Good afternoon Guy, I hope you're well.
My question (and I apologise at this point if its a stupid one) concerns the title, but more specifically, In your experience are there any circumstances whereby valve-in flow can exceed bare port flow on a 16v head?
16v head porting: importance of BPF vs valve-in flow.
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4v6
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16v head porting: importance of BPF vs valve-in flow.
Tony Warren. GC #96.
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Guy Croft
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Re: Bare port flow vs Valve in flow.
Not a stupid question at all, and the answer is yes, it can happen to those heads too.
I did one example recently (a development job for well-known Ric Wood - owner of 'CNC Heads'), a Renault Clio 16v. The OE head had an, er, 'interesting' degree of 'cnc' machining on splitter and SSR as you can see, but they got it wrong and the valve-in flow did exceed the bpf as the graph shows, an annoying thing that I was able to get rid of without too much trouble. There may have been others, I've done so many, I'd have to look it up.
The thing about cnc is it's got to be dead-accurate and very smooth to work well, definitley not an easy thing to programme into a production line, with all the variables production engineers have to allow for.
Much depends on the SSR profile and the port downdraft, fortunately this one responded quite readily.
GC
I did one example recently (a development job for well-known Ric Wood - owner of 'CNC Heads'), a Renault Clio 16v. The OE head had an, er, 'interesting' degree of 'cnc' machining on splitter and SSR as you can see, but they got it wrong and the valve-in flow did exceed the bpf as the graph shows, an annoying thing that I was able to get rid of without too much trouble. There may have been others, I've done so many, I'd have to look it up.
The thing about cnc is it's got to be dead-accurate and very smooth to work well, definitley not an easy thing to programme into a production line, with all the variables production engineers have to allow for.
Much depends on the SSR profile and the port downdraft, fortunately this one responded quite readily.
GC
- Attachments
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- note that 11.3mm inlet valve lift, it flows more than bpf. After rework the two intersect as they should at high lift.
- Renault Clio 16v 07.155.GIF (22.67 KiB) Viewed 16339 times
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- view down inlet as-is, showing fairly basic factory cnc machining.
- GC 017.jpg (114.78 KiB) Viewed 16334 times
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- view of SSR as-is, again a degree of (rather ineffective) factory cnc machining.
- GC 018.jpg (112.62 KiB) Viewed 16332 times
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- SSR in final, slightly more successful trim. Another victory of man against machines..
- GC 019.jpg (112.69 KiB) Viewed 16331 times
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- finished chamber and valves
- GC 020.jpg (114.13 KiB) Viewed 16328 times
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4v6
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Re: Bare port flow vs Valve in flow.
Thank you for your lightning fast reply Guy and the photos, the finished product looks absolutely superb!
However, your reply answered one question but unfortunately its prompted another, if i may.
I'm a little confused as to why valve-in flow exceeding bare port flow is an annoyance rather than a desirable state of affairs?
My reason for asking is because i find myself confronted by this very situation.
Many thanks once again Guy, your replies and the time put into them are very much appreciated.
However, your reply answered one question but unfortunately its prompted another, if i may.
I'm a little confused as to why valve-in flow exceeding bare port flow is an annoyance rather than a desirable state of affairs?
My reason for asking is because i find myself confronted by this very situation.
Many thanks once again Guy, your replies and the time put into them are very much appreciated.
Tony Warren. GC #96.
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Guy Croft
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Re: Bare port flow vs Valve in flow.
What’s under discussion here goes to heart of flowtest and head development fundamentals. It is predisposed that you accept (as I do) that, when using a flowbench to evaluate and optimise a cylinder head, a loss of flow (actual or apparent) can be taken to mean that there will be a loss of performance on engine test. Ignore that the flowbench operates at a vastly lower pressure ratio than an engine. Ignore that, by doing ‘steady-state’ testing of airflow the tests have little in common with the peculiarities of real-time on-engine transient airflow behaviour. So far, with an amalgam of my own years of exp (getting on for 20 now) and excellent feedback from many close sources, I have found this to be true in every case!
What we are discussing is that tests of bare port flow and flow at max valve lift will ideally show, that at some high lift point, the valve 'no longer presents an intrusion to the airstream'. To put it another way, the valve will always generate a loss, until it's lifted high enough to be no longer obstructing the airstream. Anyone who thinks it’s better if the port flows more with the valve in is either 1) short of cutting-edge race engine and flowbench experience, or 2) a combustion specialist who has hit on a novel way of improving the burn rate. You can be sure it’s not 2). It’s an airstream ‘instability’ problem.
