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For what it’s worth, the old notes I have say that the ‘87 stock head has a chamber volume of 38.7cc and it goes down to 34.5cc with a 0.020”/0.5mm cut.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
This head in your picture looks pretty close to the maximum you can remove, did you used this head and did you experience water bridge issues?
That is a scrap head I have been using for head porting experiments. If you like to know more about porting have a look here (start at post # 218). https://rennlist.com/forums/928-foru...ughout-15.html
I think the head is shaved off about 0,2 mm. The water bridge is not a big issue, I think you can file the bolt holes. I do not think it will be an issue where it fit into the block.
Regarding the Volvo head (post #12), which was shaved off by one mm, I later advanced the camshaft setting by four degrees (two degrees at the cam) which lead to a noticeable improvement of the mid range torque.
Åke
For what it’s worth, the old notes I have say that the ‘87 stock head has a chamber volume of 38.7cc and it goes down to 34.5cc with a 0.030”/0.5mm cut.
Depends on which cut. A half mm cut is just a hair under 0.020", not 0.030".
Depends on which cut. A half mm cut is just a hair under 0.020", not 0.030".
That was a typo, both the compression ratio and chamber value guesstimates correspond to 0.020”/0.5mm cut where original measured units are the imperial 0.020”.
That is a scrap head I have been using for head porting experiments. If you like to know more about porting have a look here (start at post # 218). https://rennlist.com/forums/928-foru...ughout-15.html
I think the head is shaved off about 0,2 mm. The water bridge is not a big issue, I think you can file the bolt holes. I do not think it will be an issue where it fit into the block.
Regarding the Volvo head (post #12), which was shaved off by one mm, I later advanced the camshaft setting by four degrees (two degrees at the cam) which lead to a noticeable improvement of the mid range torque.
Åke
That porting thread was quite a read. Having been through it I will probably have a play about with the intake valve seat area as per the ‘budget porting standard valve’ approach which would seem cost effective and reasonable for my set up.
That porting thread was quite a read. Having been through it I will probably have a play about with the intake valve seat area as per the ‘budget porting standard valve’ approach which would seem cost effective and reasonable for my set up.
If you do it right you will end up with a good improvement of flow and power. I remember you have a prototype intake manifold. Trust it will outflow the stock manifold which is designed for good engine torque in the lower to mid range rpms. The picture is showing the difference between a racing S4 intake camshaft and a stock ditto. You need something in between.
Åke
If you do it right you will end up with a good improvement of flow and power. I remember you have a prototype intake manifold. Trust it will outflow the stock manifold which is designed for good engine torque in the lower to mid range rpms. The picture is showing the difference between a racing S4 intake camshaft and a stock ditto. You need something in between.
Åke
I have Colin’s cams which are high lift for the standard head (not requiring the head to be machined)
The intake is a single plenum long runner type to try and counter balance the lack of a flappy and the fact that I will not be using high RPM. When I say long runner they are calculated to reach maximum power at about 6k. Even achieving a length that long was pushing the boundaries of space available. It is difficult to say without testing back to back on a flow bench but the intake should provide a big improvement over stock.
Are you going to get a test results with new manifold vs stock manifold with everything else held constant?
I will be doing a back to back test on the manifold, standard vs the new one although the engine is not in standard spec......should still give a good idea of what increase it achieves.
I did take the time while the head was off to perform a "budget porting job" retaining the standard valves. Given the increases in flow measured in the porting/polishing thread I thought it worthwhile doing. The finishing on the standard head around the valve seat inserts are quite 'basic' and there is a good amount of meat on the valve seat without destroying the 3 compound curve to play with. I also did a minor amount of valve deshrouding on the exhaust valve for what it's worth. I try to use Dave Vizard principles where possible but the heads as great in design to start with that there is not a huge amount that can be done. I was careful to try and leave the work I did rough enough not to destroy any laminar air flow properties that the rough casting has.
I am currently putting the engine back together after doing the head gaskets and water pump. I will be fitting the new manifold now to see how it goes and hopefully get some mileage under the belt.
07-06-2020, 09:10 PM
