chip off the old block!

[Royboy66]

Decided its high time my engine became less wheezy !

A few who have followed my GT6 on the road have said how well it goes given the spec of the engine ....

2.5 TR short motor,flat pistons
GT6 mk2/vit cam 308778 (25/65)
HS6 carbs
standard manifold/exhaust
standard 2.5 head 219016 , measures 3.475" !!

At a guess I reckon I'm only running around 8.5-9.0 to1 comp ratio !

I have just done a comp test,  engine warm, plugs out, throttle wide open,
Results are all cylinders in 125-135 psi range.

I think its about time I took the head off, took some measurements and work out what comp ratio I'm actually running. (I know I know Bruce !! told me to do this 2 yrs ago !  :B)

Any opinions on what it may be are most welcome
Also any opinions on what I should raise it to also most welcome

Im going to take the head off next week ( need car running for this weeknds drive to CT dinner)

Hmmm perhaps I should start a 'guess my CR thread !   ;D :)

Any thoughts people!

Royboy wheezer !  8)

[GT6 M]

Royston, I take it you going to sort the valve seats out too, and a generall clean up.!!!
need 3 angle seat at least. taking you just leaving rest alone, then this is what I gusee.

Ohhh, whats the prize, got to have a prize. ;) ;)



comp now      comp needed       HP      RPM        T        RPM     comp
  8.5.1                9.7.1           123      5400     145       3200     207

[Royboy66]

Markuston !  :P

Yeah I was planning on just the skim, and having them check that all valves are sealing properly etc

.I'm not at the 'porting/polishing' stage yet, that can come next yr!  :B

ok, talk me through 3 angle seating ??  Im very clueless on heads !  :B


I best start a 'guess my CR' thread , and think of a prize!   hmmm cupcakes maybe!  ;)

[GT6 M]

Mr Roy, its a job that will need dooing,so might as well get a 3 angle seat done,
basicly, seat is 45 or what ever you want it, and the cuts either side  blend in the first cut, so that it is a more rounded seat,so air will flow  /attach its self to it, and not break away,causing eddies.
this goes for valve seat,and valve, inlet and exhaust.

if the garage/engineering shop say its not needed, then bogg off to another one.

alot of folk over look how important the seat area is,.
noo doo as your told, get a clean up,and 3 angle cuts. that should suffice you with my guesstimate

[thebrookster]

royboy66 wrote:

Markuston !  :P

Yeah I was planning on just the skim, and having them check that all valves are sealing properly etc

.I'm not at the 'porting/polishing' stage yet, that can come next yr!  :B

ok, talk me through 3 angle seating ??  Im very clueless on heads !  :B


I best start a 'guess my CR' thread , and think of a prize!   hmmm cupcakes maybe!  ;)

Roy, sounds like a plan. I agree with everything Marcus has said, the man seems to have a penchant for fast cars  ;)

You say you are not at the porting/polishing stage, had you considered a wee DIY job?? I am more than happy to lend you a die grinder (although you will need a 230-110v transformer, like builders use) if you were tempted to do a la'al clean up. Plenty of people on here and the dark side to give advice as well!!

Marcus has described the 3 angle seat nicely, well worth the effort. I would also get the valves back cut as well, might as well do the lot in one go.

Other than that, have you port matched the manifold's to the head?? You should be able to make some gains there as well.

[Royboy66]

Hey Phil

thanku for the offer, I may be in touch.

I prob could try a bit of diy on the head as long as I get clear do's n dont's & a good pic/diagram of where to do the  work!  ;D :B

back cut the valves?  whassat then? ? :B

[thebrookster]

When you do a 3 seat cut, you would normally get the valve seat cut at the same angle as the middle of the three seats, so as to allow a proper seal. Back cutting takes a shallower angle so to speak to smooth the back of the valve of slightly, and improve air flow around the valve.

3 seat cut will improve flow around the edge of the head (seat) into the combustion chamber, the valve work improves flow around the valve edge/back into the combustion chamber. I can't recall off-hand what I payed for my four cyl head, but it was not too bad IIRC (although my guides were shagged, so I had to get those replaced as well :( )

[Steve Cureton]

Roy, the March 2012 edition of Practical Classics has a guide to head modifcations including porting. If you haven't got a copy already then you can have mine.

[Royboy66]

cheers Steve  :)

[Nick Jones]

There is also this

http://sideways-technologies.co.uk/forums/index.php/topic/690-diy-heads/

excellent guide, by someone who knows.

Nick

[Royboy66]

Yes Nick, that excellent thread is my ' bed time reading'  for the next week!
I fancy having a go at that, but ideally on a spare head if I had one, then I could take mine off, measure CR, then get  the 'diy'd head skimmed & fitted.  :)

[thebrookster]

The find another head ;) Go on, you know you want to :)

Also, whilst going through all of this do remember that GT6Steve (the Las Vegas racery type) had some pics posted up on his photobucket of some cut heads, including some that had been modified. My experience was a picture said more than a thousand words, I actually did the work by the pc just so to be able to put the images I wanted in instant view!

In fact, here you go, found the album:

http://s206.photobucket.com/albums/bb46/GT6Steve/Head%20sections/

Phil