Why were some characters banned? Because more fuel = more power. - Page 6 - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Front Desk Questions, suggestions, site problems? Put all your site related threads in here.

Reply
 
 
 
LinkBack Thread Tools
Old 09-20-2011, 08:13 PM   #101
Supporting Vendor
iTrader: (31)
 
Savington's Avatar
 
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 14,363
Total Cats: 1,323
Default

Quote:
Originally Posted by y8s View Post
You treasonous *****
Savington is offline   Reply With Quote
Old 09-20-2011, 08:49 PM   #102
Ben
Supporting Vendor
iTrader: (33)
 
Ben's Avatar
 
Join Date: Jul 2006
Location: atlanta-ish
Posts: 12,689
Total Cats: 99
Default

Quote:
Originally Posted by Savington View Post
So you're saying that if I had run a little less advance at 12.0:1, I could have made the same power as I made at 11.6:1?
I'm saying it's possible that 2 scenarios can make the same power
  • Scenario 1 is slightly leaner and has a little less advance
  • Scenario 2 is slightly richer and runs a little more advance
I have read arguments from respected tuners and engineers over which approach is best, but unless the car is running enduros my preferred approach is slightly rich and slightly less advance of peak torque. Most people I speak to gladly trade off a few hp for added peace of mind.
Ben is offline   Reply With Quote
Old 09-20-2011, 08:59 PM   #103
Elite Member
Thread Starter
 
Join Date: Jul 2005
Posts: 6,454
Total Cats: 80
Default

Agreed.

Quote:
Originally Posted by Sav
So you're saying that if I had run a little less advance at 12.0:1, I could have made the same power as I made at 11.6:1?
You would have MORE torque if the burn rate at 12:1 was faster than at 11.6:1. However your description sounds like 11.6:1 was faster.

Last edited by JasonC SBB; 09-20-2011 at 10:09 PM.
JasonC SBB is offline   Reply With Quote
Old 09-20-2011, 09:49 PM   #104
Elite Member
iTrader: (2)
 
Join Date: Jan 2007
Location: Los Angeles, CA
Posts: 8,782
Total Cats: 119
Default

Quote:
Originally Posted by Ben View Post
If you're just tuning for "best" AFR on the dyno, you're doing it wrong.
Assuming you're not detonation limited. Just wanted to mention the caveat
Faeflora is offline   Reply With Quote
Old 09-22-2011, 04:30 PM   #105
Junior Member
iTrader: (1)
 
Join Date: Aug 2008
Posts: 373
Total Cats: 36
Default

All other discussion aside, leaner + less advance = more higher EGT in your cornhole
JKav is offline   Reply With Quote
Old 09-22-2011, 04:46 PM   #106
y8s
2 Props,3 Dildos,& 1 Cat
iTrader: (8)
 
y8s's Avatar
 
Join Date: Jun 2005
Location: Fake Virginia
Posts: 19,038
Total Cats: 407
Default

OK Mister turbo engineer type... does that higher EGT spool your cornhole any Harder Better Faster Stronger?

Or maybe the question is: is peak cylinder pressure worth more power than high turbine inlet enthalpy?
y8s is offline   Reply With Quote
Old 09-22-2011, 04:57 PM   #107
Junior Member
iTrader: (1)
 
Join Date: Aug 2008
Posts: 373
Total Cats: 36
Default

yes, higher inlet temp for turbine will result in somewhat lower exp ratio (lower exh man press). but not enough better to be worth the much higher head temp.

example - 1.8 liter at 4000 rpm, 18 psi boost, smallish turbo, lots of assumptions (VE, i/c parameters etc etc)... assume 1600 deg F EGT and 28% flow wastegated. If EGT is increased to 1700 deg F, backpressure drops by less than 1 psi.

-1 psi not worth +100 deg EGT
JKav is offline   Reply With Quote
Old 09-22-2011, 06:33 PM   #108
Elite Member
Thread Starter
 
Join Date: Jul 2005
Posts: 6,454
Total Cats: 80
Default

Turbos aside, I do believe that fastest burn happens at some theoretical AFR (12.5:1?) which then yields lowest MBT and most torque.

Last edited by JasonC SBB; 09-22-2011 at 06:56 PM.
JasonC SBB is offline   Reply With Quote
Old 09-23-2011, 03:08 AM   #109
Supporting Vendor
iTrader: (31)
 
Savington's Avatar
 
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 14,363
Total Cats: 1,323
Default

I think burn rate is dependent on way more than just AFR (specifically, chamber turbulence has a HUGE effect).
Savington is offline   Reply With Quote
Old 09-23-2011, 11:23 AM   #110
y8s
2 Props,3 Dildos,& 1 Cat
iTrader: (8)
 
y8s's Avatar
 
Join Date: Jun 2005
Location: Fake Virginia
Posts: 19,038
Total Cats: 407
Default

Most cars can't do much about combustion chamber shape while they're running. Some can change tumble and swirl characteristics (2001 miata!) and some actually have variable chambers (Some crazy Saab motor) but I think we're comparing similar operating parameters... for example: 6000 rpm on a 99 miata motor without vvt or VTCS.

changing spark and fuel a few percent wont really affect chamber turbulence, will it?
y8s is offline   Reply With Quote
Old 09-23-2011, 12:47 PM   #111
Elite Member
Thread Starter
 
Join Date: Jul 2005
Posts: 6,454
Total Cats: 80
Default

As I said earlier
--------
The reason is that later spark (at MBT) means less work goes into compressing the charge up to TDC as the burn begins to raise cylinder pressure.

Fast burn combustion chamber design is THE main reason more modern engines make more BMEP (more torque, see my other thread ) than older (e.g. 1960s) designs. The old-school "hemi" chamber designs were bad (with domes pistons and thus an orange-peel shaped combustion chamber), later design pentroofs with narrower angles between the valves and flat-top pistons for the same compression ratio, were much better. Swirl also improves burn rate. Pentroof 4-valve combustion chambers gained as much from the fast burn chamber shape as they did from the improved hi-RPM VE. Modern LS motors show the same compact combustion chamber (short distances from the plug to the farthest corners of the chamber), as well as strong swirl.

Again for the particular motor Sav was tuning, fastest burn may have been at said indicated 11.6:1, due to perhaps an off-cal AFR gauge, lopsided injector imbalance, or huge injectors injecting short squirts at a non-optimal point in the cycle.
JasonC SBB is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 58 Yesterday 10:04 PM
1994 Spec Miata Race Car SM/SM2/SSM For Sale Quinn Cars for sale/trade 6 10-23-2016 08:58 AM
Walbro 255lph Fuel Pump $50 lsc224 Miata parts for sale/trade 2 10-01-2015 10:17 AM
"Chimney Ethanol" E100 MiataGarage Engine Performance 5 09-30-2015 12:04 AM


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 09:41 AM.