Head Porting - Can of worms

[Benzo4gT]

Hi all, as can be seen in my previous posts I have done some porting to my 63 head. Now, I don't mean to be a complete knob and I have tried to search the forums for some answers, but have not really found any regarding what I'm after.

OK, I was of the belief that porting a head for more flow was not a bad idea as long as you pay attention to the way you need to port the particular head i.e. what intake, cams, turbo size, desire driving style etc. which will give an idea of how much you need to take out. Obviously cleaning up the casting dags and smoothing out the bowls goes without saying, and possibly a polish of the EXHAUST ports only, will help resist carbon build up ( as a side point, I have always gone to my local Subaru dealer and used their own OEM decarbonizing spray for all of my performance cars at least once a month, or before any drags or happy nights)

This guy says smaller is better based on port velocity, but he does a lot of motorbikes and I think he is only talking about atmo builds, but it is hard to discern from how he goes on.

http://www.mototuneu.../think_fast.htm

Anyway, what I want to ask is; What is the actual truth about porting a head for turbo aplications? i.e. 25+ psi boost
The reason for this post is to get the right info based on how you guys have set up your rides, and do forgive me if this has already been addressed, but I did look and came up empty.
Does port velocity factor in when the intake valves open up with 25psi behind them?
Does plenum size and shape help, and does it make a huge difference? I have seen some setups using rv4? atmo intakes and wondered why.

I will be going ball bearing for the turbo and getting some solid advice on cam lift, duration etc. I am aiming for 500hp and don't beleive it will be overly hard to achieve given some research and a bit of advice.
It is proving hard to find solid proof with backed up claims in the subject of 4g63ts and head work, and by that I mean REAL big power figures. Do they run large ports and valves, decent cams i.e. 272s, 280s?The people in the know who run big power 4gs are very tight lipped.........Bastards LOL

Have a look at the size of this 63 head

 

[brisvr4]

Just clean up the rough spots and the entry area behind the valves.
Be very careful on the exhaust port roof (or it might be floor, can't recall!), you can break through to the water jacket real easy!

 

[Benzo4gT]

Hmmm, too late for me I'm afraid, head is already done lol. I do have a virgin head though AND would be willing to do an experiment when I have the engine in and tuned.
I will get my setup tuned and dynoed, get the figures, then swap the head to the virgin head then repeat the process.
The real can of worms is in the fact that most of us have forced induction and as such may not have to rely on port velocity, but on this I am not sure hence the post.

Just clean up the rough spots and the entry area behind the valves.
Be very careful on the exhaust port roof (or it might be floor, can't recall!), you can break through to the water jacket real easy!

Yeah, I have gone very light on the Exh. side, just cleaned up the bowls and dags.
The roof of the head is relatively safe to port a bit as it is on the top side as you look down at the valve gear, and on top of that is the right place to port to get the flow to angle as vertically as is possible on intake side, well that's what I have read anyway, and what I have done to my poor head.........shit I hope I have done the right thing

This is the only thing regarding port size, it is an explanation of port velocity that I can actually understand, but find it hard to apply to a turbo engine. What he mentions regarding valve timing is similar to that which occurs on a Miller cycle engine

"The valve opens, and soon after, a large suction builds up as the pistons speed down the bore increases and reaches a maximum. During that phase, yes, it is like a flow bench, and yes, smaller ports will reduce the flow slightly there. However although the mass flow rate will be smaller, the larger pressure differential means the average flow speed is increased. This is useful later in the intake cycle.

Nearer the end of the stroke, the piston is moving quite slowly again, the valve is still quite open and flow in continues. A few moments later the piston is actually coming up the bore but the valve is still open, and get this, even though the piston is going up the bore, air is probably still flowing INTO the cylinder, instead of out of it. Why?

Because during the first phase where the piston was descending fast, all of the air in the port, and in the intake runners, right the way back to the plenum, took a moment to accelerate to full speed and start flowing into the cylinder and when the piston stops moving and reverses, all the air that was rushing towards the cylinder continues to rush toward the cylinder since it's going to take a moment to slow down as well, and that effect crams more air into the cylinder than there otherwise would be.

The key here is that the air has inertia. When the piston stops pulling on it, it keeps moving for a while. The faster it was going before the piston stops pulling on it, the more kinetic energy that column of air has and the longer it will take to slow down. Smaller ports, and smaller runners, force the air to go faster during the earlier intake phase, thus take longer to stop flowing in the later intake phase."



This does my head in, no pun intended

 

[4piknup]

Other than cleaning it up, i leave the porting to someone with a flow bench. also the valve is at low lift more than high lift, so low lift flow is important. this is improved by bigger valves and 5 angle seats.

 

[cbgsr]

You need to make sure the ports arnt to big as it will reduce air speed making it laggier same goes when you remove the squish around the valves.

 

[4piknup]

How did you go with this?

I think 500awhp is achievable on stock head and mild clean up.
Would love to see a comparison with stock head. Esp regards coming on boost.

