# 8mm inlet valves with 7mm exhausts???



## garryt (Dec 22, 2016)

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


----------



## Butcher (Jan 31, 2001)

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.


----------



## garryt (Dec 22, 2016)

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.


----------



## garryt (Dec 22, 2016)

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.


----------



## garryt (Dec 22, 2016)

Butcher said:


> 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.
> 
> ...


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.


----------



## Butcher (Jan 31, 2001)

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.


----------



## garryt (Dec 22, 2016)

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.


----------



## Butcher (Jan 31, 2001)

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.


----------



## garryt (Dec 22, 2016)

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???


----------



## garryt (Dec 22, 2016)

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???


----------



## Butcher (Jan 31, 2001)

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.


----------



## garryt (Dec 22, 2016)

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.


----------



## garryt (Dec 22, 2016)

Butcher said:


> 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)?


----------



## Butcher (Jan 31, 2001)

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.


----------



## garryt (Dec 22, 2016)

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.


----------



## garryt (Dec 22, 2016)

Butcher said:


> 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?


----------



## Butcher (Jan 31, 2001)

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.


----------



## garryt (Dec 22, 2016)

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.


----------



## Butcher (Jan 31, 2001)

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.


----------



## garryt (Dec 22, 2016)

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:sly: with it being a german company that's a stones throw from the uk.


----------



## Butcher (Jan 31, 2001)

I did not know you were in the UK but if VW did do their job better, we would have nothing to tinker with.


----------



## garryt (Dec 22, 2016)

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.


----------



## garryt (Dec 22, 2016)

how do folks:wave: looking for some valve guide info. I have a set of abf (35 mm) guides and a set of vr (38 mm) guides, so my question is. would I be better with the shorter blunt guides or the longer (very tapered) guides??? the standard taper on the abf guide doesn't protrude fully through the guide boss, but the taper I put on the vr guides blends in quite well to the guide boss taper.


----------



## Butcher (Jan 31, 2001)

I suspect that the longer the guide, the better the support. The better the support, the better the valve sealing would be. 

So is there a benefit for shorter guides? Probably allows for more air flow but I really could not say how much more or if reliability is worth the extra hp.


----------



## garryt (Dec 22, 2016)

well the abf guides arrived today, and upon measuring them. they are 36.5mm instead of 35mm as advertised. but the guide design would have it sitting higher in the head than standard (shoulder is lower on the guide) so the guide is the same length as standard, but doesn't protrude through the boss as much when driven fully home.


----------



## Butcher (Jan 31, 2001)

So would the valve guide seal be so high that the valve retainer would hit it?

I have a small lathe that I have cut down/tapered the valve guides in the past because I was too cheap to have someone else modify them.


----------



## garryt (Dec 22, 2016)

being cheap=knowing the value of money. always more job satisfaction doing it yourself. anyway, I should be left with 1.5-2mm between the seal and retainer at full valve lift. that's with a schrick 268 cam (11.2mm lift). fitted them today and after they have been reamed and the seats redone, going to blend them into the guide boss carefully with the die grinder. fitted the 7mm inlets too. used the 38mm guides with the same taper angle but increased the taper length to 7mm, and set the guide shoulder 1mm proud of the cylinder head. so plenty support and heat transfer area there. if you google "febi bilstein 10669" you will see the difference in the abf guides.


----------



## Butcher (Jan 31, 2001)

I do it myself so I know who to blame when it does not go right. Better to blame yourself than someone else. If it all goes well, then I can think I'm as good as I think I am.


----------



## garryt (Dec 22, 2016)

the person that has to live with the end result will always do the best job put the head to the shop today for the guide reaming and seat grind. hopefully be built up again by the weekend. car is still puffing out smoke though, even with the second head fitted:facepalm:. now thinking it might be the small holes in the pistons, behind the oil rings that are coked up. guess it's time for my rebuilt 2 litre block to start work:thumbup:


----------



## garryt (Dec 22, 2016)

Butcher said:


> I do it myself so I know who to blame when it does not go right. Better to blame yourself than someone else. If it all goes well, then I can think I'm as good as I think I am.


 I recall you mentioned before about checking the "free play" between the lifter and cam base circle when you were fitting the 7mm valves. what clearance were you getting and is there actually a workshop manual clearance? I have a spare ina lifter with the spring removed for testing.


----------



## Butcher (Jan 31, 2001)

I do not recall mentioning that but without a doubt, it's good practice if you are not familiar with what you are doing. There is little you can do once the head is installed.

The way a butcher would do it is if the valves are the same height, then in theory, they would seat at the same height. The 7mm and 8mm valve height are the same. The exhaust valves have the same diameter as the 8mm's. The intakes are slightly smaller at 39.5mm. So they would probably sit lower in the head and therefore it's a good idea to measure the height. The stem would probably have to be shaved a bit so it would be the same height. The lifter can only work in a small range. If the valve height is too low, the valves will be noisy. If the valves are too high, the valves would not close.

The last one I did I used Techtonic Tuning's 41mm head and machined the stock seats to accept them. I then ported the head to the new seat diameters. I do not recall what I ended up but whatever it was, the engine runs extremely well.

What I would do [If I was working with odd ball parts] is take the valve stem height measurements off the stock head and when you are done with the 7mm stems, make certain they are all within that range. If I was working with stock everything, I would flat rate it since good part tolerances are fantastic these days. I have yet to be burned by a faulty machined valve. The day may be coming but my days are numbered anyway. We'll see who wins this race.

I'm certain the Bentley has that info but sadly my copy of the Bentley is on my other computer. I have not transferred it over yet.


----------



## garryt (Dec 22, 2016)

yeah there's not a lot off give in the hydro lifters. maybe 1-1.5mm. I have already had the inlets cropped by 0.6mm. initial measurements were only showing 0.2mm clearance with lifter fully compressed. exhausts were over a mm clearance, so no worries with them. will be slightly less after the seats have been ground, but shouldn't be more than 0.1-0.2mm less. thinking I could use the "shim" style lifter clearances as an absolute minimum gap.


----------



## garryt (Dec 22, 2016)

so the seats have been cut and clearances checked. getting 0.5mm on the inlets and 0.75mm on the exhausts. also had the head skimmed another 25 thou to get the comp up to about 10.3. checked the combustion chamber volumes and only have 0.5cc difference between them. regarding the audi 3a engine that was meant to have a 10.5-1cr. im really doubting that now:sly:


----------



## garryt (Dec 22, 2016)

would any of you guys happen to know the piston dish volume of the 1.8 gti??? the 10-1cr version.


----------



## Butcher (Jan 31, 2001)

I do not, but this site does.

http://www.not2fast.com/vw/stuff/vw_engines.shtml


----------



## garryt (Dec 22, 2016)

cheers butcher:thumbup: I have seen that page before, and to be honest. there looks like a lot of mistakes and too much guesswork going on there:sly:


----------



## Jettaboy1884 (Jan 20, 2004)

Great thread and nice to see such a quality discussion on the 8v! I feel like I haven't seen this in years, and this is the reason I keep coming back. :thumbup:


----------



## garryt (Dec 22, 2016)

nowt wrong with a decent 8v


----------

