Porting a china girl

[HeadSmess]

i shall re-phrase the comment to..."heavy porting is always slightly disappointing"

oh, sure, the effects on performance are great but its those little bits of metal that fall off, the ones you have no control over, that cause the disappointment... in my case it was usually the piston anti-rotation (?!) pin that came out. probably due to too much ring jiggling through the exhaust cycle... its the several hours you spend doing the work, only to have it destroyed in sometimes just minutes that is dis-heartening... and of course, when you do all this work and it sometimes creates an instant anchor... has to happen as well

then having to redesign/make a pipe to suit the new porting...arrgh... yes, i am lazy...or have far too many other things to do?

the enjoyable bits are when you get an engine to explode, seize, or do something completely left-field... after several hours of good hard thrashing, at least.

never had a retainer clip bust. still, i prefer real circlips, failing that... point tangs in direction of stroke, or cut them off completely!

glad a few people have tried the teflon out and like it... the less, the better. it squishes to virtually nothing, pretty close to metal metal contact.

does not like polished surfaces, it does need some sort of surface roughness to "key" into.

i never had a 48 with a slant head, the only 66 i had which did have a slant head turned me off for life... that whole engine was a dismal failure from the very first startup though, nuff said...

 

[Deleted member 12676]

Steve, what was the cranking pressure of the head that cracked?

 

[Deleted member 12676]

concerning the comment about porting giving disappointing outcome;
these are 2-3 hp engines and so anything less than doubling the power may seem disappointing, of course.

 

[Frankfort MB's]

concerning the comment about porting giving disappointing outcome;
these are 2-3 hp engines and so anything less than doubling the power may seem disappointing, of course.

Has there been any dyno runs on these engines? Or some dyno big enough for it cuz after all it's a huge motor

 

[HeadSmess]

Has there been any dyno runs on these engines? Or some dyno big enough for it cuz after all it's a huge motor

i started making a dyno just before the MB with internal combustion engine got banned here... so of course, it never really got finished. ended up pulling all the magnets out and using them for other things, and as for the main body of it...its just sitting on a shelf, gathering dust. shame, because it actually worked

not that the video really does it any justice...

 

[Frankfort MB's]

That motor sounded mean!!! Or was it just due to no exhaust???

 

[Frankfort MB's]

What did it run?

 

[Steve Best]

Steve, what was the cranking pressure of the head that cracked?

Jag, I didn't test it, sorry.
A judgement call based on starting compression would say less than the slant plug head.
I was breaking in the new cylinder and the head failed on big hill. Cracked in several places.
My camera took a big salty wave on the sea trip. When I get another I'll send picts.
The older hemi head was thinner and lighter than the new slant head.

Steve

 

[Frankfort MB's]

I had a head crack on me and the cranking pressure was barely enough to let the engine run (I could start engine with just moving back wheel) it also let the engine change the air:fuel ratio and leaned everything out so it would revv to the moon lol

 

[Deleted member 12676]

yes it is a lean fuel/air ratio that is the main culprit of high head temperatures.
But when you have the right ratio if you increase the compression then that increases temperature
which is why I recommend not raising it too much.
going from 90 to 135psi is enough. most aftermarket heads bring it up to around 160 which is way too much.