 

[EVO-00X]

Basically in a nutshell, small ports for higher velocity and instant / better throttle control down low, however its not the best for WOT and top end.
Big ports has less throttle control down low but if you drive at WOT then you want as much air and fuel in as possible.

 

[Benzo4gT]

Well, I thought I'd Lazarus this thread with some pics. I had a nice port job completed a few months ago, but when I checked with a head specialist he said pull some more out and

make the bowls bigger, shave down the guides and make the approach to the bowls as straight as possible. So this is the result. I've chucked in a pic of a std intake port just for reference. Also to note,

the areas that narrow in the port were only enlarged just over 1mm so the ports should still have some low rpm velocity, and only the ceiling was touched with no alteration of the shape of the port floor.

There are some marks around the valve seats that don't belong to me, another head shop had tried a clean up at some stage so I inherited the overport, it's only tiny though so shouldn't affect anything.

Seats are yet to be cut so I'm tempted to go 1mm oversize

For my next head port job I'm thinking of experimenting with the polyquad way of porting, I have 4 heads atm so why not LOL

 

[DOUGMO]

I make 520hp @ wheels with 264 cams and a mildly ported head and 1mm over valves

 

[Benzo4gT]

WOAH, nice! What turbo/boost were you running?

 

[Benzo4gT]

Update: After taking it to the professionals I got 2 thumbs up for the port job, these guys do speedway engines a lot of which are motorbike engines so I'm pretty happy with the feedback :thumbsup:


Here are some pics of bowl roughout and 1 ported runner vs untouched. The angles on the divider are not altered, the floor has no material taken off it, and the port roof and entrance to the bowls are

blended with next to no material taken from the runner sides. The choke area (for want of a better description) has been moved slightly closer to the entrance of the runner and the length reduced.

Only thing left to do is hit it all with some fine grit rolls to finish it up to a smooth finish (not polished)

I'm hoping that I will still have some nice port velocity with this alteration, but the flow bench will give me an indication, the real answers will be on the dyno.


WARNING: The following images may scare those who don't have a spare cylinder head, or those who care about bottom end power

 

[4piknup]

Looks good. Would like to see flow figures compared to stock ports

 

[BMGTZ]

Ive done this twice

remove dags and casting imperfections...fit 1mm oversize valves and blend the bowl area.

the one engine was due to having a blown head gasket and needing MLS gasket......so did it because we could at the time. That car was later dynoed and showed a much better gain than just fitting BC272 cams.

for my money...always bigger valves.

 

[DOUGMO]

WOAH, nice! What turbo/boost were you running?

Im running 27-28psi at the moment (out of injector)with a borg warner S259 turbo (old school, oil cooled only, non BB)

 

[Benzo4gT]

Looks good. Would like to see flow figures compared to stock ports

I'll definitely put some figures up. I'm mapping out the ports today using side and front scale drawing with measurements taken every 8mm on both axes. 225 points of measurement

per port. I swear I'm crazy as batshit sometimes :wacko:

My goal is to get as close to a perfect match in each port both in flow and shape.


Good to hear the feedback on the O/S valves guys, the head had been molested before I got it with overporting on the bowls, so 1mm O/S will clean that up as well as make more POWAAAAAH

 

[Benzo4gT]

So I started the measuring process this afternoon, I ended up with 115 measurements and I was only within the first 30mm from the port entrance. Most were within less than 1mm of each other with most within a tenth or right on.

I marked it all out on my scale paper drawing with 1-9 for the x axis, and a-o for the y, and roman numerals for the z axis. I took some pics to help describe the process and also to point out to everyone that I don't have a

life

In the pics you can see the rudimentary tools used, I would have used sticks and rope but I found verniers, telescoping gauges, a straight edge and a T-square :thumbsup: I marked out he telescoping gauges with increments of 10mm

and used the straight edge and T-square to help position the gauge, vernier calipers took the measurement from the telescoping gauges. I originally had the increments at 8mm, damn ruled lines I changes to 10mm because it

was easier. I threw in a pic of some of the points I measured, I marked them so they're easy to see.

I'll finish up the measuring tomorrow. I'm expecting to see more of a variation as I head deeper into the port. With all of them mapped I'll set about readjusting them to the same numbers. Hope you find it entertaining

 

[GeoKez]

Wow Ben. Now that's how it done. Watching with interest for the flow numbers.

 

[4piknup]

Often they fill the port with a jelly stuff (maybe ballistics jelly, like on mythbusters) then push out the gel and measure with verniers.

Maybe from there you could slice the mold at 1cm and stack it in the next port to compare

 

[Benzo4gT]

That sounds interesting. I only have aeroplane jelly in stock atm, maybe if I mix it really stiff it'll work, I could have each port a different colour and flavour. I can just see myself now, hmmmm, runner number 3 tastes a bit narrow before

the bowls, with a strong raspberry tone and a hint of aluminium

 

[4piknup]

Alaminim