I am currently rebuilding an 8v head and have heard for the yanks that 7mm valve guides and valves can be fitted to the 8v engine for an improvment in flow. The engine code that they have suggested is ABA but I dont think that that engine is available over here. What engine has 7mm valves and guides that will fit my 8v (38/33) valves. I am also thinking about shorter valve guides, anyone know a company that makes these out the box or will taking them to a machine shop for cutting down do? They also say that you can use oversize valves by 1mm using the standard valve seats, how this possible or does it do much good. Techtonics sell them on their website. Cheers, Chris Edited by: Jettin'
I had new guides fitted to an old "DX" head a couple of years back. Took longer to get done because the guy said it had a mixture of standard Dia and oversize Dia guides on it. Said it was down to oversized bore on original manufacture. Makes sense, to step up a size! Don't know if heads are perposly made with finer Dia guides though mate. Sorry. Domma..........
You want to go smaller so that there is less obstruction for the air to flow arround the guide. The standard is 8mm while 7mm is used on newer engines. The x-flow american head had 7mm valve stems along with other engines. I just don't know which engine we had over here (Europe) that has 7mm valves and guides that will fit the 8v head.
most of vauxhall valves are 7mm stem OD. off the top of my head, the 1.3 8v engines used valves with a 33mm head, as do the 20XE (2.0 16v) for the inlet (x2). guides are 11mm OD, valve stem length 105-106mm Edited by: 0ddball
what in the name of ridiculous ideas could u possibly hope to achieve by this? decreased flow? better shrouding?
I have now worked out that the 16v guides will work fine, thanks dave, and the stem seals off a 16v will work also. Now the only problem I have is finding valves of the correct size with a 7mm stem. Namely the 38mm inlet valve that I can seem to find anywhere, 40mm is available and so is 33 or 35. So... ...How much would it be to have the valve seats replaced to go to 40/35? Skim of the head and press the guides in. Dex, I dont know what the American's were thinking with the 1mm oversize valves as I can't figure out any performance benefit either.
This is a hot topic for myself at the moment. I have been working out what to do to the head on my 1.6GTi (EG). I've been given loads of advice by different people, but in the end went to a guy named Bill Blydenstein. He is 75 years old and has worked on more cylinder heads than......erm....well you get the picture. Here are the conclusions from speaking to him: The valves guides are stupidly short anyway, thats why they only last half as long as the equivelent Vauxhall. You can go shorter, but then expect to be replacing them regularly. As for valve size, yes you are correct, you can go 1mm larger on both valves using the standard seats and a 4 angle cut. As the 1600 head is flat, you wont suffer shrouding in the cobustion chambers, so thats not an issue. As far as stem diameter goes, it is possible to buy valves with wasted stems, even thiner than 7mm, so you can maintain the standard diameter guides. As I mentioned before, the head surface is flat, which makes it 0.5cm longer than your average valve , say in a Nova, but he had a valve that was fitted to a 1600 vauxhall (strange head design) that was fitted to caterams. It was 1mm larger, the same length and wasted. It had a slightly different groove for the collet attachment though, so he is going find one to fit perfectly. Once I have the details, I'll let you know. If you want any more info, let me know, MC
Thanks for the replies people. The more I think about this the more things I have to think about. I have a 1.6 engine at the moment and have a couple of old carb heads lying arround, I thought that I would rebuild one of the heads and do some p&p, matching of manifolds, re-grind valves etc myself for a small cost and small performance increase. I will be dropping something better in there soonish or in a new car, 2L 16v in about a year or two so this project was only a stopgap solution and allow me to get some experience on a cheap head. I read up about the 7mm stemed valves and thought that with undersize guides it would improve the flow by about 10%+ (percentage quoted from vortex forums), I'm not bothered to much about the short life of the guides as I will only need the head for 20K max. Now the big problem is with the sizes of my current valves @ 38/33, there are 33mm x 7mm valves but not 38mm x 7mm. VAG produce sizes of 33/35/40/42mm valves with 7mm stems or are available for a sensible price from techtonics. I am now thinking about getting new valve seats put in (40/35) and then buy the correspoding sized valves, trouble is now that I am now starting to spiral with the costs. So two options - stay simple and cheap with just replacing the guides. Use the 7mm guides and valves for the exhaust and stick with 8mm on the inlet. or Go 35mm / 40mm valves, 7mm stems allround, shortend valve guides, 3 cut valves. With a view to putting a 1.9 underneath it soon. Approx cost would be good. How much does it cost to have the valve seats replaced with 35/40mm ones? 3 angle cuts? I live in the northwest so I would appreciate recomendation of machine shops. Prof: The 8v beetle engine is an option and would be great with twin carbs on the front, but the problem is one of availability / cost and what to fuel it on orignally (some smartarse will say petrol!). I have a weber 32/34 at the moment and I dont think I can run that on a cross flow head with any current manifolds, then there's the cost of twin webers and manifold to factor in to even get me up and running with that head. M.C. The 1600 engine that I am refering to is the later design with the combustion chamber in the head (bathtub?) so will suffer from some shrouding with 1mm oversize valves. What is the wasted stems that you mention? Can I get 38mm, 8mm stemed valves reduced to 7mm to fit 7mm guides? or is it just a reduction near the valve face etc. Can you tell me what sort of cost I will be looking at here? Also, will I need completely different coilets, valve spring retainers for 7mm stemed valves or will the 8mm ones that I have allready fit OK. Cheers, Chris. Sorry about the essay!
