.21 Engine Intake Timing

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Marty Davis

Marty Davis

Well-Known Member
Joined
Sep 25, 2004
Messages
2,445
I would be very much interested to hear some opinions and reasons that people like high intake timing (above 128 degrees).

There are many reasons for having lower intake timings, in my opinion, but I might be persuaded if someone can tell me the WHY advantages of having high intake timing.

Would be interested in Andy's opinion since he is really a proponent of high intakes.

How about it Rod Geraghty and others....

Marty Davis
 
on my .21 k&b's, i've had better results with cutting the intake side piston skirt (to fill the case better/sooner) than changing the ports in the sleeve, or shimming up or dropping the sleeve. i've also seen better results from wider ports than higher or lower ports......
 
Jerry,

I just keep changing one thing at a time and keep testing.

It either works or it doesn't. I am not an engine guy,but

through a lot of testing we are starting to put some numbers

together that work quite well. It is the whole package together

that makes it or breaks it. I had a friend tell me run as much

sponson angle that I could get away with. Intake timing the same.

So we just keep testing different combinations until we hit it right.

We are really close right now and still learning about set ups.

Like I have said before "that is what makes this hobby so much fun".

It takes a certain amount of fuel to make these things run well,so

you have to feed the engine some fuel. Fuel = Horsepower

If you can't run with the big dogs, you have to get off the porch.

Thanks,

Mark Sholund
 
Last edited by a moderator:
I had an interesting experience with a K90 once that made me look at timings in groups, rather than singling one particular section out. The drum / disk / crank timings and the inlet timings in the sleeve seem to have a direct relationship to each other. Get it wrong and the engine will not run well at all.

The k90 in question was difficult to tune and was waaaay down on power. Dropping the sleeve, raising the exhaust back up to the same amount as before and fitting an appropriately changed head button (volume and depth to maintain same C/R and squish) totally transformed the engine. FWIW the drum had been previously modified to close at 65atdc. Ex at 186.

Re: Fuel = Horsepower. I've found this to be the case too. Whenever I've got a noticable performance gain thru testing and mod's, I've usually seen changes in fuel consumption to go with it. All of a sudden fuel cell is too small to start at the same time on the clock!

It's interesting to note that a lot of high perfomance 21 car / buggy engines have very conservative inlet timing in the crank. It's my belief that this is for reasons of fuel economy.
 
Last edited by a moderator:
Tim

spot on, car guy's need to get as much run time as possible[to certen extent]

that is why the inlet timing's are low,

i have run as nearly as much as 240 in total on induction and closing in high 70's,

with somw good results

regards Aaron
 

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