Hey Scottie,,,???? about changing injectors.

[Kennysgreen280zt]

HAHA , I am looking forward to setting up my SDS! In the instruction manual I remember seeing that they had a base curve for injector cc vs cyl displacement. I am guessing you could figure out how far off that curve you are with the injectors now , then set up the new curve off of the 680cc injectors. You may want to do it a different way , but this is my thoughts on it. hope this helps. laterz

~Kenny

[stony]

Im running 444c stock gtr injectors.. im using SDS and the rpm curve seems to be very good. it was setup by someone who had tuned many rb-26s in other cars with close to the same setup as mine. i know the booste side will have to be tweaked again my question is can i use some kind of formula to figure the changes needed to the rpm curve once the 680cc injectors go in. or is it just gonna be a wing it and redo it in the manner the SDS site says to set it up.

 

I dont know how many of you have setup SDS before from scratch but doing it on the road in a 400+hp Z is hairy to say the least ;> especially the hi rpm map settings

[Scottie-GNZ]

Stony, if the engine is running fine today, then do not change the "curve", just the numbers that make up the curve. The numbers in the curve start with the base number at idle and that number is derived from a matrix supplied by SDS and factors in the cylinder displacement and injector flow.

 

 

Use the matrix to derive your new base number. However, be aware that it is just a guide and you usually end up with a different base number after tweaking. SO, do it first with the 440s, then understand the variance between what the matrix says and what you have and apply the same to the new number. E.g., if the matrix says 80 for the 440s and the car is running fine with 76, then you know to make the new starting point 5% less than what the matrix says. Remember, it is only a starting point and still needs tweaking.

 

I do not want to make it too complex but if you want to retain the same fuel curve with the new base, then you need to understand the curve. The way I do it is to place all the values in a spreadsheet and understand the % difference for each value. Once you derive the new base, apply the %s to the new base and let the spreadsheet generate the new numbers. Simple, eh? I would venture a guess that you will not have to change the fuel values for boost (the MANPRESS map). Once you redo the curve for RPM FUEL, tune the car for normal running w/o boost first and once the car is running fine, then apply boost.

 

Hope I did not muddy the waters.

[stony]

I wish sds would come up wiotha datalogging option

 

thanks for all the info makes good sense. Ive decided against then ine inch conversion ;< too much money and time that i dont have. Just gonna do the cv swap and shoot for mid tens and try not to break anything ;>

[awd92gsx]

Maybe this concept doesn't apply to Z's, but...

 

In a DSM, we're getting about 350hp out of the 4 450cc injectors that come stock in them. Let's drop that number down to a more conservative 300hp, though, to keep the injectors from being pushed.

 

That works out to be about 75hp per injector at a duty cycle of around 80 to 85%. If we multiply the max hp per 450cc injector times the total numbers of injectors, which in a Z would be 6, we get a total potential horsepower figure of 450hp using 6 450cc injectors (easily within real world parameters)

 

So, with that being said, I don't think running injectors larger than 550 would really be necessary, unless you were putting down at least 500hp, and they'd be alot easier to tune, and 450cc injectors can be found for practically nothing from many DSM'ers and DSM shops.

 

..and before anybody starts complaining about the referral to DSM's, remember, concepts usually apply to all engines equally.

 

Of course, you know what they say about opinions, everybody has one and they all stink...or something like that =o)

[stony]

hmm not sure what your saying.... im running the stock 444cc injectors in the rb26... and getting 400+ rwhp. injector duty cycle is maxed and very lean on the top end...680cc injectors will do very nice and should get me in an range

for fuel and aloow me to run more booste ;>

[awd92gsx]

If you already have the 680's then they'll work, but 550's should easily work nicely, too (depending on how much hp you are actually going to be able to extract) and may end up being alot less expensive than the 680's (I figure about $400 for a set of 6 Lucas injectors, maybe less, though), of course, my figures are at the crank, so getting 400+ RWHP from 444's is pretty good!!

 

Of course, if you're running a standalone, you shouldn't have any problems getting them to idle, but many people with other makes have had problems getting 680's to idle right.

