Injector placement ?

[Beagle]

Some of you guys were chatting about injector placement a while back and I got a little confused. The comment that got me was intentionally putting the injectors higher on the runner instead of at the port and I'm wondering why? Other than cooling the air charge maybe, I'm unclear on the theory.

care to share?

[Bob Holmes]

Our experience has been that it provided an increase in torque across the board. However the port entrance placement proved more controllable.

But our engine is a rather specialized piece meant for a very narrow performance band.

[BOSSMAN]

Theory should still be the same but from an induction standpoint there are alot of variables to where they may work better at a different position. Better to say depends on the application......

[dieselgeek]

I vote to aim them at the valve on a streetable engine, keeping them "down low." By running them high you can get in a situation where drivability and idle are badly compromised. It's almost not worth the few percent gain you *might* see, plus if you put them up high I think you'd need to be able to tune individual AFRs on an engine dyno, which is pricey - for a few percent power gain.

[CDMBill]

Sometimes 'conventional wisdom' is based in fact and practice. The OEM's are getting great power and mileage out their hi-po engines these days and they have uniformly stuck to injectors that are at the cylinder head end of the intake manifold. F1 cars on he other hand have the injectors well above the intake throat. Horses for courses.

The EFI fueled mountain motors have the injectors slightly higher than midway up the runners under each 1800 CFM throttle bore. For a street strip car keep the injectors as da 'Geek described.

[boxer3main]

those run on pulse.

for a screamer like f1, back them away..timing is useless in ecm games of nerdy theories.
you big blocks should be benefitting right at the head.

I still can't find any combo for a 2.65 inch stroke, sharing one runner....I just let it draft.

[Beagle]

those run on pulse.

for a screamer like f1, back them away..timing is useless in ecm games of nerdy theories.
you big blocks should be benefitting right at the head.

I still can't find any combo for a 2.65 inch stroke, sharing one runner....I just let it draft.

4 x 24# at 40 psi will cover 150hp... one per side? They put them in 460's... megasquirt, any modern 4 cylinder TB will be plenty but an old Mustang V8 throttle body can be found with TPS for 20 bucks with plenum, would give you something to "adapt" with?



Part of the reason I was asking this question is thinking about turbo or nitrous setup where you might put a secondary driver and place supplemental injectores higher up stream? Seems like more of a pain to tune. Just thinking out of my butt random question. Thanks for the responses guys!

[dieselgeek]

4 x 24# at 40 psi will cover 150hp... one per side? They put them in 460's... megasquirt, any modern 4 cylinder TB will be plenty but an old Mustang V8 throttle body can be found with TPS for 20 bucks with plenum, would give you something to "adapt" with?

Part of the reason I was asking this question is thinking about turbo or nitrous setup where you might put a secondary driver and place supplemental injectores higher up stream? Seems like more of a pain to tune. Just thinking out of my butt random question. Thanks for the responses guys!

Placing upstream supplemental injectors works great. It's the primaries that do most of the work at part throttle that you want to have positioned properly. Once the air is really flowing, say in a turbo app where you stage a second set of injectors with boost - you can put them almost anywhere.

[Bob Holmes]

I was just looking at a cutaway of a new small displacement turbo engine. First set of injectors were DI, second set were up the intake runners quite a bit.

[JeffMcKC]

Mount them low for normal driving, I raised mine and have a reversion hole at 2500 to 2800 or so. Mount the secondary ones higher to cool the intake charge better. Heck I would make a E-85 tank to run them off stand alone