I've had the chance to take a look at the two heads I currently have,
comparing them with the head identification chart which John Macartney
has put together. The head that was on my 1972 GT6 when I purchased it
has a stamped number of 219019 and a raised casting number of 313247.
The thickness when we started was approx. 3.554. Based on John's head
identification sheet, it appears that this is a replacement head. We've
now milled it .263 to get to a thickness of 3.291 and combustion chamber
depth of .415.
The second head comes from an engine I purchased from Sean Alexander.
It has a stamped number of 517528 and a raised casting number of 308351.
The thickness is approx. 3.300. Based on John's head identification
sheet, it appears that this is a Mk. 2 GT6 head (early version). Sean,
is that correct?
I notice a couple of entries on the chart for Mk 2 GT6. Based on the
association with later Mk. 2 2000s, I assume the heads stamped 218225
are later Mk 2 GT6 heads? Does anyone know if there were
changes/improvements that went with the newer style?
Scott Barr
sbarr@mccarty-law.com
(920) 766-4693
(920) 766-4756 (fax)
> -----Original Message-----
> From: John Macartney [SMTP:jonmac@ndirect.co.uk]
> Sent: Thursday, April 13, 2000 2:39 AM
> To: Gt6steve@aol.com
> Cc: Friends of Triumph
> Subject: Six cylinder heads
>
> Steve wrote:
>
> I'm studying a TR-5? six cylinder head next to a late TR6/GT6 head
> with the
> immediate difference being the spacing between the intake ports.
>
> Steve, would you let me know the *stamped* head numbers for these two
> units? You'll find
> them on the front right side, just inside the valve cover seating.
> From your description,
> the TR5 unit is probably 516798 (fuel injected head) or 516323 (TR250)
> while the unit for
> the GT6 could be 219015. I'm in possession of a head applications
> chart that hopefully
> might highlight some key differences of which you presently remain
> unaware and you ought
> to know. That said, this tends to concentrate on the heads for the big
> saloons that
> stopped being sold in the States in 1967 but there are several
> references to the GT6 and
> US TR's.
>
> Is there an advantage to be exploited with the narrow port heads over
> the
> later wide ports?
>
> As your query might also affect gas flow characteristics, it has been
> proven with
> convincing evidence that the later 219015 head with a 30.3mm dia
> exhaust valve has
> improved gas flow over the earlier and larger 32.0mm exhaust dia. It
> would appear the
> narrower exhaust valve unit has less turbulence around the base of the
> valve guide than on
> its earlier and larger relative. For normal road use, I don't think
> the difference in flow
> characteristics would bother a blind man on a galloping horse - but
> they might be more
> critical in racing applications. I've driven effectively identical
> cars in which only the
> heads had these differences and I couldn't detect any noticeable
> variance in performance.
> On a flow bench, the data suggests otherwise.
>
> I guess my major question is why did the factory go to the wide port
> head at
> all when the narrow port looks superior?
>
> Mmm, with 15 different cylinder head references used in the 2.0 litre
> and 2.5 litre six
> cylinder units between the early 1960's and the termination of
> production for worldwide
> applications, we're looking at a little more than just narrow and wide
> port heads. Let me
> know if you can handle an Excel spreadsheet and I'll let you have the
> detail as an
> attachment.
>
> Cheers
> Jonmac
|