan of unshrouding the intake valve, back-cutting the head (like Ron Holleran advocates), & even simple plunge cuts above the valve - these all help earlier in the rpm range than the relief, so many view valve-unshrouding as "all you need."

FWIW, I'm far from an expert, but do research a lot on this stuff. If I can get empirical data (like flow benches & dynos), I'll take that anyday over 60-year old heresay and old wives tales. And such is the problem with flathead speed secrets - much was closely guarded & intentionally misleading to maintain the edge 'back in the day.'


EDIT - The comments about just hogging out ports vs working specific areas holds very true for normally aspirated engines. On blown engines, the air behaves the same way, it's just got pressure behind it & larger ports often perform better regardless of turbulence...

 

Thanks, Flat Ernie!

One of the goofy things about airflow is that a constant reduction in the cross sectional area of a runner will have minimal impact on pressure drop; a smallish port that necks down will once again flow better than a big honkin' port - on a normally aspirated engine.

This is all relative, though, as flattie ports and runners are pretty small compared to modern ports. Hell, a 600cc motorcycle prolly has more cross-sectional area (by cylinder) than a flatmotor does!

One of the problems with flow testing is that most folks just look at the WFO numbers; on a street flatmotor, the 'snap' you get when you tip into the throttle is a function of how well the port flows as the valve *just* lifts off the seat. Dyno guys refer to this as 'area under the curve' - a good street motor doesn't just generate a big HP/TQ number, it works well in the critical 2000-3000 RPM range.

While I'm waiting for the garage to heat up (it's been WAAY below normal here in the Center of the Known Motoring Universe for the past 6 weeks), let's talk about engine prep and tools:

Engine Prep

Porting a flatmotor should only be done on a motor that is COMPLETELY torn down - not a single part attached to the block when the first stone touches iron. Reason is - you're going to be tossing a lot of dust and grit around, and this stuff settles in every nook and cranny of both the motor - and the shop.

I'm kinda **** about keeping parts clean, so during the teardown, I bagged the guts from each cylinder, marked the bag, put it into one of those big plastic tubs and sealed it up. A buddy of mine once did a port job on his race motor (440 mopar) and a wee bit of grit made it onto a bearing; motor was toast after a couple of p***es. That's not something you want to happen to your precious flattie, so bag and tag EVERYTHING that goes into the motor. When you're done porting, the block is going outside to be treated to a nice warm soapy bath, so don't worry all that much about the grit during the work - just protect the stuff youre NOT grinding on!

Tools

Unless you're a tool freak and NEED a big honkin' die grinder, a little cheapie hand grinder will do just fine. While not recommending it, I use a Dremel 275, which is a 28,000 RPM single speed unit. The real real reason I use this is Pop gave it to me one year as a present, and I've been too cheap to go out and buy a better one.

The benefit of such a spartan tool is that it's light. You're gonna spend a lot of time with tool in hand, and fatigue is what causes mistakes. A light tool allows longer grind time, IMHO. Electric grinders are also considerably lighter than their air-powered counterparts, and allow for a more delicate 'touch' in tight areas.

Since this is Porting for Dummies, we're going to simplify stone and cutter selection by sticking with just one stone - a Dremel 952 which is pre-dressed to a flame tip. You can do the job faster with a carbide bit, but like AV8 sez, its easy for the tool to get away from you - or - you get a little rambunctious and cut too much in an area. Lemmetellya - it's real rard to stick iron back on one you've cut it off! This is a short shank stone, also - while it's nice to go deep into the port, the benefits are minimal on a street motor - and - a long shank stone that goes off center at speed can be quite umm...eventful. Soo...We're gonna stick with doing port work only about 2" in. Sticking with one stone type takes a little longer on the meaty cuts, but a novice porter can take his time without fear of ******ing up something. For the full job, expect to go thru about 4 stones.

As for marking and scribing...Pop's gonna have a fit if he reads this. While Prussian Blue is the hallmark of a tool and die guy, a novice porter can accomplish a decent enough job of inking the block with...a...permanent magic marker, and any sharp pointy thing laying about the shop (like a punch with a ground tip) will suffice to scribe the line when port matching. You're just trying to make a line on cast iron, and this works just fine without having to make a trip to the local tool and die store for one-time-only supplies.