With some heads, depending on the amount of shrouding, the valve head shape and port layout you can't get rid of the valve-in loss however high you lift the valve (given of course that the architecture of the valve train does impose practical limits to the available lift). Some heads exhibit a tendency to flow ‘better’ with the valve in at high lift in OE as-is state (cue: Renault mentioned above) and some start doing it after you’ve attempted to ‘improve’ flow by putting a nice smooth curvature on the SSR!
On any particular head the phenomenon of ‘flowing more with the valve-in’ is definitely a function of the valve shape and short side radius. I put those inverted commas to show that it’s not actually flowing more, it’s just not losing so much, and the reality is that the bare port flow is too low. The cause is simple - turbulence.
Now. The boundary layer of air flowing closest to the inside of a curve will separate if the bend radius is too small. There is an adverse pressure gradient on the curve - the velocity of air is dropping and pressure around the curve towards the valve throat is rising. Think of an aircraft wing trailing section - from the thickest chord section rearward it's carefully tapered at a shallow angle to prevent separation. Air flowing over a smooth flat plate will never exhibit separation (until it gets to the end of the plate of course..). Separation – depending on the extent of it - can have a very significant effect on the massflow of the port as a whole. In short – it drops.
On some sidedraft heads the distance from the port floor to the valve throat on the short-side radius (SSR) is very long compared with a downdrafted port, thus you have what I call a 'deep-drop' or ‘cliff-face’ SSR, lots of heads have this, see photos.
In standard trim on a deep-drop port the flow doesn't go round the short-side hardly at all (I hesitate to call it a radius because as the photo shows it doesn't have one..) but I have test data that shows the bpf and valve-in flow do intersect in some cases in standard trim. That of course is not by way of suggesting that the full as-is flow regime – when tested – is anything like enough for the kind of power I’m expected to be able to produce. It’s never been so far. But -put a radius onto that region and then the fun starts! Why do manufacturers leave the 'cliff-face' region like that? Because they can - and still meet their target power output, but that said, the practice of producing heads in that rather, er 'lazy' fashion is mercifully dying out.
Why radius it at all? Well, as you know Renault thought it was a good thing and partially succeeded I have no doubt in the case of the head mentioned earlier. If you leave the cliff-face, the air just flies off the port floor at the sharp edge and will never allow you to generate a high flow port, because not only will there be pronounced turbulence at the edge but the airstream itself will interfere with air trying to ‘make the turn’ down towards the valve. I have watched this many times with cotton traces.
You’ve got to try and reduce the turbulence and interference of the lower port section on the rest of the port. And if you can – move the separation point further down the SSR – if you cannot eliminate it completely. The cause is simple but the solution can be beyond reach. The problem is that it’s fantastically difficult to produce a perfect aerodynamic profile on a deep-drop SSR. This is the big difference between prepping say, a Vauxhall XE 16v 2 liter (or 1400) and a Peugeot 205. The XE SRR is tiny by comparison and thus has a markedly less of an effect on the rest of the port. I have experimented with such SSR regions for weeks and ended up with a compound loss that could only be recovered by welding-up and starting again. And the solution of ‘better SSR’? Well, it may not be quite so simple, even if you’re brilliant at developing nice curves with a die grinder, because every bit of the port is interlinked and you may remove metal (because that’s all you can do in porting) and get a loss that is not caused by the local removal per-se, but by its influence on an adjacent region. All very frustrating...
So let’s be clear. If the bpf is lower than the flow at the high-lift valve-in state, something is certainly wrong. If you take a look at the ‘brain-teaser’ thread on the Peugeot XSi that I posted in this section you will see a picture of a deflector in the inlet port that showed how much a port really could flow if the SSR effect was absent. Whilst it is most often evident at valve lifts higher than the actual OE spec and whilst I cannot quantify at all what effect it has on torque curve under all load/speed I’ll certainly say this: Given that we know (on flowtest anyhow..) the odd behaviour suggests to me that there could be a loss regime at work throughout the whole valve lift phase. Thus, if I am right, one could not simply assert with much confidence that ‘it will only affects engines where the valve lift is very high’!
