Injector Flow Variance - Miata Turbo Forum -Boost cars, acquire cats.

Welcome to   Members

Engine Performance This section is for discussion on all engine building related questions. KMiata

LinkBack Thread Tools Search this Thread
Old 07-21-2012, 07:30 PM   #1
Senior Member
Thread Starter
iTrader: (2)
Join Date: Jun 2007
Location: Shalimar, FL
Posts: 965
Total Cats: 7
Default Injector Flow Variance

Just got my rx-7 550s back from DW and this time the spread has increased -- looking at 4% for low and 2.5% for high duty cycles. What's the rule of thumb here for what is considered acceptable?

By my math I'd be looking at .2 to .5 point difference AFR from the leanest to the richest cylinder at worst case under high load. Obviously under cruise conditions it isn't a big deal. It has been pointed out to me that the differences in air mass getting to each cylinder will likely exceed that of the injector flow rates. My gut feeling is that this spread isn't a big deal -- then again, running one cylinder at 12.0 AFR and the other three at 11.5 with a gauge readout of 11.6 seems like risky business.

What are your thoughts MT?

Attached Thumbnails
Injector Flow Variance-2012-07-21%25252018.14.10.jpg  
messiahx is offline   Reply With Quote
Old 07-21-2012, 10:54 PM   #2
Elite Member
iTrader: (1)
Leafy's Avatar
Join Date: Jun 2012
Location: woosta, ma
Posts: 8,536
Total Cats: 87

Depends how close to the limit you want to tune it. If you're an average joe running a safe street tune thats more than fine. If you're running for a national championship and fractions of a hp matter then you need to get them flow matched.
Leafy is offline   Reply With Quote
Old 07-21-2012, 10:56 PM   #3
Senior Member
iTrader: (8)
Join Date: Jun 2010
Location: Navarre, FL
Posts: 1,127
Total Cats: 38

Any sort of flow info on the stock intake manifold and its variance per cylinder?
aaronc7 is offline   Reply With Quote
Old 07-21-2012, 11:32 PM   #4
Senior Member
Thread Starter
iTrader: (2)
Join Date: Jun 2007
Location: Shalimar, FL
Posts: 965
Total Cats: 7

I intend to get as close as my fuel system will take me to 300whp on a 2871R. The injectors will probably see a base rail pressure of 55-60psi, the effects of which I don't know for sure as far as the spread goes. To me it's looking like I will have to target a 11.2ish AFR in boost/under load to be safe across all cylinders, which means I will be giving up a bit of power even on a moderate tune.

+1 on aaronc7's question, could help with injector placement.
messiahx is offline   Reply With Quote
Old 07-21-2012, 11:59 PM   #5
Free Moustache Rides
iTrader: (8)
matthewdesigns's Avatar
Join Date: Jun 2008
Location: Colorado Springs
Posts: 1,621
Total Cats: 42

Does MS allow you to fire injectors individually? If so run the car on one cylinder at a time and tune AFR for the lowest flowing cylinder. If you had enough time on your hands you could potentially figure out if there is any difference in runner flow and match the injectors accordingly.
matthewdesigns is offline   Reply With Quote
Old 07-22-2012, 12:12 AM   #6
Elite Member
iTrader: (46)
Stein's Avatar
Join Date: Dec 2007
Location: Nebraska
Posts: 4,813
Total Cats: 138

I assume it would make sense to put the "richest" one in #4 as it tends to run hotter unless you have a reroute?

Question for the masses: Is there any other rhyme or reason as to which cylinders typically run richer or leaner? I'd guess if you have a spread in the injectors you can at least use it to your advantage.
Stein is offline   Reply With Quote

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 52 08-28-2016 04:18 AM
Changing from 460cc to flow force 610cc in diypnp 90 Turbo MEGAsquirt 19 10-19-2015 03:23 PM
Going back to stock. Need some 1.6 parts. Trent WTB 2 10-01-2015 12:15 PM
Time to start learning and play with tuning The Gleas MEGAsquirt 3 10-01-2015 09:30 AM
1996 Turbo Build Goldwar DIY Turbo Discussion 2 09-29-2015 09:20 AM

Thread Tools Search this Thread
Search this Thread:

Advanced Search

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 On
Pingbacks are On
Refbacks are On

All times are GMT -4. The time now is 08:13 AM.