Exhaust port shape
Discussion
Having got my engine out and the manifolds off for welding and wrapping, I have noticed that the exhaust ports in the cylinder heads are not round like the holes in the manifold but have a flattened bottom.
Conventional wisdom would say that the fewer steps and transitions in profile, the faster the flow therefore I was considering machining the ports to match the manifold. However, TVR designed this a a performance engine and while their machining and finish may not always have been the very best, it seems like too basic a mistake to make unless they had a good reason for doing it this way.
I recall that one or two people have reshaped the ports in the head. Was there any performance improvement from doing so? What do the expert engine builders like APM do?
Conventional wisdom would say that the fewer steps and transitions in profile, the faster the flow therefore I was considering machining the ports to match the manifold. However, TVR designed this a a performance engine and while their machining and finish may not always have been the very best, it seems like too basic a mistake to make unless they had a good reason for doing it this way.
I recall that one or two people have reshaped the ports in the head. Was there any performance improvement from doing so? What do the expert engine builders like APM do?
Edited by Tanguero on Friday 8th June 12:14
Hi Peter,
I've asked APM about this on mine too, in Andys opinion removing the step would give a small hp gain and to make it worthwhile you'd have to buy the ACT sport manifolds or go bespoke, but through his experience porting seems to increase the lumpy running at low revs/low speed.
There's an article here about the idiosyncrasy of the exhaust system on the AJP,
http://2009.tvrspeedchampionship.co.uk/index.php?o...
Hows the girl coming back together??
:-)
I've asked APM about this on mine too, in Andys opinion removing the step would give a small hp gain and to make it worthwhile you'd have to buy the ACT sport manifolds or go bespoke, but through his experience porting seems to increase the lumpy running at low revs/low speed.
There's an article here about the idiosyncrasy of the exhaust system on the AJP,
http://2009.tvrspeedchampionship.co.uk/index.php?o...
Hows the girl coming back together??
:-)
djstevec said:
Hi Peter,
I've asked APM about this on mine too, in Andys opinion removing the step would give a small hp gain and to make it worthwhile you'd have to buy the ACT sport manifolds or go bespoke, but through his experience porting seems to increase the lumpy running at low revs/low speed.
Thanks Steve! That is just the sort of info I was after. Given my plans for upgrading the engine next year I don't think I will bother doing the exhaust ports this time round. It's not as if I am short of things to do to get the car back together.I've asked APM about this on mine too, in Andys opinion removing the step would give a small hp gain and to make it worthwhile you'd have to buy the ACT sport manifolds or go bespoke, but through his experience porting seems to increase the lumpy running at low revs/low speed.
djstevec said:
Hows the girl coming back together??
:-)
The wife is fine thanks and sends her regards... or did you mean the Cerb? ;-):-)
Chassis has the suspension rebuilt and is ready to go back under the body. Just finished putting the new insulation in the engine bay today so I may tackle pairing them back up tomorrow. I have decided to leave the engine out until the body is back on and then put it in last, theory being that it will give me a bit of working room to guide things back into place.
The shipwrights disease is easing off now as I am running out of things to replace or polish.
Tanguero said:
The wife is fine thanks and sends her regards... or did you mean the Cerb? ;-)
Chassis has the suspension rebuilt and is ready to go back under the body. Just finished putting the new insulation in the engine bay today so I may tackle pairing them back up tomorrow. I have decided to leave the engine out until the body is back on and then put it in last, theory being that it will give me a bit of working room to guide things back into place.
The shipwrights disease is easing off now as I am running out of things to replace or polish.
Chassis has the suspension rebuilt and is ready to go back under the body. Just finished putting the new insulation in the engine bay today so I may tackle pairing them back up tomorrow. I have decided to leave the engine out until the body is back on and then put it in last, theory being that it will give me a bit of working room to guide things back into place.
The shipwrights disease is easing off now as I am running out of things to replace or polish.
Yeah Im getting into OCD mode soon too I think!
As always, if you need any help whatsoever, drop me a line!
S
Not sure there is much to be had and potentially something to lose, search for advantages of D port designs.
Leaving the manifold larger than the port exit will not harm here as the step is back into the port not out of it, consider it an anti reversion step if you like and can actually be beneficial, removing it may harm.
Not saying a well thought out, tested and proved improvement can't be made in this area, I just wouldn't remove metal, just because I can.
Leaving the manifold larger than the port exit will not harm here as the step is back into the port not out of it, consider it an anti reversion step if you like and can actually be beneficial, removing it may harm.
Not saying a well thought out, tested and proved improvement can't be made in this area, I just wouldn't remove metal, just because I can.
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