Forum

[ChrisD]

Hi Guys


I’ve just had the exhaust valve guide replaced on my
1996 500Classic and the engineers enthusiastically silica bead blasted all
surfaces – even the oil-tight ones (barrel-to-head, rocker box bases, rocker box
covers).  Grrrrrrrr, I’ll have to lap them
again.


But having been cleaned I can now clearly photograph the
ports and would like to know if anyone can comment on their shapes?  Two images are posted in my photobucket
account (ChrisD) of inlet and exhaust, namely: [IMG]http://i940.photobucket.com/albums/ad24 ... ar2012.jpg[/IMG]
and [IMG]http://i940.photobucket.com/albums/ad24 ... ar2012.jpg[/IMG].


 


In each case the images are annotated with dimensions
for both ports at the outside, at the valve seats, and at the narrowest
point. 


The exhaust is large throughout, so I doubt I need
much more work there. 


The inlet and exhaust at the valve seats and the
exhaust outlet are all 38x38mm. 


The inlet at the carb is 31x32mm as standard Indian,
so my new 32mm Mk2 Amal should fit nicely. 
But the inlet port reduces to 24mm high by 30mm wide at its narrowest.  Maybe this is why I can comfortably do 95kph
on less than half throttle but only ~110kph at full throttle.  I think the inlet port is too “tight” for
good air flow for an engine with ~8.5:1 compression, twin plugs, high lift
cams, oversize (Hitchcocks) inlet and exhaust valves. 


 


So, should I open up the inlet tract to at least
30mmx30mm at its smallest?  If so, how
much meat should I leave around the cylinder head studs and the rocker boxes?  I guess first prize would be from someone who
has measured up the Hitchcocks tuned 500 head!


Yes, I could buy a tuned head from our hosts, and if
that is what I need to get 100kph (65mph) cruising with a top speed suitable to
get past large trucks at up to 80mph (130kph) then that’s what I’ll do.  But cost of the head, plus the postage (adding
~35%) plus tax (adding ~14%) plus customs (adding another ~15%) would make that
a prohibitively expensive test.


Your thoughts and comments most appreciated, as
always.


ChrisD (from yet another boring sunny day in this African
paradise, Cape Town).

[ChrisD]

Aaaah!  Here's a better working Photobucket address.  I think.  Amazing how difficult something is that appears so easy.


http://s940.photobucket.com/albums/ad24 ... 0%20Ports/

[Mark M]

Chris, I'm no tuning expert but looking at the photos 2 things occured to me; 1) your inlet valve appears to be masked by a bulge in the port wall, a straight line would be better?, and 2) there is a theory that an inlet tract that is slightly tapering to the valve increases gas speed. Generally, your valve guides appear quite obstructive, maybe some more metal could come off them but otherwise the port surface is quite good compared to other Indian heads I've seen! Hopefully Paul Henshaw will be along soon, his work has been well demonstrated on the track so listen to him! (I have watched Hitchcock's expert profiling a 500 head but unfortunately forgot to ask for a demonstration!)


REgards, Mark 

[Bullet Whisperer]

Hi Chris,


 Here's one I did earlier [inlet side]


 Hope this helps,


 Regards,


 Paul.


http://i956.photobucket.com/albums/ae50 ... 500018.jpg


http://i956.photobucket.com/albums/ae50 ... 500019.jpg

[simon]

I ported my 350 bitsa and port matched it to the 1 1/8 389 amal carb. Before I did it I consulted a local engineer who builds race engines and he told me that you need to remove anything that will disrupt the gas flow but that you don't want to open the port out right the way through as a slight hour glass shape will increase gas speed and make the port work more efficiently. I highly recomend the bigger carb as the difference in the breathing is very noticable.

[ChrisD]

Guys, thanks
for all the inputs.  I have taken advice
from Simon and BulletWhisperer and opened the port getting rid of the straight
bulge as Mark suggested but kept it with a slight hourglass shape (narrowest
point in the inlet is now 27mm high).  Still
have to smooth it out and trim down the guide a little – something to while
away the long hot days this week.  I’ll
post an image as soon as that’s done.


Cheers all,
ChrisD

[Midge]

Paul the Whisperer, has your camera got a macro button, normally looks like a flower.


It makes a close up image much clearer, I hope you don't mind me suggesting that, no offence intended.

[Bullet Whisperer]

Hi Midge,


 I will give that a try - I've been a bit dissappointed with a lot of my pictures, maybe this could sort the problem !


 Thanks,


 Paul.