So - a naked flathead block one electric hand grinder, a handful of off-t******lf stones, a permanent magic marker and a sharp pointy thing. Once these are in hand, you're almost ready to put stone to iron!

A couple of items before we start:

1) while a full-on respirator is best, at least wear some sort of dust mask. There's silica in the grinding stones, and you really don't want to ****** up your lungs. I didn't care when I was a kid, and nowadays I'm real susceptible to pneumonia. While I can't prove it, I'm convinced it's a result of all the **** I inhaled and then hacked outta my lungs two days later when I was a kid. take the time to treat your body right.

2) Same thing holds true for your eyes and hands. Wear gloves and eye protection. a high speed stone can cause a LOT of damage if it gets away from you, and I've been to the E-room so many times back in the day that they knew my by my first name. It's no fun having a piece of grit yanked from your cornea, so use protection.

3) Finally - hang the block on a stand. It's much easier getting into those nooks and crannies if you can rotate the block to a comfortable position; you'll make fewer mistakes thataway.

Okay - I'm gonna kidnap a kid camera and start taking pix next...

 

chuck,
great post
i was wondering what your, or anyone else's opinion is on opening up the heat riser that normally goes to the intake
it seems as those the center exhast could use a bit more room to vent....but maybe its not a big concern and not worth worrying about?
i had thought of just making a tube the same size attach to the intake and extend down and bolt to the header....
i believe it was doane spencer who had this done on his car in the 40's
any thoughts?
thanks
Zach

 

when you look at the cutaway pic you gotta say that the flattie will be strangled at higher r's!. definitely needs room around the valves to breath. Yes from my perspective airfow is like a train, and turbulence is like a train wreck. turbulence is actually useful sometimes, say for anti-reversion in headers etc, so a smooth flow is needed. My experience with flatheads, both v8,s and inlines, just driving them there was a 'flat' spot at higher rpm,s and then they would get 'another wind' and keep accelerating, and the big cubic inchers were harder to 'feed' on the top end. Barney was right, yes porting does help but the ol' flatty just begs for a blower.

 

yes 'SUHRsc', mr. flathead, John Bradley, and others had pipes sticking out all over the flatty. even ol man Henry's early prototypes had exhaust ports outside the ends of the block.

 

What about head design affecting flow?...a runner can flow huge amounts of air but as soon as it hits the head alot of times isnt it like hitting a wall? I mean what about flame travel, the area around the back of the valve and step relieving the Heads instead of the block, maybe in conjuntion with a mild polish instead of a full on port. You have to think about one if your thinking about the other... Any thoughts here?.........nice thread so far

 

Okay...

the kids have yet to give up the short focal length camera so, more thoughts....

Paulie -

Yes, head design has a HUGE impact on flow, but not like you think. If there's a wall to be hit - it's the SIDE of the combustion chamber in the head - not the top of the head! You're limited as to how much 'meat' you can take outta the head, as gaskets limit how deep a back cut can be on a head. There are big bore gaskets - but keep in mind that a heavy back cut to improve air flow in the heads will *kill* the compression ratio, reducing brake mean effective pressure (BEMP) and horsepower in the process.

Remember - this is porting for dummies; we're not gonna get all fancy and muck about in the combustion chamber. That's dangerous for a couple of reasons; one is that a runaway stone can leave a nice deep groove across a sealing surface - that's bad. The second is CC-ing'; that's a science unto itself. Nope - we're just gonna focus on what the average joe can do to add xtra HP.

Zach -

Your point is well taken. Kicking exhaust out the crossover port nearly doubles the volumetric efficiency of the siamesed port - in theory. Problem is, there's a K value embedded in the equation - and I can't find my K value table to 'splain it...the K value is the constant attributed to turbulence; sending exh flow in two directions is very turbulent. Better to place an exhaust divider in and allow the port to share duty with the adjacent cylinder - this will be covered in 'Bolt on Porting' later in the thread.

 

Great thread Chuck!
Didja find that camera yet?

Flatman

 

BTT

Anymore to this great thread?

 

Anyone know what, if anything, happened to this thread?
Did it get renamed, or go somewhere else?

 

Maybee Santa will bring Chuck a didgital camera for Christmas...I'm dyin' to see pics...