Cylinder Head Porting

[tibbs.james 1]

Hi Guys

I have recently purchased a Die Grinder and a vast array of grits and cartridges for doing a fairly good tidy up job on a Pair of Nissan v6 Heads. ( 2 opposed valves similar to the E30 head, camshaft in center ect)

Despite not being a BMW head, would the forum be interested in my time to do a write up of materials, methods and the process of doing casting tidy ups, polishing combustion chambers and of course port matching intake manifolds etc ?

I am a DIY guy and Have no experience, however I have had an offer from an experienced engine builder to show me some stuff for keeping things inside the head tidy to improve the efficiency.

Also i thought this topic might be a good place for others to leave their idea's information and experience on this type of engine work as a reference for others.( including me ) to refer back to.

ok .... GO

[ashy_aye 3]

if your stuck there is heaps of porting templates on the net just print them off and away you go,

im sure there is alot of people that would be interested in a write up, as it is quite a good mod for average the d.i.y'er, when replacing headgaskets and the like.

[CamB 48]

I dunno - other than port matching and incredibly minor tidying I understand it's not that great an idea to try and port a head without a flow bench.

Conceptually I really don't consider it DIY.

[DRTDVL 0]

Generally when you do work to a port/head you will gain CFM but lose VELOCITY... A good porter will be able to increase both. A lot of people go balls out for cfm but they kill the velocity of the port and wonder why it doesn't go as well as they thought it would...

Tip 1 = Do not start going down the path of removing lots of metal if you do not know what your doing!

Tip 2 = Remove the as cast surface using no smoother than 150 grit sandpaper rolls. removing the as cast surface can increase flow by 4-8% depending on casting quality. if you make it too smooth you will increase the boundry layer effect (think golf balls).

Tip 3 = Make friends with some one with a flow bench.

Tip 4 = find a spare head thats F!@Ked... find someone with a bandsaw and cut down the lengths of the port (as close to the center line of the port as possible. This will let you see the material thickness along the port as if you go too deep and puncture the water jacket thats it buy a new head

Tip 5 = Port the head to the CAMS YOUR USING OR INTEND TO USE! not point making a port that flows amazingly at 11mm lift when your cams only go to 8mm. 

Tip 6 = Port matching - blend the intake port to the intake manifold port to make it as smooth a transition as possible will prevent turbulance with the air moving between the two. Same with the exhaust ports and exhaust manifold

Biggest area of possible gain depending on manufactures, is typically the port wall to valve seat inside edge alignment. I've seen a few shocking heads, some with as much as 3mm overhang... this will kill flow over the seat or into the port depending on the way it's overhung... 

for example (this is hard to do with out a picture): 

....\ 

......\ <--- seat 

...| 

...| <---- port wall... i would call this overhang 

..\ 

....\ <---- seat 

.....| 

.....| <--- port wall i would say well blended 

\ 

..\ <--- seat 

......| 

......| <---- port wall underhang...

Go and sit with the experienced engine builder 

Edited April 7, 2009 by DRTDVL

[DRTDVL 0]

This wasn't finished (not i didn't do the porting) but you can see that you can also decrease the thickness of the fin between the ports, again becareful not to remove too much and puncture or weak the port.

If you read up about flow in pipes it directly relates to air flow in ports. boundary layers, turblance is other things to have a good knowledge on.

[tibbs.james 1]

I dunno - other than port matching and incredibly minor tidying I understand it's not that great an idea to try and port a head without a flow bench.

Conceptually I really don't consider it DIY.

Thats a good no S**T reply camB, My intentions are to do a good solid tidy up but not to disturb anything that should stay as it is.

1.Match the intake ports

2. tidy up the casting on these heads by giving it a good uniform finish across the entire length of the port. - I have been recommended to use up to 80 grit on a cartridge roll.

3.Polish up the combustion chambers ( boosted motor )

4. Tidy up the exhaust ports and try and smooth out any real rough or sharp edges while again keeping the original shape of the port.

I do not intend to do any actual reshaping or removing any amount of material from the heads, only what might be considered finishing work.

I have seen flow bench charts of the same heads with up to a 15% increase in flow from doing a similar amount of work as what I intend to do.

The heads are not the most sophisticated and neither is the quality of the casting.

Thanks for the reply's guys. DRTDVL- you information is consistant with what has been explained to me by others thanks.

[DRTDVL 0]

2. tidy up the casting on these heads by giving it a good uniform finish across the entire length of the port. - I have been recommended to use up to 80 grit on a cartridge roll.

