Bigger pipes & ultra-flows killed torque...

[beanhead]

..but ma they sound sweet! okay seriously though, after making the exhaust switch I have lost a noticeable amount of get up in the lower and mid-range yeah... What do I need to do to get this back, as I'm sure it's a matter of retuning.. Right? 440, somewhere between 9 and 10 to 1 compression, xe274 cam, inch and 7/8 headers, 850 demon jetted 85 93, 2500 stall to 3.73 gears, Edelbrock RPM heads
Forgot to add..firecore distributor/2 blue springs, 22° initial/37° without vacuum advance connected

 

[1967coronet440]

Odd... could the new exhaust set up be to open, Are you sure you’re not spinning?

 

[moes]

found this on a chevy site, it good reading about exhausts. I learned alot from it.

http://www.superchevy.com/how-to/exhaust/0505phr-exh/

 

[aeon280]

Had this happen on my daily driver. 2010 Nissan frontier. Had the 2 in to 1 y pipe cut out and went true dual,s into a Magnaflow xpipe muffler. Killed my low end torque out of the hole. After putting a hypertech tuner with 91 octane tune I have the low end back. Reducing backpressure in NA engines can it seems have an impact on the torque curve.

 

[beanhead]

I have made some minor adjustments to timing and float levels, but I'm thinking to get this thing back to neck-snapping between 1000-3500 rpm maybe I need to get into the carb for re-jetting or alter the distributor curve? Not sure where to start at this point...it used to be much more fun without having to floor it... I would think I should be able to make it work with the more free-flowing exhaust as I know many of you guys use a similar setup

 

[lewtot184]

..but ma they sound sweet! okay seriously though, after making the exhaust switch I have lost a noticeable amount of get up in the lower and mid-range yeah... What do I need to do to get this back, as I'm sure it's a matter of retuning.. Right? 440, somewhere between 9 and 10 to 1 compression, xe274 cam, inch and 7/8 headers, 850 demon jetted 85 93, 2500 stall to 3.73 gears, Edelbrock RPM heads
Forgot to add..firecore distributor/2 blue springs, 22° initial/37° without vacuum advance connected

what size are the bigger pipes? whats the ignition curve with "2 blue springs"? what intake manifold? why 85/93 jets?

 

[Jcharger]

Interesting read and observation. I would just make sure you have not changed your flow such that you are out of the optimal A/F mixture range.

 

[beanhead]

what size are the bigger pipes? whats the ignition curve with "2 blue springs"? what intake manifold? why 85/93 jets?

Went from 2-1/2" & super turbos to 3" pipes/ultraflows..performer RPM intake..the 85/93 jets are what was on outta the box, worked well so I didn't mess with them before..advance now starts 1800 all in at about 3000

 

[beanhead]

Interesting read and observation. I would just make sure you have not changed your flow such that you are out of the optimal A/F mixture range.

I'm suspecting this to be the case... But shouldn't I be able to recalibrate to get it back where I want it. I'm doubting that it's too big an exhaust for my setup and cubic inches? But maybe I'm wrong, it's definitely lost a little burst on the street..

 

[lewtot184]

I looked at some factory demon jetting for 850's. the one you have seems to be butt ugly rich. that will definitely kill torque off. I run 3'' pipes and 2" headers and know they are a little big for what I do, but I couldn't stand much more low or mid-range torque. keep the pipes and go after the carb.

 

[HEMI-ITIS]

Does it smell fat when you stand behind the car? I would also consider take a little timing out..........

 

[beanhead]

Does it smell fat when you stand behind the car? I would also consider take a little timing out..........

Somewhat, not an eye-burner though... I can try dialing the timing back a little too

 

[oldbee]

So we all agree, it's all a balancing act. What talks good isn't always the right to go. ( carb too rich!)

