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ultimate compression?

Taffy

Taffy

Joined Nov 2001
17K Posts | 774+
Ely, England
what do you all make to be the ultimate compression given your CC of engine and the type of fuel used?

even the grade of spark plug would be important!

i have run 13.5:1 measured on a 90mm bore. this was my old WR400. i had no problems at all. i could feel more resistance on starting and that was that!

didn't even change the grade of plug.

just wanted views on this as the question of pistons came up the other day....

regards

Taffy
 
thanks taff ...

i have 13.5:1 comp with a JE piston 94mm bore , + 5 mm stroke , BP ultimate unleaded with amsoil octane booster

plug is iridium with 1 stage colder heat range

a whopping 470 cc
 
there must be a lot of piston slap! the bore on those is normally 100mm!

name your plug? regards

Taffy
 
the standard bore is 90 mm not 100 .

i am unsure of the exact code the plug is in the head and the head is having oversize ferrera valves with titanium springs fitted

the brand is ND OR NGK depending on availability .
 
G'day,
I know sometimes sticking your head gets it chopped off, but a std 470 does have a 100mm bore. A 400 has a 92mm, 501 is 95mm. So Whosahberg what have you built yourself? Custom crank? 501 piston? What have you created Dr Frankenstein.
Best Regards
Sutto
 
LOL !! ... i gotta come clean :D , this is my project DRZ 400 bought new and converted into
crf and wr 450 eater :twisted:

taff did not mention berg or hirosheema screema
 
you cheeky bugger! :p

i even love the bit about the plug! ah! the cat's eaten it! but the good news is that it's made by either NGK, nippondenso, champion or bosch!

funny or what. well you've been found out!

regards

taffy
 
you mentioned harder starting , i had the same problem . i have had cams made to suit my stroker motor , long duration with no decomp . i had to fit a manual decomp just to help my starter out .
 
There is no way to recommend an optimal geometric compression ratio, without knowing a bunch of other facts, especially the cam data. I have run up to 13,7:1 with a #62 cam (data close to the KTM Crate cam) without any problems at all. Well, the mains didn´t last very long :) I have also tried 14,0:1 with 1,3mm squish, but that was no good. The motor pulled so strong in the mid range so it was either sliding or wheeling instantly when addressing the throttle. It may sound like a lot of fun, but it was not very good for my lap times :cry:
 
sorry didn't i say?

i EXPECTED you to have a race cam. why else would you have an HCP and run a cooking cam?

i'll explain a little slower to those at the back next time.
 

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Taffy
Taffy

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