[stony]

i will be pushing 600 rwhp with the 680cc inj and turbo upgrade

[Scottie-GNZ]

Stony,

 

the 550s should be able to support more than your estimated 410rwhp. I am running 50# injs (525cc) and when the engine is tuned correctly I am in the 80% DC range. When I am running too rich, it can go as high as mid-90s. That is with 42# static FP, 24+# boost and 24* total timing at full boost. That is getting me an estimated 440rwhp.

 

Why don't you try a 3rd or 4th gear full boost blast and tweak the R/L knob towards lean. I would be willing to bet you would feel a little better acceleration and a drop in DC. Remember, I said TWEAK .

[stony]

scottie.

 

the last run i did top end in 3rd heard a slight knock....af ratio was lean and the injectors read 112% on the sds screen. this tells me they are not giving me enough fuel lean rich knob or not

 

I agree the 550cc inj would have worked well but with the plans i have teh 680s are closer to what i want to end up with. I went with 680cc injectors cause i got a great deal on them, 280 bucks . i wanted 720s for future turbine upgrade but these should work fine. i always felt a little overkill on the fuel system cant hurt. you should know remember Mark he was running 720cc inj on that ca 18 (1800cc 4 banger) he had

 

this may be hard to believe for alot of guys but by upgradeing the turbine wheels to super 60s , a 272 cam, and the 680 injectors and turning the booste up 1.2K the rb26 will be well into the upper 500hp range ( i hope) Ive seen others in this reange with teh same mods ;>

[awd92gsx]

Damn. It's hard to be 6 680cc injectors for under $300!! Good find!!

[stony]

OK lets bring this back to life.....

 

Scottie... thanks for your info on the rpm fuel curve (EMAIL) this helped alot. what i did with the 680s was disco wastegate act and the intake pipe to the motor so it was a true N/A motor. Once i did this and started setting it IAW the SDS manual the low end numbers came up a little and the high end numbers came way down!!!!! i no longer have that steep curve like the excel sheet i sent you.

 

the numbers range form 60 at 1500rpm to 90 at redline... only real jump is right above idle. I then reco'd the turbos and intake pipe and started my full booste tuning (My old map curve was still there) its was really rich!!! so i started backing it off and it got better and better... still have some lowend rich stumbles but i can fix that later point is .... this MOFO RUNS It never used to break the stock tires in 3rd but now it smokes them!!!!!

 

I understand now what you were talking about with all the curves and stuff but i still think the 444cc were maxed even if i did tune them the same way .... the 680s are running right at 80-85 duty cycle all the way thru the redline and im still a little rich as mentioned before.

 

So now all i have is to get my tires and take a trip to the track and see what i break hopefully its only my personal best

 

wish me luck

 

[Scottie-GNZ]

Good luck and glad to see you realize tuning is not a one-time thing. We make about the same HP and so should have the same fuel demand. I have mine tuned correctly now and run about 78-82% with 50#ers. Once you get that richness down at little at WOT the DC should come down below 80%. You might want to consider an EGT gauge. I used a Westach but recently switched to a Dakota Digital so I do not have to focus on it.

 

I probably said this before, but make sure the FP is dead on to the Inj manufacturer's spec else the SDS will be off since the inj would have a different flow rate. Common mistake to see folks go to an aftermarket inj and forget to change the FP from the factory setting. I am sure you are aware but others should take note.

[stony]

sorry scottie may not be as much a technical wizard as you think.... FP= fuel pressure right?

 

right now all im running is a 600hp bosche fuel pump. the rb26 has a booste sensitive fuel regulator. If i understand you, i need to know the recommended fuel pressure for the injectors then make sure my system is set to that ... or SDS will not be right? What will not be right duty cycle?

[Scottie-GNZ]

That's correct. Someone else asked the same question. Most aftermarket injs are flow rated at 43# (3-bar) and a lot factory setups are 36#. If you told the SDS the injs flowed 680cc and your FP was set to 36#, the 680cc injs would be flowing about 620cc and the fueling would be off. Remember that all SDS fueling is dependent on an accurate base number derived from inj flow rate and cyl displacement (see matrix above). Be sure to set the FP at idle with the line off and capped to retain a smooth idle. You will see pressure drop when the line is connected and that is OK.

[stony]

scottie you still running SDS or did you go with something else?

[Scottie-GNZ]

Stock Buick ECM, an open-loop chip that has a little adjustability and an add-on datalogger.