I'm here to discuss the pro's and cons of dished versus flat pistons. I've done some reading and a lot of it is theory... anyone with some practical experience have an opinion?
I'm not sure if I can tell what pistons I pulled from my engine - would I be able to see if the pistons were curved, if so it looks like they were flat pistons.
they're refered toas dished
most flat tops, although dead flat accross the top as the name implies, usually have like a moon shaped releif (x2) cut into them that allows clearance for the valves
the general idea is to has a tighter combustionarea for a better burn of the fuel
to be honest, unless you're trying to get a real 600+ aspirated from a motor it will meke stuff all difference
People often put a lot of impostance on things like flat top pistons as a feature of the motor when it doesn't really mean much
like putting roller rockers on when you never rev past 6000 rpm - waste!
what are you trying to do exactly?
Agree with the above post. It mainly effects the "squish" which causes more turbulence at top dead center. Valve reliefs in pistons are just that. Valve reliefs.
If you want to make it go Blocker, stick to the 3 C's. Cam, carb and compression.
Also have to say that when I down graded my CRF450 to stainless inlet valves it made very little difference to riding the bike. Might have lost a few hundred rpm and its a fraction less snappy but it will go for another years. The titanium valves were unreal.... for 1500km and then they hammered into the head. Performance is all relative to usability.
It has a flat top piston by the way, runs only two rings and has virtually no skirt at all.
141_0607_13_z+2005_honda_crf450x+piston_skirt.jpg
Last edited by wbute; 19-07-2011 at 12:29 PM.
Are we talking 253 here Blocker? Original 253's were flat tops and later (HX-VB/HZ) were lumpy tops. Dish tops in a 253 would suit turbo applications or a low compression engine.
if you're doing a motor / driveline these will help
ABOUT DISPLACEMENT, VOLUMETRIC (VE) EFFICIENCY, AND CFM
http://www.edelbrock.com/automotive_...disc_cfm.shtml
ABOUT COMPRESSION RATIO
http://www.edelbrock.com/automotive_...mp_ratio.shtml
COMPUTING HP AND TORQUE
http://www.edelbrock.com/automotive_..._disc_hp.shtml
It's no big secret dispite what most mechanics will try to make you believe
Cubes x rpm x compression = X hp (providing the VE is correct)
Just like ETs. If you dont have the correct ratios / tyre size etc 2million hp wont do shit
math is everything
Yes mate it is my late 1974 253. I have misplaced my HJ workshop book so thanks for clearing that up.Originally Posted by HK1837
Thanks for the links they will come in handy when I'm talking to mechanics who can rebuild this for me.
I thought the 3 C's to make it go was cubes,cubes,cubes.
I thought the 3 C's to make it go was cubes,cubes,cubes.
No its a light flywheel, short stroke, light piston and a decent valve train that doesnt float at revs. Add that to a light alloy block and a light machine and you have speed. Its all about revs, more than 10000 is the go.
This all comes packaged in a motorbike frame. When you can light the back wheel up in top gear with a flick of the clutch, thats power. All this for around $12000 in a bike shop near you.
Your preaching to the choir here. I started off on a CBR250RR (18k redline) followed by a VFR400 and then a CBR1000RR the week they were released in shops. Then I got converted to Motards (KTM 640 and 690) and picked up a VTR1000SP1 for the hell of it. I also spent 4 years as Service Manager at a Dealership where I got to ride everything with 2 wheels. Been through a few dirtbikes as well. Currently have a WR250R (enduro) and a WR250X (motard) in the shed. Main reason's for the 250's was preservation of licence and cheap rego. The missus can use both as well. There was one stage where there were so many different bikes in the shed it was getting ridiculous so we decided to cut back.
the real fun it pulling up next to somethig like a Ducati 900 (in your car) and smoking them
the look is priceless
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