Big valve myth...

Benjamin · backyard mechanic Joined: 05 Oct 2001 Posts: 525

I just whipped the head off my TF, which was stamped 14 on the side. I remember Ben Wight saying that the heads marked 7,14,21 are NOT large valved (from his experience, am I right Ben??), contrary to popular belief.

I would like to put my 2c worth in and say that it must be a myth. I measured the TX and TF valves to be the exact same size. If memory serves me correctly they were either (44in, 31ex) or (46in, 33ex). Either way, my TF head stamped no14 did not have larger valves.

Cheers

CuGem · backyard mechanic Joined: 07 Oct 2001 Posts: 599

Hmmm, I'm confused too. I had been told that all TX heads had the larger valve size. If so I guess that would fit with your No14 having the same size as the TX according to Ben's rules.

FrAsErTaG · tinkerer Joined: 04 Oct 2001 Posts: 166

I measured my TX head up with my mates TF head and there is a Difference by looking I didnt even have to measure?
hmm interesting

Tooleeda · tinkerer Joined: 04 Oct 2001 Posts: 93

Maybe its had some work done? It is possible to put bigger valves in the late model head.

PS
Its probably not what you meant to say, but smooth bores are a bad thing, they ideally should have slight hone marks present and no lip within around10mm from the top of the block.

Ben Wight · backyard mechanic Joined: 04 Oct 2001 Posts: 946

Sorry Benjamin, I was asking the question about whether the numbers 7, 14 and 21, represented big valve heads, someone else told me that, but from memory I checked and had a head marked 14 or something with small inlet valves. I think it was a TE or something model head.

My theory was simply that TX and TD (and presumably TC aswell) all have the same size inlet valves (BIG valve heads) as I have 3 standard TD heads that have the bigger valves than the later pollution heads. None of these TD heads had the numbers 7, 14, 21.

Ben Wight

TXcoupe · petrol head Joined: 05 Oct 2001 Posts: 1675

okay if you want a big valve head you have too look at the numbers stamped on the inlet valve. these should start with 00 then i think 178 after it and yes there is a BIG difference betwen a small valve head and a big valve head it equates to about 10hp and 15lbft of power standard and also when buying after market heads if it has the izusu stamp on it make sure you check the valve size in the inlet as these can be small valve heads found on 1600 rodeo's. ( i have one and i when shit at the engine builder for saying it was a shit engine until i put the big valve head on and it went like a shower of shit)

Slug · tinkerer Joined: 06 Oct 2001 Posts: 196

Being as though you cant even remeber the size of a TX nor the TF head you are telling us about this post holds NO WATER. Try again when you have more information .... Michael

Loz · backyard mechanic Joined: 05 Oct 2001 Posts: 943

Well this is what I know.
I have 4 heads sitting in my garage.
A pollution model head, TF/TG. An early head (unknown origin, no numbers on it), a TX head and another TF head.

The unknown has 42mm inlet and 33mm exh. A big valve head.
The TF etc heads have 40mm inlet and I cant remember the exhaust.
and my good TX head had 44mm in. and 36mm exh. (This head is of no relevance as it has LARGER mazda valves in it.

Therefor I believe that the big valve heads have 42mm in. and 33 exh valves. Whatever the other heads have they are smaller than that, about 40 and 33mm.

Adam · Site Admin Joined: 04 Oct 2001 Posts: 682

You wanna double-check your measurement on the exhaust valves... I reckon you'll find they are (or at least 'were') 1mm bigger.

Mooch · backyard mechanic Joined: 17 Oct 2001 Posts: 573

He's right, 42mm and 34mm.

Adam · Site Admin Joined: 04 Oct 2001 Posts: 682

Um, you don't know what sizes the valves but you know they are bigger/smaller??

Ok, standard small valve head valve sizes are 40mm inlet and 34mm exhaust, if anyone wants to argue, I have two standard 'small' gemini valves sitting in front of my keyboard and a set of vernier calipers.

The large valve heads are 42mm inlet and the same 34mm exhaust.

The story of 7/14/21 came from the mouth of George Sheppard (of gemini rallying fame (www.GSAD.com.au)), so any argument should be taken up with him. I don't guarantee its accuracy but it beats workin' blind.

Adam · Site Admin Joined: 04 Oct 2001 Posts: 682

See my other post... I really do have the valves on the table right here...

Benjamin · backyard mechanic Joined: 05 Oct 2001 Posts: 525

42 and 34 sounds good. I was only working from memory and hadn't written anything down.

This whole big valve thing is too confusing. Comparing my TX and TF heads must then reveal that my TF has larger valves.

Ok, well I know a little more now Smile

Benjamin · backyard mechanic Joined: 05 Oct 2001 Posts: 525

Now now, Mr. Slug, no need to be nasty! Smile

Ben Wight · backyard mechanic Joined: 04 Oct 2001 Posts: 946

I really think the power increase found from the earlier model heads has a lot more to do the the fact that they have smaller combustion cahmbers (higher compression) and better flowing inlet ports than the fact that they have slightly larger valves. I'm sure the valves would contribute, but I am also sure that more power would be gained from the higher compression.

If anyone is concerned about valve size though, brand new valves can be bought for around $20 each, and then the standard valve seats can be cut to accept the larger valves. The machine work only cost me about $40 from memory.

Ben Wight