Certainly, to get high torque and bhp on the kind of engines I'm engaged with the valve lift generally needs to be pretty high and so I'd be pretty worried about valve-in flow exceeding bare port. Especially as I have seen cases where the flow goes over bpf at high lift and then drops ...
How much power loss can an unstable flow regime cause? I reckon over 7% peak power based on dyno tests of 205Gti engines. That's not a general rule but I will go so far as to say that if the engine supposed to develop very high poewr (8 or 16v) it will always be a measurable loss compared with one that flows predictably.
The phenomenon is almost certainly a result of a shifting in airflow distribution thru the valve throat caused by the intrusion of the valve head itself. On tests of sidedraft heads you can observe the highest velocity airstream lifting further and further off the port floor as the valve is lifted quite readily using a trace. When the valve is absent there is a bias in the airstream to the (inefficient) port floor section. When the valve is fitted the distribution is in effect ‘better’, ie: more ‘advantageously’ distributed around the further reaches of the valve circumference and thus the mean port velocity is higher. I hesitate to say ‘evenly’ because you’ll never get even distribution of flow around the valve on a sidedraft head, not on a flowbench anyway.
GC
What we are discussing is that tests of bare port flow and flow at max valve lift will ideally show, that at some high lift point, the valve 'no longer presents an intrusion to the airstream'. To put it another way, the valve will always generate a loss, until it's lifted high enough to be no longer obstructing the airstream. Anyone who thinks it’s better if the port flows more with the valve in is either 1) short of cutting-edge race engine and flowbench experience, or 2) a combustion specialist who has hit on a novel way of improving the burn rate. You can be sure it’s not 2). It’s an airstream ‘instability’ problem.
With some heads, depending on the amount of shrouding, the valve head shape and port layout you can't get rid of the valve-in loss however high you lift the valve (given of course that the architecture of the valve train does impose practical limits to the available lift). Some heads exhibit a tendency to flow ‘better’ with the valve in at high lift in OE as-is state (cue: Renault mentioned above) and some start doing it after you’ve attempted to ‘improve’ flow by putting a nice smooth curvature on the SSR!
On any particular head the phenomenon of ‘flowing more with the valve-in’ is definitely a function of the valve shape and short side radius. I put those inverted commas to show that it’s not actually flowing more, it’s just not losing so much, and the reality is that the bare port flow is too low. The cause is simple - turbulence.
Now. The boundary layer of air flowing closest to the inside of a curve will separate if the bend radius is too small. There is an adverse pressure gradient on the curve - the velocity of air is dropping and pressure around the curve towards the valve throat is rising. Think of an aircraft wing trailing section - from the thickest chord section rearward it's carefully tapered at a shallow angle to prevent separation. Air flowing over a smooth flat plate will never exhibit separation (until it gets to the end of the plate of course..). Separation – depending on the extent of it - can have a very significant effect on the massflow of the port as a whole. In short – it drops.
On some sidedraft heads the distance from the port floor to the valve throat on the short-side radius (SSR) is very long compared with a downdrafted port, thus you have what I call a 'deep-drop' or ‘cliff-face’ SSR, lots of heads have this, see photos.
In standard trim on a deep-drop port the flow doesn't go round the short-side hardly at all (I hesitate to call it a radius because as the photo shows it doesn't have one..) but I have test data that shows the bpf and valve-in flow do intersect in some cases in standard trim. That of course is not by way of suggesting that the full as-is flow regime – when tested – is anything like enough for the kind of power I’m expected to be able to produce. It’s never been so far. But -put a radius onto that region and then the fun starts! Why do manufacturers leave the 'cliff-face' region like that? Because they can - and still meet their target power output, but that said, the practice of producing heads in that rather, er 'lazy' fashion is mercifully dying out.
Why radius it at all? Well, as you know Renault thought it was a good thing and partially succeeded I have no doubt in the case of the head mentioned earlier. If you leave the cliff-face, the air just flies off the port floor at the sharp edge and will never allow you to generate a high flow port, because not only will there be pronounced turbulence at the edge but the airstream itself will interfere with air trying to ‘make the turn’ down towards the valve. I have watched this many times with cotton traces.
