Porting Cylinder Heads - is it worth it?

[Peter H.]

I'm thinking of getting my engine (1988 2.2 HC N/A 63,000 miles and currently generating 143hp at the flywheel) professionally reconditioned this winter. I've spoken to Mike at Lotusbits and Steve Williams Lotus, but I still have a bit of a dilemma.

I'm thinking a standard rebuild will hopefully get the engine nearer 170hp (right?). So the dilemma is.....is it also worth getting the cylinder head ported while the engine is out?

Its a pricey additional thing to get done and I know it needs a new inlet manifold to go with it. So I wondered if anyone had any opinions or first hand experience of getting this done.....or even what sort of performance gains they experienced?

If its 10-15hp improvement, I probably would not bother.....but if it is +20hp, then perhaps its worth it?

[andydclements]

I think you should see at least that 20hp, perhaps even 30 if you altered the exhaust manifold. One of my Excels has a flowed head and standard exhaust manifold and the power delivery is noticeably different from my standard Excel.

[snowrx]

I'd love to see some data/templates/dyno sheets on ported heads on the 2.2.  I cleaned the out rough casting finish and made sure the runner was smooth going into the valve seat before a multi angle valve cut on mine,  but I did not want to change port shape or size without more guidance.  But I've got a turbo to push past some amount of head issues.

[lotus-62]

all I have done (myself, easy diy job)  is make sure the ports are in line with the manifold  (port matching)  apparently so many are not, usually just a few mill (1-3) using a piece of paper to draw both sides and see where they aren't in line. then clean the ports from casting debris.  only polish the exhaust side as the inlet side benefits from a matt finish. (the wet parts in the mixture release easier from a matt than from a polished port)  al this can be done yourself, and make up for a good improvement but it does not give you the max that can be.  

apparently Mike his 4-2-1 exhaust is a big improvement in mid range (where it counts on the road) 

why do you need another inlet when porting the head?  as far as I know it's  the shorter the ports the less for midrange (but good for top)  

 

[andydclements]

I think that what Peter means is, the inlet manifold has to be ported as well as the head and Lotusbits supply them ported rather than take the existing and have them machined then returned. The ideal inlet is off something like a 911 used in the Talbots as they had the shorter tracts.

 

Thomas.

My engine was dynoed and was showing over 200 (if I recall correctly).

[jonwat]

I gas flowed the twin cam head on my Europa many years ago after reading this by David Vizzard, a very well known tuner of the time.

Simply use the carb spacers as a template to open the inlet ports & the exhaust manifold gaskets similarly.

I also reshaped the valve seats & heads to increase air flow.

I mounted a rotary file in an electric drill for working on the alluminium head & changed to a grind stone for the valve seats & heads. I also opened out the cast iron exhaust manifold.

The effect was very noticeable for little effort & money. 😀

[Peter H.]

Many thanks for the input guys. I think I am currently sitting at 60/40 in favour of doing this.

[andydclements]

I'd say, look at it as a cheap way to move from NA performance to near-turbo performance. The NA Turbos were 210-215 hp and had lag (as with all single turbos), whereas you could get 200+ for just the cost of porting & flowing the head & rebuild costs (labour + gaskets etc). Is that now closer to 95/05 in favour?

[Peter H.]

Thanks Andy, appreciate that.....perhaps maybe 80/20

[andydclements]

42 minutes ago, andydclements said:

........ The NA Turbos were 210-215 hp and had lag ...........

Oops, means carb Turbos.

[jonwat]

1 hour ago, andydclements said:

 whereas you could get 200+ for just the cost of porting & flowing the head & rebuild costs (labour + gaskets etc). Is that now closer to 95/05 in favour?

That's a 27% increase, I doubt if you'd manage that without changing cam shafts & re jetting the carbs.

I'd think a 10% to 15% would be more likely, which is 180 to 190 BHP but still worth it. ☺

[Peter H.]