If you use thinner stems, you'll need to change the collets, not sure about the retainers though. The wasted stem valves are standard diameter through the guide, ie 8mm, and are thinned to about 5mm in the port and down to the valve head. They are excellent, and I have used them in every Vauxhall head that I have had. They don't cost any more than standard valves, but if you over rev during a missed gear change, they are a weak spot. I missed 5th in my 1400 at 7500rpm and hit 3rd. Normally on a Vauxhall, the followers snap, but my valve head came off and proceeded to destroy both the head and block. I am waiting on the part no. info for these valves, should hear today or tomorrow. If for some reason they dont produce one to fit straight in, bill said that he will machine them himself. I will have my head back in two weaks, and will take pics for you. The basic spec is 1mm larger inlet and exhaust with a 4 angle cut on standard seats with porting. MC
head. I forgot to ask you about the shrouding. Is there enough room in your head to increase the combustion chamber to reduce shrouding? Some careful work with grinder would eliminate this problem. I'm not familiar with your head so don't know how close the valves are to the cylinder wall. If you do increase the combustion chamber, you'll need a skim to bring the compression ratio back up. MC
But then I still need to fuel it! A 32/34 would not be up to the job. There is a 2l 8v from an Audi A6 in the scrappers that looks in very good condition (dont know milage as digi clocks) for 150 with all anciliaries, no G/Box. To do this properley would need to move to fuel injection, the code is AB? I think! It could be a good engine but then its a tall block, I will also have to use my current gearbox etc. I want to sort the head out first and then get a bottom end sorted for it. I want to stay with carbs for simplicity (although I do have CE2) as I am going to get a new car soonish.
the mk4 1.6 and 2.0 8v both use 7 mm valve stems, the actual stem dia is quoted in haynes as 6.92 +/- 0.02mm. the valve heads are (inlet)39.5 +/- 0.15mm and 32.9 +/- 0.02mm, these are 91.85 and 91.915mm long, respectively. M.
Thought I'd give you an update on my head: This engine is expensive to tune! Bill contacted me to say that he cannot get ready made valves to my spec, so he is having them made. The valves are going to set me back about 35 each, so I have decided not to go for larger exhaust valves. he is going to make the inlet valves to exact specifications, 8mm diameter stem, 39mm head, 4 angle, flatter head, and wated down from 8mm to 6mm for the area in the port. The exhaust side is just going to be ported with 4 angle seats. He said that if I had inlet and exhaust valves, 80% of the power increase would be the inlet, and 20% the exhaust. So all in the head is costing 490 for a 15-18% gain. The block is costing some too, the pistons retail at 77 each, but managed to get a good deal and an all in of 350 (including 1mm overbore, pistons, rings, crank grind with shells). Just hope the wife doesn't find out how much this costs! MC (an extra tip: Bill said to get the overbore done 1 thou larger than specified. It'll be worth 5bhp over a new recon engine, and will reduce time to run in.)
I get great enjoyment from trying to get power out of engines, doesn't matter what capacity. I drive an M5, so get high horse power kicks from that. I recently got rid of a V6 4-motion too. I managed to get stupid power and torque from a 1.6 8v vauxhall, I use a 1.4 16v Nova track car that is running at 185bhp, and I'm also seeing what I can get from a 1.2 8v vauxhall lump too. The 8 valve vauxhall lump is easy to get power from, so this GTi is a new challenge. With the mk1, I wanted to get as much power as possible from it without it being apparent in the engine bay. I'm restoring it and want it to go faster but look original. MC