You’ve got to try and reduce the turbulence and interference of the lower port section on the rest of the port. And if you can – move the separation point further down the SSR – if you cannot eliminate it completely. The cause is simple but the solution can be beyond reach. The problem is that it’s fantastically difficult to produce a perfect aerodynamic profile on a deep-drop SSR. This is the big difference between prepping say, a Vauxhall XE 16v 2 liter (or 1400) and a Peugeot 205. The XE SRR is tiny by comparison and thus has a markedly less of an effect on the rest of the port. I have experimented with such SSR regions for weeks and ended up with a compound loss that could only be recovered by welding-up and starting again. And the solution of ‘better SSR’? Well, it may not be quite so simple, even if you’re brilliant at developing nice curves with a die grinder, because every bit of the port is interlinked and you may remove metal (because that’s all you can do in porting) and get a loss that is not caused by the local removal per-se, but by its influence on an adjacent region. All very frustrating...
So let’s be clear. If the bpf is lower than the flow at the high-lift valve-in state, something is certainly wrong. If you take a look at the ‘brain-teaser’ thread on the Peugeot XSi that I posted in this section you will see a picture of a deflector in the inlet port that showed how much a port really could flow if the SSR effect was absent. Whilst it is most often evident at valve lifts higher than the actual OE spec and whilst I cannot quantify at all what effect it has on torque curve under all load/speed I’ll certainly say this: Given that we know (on flowtest anyhow..) the odd behaviour suggests to me that there could be a loss regime at work throughout the whole valve lift phase. Thus, if I am right, one could not simply assert with much confidence that ‘it will only affects engines where the valve lift is very high’!
Certainly, to get high torque and bhp on the kind of engines I'm engaged with the valve lift generally needs to be pretty high and so I'd be pretty worried about valve-in flow exceeding bare port. Especially as I have seen cases where the flow goes over bpf at high lift and then drops ...
How much power loss can an unstable flow regime cause? I reckon over 7% peak power based on dyno tests of 205Gti engines. That's not a general rule but I will go so far as to say that if the engine supposed to develop very high poewr (8 or 16v) it will always be a measurable loss compared with one that flows predictably.
The phenomenon is almost certainly a result of a shifting in airflow distribution thru the valve throat caused by the intrusion of the valve head itself. On tests of sidedraft heads you can observe the highest velocity airstream lifting further and further off the port floor as the valve is lifted quite readily using a trace. When the valve is absent there is a bias in the airstream to the (inefficient) port floor section. When the valve is fitted the distribution is in effect ‘better’, ie: more ‘advantageously’ distributed around the further reaches of the valve circumference and thus the mean port velocity is higher. I hesitate to say ‘evenly’ because you’ll never get even distribution of flow around the valve on a sidedraft head, not on a flowbench anyway.
GC
- Attachments
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- Peugeot std SSR cliff face.JPG (155.24 KiB) Viewed 16243 times
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- Suzuki 16v ssr before.JPG (20.44 KiB) Viewed 16241 times
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- Suzuki 16v ssr mod.JPG (21.22 KiB) Viewed 16239 times
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- Lotus Twin-Cam - with 20 deg port downdraft a really high flow port, even with only 29mm dia port smallest section 40m inlet valve
- 07.154 Lotus TC 009.jpg (113.61 KiB) Viewed 16234 times
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- fully developed XE 2liter SSR - head flowed bpf c145cfm @ 10", gave 270bhp and 181 lbf ft on 'mild' tarmac rally cams. In 2.1 liter spec these GC/CIT units with full-spec cams give 278-282bhp again and again and over 200lbf ft in 2.3 liter spec.
- GC 022.jpg (111.97 KiB) Viewed 16228 times
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4v6
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Re: Bare port flow vs Valve in flow.
Good afternoon Guy, many thanks for that in depth reply, it has comprehensively answered my query.
The idea of turbulence being the cause had crossed my mind briefly but as i dont yet possess the necessary experience, equipment and diagnostic capabilities i was a little unsure, hence my questions.
Ive also noticed a degree of "screeching" occuring at low lifts of 1 to 2.5mm which i presume is a symptom of such turbulence?
The "cliff face" shown in your excellent photos seems to mirror those in the ports i'm working on, indeed these are very high at some 6.70 mm from the insert to the sharp edge (separation point?) on the SSR.
To clarify, the solution to the valve-in flow problem is, if i am interpreting correctly, to engineer the SSR so that its separation point is closer to the seat, via elimination (if possible) of the "cliff face"?
I realise that this may not be entirely possible due to the ports current shape, indeed it would appear to be a challenging task with this port.
Heres a photo of the "cliff face" mentioned in my post, many thanks for all your thoughts on this Guy.