Isn't the standard HC N/A car around 175HP, therefore a 15% increase would put it around the 200+HP Andy mentions

[drdoom]

On 21/09/2019 at 07:27, jonwat said:

I gas flowed the twin cam head on my Europa many years ago after reading this by David Vizzard, a very well known tuner of the time.

Simply use the carb spacers as a template to open the inlet ports & the exhaust manifold gaskets similarly.

I also reshaped the valve seats & heads to increase air flow.

I mounted a rotary file in an electric drill for working on the alluminium head & changed to a grind stone for the valve seats & heads. I also opened out the cast iron exhaust manifold.

The effect was very noticeable for little effort & money. 😀

Like John, I did this on the head of my very early Elan TC to good effect as there was striking mismatch between carb centres and the inlet ports. I'd be quite surprised if Lotus were producing 90x series engine components with that sort of defect but who knows? DV has a distinguished record in working engines over with plenty to say regarding the lovely, classic TC. A number of factors indicate that the modern engine series likely had ports and valves rather larger than optimal, illustrated most tellingly in how much the torque band thickened when spec changed to 2.2 from 2 litre. It is always vital to performance that the valve seats and adjacent regions of the ports are of correct form so there's that even if enlarged valves aren't warranted, and the inlet to head match absolutely should be checked.

I believe the HC is rated at 172 in the Esprit, and runs 104 inlet, 107 exhaust cams on 104 MOP green dot pulleys. Well regarded engine tuning software I tinker with indicates a very streetable 210 HP is to be had using those cams  if valves/ports and both inlet and exhaust side tracts are optimal. I have found exhaust cam MOP at 110 - 114 seems beneficial if that tract can be made optimal. Interested in hearing what Mike will specify, also Garry Kemp is a noted specialist worth speaking with.

Cheers 

[andydclements]

2 hours ago, jonwat said:

That's a 27% increase, I doubt if you'd manage that without changing cam shafts & re jetting the carbs.

I'd think a 10% to 15% would be more likely, which is 180 to 190 BHP but still worth it. ☺

No, not 27%. 200 from what was 180 is an increase of 11.11% It's starting from a HC NA so starting at 180.

[jonwat]

24 minutes ago, andydclements said:

No, not 27%. 200 from what was 180 is an increase of 11.11% It's starting from a HC NA so starting at 180.

My mistake, espritworld quotes 172BHP so 200BHP would be an increase of 16%, still a bit of a stretch for porting & polishing though. 😯

[andydclements]

Somewhere I've got a dyno from a ported and polished Excel at 210, so even given the different exhaust configuration on an Esprit I'd think 200 is equivalent.

[gvy]

When I got my engine out in 2014 , I portmatched in and outletports. I used the gasket between manifold and head. I Placed the gasket on the head and with a marker I could indicate the opening. and I did the same on the manifold. After that I could take material away until ports in the head, the gasket and the manifold were identical, so portmatched for optimal flow.

You'd be surprised how much difference there is on the openings

[naasaa]

3 hours ago, jonwat said:

My mistake, espritworld quotes 172BHP so 200BHP would be an increase of 16%, still a bit of a stretch for porting & polishing though. 😯

Dont forget, or underestimate, the significans of the turbos higher torque. 

[CHANGES]

As someone who does this work and understands the dynamic of porting i thought it may be worth me pointing out a few things the lay man is not aware of...   

Firstly port /manifold alignment is crucial as first move as it disrupts the air flow significantly.  See Pic .

This is typical on what you see with most 900 series, some worse than others ..   However, you first need to ask why would Lotus leave this when they are a performance orientated car maker...   The answer could well be that any disruption will assist in the fuel atomization at lower velocities..   What can not be ignored is the performance on cylinder filling (VE) will be reduced and so performance..  So it may mean the fueling system needs refining to match any porting..   We will never know why Lotus didn't address it, but i expect the cost of any refinements would be unacceptable at the time especially when you consider the performance figures were still up there .. 

