DIY head porting

ppyvabw · Post by **ppyvabw** » Fri Nov 18, 2011 12:43 am

I'm going to start porting my cylinder heads whilst I am waiting for things to happen with my bottom end - balancing etc: my block is currently at the shop being bored.

It's a 3.9, and the pistons I am using are flat tops. I'm going to use early heads with 36cc chambers and composite gaskets to skim the heads afterwards to aim for 10.5:1 compression. I am aiming for (I think reasonable) 240/250bhp. I have not decided on a camshaft yet, but I won't be going beyond 7'000 RPM, and it's going into my road-going MGB so I don't want it to be completely undriveable, but as it won't see much traffic I can put up with a peaky feel. It might even see some track-day use.

I understand that Rover heads see a lot of benefit from opening up the throats and blending into the short side, which is fairly straightforward. I'm fairly confident about cc matching the chambers too (I have a burette).

I have a few questions:

I have read that the inlets need to be finished with a slightly coarse finish, and the inlets a polished finish. Is this correct?

I'm not certain about opening up the ports at the manifold because making them too big will have a detrimental effect on flow. If I open them out to the gasket, will this be too much? I may have an attempt at making a flow bench as per one of David Vizard's articles, and stop grinding when I stop seeing improvements at my desired valve lift? I have a set of heads to practice on.

I have also had a look for any pictures there may be showing where to grind, similar to ones my old man used for his TR6, but I can't find any. I have seen the posts on here with the sliced up cylinder head which are helpful in as much as I can see when to stop grinding. I wouldn't know what to do around the short side and the valve guide apart from polishing.

Also, the issue of valves and valve shrouding problem with Rover heads. I would go to the 1.63/1.4 inch valves, but I wonder if retaining the standard size valves would yield a better improvement for my desired output by keeping the valve unshrouded, away from the cylinder wall. I am using 95mm pistons, so larger than standard.

Any input and advice at all would be helpful.

Edit: Also, who supplies those valve guides with the step in them at the correct installed height to stop the guide dropping through? Thanks.

Pocket rocket · Post by **Pocket rocket** » Fri Nov 18, 2011 7:35 am

I'll wait for the experts to give you a detailed reply but here are a couple of articles which may help whilst you're waiting..

http://www.popularhotrodding.com/engine ... index.html

http://www.allpar.com/fix/holler/head-porting.html

ged · Post by **ged** » Fri Nov 18, 2011 7:39 am

Hi ppyvabw,

I found this book helpful.

How to Power Tune Rover V8 Engines (By Des Hammill)

http://www.britishv8.org/Articles/Power ... ver-V8.htm

It has full size diagrams for standard & ported heads.

Regards Ged

kiwicar · Post by **kiwicar** » Fri Nov 18, 2011 10:04 am

Hi
Surface finish is normally recommended as that achieved by 120 grit emery both inlet an exhaust, some swear by 80 grit finish and some a two stage finish of 120 grit over 80 (like cylinder bor honeing) personally I would just go straight to 120 grit and not phaf about.
The short side is best left alpne beyond removing casting marks and blending in the valve seat unless you have a flow bench and 20 years experience of grinding heads

match the heads to the inlet manifold using ceriel box card of drafting paper but take as little material out as you can.
Avoid opening out the inlet tract at the head face it really kills flow unless you are creating very high flow heads.
Inside the port at the point where the push rods go through is the most restrictive part of the port appart from the seat insert so concentrate on that area once you have bored and blended the seat insert.
Best regards
Mike

ppyvabw · Post by **ppyvabw** » Fri Nov 18, 2011 2:35 pm

ged wrote:Hi ppyvabw,

I found this book helpful.

How to Power Tune Rover V8 Engines (By Des Hammill)

http://www.britishv8.org/Articles/Power ... ver-V8.htm

It has full size diagrams for standard & ported heads.

Regards Ged

After being recommended that book several times before, yesterday I finally looked for it on Amazon. It is out of print now apparently, so I have email notifications for if it comes available on Amazon again. There's a copy on 'the bay' that I'm watching out for.

Darkspeed · Post by **Darkspeed** » Fri Nov 18, 2011 5:45 pm

250BHP will need bigger valves than the stock ones - standard valves will limit you to aorund 220/230 depending on the rest of the work on the engine. Just working the throats will get the flow up for the standard valves but the extra power available with the big valves will need to come from opening up the ports.