The idea of turbulence being the cause had crossed my mind briefly but as i dont yet possess the necessary experience, equipment and diagnostic capabilities i was a little unsure, hence my questions.
Ive also noticed a degree of "screeching" occuring at low lifts of 1 to 2.5mm which i presume is a symptom of such turbulence?
The "cliff face" shown in your excellent photos seems to mirror those in the ports i'm working on, indeed these are very high at some 6.70 mm from the insert to the sharp edge (separation point?) on the SSR.
To clarify, the solution to the valve-in flow problem is, if i am interpreting correctly, to engineer the SSR so that its separation point is closer to the seat, via elimination (if possible) of the "cliff face"?
I realise that this may not be entirely possible due to the ports current shape, indeed it would appear to be a challenging task with this port.
Heres a photo of the "cliff face" mentioned in my post, many thanks for all your thoughts on this Guy.
- Cliff face (toyota)
- cliff face.jpg (274 KiB) Viewed 16208 times
Tony Warren. GC #96.
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Guy Croft
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Re: Bare port flow vs Valve in flow.
Can I have a shot of the intake end of the port?
My advise might be just polish it up at 80 and 120 grit and leave it at that, because if it's a sidedraft port (not sure yet) then unless you have a spare head, a week to spare and an accurate flowbench you could just as easily generate a loss as a gain by going any further with it. Finding the optimum curvature for a deep-drop SSR - and putting it where it belongs - is quite simply the most difficult head dev exercise there is.
The screeching at low lift could be well be turbulence. Check your manometer. If the manometer (or other flow measurement device) is fluctuating it definitely is. If not then it's just whistling to itself! BTW I think you could do flowbench dev with a sonic probe - efficient/high flow ports and valve seat combos are much quieter than turbulent ones.
GC
My advise might be just polish it up at 80 and 120 grit and leave it at that, because if it's a sidedraft port (not sure yet) then unless you have a spare head, a week to spare and an accurate flowbench you could just as easily generate a loss as a gain by going any further with it. Finding the optimum curvature for a deep-drop SSR - and putting it where it belongs - is quite simply the most difficult head dev exercise there is.
The screeching at low lift could be well be turbulence. Check your manometer. If the manometer (or other flow measurement device) is fluctuating it definitely is. If not then it's just whistling to itself! BTW I think you could do flowbench dev with a sonic probe - efficient/high flow ports and valve seat combos are much quieter than turbulent ones.
GC
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4v6
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Re: Bare port flow vs Valve in flow.
Thank you Guy, here are a few photos as required.
Please let me know if you need more from other angles.
- Intake port 1
- intake1.jpg (205.48 KiB) Viewed 16176 times
- Intake port 2
- intake2.jpg (213.99 KiB) Viewed 16169 times
Tony Warren. GC #96.
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Guy Croft
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Re: Bare port flow vs Valve in flow.
Thanks for the good photos. I have some exp of these 'modern' port designs. Virtually no downdraft, very roomy, very short splitter. I don't know this one but some of them are designed more for in-cylinder turbulence and not high flow and develop peak flow at relatively low lift.
You definitely should just put a modest radius on the SSR, smooth the port, maybe thin down the splitter front profile and leave it at that. Sidedraft ports with deep-drop, frankly, are fraught with hazard for the unwary and are best avoided. It's a fact that the capacious ports so many designers use now are hopeless for bottom-end torque except with variable valve timing; I just don't know why they design them that way, I don't agree with the practice, and there is no point trying to find it. Take the Honda VTEC: sure you can get 'OK' high top end power but the useable torque curve is, well, useless really. Driveable, yes, even without VVT, but very disappointing from an engine tuner's point of view. It's all to do with port velocity. If your port is huge the velocity is low and so is the cylinder filling and torque and messing around with cam timing ain't going to change that.
The sad fact is that current generation production engines with a few exceptions, do not lend themselves to 'modification' to get more power. This is no fault of the manufacturer, they design things with less 'redundancy' - in other words if they get the job done there is no 'spare' in them at all.