So onto porting.. Align joints, yes , but don't barrel the port.. this will give you velocity pulses , disturb and vary the pressures on the back of the inlet valve,  the port should be consistent or necking down towards the valve ..  Your starting point should be calculations based on projected flow which will be influenced first of all be the Choke you intend to use within the carburetor.  There will be  laminar layers produced by the surface disruption within the port which can be reduced in line with projected requirements.  (porting/polishing.)   What you need to consider is that biggest is not best when porting..  For eg. there are some CNC machine ported heads available which look really good , but have far to big a port size for most basic road tune ups..   The reason for this is loss of velocity.  For a given flow volume large ports have less velocity smaller higher.  What you are looking for is the optimum for your particular engine tune .. So what is that..  

Well once again it gets more involved and a secondary starting point is the exhaust system, particularly the manifold.. If you can not get it out you wont put it in.   This is a subject on its own, technical points covered in threads on the turbo systems that have been developed.   Fortunately there are already LCB systems available for the N/A engine  which will give something to work from..  I have not studied them so can not comment, but what is important will be the length of the primary's and the expansion of the collectors.  This aspect will have a big effect on the pressure wave inversion within the flow which greatly assist performance when timed correct. 

Back to the inlet ports .. As you can appreciate max VE is only obtainable through a balance of exhaust and inlets.  Assuming the exhaust is optimum then porting size , flow , velocity, can be arrived at .    Achieving the best for your engine will require each port to be as close to identical, in shape, volume and surface texture,  deviations in this will create anomalies through the tuning process. Volume is easy to check using fluid measuring , same as when doing the combustion chamber, just a lot larger.  Shape can be more testing.  You will need to be diligent if altering the shape to achieve certain swirl benefits, otherwise following the original form using calipers and care should achieve the desired effect.   The pics below shows work in progress from std (left) to porting (right) 

When you have arrived at the desired finish, it is always best to have it checked out on a flow bench , this will confirm you have the balance across all cylinders.  if not then small mods can be done to correct.. 

The whole idea of porting is to get the max pulsed pressure on the back of the inlet valve prior to it opening..  This is achieved with volume and velocity.   The air moving through the valve is momentarily interrupted as it closes, but its mass continues forward compressing a pressure zone on the back of the valve.  When the valve opens this pressure acts like a tiny turbo forcing the air into the cylinder which aids better siphoning , This removes more of the exhaust gas , allowing more area for fresh charge , better VE.    So what we can appreciate from this is the balancing act on porting , to big causes loss of velocity , to small loss of volume. Both are needed for optimum performance..  when achieved another benefit  is being able to then modify cam timings and profiles to assist performance further.  

There are definitely gains that can be made, but the devil is in the detail . There is a reason why pro performance engine builders charge what they do ..  

hope that helps answer a few questions for you @Peter H. 

PS , any mods can only be properly quantified by dyno tuning when completed . To to honest i can not see how you could complete a porting process without full dyno set up to finish off.   

   

 

        

   

        

[jonwat]

17 hours ago, gvy said:

When I got my engine out in 2014 , I portmatched in and outletports. I used the gasket between manifold and head. I Placed the gasket on the head and with a marker I could indicate the opening. and I did the same on the manifold. After that I could take material away until ports in the head, the gasket and the manifold were identical, so portmatched for optimal flow.

You'd be surprised how much difference there is on the openings

Geert,

Did you open out the carb ends of the inlet manifold? If not it's worth doing as they can be quite a bit smaller than the O ring spacer.  Also, if your O rings have constrictions on them they're only there to aid emmissions & it's worthwhile removing them as they restrict flow, although you'll need a lathe to do it.

For some unknown reason the first Lotus, twin cam 8 valve cylinder heads had the inlet manifold cast with it (see pic) so the only inlet port matching possible was to open them out to fit the spacers. Made adifference though. 😊

Check your spacers are flat & have not been distorted through overtightening by placing them on top of each & looking for rocking.

 

[Peter H.]

Loving this detail. Thanks everyone.