A Little Top End Tuning Help Please

[kidturbo]

Hi guys got the LLY back in our boat and she is hauling A$$ again. Now trying to break 100mph without smoking the new pistons. But I've hit a wall now around 3600rpm, or 85mph and could use some advice on timing and PW values.

The current fuel system build is a single CP3 with 50% over injectors, all the larger rail fittings and electric lift pump. Have a good custom tune from Nick that needs just a bit more tweaking. My fuel pressure is tracking within requested levels, so I don't think its running out of fuel yet. Just not pulling on up to 4000 R's like I need to see with the prop I use for top end speed.

The data [image below] shows where she is running out of power:
3600rpm, 26minjt deg, 2000us, 102.7mm3 and 160mpa frpact, with the EGT's touching 1500deg and holding steady there.

I created a new dsp position keeping everything at this same level then bumped the max pulse up to 2250us. I left timing alone since it computed to about 55-60% btdc in this rpm and pw. Changes didn't help much, fuel pressure fell off by about 2000psi under requested and EGT's jumped to 1600deg before I lifted at 3500. So I'm guessing the single CP3 is about topped out, and she is obviously burning more fuel in the pipes at 2250us.

Since I can't add more air to cool it [non-vgt 4094R turbo] what options do I have to build rev's up this high? I know the turbo can handle the heat above 1600, I've sustained above that for a minute or more in the past. But would rather not hang there again since the old stock pistons didn't seem to like it. New pistons dropped compression to 16.4 but she still has stock rods, so I've been attempting to error on the side heat vs pressures moving up.

Thinking my best option is to bring the pw back down to 2000us and add a couple more deg of timing? Or should I leave the PW higher and add the timing, allowing fuel pressure to tale off? Looking for the safe timing number up there to build a little more top end power and back off these EGT's?

On a side note, I usually run about a B50 biodiesel blend, typically you need a little less advance than on D1 cause it burns quicker. Would really be nice to see the cylinder pressures I'm hitting, anyone have a probe I could borrow?

Thanks for any advice.

-K

 

[SSchmi5519]

Bumping the uS up, without also upping timing, not only adds more fuel (duration wise), but also increases the amount of time until you begin injecting the fuel, which you are already injecting too late.

 

[x MadMAX DIESEL]

Bumping the uS up, without also upping timing, not only adds more fuel (duration wise), but also increases the amount of time until you begin injecting the fuel, which you are already injecting too late.

how much timing do you need at that rpm then? I run 26 there also but with more us

 

[catman3126]

do you have your TBIQ table extended out to the desired rpm you are trying to achieve? stock tune only fuels to 3600, copy and past the 3600 row in to the higher rpm rows unless that is already done and also what do you have the rev limiter set at? mine is at 4400 and my TBIQ table goes to 4200rpm.

 

[catman3126]

also higher rpm requires higher timing, i run 28deg on my hot tune with the max timing table set to 28deg also i have been running 28 deg and 3150US for 2.5 years and have not bent rods or melted pistons yet. 2250us should not get that hot really and a little more timing will help keep the fuel in the chamber and should help with egt's seems odd you would be getting that hot with only 2250us.

 

[kidturbo]

Bumping the uS up, without also upping timing, not only adds more fuel (duration wise), but also increases the amount of time until you begin injecting the fuel, which you are already injecting too late.

I'd tend to agree with ya here. The original data in dsp3 position I replaced was 28deg max and 2900us @ 150mpa. Nick had written this tune based on 50hp not 50% injectors [my bad], we considered that dsp slot to be off limits with these larger injectors. The 26 and 2000us tune slot runs sweeeet with the +50% sticks...

So do you think 28deg @ 2250us would be enough to compensate? That's gonna put me over 60% btdc at 3600R's.

do you have your TBIQ table extended out to the desired rpm you are trying to achieve? stock tune only fuels to 3600, copy and past the 3600 row in to the higher rpm rows unless that is already done and also what do you have the rev limiter set at? mine is at 4400 and my TBIQ table goes to 4200rpm.

Mine is same as yours, 4400 and TBIQ to 4200. Max TBIQ is 110mm3, is there any possible gain to raising that value? See where EFI max is 200 in TBIQ, but every other table is 110 for the bottom line?

That 3100us you run is on stock injectors correct?

-K

P.S. I swapped out the prop today for a smaller pitch, which will turn less speed at higher rev's just to verify it's power related not being rev limited by tune. Will update later.

 

[catman3126]

Yes mine is with stock injectors, and no I don't think there would be any advantage to doing 200 in the tbiq table. so are you thinking that the prop is holding the engine back from turning more then 3550? and I didnt relize you were running bigger injectors so I wouldnt go more timing either. My bad. so are you just want to get more rpm?

 

[kidturbo]

Yeah it's all about the max revs and power range vs prop pitch.

