hey grumpy do I need bigger injectors?



hey grumpy do I need bigger injectors?

Postby grumpyvette » October 11th, 2011, 6:08 pm

"I swapped my stock 350 engine for a 383 with bigger heads and a bigger cam and re-installed my old TPI intake and stock injectors and its just not running correctly, any ideas ?"?



obviously you need to check for vacuum leaks bad electrical connections, faulty ignition timing curves a badly adjusted CPU or low fuel pressure and any mechanical or electrical issues first,and verify every system is working correctly, that theres no mechanical issues like a cam installed incorrectly or a worn cam lobe, low fuel pressure a defective injector, a broken piston ring, a restrictive exhaust,
Id suggest pulling trouble codes and doing a compression check and verifying the ignition advance etc
your horsepower is based on how much fuel/air mix you can efficiently burn per second, you'll burn about 12-15 pounds of air per pound of fuel, all modifications that increase power concentrate either on increasing efficiency like increasing compression or reducing friction , or increasing exhaust scavenging or on burning a greater amount of that fuel/air mix per revolution, such as increased displacement or packing the cylinders with higher pressure like a super charger or a turbo, or increasing the number of power strokes per second, like with longer duration cams,
the most common reason , a new 383 stroker,with a larger duration cam, installed in place of a stock 350 sbc won,t run as expected is failure to realize the new engine combo will need to run at a higher average rpm, and it will require noticeably more air and fuel to make that extra hp,if you just went from 240hp in a stock TPI and built a 470 hp 383 thats a 100% increase in hp it only makes sense that the injector size must jump up to almost double the original flow rate to compensate also,
and the new cam is very likely to require a different ignition advance and CPU tune plus a higher stall converter and a 3.54:1-3.73:1 rear gear should be used so the engine can spend most of its time in the higher average rpm range the cams designed for, all the changes were made so you could burn MORE FUEL and AIR in each power stroke and have MORE power strokes per minute, one of the most common mistakes,is not swapping to a matched rear gear and higher rpm torque converter stall speed,followed buy guys not upgrading the exhaust and understanding the need to upgrade the injector size to supply the higher demands for fuel and air the new engine will maker because its going to need to be supplied with more fuel to maintain the correct fuel/air ratio.
actually 36 lb- 42 lb injectors are very commonly used on the better 383 engine builds, one of the most common problems I see is guys trying to reuse stock 24 lb injectors to build a 400hp plus engine that results in a constant lean upper rpm condition that eventually results in detonation damaging pistons but always results in lower power than expected

heres a basic chart on injector size and expected power levels reached before potential higher rpm lean condition

24 lb/hr 326 hp
30 lb/hr 408 hp
32 lb/hr 435 hp
39 lb/hr 530 hp
42 lb/hr 571 hp

watch these videos

http://www.youtube.com/watch?v=Emnax2J4FX4

http://www.youtube.com/watch?v=l2ne6AVn ... re=related

http://www.youtube.com/watch?v=aIUJbTXN ... re=related

http://www.youtube.com/watch?v=49WXmzfO ... e=youtu.be

viewtopic.php?f=32&t=3429&p=9084#p9084

HERES SOME THREADS TO HELP YOU LOCATE YOUR PROBLEM
http://forum.grumpysperformance.com/viewtopic.php?f=55&t=1200

viewtopic.php?f=44&t=38

viewtopic.php?f=32&t=596

viewtopic.php?f=44&t=773

viewtopic.php?f=80&t=728

viewtopic.php?f=32&t=168



viewtopic.php?f=44&t=5575
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

User avatar
Site Admin
Site Admin
 
Posts: 14105
Joined: September 14th, 2008, 1:40 pm
Location: florida

Return to Engine: Repairs and Modifications & generally corvette related

Who is online

Users browsing this forum: No registered users and 3 guests

cron