GC
You definitely should just put a modest radius on the SSR, smooth the port, maybe thin down the splitter front profile and leave it at that. Sidedraft ports with deep-drop, frankly, are fraught with hazard for the unwary and are best avoided. It's a fact that the capacious ports so many designers use now are hopeless for bottom-end torque except with variable valve timing; I just don't know why they design them that way, I don't agree with the practice, and there is no point trying to find it. Take the Honda VTEC: sure you can get 'OK' high top end power but the useable torque curve is, well, useless really. Driveable, yes, even without VVT, but very disappointing from an engine tuner's point of view. It's all to do with port velocity. If your port is huge the velocity is low and so is the cylinder filling and torque and messing around with cam timing ain't going to change that.
The sad fact is that current generation production engines with a few exceptions, do not lend themselves to 'modification' to get more power. This is no fault of the manufacturer, they design things with less 'redundancy' - in other words if they get the job done there is no 'spare' in them at all.
GC
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4v6
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Re: Bare port flow vs Valve in flow.
Many thanks for your efforts and comments on this one Guy, they are as ever, very much appreciated.
Ive spent most all of today experimenting on the spare heads i have, prompted by a sleepless night and your suggestion to investigate the ssr, i can confirm the effort has paid off though with a substantial gain in bare port flow over stock (123.1cfm) now up to 144.7cfm@10".
The valve in problem has also disappeared with flow at full lift now also substantially improved.
I must confess i adapted my flow rig to accept a vacuum bag so i could remove material while on test to observe the results of altering the ssr profile without the material going through the rig itself, a rather unorthodox method i realise and one which may be frowned upon but one which has speeded up my development on this port neverthless.
Ive since transferred the profile generated from plasticine cut in half to a fabricated radius gauge to enable reproduction on the other ports, and it has worked very well so far.
I wish to thank you once again for your efforts and suggestions Guy, i wouldnt have been any closer to a solution but for your valuable input.
Best wishes, Tony.
Ive spent most all of today experimenting on the spare heads i have, prompted by a sleepless night and your suggestion to investigate the ssr, i can confirm the effort has paid off though with a substantial gain in bare port flow over stock (123.1cfm) now up to 144.7cfm@10".
The valve in problem has also disappeared with flow at full lift now also substantially improved.
I must confess i adapted my flow rig to accept a vacuum bag so i could remove material while on test to observe the results of altering the ssr profile without the material going through the rig itself, a rather unorthodox method i realise and one which may be frowned upon but one which has speeded up my development on this port neverthless.
Ive since transferred the profile generated from plasticine cut in half to a fabricated radius gauge to enable reproduction on the other ports, and it has worked very well so far.
I wish to thank you once again for your efforts and suggestions Guy, i wouldnt have been any closer to a solution but for your valuable input.
Best wishes, Tony.
Tony Warren. GC #96.
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Guy Croft
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Re: Bare port flow vs Valve in flow.
Well done indeed Tony!
Nothing wrong with your collector system, great idea. I wish I had more time to experiment with techniques, apart from the little breaks I get (and need) writing here I don't have any time to spare.
I would enjoy reading your before-after graphs - if you don't want them on show here do feel free to send them by email in Excel format, to:
croftengines@aol.com
I am very pleased you derived the results you wanted. I think the next time I have to do a Peugeot XSi I might send it to you!
GC
Nothing wrong with your collector system, great idea. I wish I had more time to experiment with techniques, apart from the little breaks I get (and need) writing here I don't have any time to spare.
I would enjoy reading your before-after graphs - if you don't want them on show here do feel free to send them by email in Excel format, to:
croftengines@aol.com
I am very pleased you derived the results you wanted. I think the next time I have to do a Peugeot XSi I might send it to you!
GC
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4v6
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Re: Bare port flow vs Valve in flow.
Thanks for those comments Guy, ill try to convert the graphs over, theyre in some kind of odd format at the moment but i can convert them to bmp/jpeg and probably then on to excel, ill give it a go.
Now all i have to do is improve the exhaust ports somewhat, at least i have a better idea of where to look for such improvements now.
Peugeot XSi heads, Erm, um, thanks but ill pass on those, if its all the same to you ill leave those to the professionals such as yourself, i have quite enough fun with just one type of port as an amateur.
Once again, many thanks sir.
Best wishes, Tony.
Now all i have to do is improve the exhaust ports somewhat, at least i have a better idea of where to look for such improvements now.
Peugeot XSi heads, Erm, um, thanks but ill pass on those, if its all the same to you ill leave those to the professionals such as yourself, i have quite enough fun with just one type of port as an amateur.
Once again, many thanks sir.
Best wishes, Tony.
Tony Warren. GC #96.
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