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    Thread: 8mm inlet valves with 7mm exhausts???

    1. 10-27-2018 06:08 AM #1
      hey folks, I have been considering fitting the 7mm agg/aba exhaust valves into my pb head along with the standard 8mm inlets. so my question is, would the single springs fitted to the exhaust valves work ok with the doubles on the inlet side??? as in, would it cause some kind of imbalance??? I was thinking that due to the exhaust valve being much lighter than the inlet that it would work fine. opinions please

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    3. 10-27-2018 11:45 AM #2
      I do not think you will find facts but a lot of opinions.

      My opinion is that you will be fine. If I was the one doing it, I would install the higher rate springs just because I think more it better.

      What are you building?

      I built a 8V head using 7mm intake stems and 8mm exhaust. The reason was because the exhaust valves were sodium cooled and it would be better suited for the turbo engine I was building.

    4. 10-27-2018 06:24 PM #3
      I had considered this option before, and got an agg head for the parts. turned out the single coil spring caps won't work with the doubles. and the doubles cap won't work with the 7mm collets. and the single spring won't sit right on the lower spring seat (steal washer kind of thing between the spring and head on the mk2s) so if you fit the singles direct to the head there is nothing to locate them properly. the agg heads have a small recess where the spring sits to locate the lower end. oh it's a mk2 hydraulic head i'm porting/valve angles and 15 thou skim. going on an ace block with 3a pistons and a schrick 268 cam. 3.5 bar fuel regulator too.

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    6. 10-27-2018 06:30 PM #4
      I thinking now just to use the 8mm's. going to have the seats/throats bored out slightly, 3 angle seats. grind down the guide boss a bit and have the new guides tapered before I fit them.

    7. 10-27-2018 06:39 PM #5
      Quote Originally Posted by Butcher View Post
      I do not think you will find facts but a lot of opinions.

      My opinion is that you will be fine. If I was the one doing it, I would install the higher rate springs just because I think more it better.

      What are you building?

      I built a 8V head using 7mm intake stems and 8mm exhaust. The reason was because the exhaust valves were sodium cooled and it would be better suited for the turbo engine I was building.
      I remember the 7mm inlets being half a mm longer than the 8mm ones. you would have to be careful how far you cut the seats, or have the top of the valves skimmed. I don't think there is a lot of room to play with on them hydro heads.

    8. 10-27-2018 08:22 PM #6
      One advantage of working in a shop is that we had all the tools to perform a valve grind. It was awhile ago, but I measured the top of the stems when they were installed and they were within specs. I ported the heads with the guides out and shorten/tapered the guides before I installed them. I used titanium retainers and the stock spring cups.

      The original question about can it be done, with the right parts and set up right, yeah. Will it change the flow that much? I do not know, I would lean on the side of 'not much' for the type of driving I do.

    9. 10-28-2018 08:22 PM #7
      well I guess every little helps. vw must have had a good reason to reduce the valve size. less weight=lighter springs. i'm just going to stick with the 8mm all round. iv'e already bought the guides and stem seals anyway. just going to work the ports well and get the seat angles done. only looking for about 130bhp and some decent torque. cr should be about 10.9-1 which should work well with the 268 cam. the last 3a engine I had. the head had been skimmed 1mm and it was giving 215psi on a compression test. which would explain why it spun a big end after a short time.

    10. 10-29-2018 10:47 AM #8
      You are right, every little thing adds up. 130hp should be doable.

      I had a 1.6 stroked to 1.7. Back in the day, you would use the stock 1.6 pistons but just shave them down so they do not hit the head. I believe I had 225psi compression. Way to much for the street so I had to retard the timing a lot. I ended up taking off the head and enlarging the combustion chambers to get it down. Cheaper and faster than removing the pistons and have them machined even more.

    11. 10-29-2018 11:29 AM #9
      225psi! that must have been a bit heavy on the old starter motor. got my head back from the shop today. looks like a fairly decent job. the angles aren't perfect of course, due to slight variations in seat to guide alignment, but nowt you can do about that I guess. had a 15 thou skim/3 angles all round/exhaust throats opened out slightly/ backcut on 8 inlet valves (4 are for another head i'm doing) 4 valves ground slightly on the top and they gave it a bath by the looks of it. how much for that lot would you say???

    12. 09-08-2019 02:43 PM #10
      so I got hold hold off the 7mm valves/springs for my mk2 gti head. the only thing I'm wary about is the lack of spring base location when the single spring is installed. and with the cam i'm using there would be no room for a spring seat. would it cause any issues fitting the spring base direct to the head? anyone here done it before???