The Peter Burgess speedpro book is well worth having.

Andrew

ppyvabw · Post by **ppyvabw** » Fri Nov 18, 2011 7:51 pm

Thanks for that info Andrew. I'll upgrade to the bigger valves then, and grind the chamber around the valves to de-shroud them.

I've read about modifications to the backs of the valves. What's needed in that respect?

Darkspeed · Post by **Darkspeed** » Fri Nov 18, 2011 7:56 pm

Nothing required on the big valves and the chambers need very little work as the shrouding is minimal.

ppyvabw wrote:Thanks for that info Andrew. I'll upgrade to the bigger valves then, and grind the chamber around the valves to de-shroud them.

I've read about modifications to the backs of the valves. What's needed in that respect?

Andrew

ppyvabw · Post by **ppyvabw** » Sun Nov 20, 2011 1:49 am

What order is best to do this?

Do the porting and then have the seats cut? That way I can get on with it - Something I don't have a lot of at the moment is money to buy valves and have the cutting done, but an awful lot of time.

Or have the seats cut first so I know how much I am opening out by. I am guaranteed to nick one or more the new valve seats this way though...

kiwicar · Post by **kiwicar** » Mon Nov 21, 2011 10:43 am

Hi
if you are fitting bigger valves the seat inserts need opening out (they do to get the best out of standard valves) before anything else is done, otherwise how do you know what to blend the rest of the bowl to

I hate to say this but if you are looking for more power than a stage 1 porting job will give you then you will need the flow bench and an engine on a Dyno to develop the heads properly. You are looking for small incriments and changes in port shape to get the flow you are after. High flow big valve heads are not really something for the home porter to tackle. Stage 1s yes no problem if you are sensible then you should get good results, stage 3 and above are really for the profesional porter with several years of porting behind them. If you are going to do this yourself start with a slightly less ambitious target output and you have a very good chance of producing a good result.
Best regards
Mike

DaveEFI · Post by **DaveEFI** » Mon Nov 21, 2011 11:04 am

I have a spare set of heads from a 3.9 which look to be in good condition and would like to have them ported for my standard Vitesse engine.
What firm offers the best value for this, and how much? And what sort of improvement would I get?

Darkspeed · Post by **Darkspeed** » Mon Nov 21, 2011 7:28 pm

Lets have a play.

First off lest get the necessary tools together

Something to test - at a reasonable size - it's a later head but not with waisted stems and one of the odd ones with the exhaust gas port things I wish I had a band saw.

A couple of bits of scrap to work with.

Look at the amount of carbon in here

The one we will start with first

And a choice of valves

The standard valve and that silly ridge

An open flow test with nothing in the port just to get a datum

The first parts in the port that need to be removed - no changes to the seat internal diameter at this stage

Thats got it started - see if i can get it progressed during the this week

A I have a base run with the standard head and valve

B run with the waisted valve with a cut back

C run with the waisted valve and a basic port blend std seat id at 34.7mm

D run with the waisted valve and the insert taken to 36mm and blended

Just need to combine the graphs.

But here are the flows at 450" - @ 28"

Open - 141.5

A= 134.5 cfm
B= 137.0 cfm
C= 138.9 cfm
D= 137.1 cfm

None of the porting work at present extends further than 3/4" into the port

Andrew

Darkspeed · Post by **Darkspeed** » Mon Nov 21, 2011 7:41 pm

I can recommend Roy Burrell in Coventry he is retired but still does the odd bit of work

http://www.royburrellengines.co.uk/

Rovers are his speciality

DaveEFI wrote:I have a spare set of heads from a 3.9 which look to be in good condition and would like to have them ported for my standard Vitesse engine.
What firm offers the best value for this, and how much? And what sort of improvement would I get?

sean · Post by **sean** » Mon Nov 21, 2011 7:48 pm

Show off!!

They aren't my heads are they?

Darkspeed · Post by **Darkspeed** » Mon Nov 21, 2011 10:15 pm

Sorry mate its all in the name of knowledge I thought you would be ok with the sacrifice

sean wrote:Show off!! They aren't my heads are they?