srx 780 BB jetting info

C

crazykid

New member
Joined
Nov 21, 2004
Messages
238
Age
49
Location
WINNIPEG MB
Like the title says im looking for jetting info for a 780 BB i just bought. Now first of all i dont know whos bb it is,bought of ebay and the seller just says that it was from a local shop in NY,The porting seems to by quite agressive.Can some one give me a good starting point for jetting, i cant really see there being too much of a difference in jetting from 780 to 780 to a point that is.So agressive porting and a 780 bigbore, some baseline jetting? Anyone? Thanks in advance.
 
Stock pipes, stock carbs, for now, thinking of using mach z carbs later on but dont know if it will be worth it.Dont know the compression yet,i havent actually put the top end on yet,was hoping to get some baseline jetting for when i do put the top end on. Thanks for any replys though.
 
i think i know what kit he's talking about. it was the one that was in the classifieds on this site. the seller at the time, said a local shop did it up and that the top end is set up for 660ft drags. i'll try to find the link of the original ad.
 
mopar1rules said:
i think i know what kit he's talking about. it was the one that was in the classifieds on this site. the seller at the time, said a local shop did it up and that the top end is set up for 660ft drags. i'll try to find the link of the original ad.
Click to expand...
Yeah thats the one,I guess i now know what the compression is, around 145psi, wasnt even aware it was that high, another question now, Can i run premium or am i going to have to use race fuel? Anyone know baseline jetting based on the info so far, Stock carbs, Stock pipes, About 145psi compression,Aggressive porting.Anyone?
 
Compression isn't all that relevant. It is very dependant on port timing (taller exhaust port = less compression). Compression ratio is what is important. You'd have to calculate it, and then we'd be able to tell you what kind of octane you will require.
 
Ok, I dont know how to calculate compression ratios, can it be explained? Now i sure wish i knew what fuel to run,cause too high an octane will hurt performance as well wont it?Damn these cylinders are starting to be a little scary for me to run.I think im in over my head here. Any help will be greatly appreciated. Oh well ive got all summer to try to figure things out i guess.
 
I dont know what fuel the previous owner was running, ill try to get a hold of him and see if i can get some info. But does anyone have some baseline jetting for a 780 BB,Can someone post what jetting they have in their 780 bb,so i can atleast have a starting point? Mainjet, needle position etc. Any info would be great,id rather start rich and tune from there, I am presently running 148 mains and i beleive 3rd clip with both spacers underneath and a 45 pilot. Should i lower the clip one more groove and what main? Anyone something?
 
I'd would like to see you start in the neighborhood of 158's, and come down from there if you need to. Keep the needle in the mid, and run 45 pilots. Start from there, and do alot of checks. I don't want to see you burn down.
 
Thanks ill try that, i needed a good number to start at,didnt want to start too lean and find out the hard way. So you think the needle is good where it is? Thanks alot for the reply. Awesome,Thanks
 
Oh by the way,the jetting i posted is what was in the carbs before the BB,i have not yet run the big bore,just in case someone didnt pick that up. I previously had so called ported cylinders but i dont think there was much porting to them,they measured out to be less agressive than the 2000 and up cylinder specs in the tech section. Oh well. Thanks again to all replies
 
I (and most of us) hate giving jetting and setup info for those reasons.....which is why i was asking so many questions previously. There's nothing worse than someone coming back on us and claiming that it was our fault that the motor didn't live. Be warned that this jetting might be lean, or that your head configuration won't allow you to run pump gas.

I could get you pretty close if I knew the porting specs and head configuration.

Also remember that with this motor, you are going to have to let it warm up thoroughly, EVERY time you leave. If not, the forged Wiseco pistons will expand too quickly, and you will hurt the motor. A water temperature gauge is a good idea, then you can be sure it has enough heat in the motor so you won't do damage.
 
Well guys,ya got me thinking here, which is a good thing.I think i should get more info for my sake and your peace of mind. AND i would never blame anyone on this site for any info given or taken, Without any input i would for sure burndown and ruin a good bigbore. So thanks for the info guys. Ill keep ya posted as i get more info. Thanks
 
You must log in or register to reply here.


Back
Top