 

[HEMI-ITIS]

When you retard the timing it might fatten up,so take 2* out and road test.Then take 2 jet #s out front and back.Do you have any way to read the AFRs??If not the only way is a plug reading clicking the key of at the top of 2nd and roll into a safe place.Let it cool off some and read a few spark plugs.I keep 4 plugs on the floor behind my seat so I can pull 2 on each side and put the spares in so I can have a group consult.

 

[moper]

If it was me I'd quicken the advance. Get it all in by 2500. Add the vacuum advance if the distributor has one. Then work on tuning the carb because it's fat. Always do timing first, then carb. Start with power valve and jetting. As it's a Demon I'd also pull it all apart and make sure there are no bits of metal, or "hanging chads" on the metering blocks. When the jetting and PV are good, look into the accelerator pump squirtor. It all has to work together, and Demons can be finicky. So you have ot be equally finicky and persistent.

 

[beanhead]

When you retard the timing it might fatten up,so take 2* out and road test.Then take 2 jet #s out front and back.Do you have any way to read the AFRs??If not the only way is a plug reading clicking the key of at the top of 2nd and roll into a safe place.Let it cool off some and read a few spark plugs.I keep 4 plugs on the floor behind my seat so I can pull 2 on each side and put the spares in so I can have a group consult.

If it was me I'd quicken the advance. Get it all in by 2500. Add the vacuum advance if the distributor has one. Then work on tuning the carb because it's fat. Always do timing first, then carb. Start with power valve and jetting. As it's a Demon I'd also pull it all apart and make sure there are no bits of metal, or "hanging chads" on the metering blocks. When the jetting and PV are good, look into the accelerator pump squirtor. It all has to work together, and Demons can be finicky. So you have ot be equally finicky and persistent.

Thanks a lot guys, this is good stuff...I don't have an a/f gauge buuut there's lots of lonely roads very close by! I monkeyed with it a little today, first hooked up my vacuum advance and that seemed to help. Then backed off a little timing, didn't notice any difference..lowered the floats a teeny bit more all that did was give me a bog/hesitation if I gave it too quick a throttle hit. Put them back (primary at the bottom line, secondary closer to the middle line)and it was lugging a little idling in gear (E-brake on in the driveway)... that could be the warmer temps today too, I was driving and tuning and things were getting pretty hot, engine temp was at 200 which is only slightly hotter than normal but I'm sure the gas in the bowls was cooking...I did rebuild this carb a few months ago, douched it out real good so the passages should be ok. (I do remember getting a couple of small flecks of metal out--it's not a myth!) I plan to get it back where I started today and try to add one lighter spring, as it seems that it likes the extra timing down low that the vac advance gave, then adjust the fuel again..

 

[moparcrazy]

..but ma they sound sweet! okay seriously though, after making the exhaust switch I have lost a noticeable amount of get up in the lower and mid-range yeah... What do I need to do to get this back, as I'm sure it's a matter of retuning.. Right? 440, somewhere between 9 and 10 to 1 compression, xe274 cam, inch and 7/8 headers, 850 demon jetted 85 93, 2500 stall to 3.73 gears, Edelbrock RPM heads
Forgot to add..firecore distributor/2 blue springs, 22° initial/37° without vacuum advance connected

What's your Fuel Pressure @ idle & @ WOT??, AFR !! Gotta Have it Dude or your chancing your tail, Chasing Sorry.

 

[HEMI-ITIS]

Either you need to get a logger,or get on a chassis dyno,,,,or go to the track so you can read plugs and actually see if your adjustments are doing anything! My *** dyno makes me smile,but it LIES!!!!

 

[beanhead]

Thanks guys well I'm looking into the meters. One thing I did find, is the new Summit PCV was not flowing causing the poor idle... Put my old valve back on and cured that part at least..

 

[moes]

check this one out, installed it on my car and it works great, no free air sensor calibration required - ever and if you sell your car you can transfer it to your next car, just install a plug in the bung when you remove the 02 sensor.

https://www.ebay.com/itm/AEM-30-411...ash=item3ce6dec863:g:NCIAAOSw0HVWDxGI&vxp=mtr