    13. 09-09-2019 10:30 AM #11
      I have installed 7mm valves in most of the 8V heads that I do anymore. The stock intake valves are .5mm smaller therefore I do not use the stock ones. The last intake valves [41mm] I purchased was from Techtonics Tuning. I use the stock 8mm springs with TT retainers.

      Never had a problem.

    14. 09-12-2019 09:11 AM #12
      ah so it's the spring cap that matches everything up. I was hoping to use the single springs to reduce a little strain on the valve gear. should free up a little power and maybe slightly better fuel economy. the 7mm valves are about 10 grams lighter than the 8's. and as I wont be increasing the rpm limit the single springs should keep the lighter valves in check. if I fit a 2 litre block that will bring the max power rpm down slightly but of course I might want to upgrade the cam at some point. it's all a compromise I guess.

    15. 09-12-2019 09:13 AM #13
      Quote Originally Posted by Butcher View Post
      I have installed 7mm valves in most of the 8V heads that I do anymore. The stock intake valves are .5mm smaller therefore I do not use the stock ones. The last intake valves [41mm] I purchased was from Techtonics Tuning. I use the stock 8mm springs with TT retainers.

      Never had a problem.
      is this the retainers you use (109 085)?

    16. 09-12-2019 11:05 AM #14
      I believe so. I have an account with TT so I made a call and they shipped the parts. I only purchased the intake valves and retainers since I could source everything else locally and much less. The next head I do will be with the 42/35 valves.

    17. 09-12-2019 11:51 AM #15
      made an interesting discovery today. if you take the double spring lower seat and turn it upside down, the standard 7mm valve spring retainer fits in it pretty well (might need a little buzz with dremel). of course if you were to use that method, you would be compressing the spring an extra mm. sits very close to the inside of the hydro follower too.

    18. 10-05-2019 11:05 AM #16
      Quote Originally Posted by Butcher View Post
      I believe so. I have an account with TT so I made a call and they shipped the parts. I only purchased the intake valves and retainers since I could source everything else locally and much less. The next head I do will be with the 42/35 valves.
      hi butcher, do you do back cuts on the aba inlet valves? looks like it might weaken them due to the large concave on the valve head. could be wrong though. got some standard vr6 spring retainers. turns out they are compatible with the 8mm-7mm valve conversion and double springs. do you taper the guides?

    19. 10-06-2019 11:19 AM #17
      Once I get all the cuts I want to the seats, I lap the valves to make certain the sealing is where I want it on the valve. Then I do back cut the valves to the lapping marks. I actually cut both sides of the lapping marks. It's not a lot and I'm certain it does not help much. In theory, it would allow a smoother transition and it's all just time wasted for me if there is no improvement. Kinda like a 5 angle seat job just done on the valves.

      I'm no engineer, but I do not think it would cause an issue.

    20. 10-06-2019 12:00 PM #18
      yeah I like to stick to the minor improvements all round too, instead of hogging out the ports and hoping for the best. I had a 4 angle done on the inlet seats and a 3mm backcut on the 40mm valve, so will probably stick to them and concentrate on the exhaust side. I can't understand why vw felt the need to go from 38-40 on the inlet. didn't seem to do anything for power on the standard engine, and the throat/bowls are a mess. I had a 38 head once and the throat/bowl area was a far better finish than any 40 I have worked on. it was a carb head though, so no use to me.

    21. 10-07-2019 10:05 AM #19
      You are probably working on a Mexican casting. The German cast heads are much better. Less porous, less flashing, etc.

      It's hard to find a German casting. Usually they are on the Cabriolets and Corrados. Both of those were made in German.

    22. 10-07-2019 11:55 AM #20
      I would say you're more likely to get a "poor" Mexican casting. but in general, all the heads iv'e had needed tidying up. you tend to find more german heads here in the uk, and less Mexican ones. I have 2 of both at the moment. I do wonder why the Mexican heads made their way over head with it being a german company that's a stones throw from the uk.

    23. 10-08-2019 10:09 AM #21
      I did not know you were in the UK but if VW did do their job better, we would have nothing to tinker with.

    24. 10-08-2019 09:28 PM #22
      that is very true. being over here is the reason I couldn't order the tt retainers. can only find titanium ones over here afaik. found a full set of vr6 springs/caps on ebay though. which ironically enough, came from a fellow in florida. £45 delivered, so cant complain about that. I had put an offer of £45 on a complete vr6 head over here, but never heard back from them, so just ordered the ones from over that way instead.

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