gregs
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| posted on 9/6/07 at 08:30 AM |
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Pinto valve sizes with 38mm ITB's
All,
Planning what to have done to my Pinto head, and I'm stuck with the valves (no pun!), wether to enlarge or not. I will be running GSXR 600 TBs
which have a bore of ~38mm, so am struggling to figure out whether I have anything to gain by enlarging the std valves 42.1mm inlet & 36.2mm
exhaust? or do I just need to enlarge the exhaust valve?.
I am starting to think a good port and polish, 3-phase valve seats and new guides & bearings will get me as far as I will go with these throttle
bodies?
Any advise welcome (other than fit a Zetec, put a bike engine in etc  )
Greg
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jacko
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| posted on 9/6/07 at 08:49 AM |
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What amount of power are you trying to get from your engine ? .i used bike carbs, planned the head by 1mm ported & polished and have a 285 piper
cam this gives me 175-180bhp -140 at the wheels
+rebore by 60th
Jacko
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gregs
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| posted on 9/6/07 at 08:53 AM |
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jacko - if I get above 150 at the fly I will be happy, so reading into what you are saying I don't need to enlarge the valves? (I am also
planning on a 285 cam)
Greg
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rusty nuts
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| posted on 9/6/07 at 11:49 AM |
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Not a good idea to polish some Pinto ports IIRC
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andyharding
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| posted on 9/6/07 at 12:15 PM |
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quote:
Originally posted by rusty nuts
Not a good idea to polish some Pinto ports IIRC
What?
Are you a Mac user or a retard?
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rusty nuts
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| posted on 9/6/07 at 01:33 PM |
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All you need is a smooth port surface, not polished . Polishing actually reduces power on a Pinto
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jacko
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| posted on 9/6/07 at 01:46 PM |
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quote:
Originally posted by rusty nuts
All you need is a smooth port surface, not polished . Polishing actually reduces power on a Pinto
That's wright just a Smooth :Surface
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andyharding
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| posted on 9/6/07 at 05:52 PM |
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If you want to split hairs - you want a mirror polish on the exhaust ports and a smooth but not polished surface on the inlet ports.
Once the ports have been enlarged and roughly smoothed any gains from further polishing will be minimal.
Are you a Mac user or a retard?
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bike_power
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| posted on 9/6/07 at 07:12 PM |
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It's not neessarily the size of the valves that need changing, I know almost nill about the Pinto engine but in general the valve seat shape and
the area immediately in front of and behind the valve seat will have a far greater effect on power than polishing.
Get a copy of David Vizzard's book about the A series, it's not the same engine but he does demonstrate exactly what does and
doesn't work in there and you can relate what he shows to any engine.
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rusty nuts
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| posted on 9/6/07 at 07:16 PM |
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quote:
Originally posted by andyharding
If you want to split hairs - you want a mirror polish on the exhaust ports and a smooth but not polished surface on the inlet ports.
Once the ports have been enlarged and roughly smoothed any gains from further polishing will be minimal.
Some Pinto ports are too large as standard .
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gregs
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| posted on 10/6/07 at 08:42 AM |
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thanks for the responses guys - the info I am really after I guess is how a 42mm valve (assuming the port shape is optimised) flows compared to the
straight tube that is a 38mm throttle body?
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bike_power
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| posted on 10/6/07 at 07:30 PM |
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quote:
Originally posted by gregs
thanks for the responses guys - the info I am really after I guess is how a 42mm valve (assuming the port shape is optimised) flows compared to the
straight tube that is a 38mm throttle body?
The size of the valve head is just one part of the picture, the shape that actually allows air into the chamber is a circular curtain that has the
same diameter as the valve seat and the height of the max valve lift less the valve clearance. It's more of a curtain shape around the
circumfrence of the valve.
The valve is only lifted to max valve lift for part of the intake or exhaust cycle, it spends a lot of time at low-medium lift so the area of the
curtain is changing all the time the valve is opening and closing.
It's this area which you need to ensure is able to allow sufficient cylinder filling to meet your power requirement.
The 38mm throttle body is much bigger and better flowing than the 42mm valve curtain area unless you'e got massive valve lift, excellent
valve/valve seat//chamber shape and get a lot of cylinder packing.
[Edited on 10/6/07 by bike_power]
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