commer brake mean effective pressure

commeracer

commeracer

0
been running the commer engine figures through my engine design/simulation programme, it works out to have 7.0 bar(101psi )b.m.e.p (in the cylinder).
average lawn mower 8.0-9.0 bar
turbo race car 14-16 bar
its basically a measure of cylinder pressure at a given volume so is good for comparing engine efficiency regardless of c.c.
explains why the commer engine is so limp [xx(]
it is related to fuel consumption as well, an under powered engine has to be throttled more, so it works harder to draw in less air which uses more fuel :(
a more powerful engine works less to produce more power for the same fuel:)
will & dave get about 35 mpg which is as good or better than std, but with twice the power:p[^]
so the moral is , fit a 10.L keith black chrysler hemi and have fun [^][^]:p:D;)

"you were only supposed to blow the bloody doors off"
 
Engine stimulating thing [?] Good grief your a boffin [:0]

Would a head skim and a port and polish do the trick, or is the poor old 1725 just too far gone [V]
 
i nearly fell asleep myself :D
first rule of economy AND power is to loose as much exhaust back pressure as possible. if i had a brussel sprout for every time i,ve heard "an engine needs some backpressure to work properly" i,d have a sackful by now. its negative energy working against the engine, you burn fuel to produce power just to push the waste gases out [:0].
and it runs hotter as a consequence..........very useful!!!
the mini rc40 silencers offer virtually zero b/p up to 125hp ,you should have one on the mini and the commer panky.
head skim is good ,more compression = more torque and thermal efficiency(economy).
porting the head exhaust side only gives more economy and lower running temps, porting inlet as well gives more power and torque.
polishing inlet port is a waste of time and actually lowers economy due to fuel droplets condensing on port walls (liqiud fuel burns badly). polishing exhaust ports helps as a polished surface absorbs less heat ,hotter exhaust gas exits faster :D.
so theres life in the 1725 yet[^]

"you were only supposed to blow the bloody doors off"
 
Originally posted by Panky

Engine stimulating thing [?] Good grief your a boffin [:0]
lol suggested earlier that I would like to see what he could do for a standard engine ;)
 
all very well, but the tensile properties and fatigue factor of the elastic band hasn't figured in the above equations and you have no reference point to the velocity, age and endurance qualites of the hamster or drag factor on the bearings on his little wheel[:0]
 
damn! i forgot to figure that into the equation.
it means the decimal place moves and the commers 58 bhp becomes 580bhp :D

"you were only supposed to blow the bloody doors off"
 
oh no that's another thing that i was taught which is crap along with theres a dinosaur called a brontosaurus and we'll all be driving hover cars by the year 2000,so why does the engine run crap if the exhaust is blowing at the manifold if it doesn't need the back pressure? I'll be getting told the earth isn't flat next, knew it was a waste of time having education,now where did i park the hover car?
 
ah ha, i think thats where the myth comes from, what happens when the exhaust blows is the back pressure drops which affects the carbs metering signal and the engine leans out(runs weak)and falls flat on its face. so with a drop in b/p should come a change in carb jetting.
normally silencer removal needs 2-3 sizes bigger main jet or a tow from a brontosaurus [:0]

"you were only supposed to blow the bloody doors off"
 
ooooh.... me likey!

I have this spare engine you see....

so where do you get to with the alloy headed engine vs the steel one. (I have this spare 1725 in the back garden you see ;) )

www.littleyellowcar.co.uk
 
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