3.Polish up the combustion chambers ( boosted motor )

We would use 80 grit to really get at the as cast and then as a "polish" would use 150 it gave good results without getting too smooth... When your attacking the ports put some nice thick tap like electrical tape or something over the seat so should you nic the seat you don't have to get them recut.

Same when you polish the chamber you want to make up some blanking valves or use old valves so again you don't nic the seat.

[kerrynzl 3]

As a DIYer use caution or better still don't f**k with it at all [ remember it is difficult to un-port a head]

90% of the gains are from doing a good valve seat job [ and thinning the valve faces ]

Every porter I know will accidentally 'nick' a valve seat while porting .so they get the machinist to do a seat job, then "presto" more airflow [ they don't realise the gains were from someone elses work ]

I've spent a bit of time on a flowbench and have learnt "what looks better ain't neccessarily so"

On my old Chevy ZL1 heads we welded up the floors of the exhaust ports to make "D" ports ,that some "expert" had previously hogged out and we gained 35% on the flow bench

Remember an engine breathes in "gulps" or "pulses" so velocity is more important than CFM

[ you can mask poor CFM flow by upping the static compression ratio and using more valve timing ]

If you are interest in "cheating" [remember it is innovation until you get caught] for the E30 series. there are many ways to gain airflow. [ formula ford boys are experts here ]

[Silver Fox 43]

As a DIYer use caution or better still don't f**k with it at all [ remember it is difficult to un-port a head]

90% of the gains are from doing a good valve seat job [ and thinning the valve faces ]

Every porter I know will accidentally 'nick' a valve seat while porting .so they get the machinist to do a seat job, then "presto" more airflow [ they don't realise the gains were from someone elses work ]

I've spent a bit of time on a flowbench and have learnt "what looks better ain't neccessarily so"

On my old Chevy ZL1 heads we welded up the floors of the exhaust ports to make "D" ports ,that some "expert" had previously hogged out and we gained 35% on the flow bench

Remember an engine breathes in "gulps" or "pulses" so velocity is more important than CFM

[ you can mask poor CFM flow by upping the static compression ratio and using more valve timing ]

If you are interest in "cheating" [remember it is innovation until you get caught] for the E30 series. there are many ways to gain airflow. [ formula ford boys are experts here ]

As far as I know there are examples of this innovation already in the series.

[tibbs.james 1]

Its a good thing Nissan's don't race in the E30 Series

Another good Practical Reply Kerrylnz.

A 5 angle or "suitable" valve job is on the list.

More and more it seem the word "porting" is a bad one to use

Perhaps "blue printing" is a better way to describe it. Anyhow if the V6 Heads were as god as my E30 heads (quality of casting) i would not need to go near them with anything but some degrease.r

I may get a stock head and a finished head flow benched to see the difference before they get machined up. so that i have some real proof of the worth of this project before results can be skewed by valve work.

[DRTDVL 0]

If you are interest in "cheating" [remember it is innovation until you get caught] for the E30 series. there are many ways to gain airflow. [ formula ford boys are experts here ]

Look up extrude porting - leaves an as cast looking surface... Basically an abrasive sludge is pumped throught the port increasing the overall size of the port while looking basically "stock" - was big a few years back with the v8 boys... a  few got caught

A 5 angle or "suitable" valve job is on the list.

We found some heads flowed better with a 5 angle seat vs a full rad seat cut

[kerrynzl 3]

Look up extrude porting - leaves an as cast looking surface... Basically an abrasive sludge is pumped throught the port increasing the overall size of the port while looking basically "stock" - was big a few years back with the v8 boys... a  few got caught

Hahaha! I better not let too much info out.

There is an outfit in the States called "Brzezinski Racing Products" that specializes in cheatin'

They do "Acid Porting" etc.

They will even weld GM casting #'s onto "world product" heads

check out http://castheads.com/

It reminds me of a Camaro I had years ago where I had to use the stock engine block and stock casting numbers [ but the rules allowed any block modifications or repairs ]

So I used about 10 sq inches of the original 305 block and 'repaired' it with a 400 block.

There's an old saying : " I know you're cheating , because I am cheating and you are beating me "

It's all about how thin your interpretation of the rules is !

there's an old saying: " I know you are cheating, because I am cheating and you are beating me "

[tibbs.james 1]

So after all this talk i did some " TIDYING UP & PORT MATCHING "

all in all i think it went rather well

1, Using a rotary carbide cutting tool I first matched to the intake manifold gasket.

