Cylinder head porting
Discussion
Hi all, I'm toying with the idea of buying a used pair of standard 3.5 EFi heads so I can have a play with them and do some porting and fettling. Many years ago I ported and polished the cross flow head on my Capri 1600GT which seemed to make a difference and prior to that I'd similarly ported the cylinder head on my Morris 1000, which was actually running a Cooper head, cam and twin 1 1/4" SU's.
The plan is to have a tidy set of clean heads ready and waiting for the time when I decide to take the existing heads off and fit a new camshaft. Anyone got any top tips for improving the breathing on a standard set of heads? I know a set of later 400/450 larger valve heads would fit but I'm looking at keeping the costs down and tidy standard EFi heads can be had for less than £50. Thanks.
The plan is to have a tidy set of clean heads ready and waiting for the time when I decide to take the existing heads off and fit a new camshaft. Anyone got any top tips for improving the breathing on a standard set of heads? I know a set of later 400/450 larger valve heads would fit but I'm looking at keeping the costs down and tidy standard EFi heads can be had for less than £50. Thanks.
You don't need to take off the heads to change the cam of course, although if you're already there, it isn't that much more work.
I would say concentrate on the inlet side first. Getting air into the cylinder is the first part of the battle and you only have the atmosphere pushing it in.
Grind out and enlarge the inlet ports and also do the same on the inlet manifold.
I would say concentrate on the inlet side first. Getting air into the cylinder is the first part of the battle and you only have the atmosphere pushing it in.
Grind out and enlarge the inlet ports and also do the same on the inlet manifold.
Edited by adam quantrill on Thursday 5th March 20:10
Well to give you inspiration, here's an NCK-ported inlet manifold vs. a standard 3.5L one...
You usually find that the aperture in the gasket is larger than that in the casting, so you can use the gasket as a guide to show how much can be removed... now some people say that the narrowing of the tract speeds up the gas which aids cylinder swirl or some such, but I just wanted to use my die grinder
While you're at it, don't forget a plenum insulator...
You usually find that the aperture in the gasket is larger than that in the casting, so you can use the gasket as a guide to show how much can be removed... now some people say that the narrowing of the tract speeds up the gas which aids cylinder swirl or some such, but I just wanted to use my die grinder
While you're at it, don't forget a plenum insulator...
mike various said:
Please forgive my ignorance but what does the plenum insulator do ?
is it some sort of heat shield if so has it been proved to give an increase over stock and if so how much ?
Mike
Likewise - I'm assuming it keeps the plenum a little cooler but does it actually improve performance? If so then I'm also up for one if available! Cheers.is it some sort of heat shield if so has it been proved to give an increase over stock and if so how much ?
Mike
bradderztvr said:
If you were to use a spacer (to increase plenum volume) as well as the insulator, is there a risk of making the plenum too high and might foul the bonnet? I know mine is already tight fit and leaves a significant impression on the bonnet padding.
EDIT due to not reading the question properly, sorry 
There is a risk of bonnet fouling although in my experience (of supplying insulators to other Wedge owners
) an extra 6mm has never been a problem. It might be if you fitted new engine mounts to replace sagging ones.There was a website article on fitting an RV8 into (IIRC) an MG which had bonnet fouling issues; they shortened the trumpet base and I think the plenum itself to get the overall height down, this would be an option in the TVR as well.
My car runs a 10mm insulator however the trumpet base was shortened by 10mm to compensate; this has the advantage of keeping the inlet tracts the original length which is obviously not the case if you just install an insulator with no other changes.
Most of the internet suppliers (unless things have changed) supply only 3mm thick which probably has a negligible effect on airflow; of course the thicker the insulator the less heat soak there is into the plenum chamber. After a good run in my car I can place my hand flat on the plenum, which you can't do on a standard setup.
Whether there's any BHP gain I don't know, nor do I claim any, but it does seem to do something
More info here:
http://www.wedgeneering.co.uk/TVR%20390SE%20p3.htm
Further edited due to typos and over-use of the word 'obviously'
Edited by Wedg1e on Sunday 8th March 12:07
Convert said:
I have to take issue with some of their statements: the inlet runners are not different lengths requiring the trumpets to be cut down. If you take the trumpets out you find they're all the same length and are set in the plenum at different heights to MAKE the runners all the same length.Also 'billet aluminium'... I wish people would just f
k-off using that term. A billet is merely a term for a block of metal as cast in a foundry, it is NOT some special, mysterious material. They could just say 'made from aluminium' and it would be equally as descriptive. If they stated the grade, e.g. 7075T6 I might be more forgiving, but that billet could be the most p155-poor slab of alloy ever poured.Here endeth the sermon (well, it is Sunday...
)KKson said:
Right, two very tidy late 3.5 EFi cylinder heads bought for the grand total of £39 off flea. Just need to get a good flexi drive and suitable grinding burrs. The room above the garage is starting to fill up with spares now, but you can never have too many!
You want the type that looks like a milling machine cutter, not those daft mounted stones as they just clog up with aluminium. Be prepared for some horrific swarf 
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