timing vs boost vs comp vs ron??

[1jzracing]

this could get a bit messy because there is so many variables but what are people running in real world examples as far as ignition timing with big boost at given compression ratios because there must be a farly consistant trend

iv heard of figures as low as 12 degrees all out with an rb26 on big boost and pump fuel making over 300kw and as high as 28 degrees on the same engine running c21 (something like 120 octane heavily leaded) at the same boost ... and picking up something like 40kw

i know it depends on combustion chambers etc and each engine reallty needs to be tuned with good knock detection but a similar thread got me thinking what results are tuners coming up with and what sort of boost is the limit for various production engines on todays fuel

[chris davey]

Great thread. I will be happy to input some info. in the coming weeks of tuning

12deg timing, 15psi, 8.5:1 and 98 RON.

That is the base that I am starting with.

Will be upping boost after the drags but only have 550cc injectors so won’t be too crazy. I suspect around 23psi. I will be using Shell optimax extreme 100oct and martini superboost.

From what I have seen with some articles, superboost with 98 can take an extra 6 degs of timing at same knock level. Similar results with optimax extreme and it is 2.5% oxygenated so it can make more power also So I think that the optimax extreme plus super boost should work out pretty well

Do you have any figures?

[1jzracing]

i do my own tuning and we dont have any real reliable knock detection when i dyno my car as my mate does it for free and he is a mechanic not a performance shop so i have run all sorts of timing on different setups and lost a couple of engines along the way too so have been wondering what other people have found is capable

supercharged i could run 24degrees @ 22psi on avgas (dangerious i think!)

turbo i have run 19 degrees @24 psi on optimax extreme 100 with 15% toluene we spat out 354kw but i feel this may still be danger teritory as far as timing goes

all in a 1j with about 9:1 comp (i know everyone quotes 1jz as 8.5:1 but believe me they are all at least 9:1 standard)

[chris davey]

I know they are different engines but have you checked out www.supraforums.com? There is a whole section about dyno tuning and the most common questions are about timing vs MON. I have found some good info. over there anyway.

Hmm, optimax extreme with 15% toluene would probably end up being pretty similar to a mix with super boost I would imagine. I used to run 98 + 30% toluene mix but have just changed to the super boost.

What are the rules re fuel in your class of racing? If you are allowed I would probably go to a mix of extreme and M110 for racing. If you think that is on the edge that is.

So what do you use for knock detection? microphone sort of device?

[pilot]

Just a hint: toluene is very bad for health (cancer related). Please be careful and take care if you are going to deal with it or any other aromathic.

[JustCallMeOrlando]

all in a 1j with about 9:1 comp (i know everyone quotes 1jz as 8.5:1 but believe me they are all at least 9:1 standard)

How did you come up with this figure? Toyota don't just make stuff up, and only the vvti version was ever rated that high CR-wise.

[1jzracing]

im a fitter machinest by trade and i measured it! .... plus if an engine has 170 odd cranking psi it must be in the region of 9:1 or more

you can work it out ... or check my calculations!

head chambers = 40.5cc, gasket 1.2mm = 6.97cc, piston valve cutouts = 3.6cc, bore 86 stroke 71.5 = 415cc displacement, pistons come exactly flush with the top of the block so there is no other volumes to consider apart from the piston/ bore clearence above the top ring ... pretty small!

total chamber vol (this is the total vol at TDC) = head + gasket + piston cutouts = 51cc
swept vol (displacement) = 415cc
so total vol at BDC = 415 + 51 = 466cc ..... divide this by the vol at TDC ( 51cc) and you get 9.1:1 that is the comp ratio!!!

[chris davey]

Now we have that sorted, back on topic

ANyone else have any figures?

[JustCallMeOrlando]

Well that is random. Thanks for the measurements

[chris davey]

bump for a bloody good idea. Does anyone have any info or you all know nothing about the tune of your cars?

[camrygt?]

I've found most engines can be tuned a bit on the rich side and run more timing or tuned a bit on the lean side and run less timing.

Most of the time both ways will make similar power but sometimes a motor will significantly prefer one or the other.

Makes it hard to directly compare ignition advance even between the same engine.

[1jzracing]

been doing a lot of lookin ...

mostly on the supra forums etc and looks like anything around 20psi the timing wants to be under 20 degrees down to about 12 or 14 if your up to 25psi... if your fuel supports it!!! .... after that you need even better fuel and lower compression etc to run any more boost and timing seems to sit on the 12 to 15 degrees

dont take my word on this as there isnt much to go on

... thats the idea behind this thread ....

anyone else have any thoughts comments or numbers to add????

[chris davey]

camrygt: thanks mate.

So how about timing vs boost vs comp vs ron vs AFR

[1jzracing]

AFR? ... just keep it FAT up top or it'l overheat the piston and damage it ideally 11.5:1 or lower on anything over 20psi

[mic*]

AFR? ... just keep it FAT up top or it'l overheat the piston and damage it ideally 11.5:1 or lower on anything over 20psi

Air Fuel Ratio. Can you explain this post a bit further...