Setting timing on a 8.7 to 1 compression turbo setup...

Joe4ta

Registered
Hey guys. I am by no means a turbo guru so I have a question on timing issues with lowered compression. I built a system for my 05' Busa from the ground up. Liquid to air intercooler , CP pistons , Carillo rods , APE studs , adjustable cam sprockets , Spacer plate , etc , etc. All the usual items are on board. Including a fully upgraded fuel rail , injectors , pump and the like. Built it around a T3/T04b 50 trim compressor initially. However I have phase 2 coming up and will be grabbing a GTX2867R from Garrett.
I rode the bike all last summer putting about 6k miles on the bike. Ran 16 pounds with autotune on the PCV ( worked my way up ) Ran 8 in the beginning. All in all the system made me crap my pants even after running an 18t front and 38t rear sprocket to help keep the nose down. Stock wheel base mind you.
Now my question is...
How far do I need to advance my timing to get this beast to go past 8k rpm without choking on itself ? And to nip it in the bud...it is NOT a fueling issue. Data logging showed an even 11.8/1 AFR regardless of boost pressures. Had to up the AFR to 12.5/1 on out of boost conditions so it would run smooth. I would hit 16 psi @ roughly 6250 rpm and it would scream like a beast until about 7500 rpm. Then by 8k start chugging out of time badly. Always the same rpm threshold regardless of what boost I was running be it 8 pounds or 10 or 16. Now having lowered my CR from 11/1 down to 8.7/1 has most likely everything to do with it. I have the beast torn apart right now for a thorough systems check. Aside from having gapped my plugs a smidge too wide everything looks great. I just need a guiding hand from a bonified turbo guru on setting my timing right. Although I know this bike rather well , this was my first turbo build ever. And jumped right into the raging river learning to swim as I go :lol:
Is there a formula I am ignorant to as far as calculating timing when lowering CR's ?
Any help would be greatly appreciated !!!!
 
what cam timing did you have ,
what injectors, regulator etc
are you asking about ign or cam timing as i believe advancing either is wrong in this case
 
I kept the stock cam timing for an 05'. Which is where I think my issue lies having lowered my compression. I have ECU editor with the black box hookup and was able to "tweak" some of the timing issues out. But I was only able to get another 750 rpm or so out of it before the timing issues arose. I am running Bosch 52lbs injectors currently. They are rated at 550cc's @ 43 psi / 630cc's @ 58 psi. I am running them @ 50 psi atm. I messed around with pressures in the beginning to get a good cold start and idle. My fuel map numbers under full boost conditions at 50 psi fuel pressure are still in the negs. Meaning ( Power Commander 5 numbers ) @ idle around 12.5 afr they are between -55% and -60% on the pulse width. Under 16 pounds of boost @ 11.5 they climb to almost zero and my injectors never go above 50% duty cycle. That still leaves +250% adjust on the injector pulse. I do not believe @ 50% duty cycle @ 16psi of boost is too shabby. Like I said my data log shows my afr maintains in the green during WOT. I have a Fuel Lab FPR with the boost reference onboard.
The bike acts like any other motor does when a timing belt slips a couple of teeth or the spark timing is way off. I tried every which way under the sun with the ignition timing ( spark ) and like I said , I was able to find a better spot with the ECU editor. But the gains were marginal at best. I triple checked the cams and everything lines up perfect as per stock settings with the crank at TDC. I am pretty sure it's a cam timing issue. I know that lowering compression in an engine allows you to advance timing ( spark ) in relation to how much you reduce the compression ratio to get it to run smoother. And I found that to be true while out of boost. Now while under boost you should retard timing in relation to how much pressure you are cramming into the cylinders. My concern is the cams. It just acts like the exhaust is fighting the intake and/or vice versa. I could be wrong though :banghead:
Which is why I have come to you guys for help !

NOTE: I did NOT degree the cams with the intial build. Just set everything as per stock with crank vs cam marks. I'm learning :)
 
Also as a side note. For my exhaust I ran a 2.5 inch 90 out of the turbine flange with the wastegate dumping back into the exhaust at the end of this 6 inch 90. The O2 sensor is plumbed in about 4 inches past this point right before I necked it down to 2 inches. the 2 inch pipe runs back the way the stock piping would and splits into two 2 inch runs and up into some standard after market cans. I wanted to keep the bike a sleeper... I have not checked my back pressure which is maybe something I should do ???
 
Well I had made a very long winded post explaining things , but it seems to have vaporized into limbo. So to simplify things I guess the root of what I was trying to say is...
When adding a spacer to this motor it in effect changes the timing of the cams if you line them up to the stock markers on the sprockets. Which is what I did without thinking about the probable timing change required of doing so. And you are correct. I meant to say I think that I need to "retard" the cams from the stock positions in regards to adding a spacer. 8k rpm from 11k is not too far off...enough I agree to make the difference. Especially with boost. I found a formula on Webcamshafts.com that seems to be what I was looking for. However , any input is always welcome !
 
That page from Web is pretty much all you need to do the cam timing
you can use your dial gauge with a extension to find tdc, rather than the piston stop , just find something like 0.5" from tdc before and after tdc and centre your wheel on these numbers

i use .030 as my measuring point, gets you further from tdc or bdc and stops you getting negative numbers which just confuses the issue
and small numbers should always be near tdc
 
Update-
I got everything I needed and degree'd the cams. Ended up with 106 / 108. Made all the difference in the world. Took the bike out this weekend for some runs and topped out at 11k rpm. Sweet music to my ears. :thumbsup:
 
Yeah took it out and started slow. The bike was actually running way too rich. I blew through a tank of gas in 60 miles. Spent a few hours running and tweaking the maps via auto tune and ECU editor. Everything is in the green for 10 pounds. I think I'll just keep it there until I can throw her on a dyno next month and shoot for the moon then :laugh:
 
Sounds good
update us when you do and include some pics
and congratulations successful home builds are not all that common
 
Back
Top