Engine feels "flat" in mid to high RPM

[Junkyardspecial]

So Ive been tuning via SAFC(I know it blows dont have to tell me twice), and a Dsmlogger tool. I have been running rich according to wideband and o2 voltage. Im trying to lean it a small bit on the mid range because when I get to about 3500-redline The car feels like I hit a wall. I am running 550cc injectors and rewired 255 fuel pump.

My fuel trims are only low 80%'s and im showing next to near 0 knock unless I shift or if I cruise at 3k in 5th. Ive tried to adjust the SAFC down but it seems to still effect the 3-5th gear WOT. when I launch in 1st now I get sideways which is a huge improvement.

My boost leak test was negative and im not really sure if I should keep giving the safc more 1% increments or less air... Everything says I should but I am skeptical to keep trying. Any tuning gurus would be lovely!

 

[genegoesfast]

What's your AFR during the wot pulls? Timing? How much boost are you running? You might just be feeling a boost spike when you initially get in it and then it levels off?

 

[cliffkemp]

So Ive been tuning via SAFC(I know it blows dont have to tell me twice), and a Dsmlogger tool. I have been running rich according to wideband and o2 voltage. Im trying to lean it a small bit on the mid range because when I get to about 3500-redline The car feels like I hit a wall. I am running 550cc injectors and rewired 255 fuel pump.

My fuel trims are only low 80%'s and im showing next to near 0 knock unless I shift or if I cruise at 3k in 5th. Ive tried to adjust the SAFC down but it seems to still effect the 3-5th gear WOT. when I launch in 1st now I get sideways which is a huge improvement.

My boost leak test was negative and im not really sure if I should keep giving the safc more 1% increments or less air... Everything says I should but I am skeptical to keep trying. Any tuning gurus would be lovely!

Here is my question to you on this.... What does your power curve look like? If you have a similar one to mine, you have more tq than hp by a good bit unless you have mods that favor topend heavily like intake, cams, and such. My car has 312 awtq but only 280awhp. It will feel like you are hauling then, level out to redline.... It feels just like a 95 camaro with 275hp and 325 tq. If you have a curve that is opposite than could be a mechanical problem but not sure what at the moment.

 

[schroder]

Since you're not showing knock, just keep pulling out fuel slowly. Also, what turbo and psi, intercooler, piping sizes, exhaust work...there's alot that goes into a set up that can keep it from performing.

 

[Junkyardspecial]

Mods are listed in my profile. Im running a big 16g with 18psi boost spikes 20, so not much there. I will keep toying with it tonight, I just put new plugs in with correct gap .28.

Relooking at my log the ONLY time I show knock is when I try to mash the gas in 5th gear and it kind of slowly accels at 3-3500 rpm. But its only 3-5 knock(on the dsmlogger scale) Ive adjusted that rpm to stay a tad richer so its safer. My A/F was .80 volts across at WOT I use this because it seems much more accurate that the A/f number Its an old wideband and I hate it. When I shift into 4th it jumps a bit to .84 then settles to .80. Timing stays at 16-20 across WOT as well.

maybe I am just crazy, maybe it was super warm today, I dont know tonight should have more results.

 

[cliffkemp]

Mods are listed in my profile. Im running a big 16g with 18psi boost spikes 20, so not much there. I will keep toying with it tonight, I just put new plugs in with correct gap .28.

Relooking at my log the ONLY time I show knock is when I try to mash the gas in 5th gear and it kind of slowly accels at 3-3500 rpm. But its only 3-5 knock(on the dsmlogger scale) Ive adjusted that rpm to stay a tad richer so its safer. My A/F was .80 volts across at WOT I use this because it seems much more accurate that the A/f number Its an old wideband and I hate it. When I shift into 4th it jumps a bit to .84 then settles to .80. Timing stays at 16-20 across WOT as well.

maybe I am just crazy, maybe it was super warm today, I dont know tonight should have more results.

I would go 25 on your gap. they increase rapidly with that kind of boost. I run 21 on my small 16g and it will sputter a little within a 1000 miles or less if I gap at .028. I have owned many of these cars and the engines are torquey. Running a big 16 at that boost on a hot day will soak that SMIC. I have a front mount and it does not like the heat that much. I would check your fuel injector connections as under that kind of acceleration, they could come slightly loose and cause issues. With the heat and the kind of boost you are running, it sounds like what I said earlier. Big 16s are not efficient in higher rpms as they generate a lot of heat as the compressor maps shows. I would have it dyno tuned as I did mine so you know what you are putting down. I bet you will see that you have gobs of tq by 3600 and about 10% or so, less hp around 6500. My car feels the same way and worse on a hot day.

 

[Junkyardspecial]

Hmm thanks for the explanation, I have leaned it out slightly and it feels good now, Its a bit sluggish still, feelsl ike from 5500 onward it takes forever to get to redline so I shift early.

 

[cliffkemp]

It may not be knock. Sounds more like a misfire that is mistaken as a knock. Gap the plugs lower and it should fix that. I have had that happen to me a few times before. I would check your manifold-to-turbo bolts too. If any come loose, it can cause issues as well. I just had an issue with that due to improper torque on the bolts by a shop. So far, after retorquing them, no issues on that but, have a blowoff valve going bad so cannot boost over 15 consistantly now but, not that bad either.

When you did your boost test, did you do a leakdown test as well? Unless you have changed your TB, it could have small seal leaks. More than likely, you would catch it in the boost test but, not always.

What does your afr meter say when at idle? What does the boost gauge say at idle?

 

[Junkyardspecial]

The car is pulling much much better now, I leaned it out to .86v across at WOT now. I have yet to gap plugs smaller, ill do that later after it rains. I did a boost test and a compression test two weeks ago, both were good. I idle a bit more lean and i boost -20lbs at idle with no surges. Im thinking if i gap plugs tighter it might give me that small bit more im looking for. Ill do .28 down to .25

EDIT: I ran my plugs at 25 then 21. The car idles and accelerates at low throttle and high throttle so much nicer now. I wonder if I was getting blow out at .28

 

[cliffkemp]

The car is pulling much much better now, I leaned it out to .86v across at WOT now. I have yet to gap plugs smaller, ill do that later after it rains. I did a boost test and a compression test two weeks ago, both were good. I idle a bit more lean and i boost -20lbs at idle with no surges. Im thinking if i gap plugs tighter it might give me that small bit more im looking for. Ill do .28 down to .25

EDIT: I ran my plugs at 25 then 21. The car idles and accelerates at low throttle and high throttle so much nicer now. I wonder if I was getting blow out at .28

very possible. My car does not like the stock gap with 20psi. amazing how much it can change just by changing the gap. It puts less stress on your coil too. I have heard/read that some with over 500hp gap less than 20. I am going to have to do the same with my rx8 as the coils are not the strongest part of the car. They have a 48 gap with iridium plugs. Going to go 42 or so.

Glad to hear your car is running better now.

 

[Junkyardspecial]

Yeah, a .04 inch difference means a huge difference. This is why I love cars and working on them.