Top Feed Primary Fuel Injectors: remove the plastic diffusers?
 

I plan on removing them. Any good reasons not to?

I heard that you get worse gas mileage and less torque.....thats what i was told when i asked a while back.

They actually don't do much harm to airflow even tough they look like they do but they do help fuel get directed into the engine better. Somehow I can't believe that anyone with a 400+ hp car is going to be too concerned with that last little bit of gas mileage. They do act as a spacer under the injector so if you don't want to use them, you will just have to break off the fuel diverter plate from out of the airstrem. Many people run without them and it is actually debatable just how much mileage changes without them, if at all.

IIRC they help atomize fuel seeing the rotary engines require a larger than average fuel delivery. Look at it this way too. The Mazda engineers took the design of the rx7 very serious, i doubt the diffusers would be there if they didnt have a good purpose.

We have ran without them for years with no problems. The tricky part is getting a good seal down there.

Jason

fuel injector diffuser
 

I dont think the side seal like being washed down with raw gas, diffuser breaks up the fuel like atomising droplets, could wash away the lube oil! Ron

Rich,

Back in 1999, I rebuilt my engine with all new parts, including them. A year later when I went from 850 to 1200 secondaries, They were pulled in order to put in new seals. One of the three legs on the #1 was missing. That means the engine ate it! Luckily nothing was damaged. The engine ran fine without them as it does now with the Bosch 1600s.

Pull because they may damage your engine if they fail.

Chuck

Chuck, I have seen them completely break off from very large injectors before. For a 1200 or larger injector, I would definitely not use them. If this is just the primaries, it probably won't matter much but then again, better safe than sorry.

Yup, I'm not surprised. Years ago when gotham had just opened we took in a car that had mysteriously popped an engine while cruising down the road at 40 mph. Come to find out, one or more of his diffusers had broken off (they were original and very brittle) and lunched his apex seals.

I am going to be running 870 primaries and 1680 secondaries, and I have the small metal spacers that I will use while installing.

I plan to take out all 4 of them, any tips for helping to make a seal? I'm thinking of just removing the lower portion so that only the top doughnut shaped portion is left and reinstall that, as was mentioned above.

They help atomization on cold engine. Gas evaporate very easy on hot engine and they don't work hence.
The best way to make good atomization is to set turbulators into primarie ports.

That works fine.

I just finished the same install and what i did was use good silicone on the outside of spacer and used the rubber stock seal and removed the diverter as my old engine eat it. I dont no if its necessary to seal the spacer but if the injecter comes up any the o-ring seals in spacer and if spacer is sealed on the outside it should not leak. I call it insurance!

Am I understanding correctly...based on the attached picture...that this is what people are suggesting to do with the injector diffusers? Please note the secondary diffusers have been filed down but the primary have not yet.

It also should be noted that I've pulled 2 full sets of injector diffusers from 2 engines...including one with 80k miles on it...and one was broken and the others were all exceptionally brittle.

Having just acquired a single turbo setup...this is of more importance than it was a few weeks ago. :icon_tup:

^I would remove them all together. I forget the o-ring size I use for customers still using the factory primary fuel rail. What fuel setup are you going to run?

Well...originally was going to run stock injectors. I just picked up a single system so...I'm think 720's and 2000's with the FFE rails...its an Aspec 500R setup.

For the initial startup...I'll probably have the stock injectors in place. Any suggests are welcome.

The diffusers do help atomize the fuel which allows for a leaner idle mixture and also low speed drivability. I took mine out initially but then ended up getting new ones to put back. Once the airflow in the intake ports is higher the diffusers probably dont matter as much, But on the same token, the larger the primary injector the more useful they probably are since larger injectors tend to have larger fuel dropplets. Some of the newer ID style injectors do have better spray patterns so maybe in those cases its less important. I can't say with full certainty if it's better with them in or out especially with the vast array of injectors and individual driving preferences, but I chose to run them and do notice a difference in smoother idle and low speed response by having them in.

Stock injectors or old pintle-type injectors (low impedence 1680cc for example) I would consider it more important. For a newer EV14 style (ID injector etc) it's probably closer to optional.

I have stock primaries, and I'd 2000 for my 500r. I run around 16psi and have no fuel issues. I'd like to increase it to 20psi in the near future though.

my bet is they do help atomise and that's why they are in the engine... however as flow rates rise (single turbo) and brittleness (age/heat/plastic) increases i do think they become hazardous.

it is possible to offset some of the atomization loss w the newer EV14/ID injectors which have a way better spray pattern.


do retain the base to promote fuel injector seal.

hc

I have both FFE fuel rails and running ev14s. I'm wondering the same thing too about these diffusers.

Howard, I thought your findings over the winter stated that extreme cold (due to methanol and extremely high air speed lowering the ambient temp) situations led to the plastic becoming brittle and destroying engines.

Is that no longer the case?

I had a similar thread about fuel diffusers earlier this month. Still on the fence about wether I should buy ridiculously overpriced new ones or somehow leave them out (running ID's).?

Anyone make metal spacers? Too bad no one makes the whole diffuser out of metal.

CJ motorsports makes a really nice metal spacer. not a diffuser, mind you, but it is a very nice piece none the less. I have four of those, along with CJ top feed rails, and ID 725 pri and 2200 sec injectors. car runs just as well as ever.
the thought of brittle plastic in my engine scares me...lol.

Thank you very much. I'll contact them soon. Nice to here input from some one with the same setup. :)

Edit: Just to be sure, this company? http://www.cj-motorsports.com/

Yep. thats them. their website *may* be a little confusing at first, but you'll figure it out.
The nice thing is, you can buy the whole kit, or just the injector spacers (which have o-rings on them.)