Lowering the pitch # moves the power range up in the revs, but lowers the potential top speed by engine red line. Much like axle ratio's, 35 pitch would be somewhere around 3.27's, was a 37 pitch in the data log above. Airplane gears, so ya need enough high rpm hp to overcome drag.

From 40 to 80mph she's a clean burning rocket ship, then peaks out on the power range. I need a little boost, literally..

-K

 

[catman3126]

Have you tried adding a couple degrees of timing in the corresponding cells where the power is dropping off? Bump it up a deg and see if it helps, but just in those 3600 and up at max fuel. It might help your egts too.

 

[kidturbo]

After a couple runs today on the other prop I noticed a couple things. First going with the lower pitch didn't help with rev's. Still peaked out at 3600 R's. However with this prop logging showed actual fuel pressure started dropping off faster after a couple seconds at WOT on the 2000us PW tune.

Requested FP was 24k and it was only holding 21k at 102mm3. I bumped it up to the 2250us tune again for a quick reality check and it fell off to 18-19k in the same RPM range... Anyone know what's an acceptable difference up there?? It didn't limp, but I have a pretty wide tolerance set for that.

I also made one run with stock GM calibrations. It maxed out at 1450us, 94mm3, and 16deg advance, she fell flat at 3300 RPM's. While EGT's never broke the 1100F barrier, fuel pressure tracked perfectly against requested.

So what you guys think? Maxing out or issues with the CP3?

Catman, I changed that advance curve to 28deg from 3600 up but forgot to load the tune today. Will give it a shot later this week as the next step.

Thanks

-K

 

[catman3126]

Cool it would be interesting to see if that helps but sounds like fuel pressure is falling off a little too much to me, what CP3 are you running again? And from what I have been told a stock LLY cp3 with 40% or bigger will not move enough fuel. might look into a LBZ CP3 and fpr. and then retune for it.

 

[kidturbo]

It's a stock LLY pump, only mod is larger fuel inlet fitting which makes no difference in my view. Gonna mod the regulator and mechanical lift pump when I get time to see if it helps hold pressure up top.

For now looks like I'll concentrate on getting the water/methanol injection on it to lower EGT's and maybe that will boost the R's a little also. Will let ya know how that 28* tune works after this weekend.

-K

 

[THEFERMANATOR]

Did you port the heads at all? Sounds like you are hitting an airflow barrier to me if stock is hitting 3350, but 2200 is only hitting 3600RPM's.

 

[catman3126]

Yeah might need a aftermarket cam too down the road.

 

[kidturbo]

Heads have not been ported. Ya think they could be a restriction?

It feels like it could pull more, but is just out of air flow or camshaft at that RPM. Reason I'm looking for someone who is turning 4k plus to chime in. The drag on a boat would be about equal to pulling a 6000lb trailer up a never ending hill, without downshifting..

Here is that log of the 2250us changes with the 2 sizes lower pitch prop. You can see she is peaked out on fuel pressure, but it still flattened at the same rev's. She is actually moving less air with the added fuel at the same RPM. Nothing that's been done like manifolds, intake, or injectors has raised that redline beyond what the original stock Dmax would turn.

-K

 

[GMC_2002_Dmax]

Drop the PW to 1800 and raise rail PSI desired to 175-180 MPA, see if lower PW and more pressure helps.

Also I hope you shut pilot injection off above 2600 rpms......

 

[THEFERMANATOR]

Personally to me it sounds like you are out of air, and the heads very well could be why. At higher RPM's, you need larger ports to move the air in the shorter amount of time so porting comes into play above 3200 or so. And a cam wouldn't hurt to get the higher RPM powerband.

 

[Stingpuller]

Rpm

Ken I wouldn't waste your money on ported heads! You will see very,very little for the cost. A cam pretty much nets the same results as heads. I have talked to Zach at hamilton cams and he seems to be on the right track with cams so I might try on of his this winter and see if there any better than what's out there now. If you need more rpm you just simply need more air! You need a bigger turbo and get away from the toy you have now. That turbo runs hot (egt's) and you will gain from a turbo swap than anything listed. You also need to not be affraid of more timing in the upper rpm range. I need to come down and take a ride and play a little.

 

[kidturbo]

LOL.... Finally someone I know who is turning 4k. Gotta agree it should take more air if I force feed it. Would ya happen to have a big GT4 laying around I could borrow for a weekend??

Thing pulls from 2600-3600 in like 4 seconds, then it's just like ya hit a rev limiter, without the bouncing or missfire effects. If it wasn't turbo charged I'd say it's camshaft limited for sure. Just crazy torque then BAM, your done. Trim it all the way up, toss the anchor and wife overboard, nothing makes a bit of difference. I' have tune ready with 29* advance curve that I'm gonna try Friday. Will see.

Gonna be on the river in the Marietta pool all weekend if you get board, come on down and play.

-K

 

[catman3126]

Any luck yet?