2, Again using the rotary carbide cutter in the die grinder i went over the entire port to remove the "as cast" surface.

3, Using a standard Abrasives brand Mandrel and Cartridge roll ( 40 grit ) I went over the port again to give it a nice machine type finish.

The intake port feels slightly rough to the touch & I am unsure if i should go over it with the 80 grit or not. It seems like such an improvement over OEM that I don't want to take it too far.

[DRTDVL 0]

So after all this talk i did some " TIDYING UP & PORT MATCHING "

all in all i think it went rather well

1, Using a rotary carbide cutting tool I first matched to the intake manifold gasket.

Have  you matched the port openning to the gasket also?

2, Again using the rotary carbide cutter in the die grinder i went over the entire port to remove the "as cast" surface.

3, Using a standard Abrasives brand Mandrel and Cartridge roll ( 40 grit ) I went over the port again to give it a nice machine type finish.

The intake port feels slightly rough to the touch & I am unsure if i should go over it with the 80 grit or not. It seems like such an improvement over OEM that I don't want to take it too far.

You will want to go over it with a 120ish to give it a "polish" no finer than 150grit tho, you want it to be smoothish to the touch but not mirror smooth.

Make sure you give the head a good wash and a blowout as you might have metal filing (most likely) in the water jacket openings now and you don't really want those going through the coolent system.

kerrynzl: those world heads are very average... I know people would change to OEM replacement heads from other manufactures as they where known to be on average 5-8% better flowing than the original OEM heads and when you in a "controlled" "stock" racing series that 5% makes a big differance. 

[tibbs.james 1]

Have you matched the port openning to the gasket also?

Yes this is what i ment. I have not done the inlet manifold yet only the cylinder head.

You will want to go over it with a 120ish to give it a "polish" no finer than 150grit tho, you want it to be smooth ish to the touch but not mirror smooth.

Thanks, i wasn't sure going that fine was necessary but i will do that too.

Make sure you give the head a good wash and a blowout as you might have metal filing (most likely) in the water jacket openings now and you don't really want those going through the coolent system.

I will have the machine shop parts wash the heads before and after they do their machine work to it.

[DRTDVL 0]

Yes this is what i ment. I have not done the inlet manifold yet only the cylinder head.

[/qoute]

You will want to do the intake manifold also... this will help to create a smoother transition from manifold to port... 

[kerrynzl 3]

Have  you matched the port openning to the gasket also?

kerrynzl: those world heads are very average... I know people would change to OEM replacement heads from other manufactures as they where known to be on average 5-8% better flowing than the original OEM heads and when you in a "controlled" "stock" racing series that 5% makes a big differance. 

Hey , I only posted that site just to show that there are people out there who specialize in cheating.[ it can be fun ]

Word of caution about matching ports to gaskets!!!!!!!!!! this is 1960's hotrod DIY technology.

I've seen gasket matched "heads and manifolds" flow less than stock on a flowbench.

WHY? because most "expert" porters usually grind a nice smooth taper from the gasket into the port [ Bell Mouth ]

Put this "Back to Back" with a manifold that is also "Bell Mouthed" and you have the opposite of a Venturi [ which slows down velocity ]

Use some "machinists blue" and match the manifold to the head [ and make sure the hole in the gasket doesn't interfere ]

It is OK for the intake manifold to be slightly smaller than the port, or the exhaust manifold to be larger than the port

it helps with anti- reversion [ some header manufacturers put anti-reversion cones on the flanges ]

[DRTDVL 0]

Hey , I only posted that site just to show that there are people out there who specialize in cheating.[ it can be fun ]

Word of caution about matching ports to gaskets!!!!!!!!!! this is 1960's hotrod DIY technology.

I've seen gasket matched "heads and manifolds" flow less than stock on a flowbench.

WHY? because most "expert" porters usually grind a nice smooth taper from the gasket into the port [ Bell Mouth ]

Put this "Back to Back" with a manifold that is also "Bell Mouthed" and you have the opposite of a Venturi [ which slows down velocity ]

Use some "machinists blue" and match the manifold to the head [ and make sure the hole in the gasket doesn't interfere ]

It is OK for the intake manifold to be slightly smaller than the port, or the exhaust manifold to be larger than the port

it helps with anti- reversion [ some header manufacturers put anti-reversion cones on the flanges ]

^^^ Thats the ideal way to do it...

I've seen people cut their gaskets to be larger as they overported the head...