17.5lb or 19lb injectors?

[RobertK]

Considering my recent problems I'm trying to decide which injectors to replace my handme down 19lbers with.

A set of 19lb Design III Bosch injectors or a set 17.5lb bosch injectors.

BTW.. Do the M50 17.5lb injectors drop right in like the 19lb injectors do?

[zaust]

Should be the same..just different colours

[RobertK]

Anyone else want to chime in?

[winstontj]

Considering my recent problems I'm trying to decide which injectors to replace my handme down 19lbers with.

A set of 19lb Design III Bosch injectors or a set 17.5lb bosch injectors.

BTW.. Do the M50 17.5lb injectors drop right in like the 19lb injectors do?

new to this and I don't know your situation buy why would you drop down or go up from stock???

You want to stay within a certain duty cycle given your cars setup. Going bigger won't always give you what you want. If you provide a little background I'll be happy to make a reccomendation - OR for a little education on injector selection hop over to the megasquirt forum (www.msefi.com) and read up on injectors, duty cycles, fuel pressures & how to choose what's best for your application....

I'd stick with stock BMW parts unless you have a reason to switch but that's just me.

[SchnellerVert]

http://www.witchhunter.com/index.php4

There rates have gone up but there is a lot of good info here. I have seen VW VR6 injectors used too.

[RobertK]

Alot of people switch from stock because BMW used 14lb 1 pintle design injectors. Ihave the M30 AFM upgrade so I went with the 19lb injector like everyone else. I honestly believe that 19lb is a bit much but I thought I remembered reading that another member used 17.5lb 4 pintle injectors from either a M50 or S14 but I cannot remember nor do I know the difference.

[SchnellerVert]

S14 has higher injection rates, I thought.

[nando]

the M50 injectors swap right in. they are a good middle ground between stock and 19#

[MrK]

I'd go for 17.5lbers for an m20 as well. Plenty of flow for even a 2.7 stroker. Any more than that is overkill IMO. I speak from experience.

[winstontj]

Again I would direct you back to duty cycle. Here is a flow rate calculator based on generic # of cylinders and HP @ flywheel (http://www.megamanual.com/v22manual/minj.htm#size). My e30 has uprated injectors (no idea which ones) but it came with a dyno sheet stating 178rwhp. Calculate in 20% loss in drivetrain (could be too liberal) and I estimate I have 213.6hp at flywheel (call it 210hp). Per the calculator I should be using ~20.5lb/hr injectors. I have no idea what your setup is but going to a ~19lb/hr injector seems reasonable if you have done some work to the car. You want to be between 80-85% duty cycle (meaning that the injectors only squirt 80-85% of the time or are closed 15-20% of the time.

Don't rule out other cars either. BMW doesn't make injectors, they only buy and sell them. We're talking about stock Bosch parts so keep in mind some Volvo 240's (and 240turbo), Mercedes, other BM's like the m30, VW's, Audi's etc. Driving style has a lot to do with it too. I like to keep my injectors down to about 80% because I have been known to drive like a jackass and when I need the fuel I don't want to be at the limits and push mid 90's% duty cycle. I'd rather be high (78+%) when my girlfriend is driving and when I drive it'll at most get up to low 90's (below 93%).

Maybe this isn't the answer you are looking for... Not sure but I'm really new & green when it comes to M20's so I hope this does you some good.

Best of luck and if you wouldn't mind could you post up what you end up going with as well as some of the mods you've done and a realistic rough estimate HP you think you are getting?

Thanks,
TJW

[SchnellerVert]

The volvo turbo ones are high rates like the M3 Evo II. I have seen a few member on the uk board using them.