Secondary injector diffuser
03-07-10, 12:48 AM
#1
Secondary injector diffuser
I'm installing some 750cc RC secondary injectors in my 87 TII
the new injectors came with 1 green o-ring on the top, and one large black o-ring on the bottom(fits in the manifold)
my problem is with the diffusers that sit inside the manifold, the factory injectors sit inside the diffuser, and the black, larger o-ring sits above the diffuser, inside the manifold.
The RC injectors sit above the diffuser, the large black o-ring sits in the manifold, but the end of the injector does not go inside the diffuser like the factory injector. It also seems to fit together loosly like this.
Now, if I remove the diffuser, and insert a second large black o-ring inside the manifold to fill the gap the diffuser normally fills. Then install the injector, everything fits snugly, and seems to be leak proof when the fuel rail is bolted down.
Is the little plastic diffuser really required?
the new injectors came with 1 green o-ring on the top, and one large black o-ring on the bottom(fits in the manifold)
my problem is with the diffusers that sit inside the manifold, the factory injectors sit inside the diffuser, and the black, larger o-ring sits above the diffuser, inside the manifold.
The RC injectors sit above the diffuser, the large black o-ring sits in the manifold, but the end of the injector does not go inside the diffuser like the factory injector. It also seems to fit together loosly like this.
Now, if I remove the diffuser, and insert a second large black o-ring inside the manifold to fill the gap the diffuser normally fills. Then install the injector, everything fits snugly, and seems to be leak proof when the fuel rail is bolted down.
Is the little plastic diffuser really required?
03-07-10, 12:52 AM
#2
What, you mean your pintle caps dont go into the diffuser?
If that's the case, ditch the diffusers. Pintle caps aren't very thick and need an assist with a heat gun and/or a socket to be installed onto the injectors. Simply changing them out wont do but if you REALLY wanted you could buy new diffusers and bore them to size with the appropriate drill bit.
Old diffusers will probably break.
Honestly, i'm curious too if you really need them or not.
If that's the case, ditch the diffusers. Pintle caps aren't very thick and need an assist with a heat gun and/or a socket to be installed onto the injectors. Simply changing them out wont do but if you REALLY wanted you could buy new diffusers and bore them to size with the appropriate drill bit.
Old diffusers will probably break.
Honestly, i'm curious too if you really need them or not.
03-07-10, 07:48 AM
#3
I think people have had vacuum leaks or fuel leaks (maybe both) by not using the diffusers, and the diffusers are there to help disperse the fuel better. My recommendation is to find a way to use the diffusers as they were intended, but I don't know a lot about them.
03-07-10, 08:02 AM
#4
diffusers make a big difference on the primaries, not so much on the secondaries. im not running any on the secodaries without any problems
is the pintle cap hitting the diffuser? I remember on the RC 1600's i had to take a dremel to the lip of the pintle cap to get it to fit. but the RC 750's didnt have that problem
is the pintle cap hitting the diffuser? I remember on the RC 1600's i had to take a dremel to the lip of the pintle cap to get it to fit. but the RC 750's didnt have that problem
03-07-10, 09:09 AM
#5
The pintle cap on the 750's are smaller than the I.D. of the diffuser, and the large black o-ring on the 750's fits around the pintle cap with about 1/8" of pintle cap protruding.
My diffusers came out of the manifold no problem. Right now the injectors are installed without the diffusers, and they fit snugly, I highly doubt they will leak.
I can not find a way to mount the 750's, and use the diffusers, feeling confident they won't leak. There is just to much play in the injector after it's bolted up.
I'll take some pics later and post them.
My diffusers came out of the manifold no problem. Right now the injectors are installed without the diffusers, and they fit snugly, I highly doubt they will leak.
I can not find a way to mount the 750's, and use the diffusers, feeling confident they won't leak. There is just to much play in the injector after it's bolted up.
I'll take some pics later and post them.
03-07-10, 09:32 AM
#6
talking head
you get the same issue with the rochy/multechs injectors
these are disc type injectors so dont actually need the atomiser under the injector for pattern diffusion
( so the brittle bastards that pose a risk to engine and an airflow spoil can be chucked far away )
myself ( and i have done this before even with the stock injector ) i just build the height back up with the large mazda base O ring ,, just as you also suggested
( so that the injector is not loose into the fuel rail )
i have had NIL issues ( with mazda O ring ),, and have done this on a few engines now !
however,, replacement non genuine base o rings dont quite have the same OD,, and same flat sides as the OEM one
-- and its these that pose a vac leak risk issue
( use some silicone sparingly for these ! )
these are disc type injectors so dont actually need the atomiser under the injector for pattern diffusion
( so the brittle bastards that pose a risk to engine and an airflow spoil can be chucked far away )
myself ( and i have done this before even with the stock injector ) i just build the height back up with the large mazda base O ring ,, just as you also suggested
( so that the injector is not loose into the fuel rail )
i have had NIL issues ( with mazda O ring ),, and have done this on a few engines now !
however,, replacement non genuine base o rings dont quite have the same OD,, and same flat sides as the OEM one
-- and its these that pose a vac leak risk issue
( use some silicone sparingly for these ! )
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03-07-10, 10:21 AM
#9
woo kinda creepy I was about to post the same question. after taking my manifold off yesterday i noticed one of the little basterds split in half, and just kind of hanging there. I felt fortunate that it didnt break into my engine, but didnt know if they were really needed on the secondary injectors.
03-07-10, 10:35 AM
#10
talking head
yes ,, double fuel pressure check also ,, prime the system and wait a while for leaks and also monitor the leak-down period
and check again after small drive , to be sure
yes the "mixing plate sockets" sit on a ledge just inside the injector boss into the manifold
they have an O ring around the lip and happily this lip and O ring correspond closely in height with a single mazda square side rubber
so, for secondaries, when deleting the "socket" you just sit another O ring to bring back the seat height close to original
the primary injectors in the middle plate have a two piece mixing plate deck
( both with an O ring seal each )
( the lower part with twin mixing plates,, one turned up against the airflow )
and you can build these up with 2 rubbers,, or one if retaining the top piece as a spacer
what is important is you have the top o rings seating properly into the fuel rail
myself i pick the marren modded import injectors as they are hassle free fit to unmodded fuel rails
( twin 11 mm top O ring seal and very good base rubber, blueprint paired )
i wrote this just yesterday somewheres elses on the webz---
and check again after small drive , to be sure
yes the "mixing plate sockets" sit on a ledge just inside the injector boss into the manifold
they have an O ring around the lip and happily this lip and O ring correspond closely in height with a single mazda square side rubber
so, for secondaries, when deleting the "socket" you just sit another O ring to bring back the seat height close to original
the primary injectors in the middle plate have a two piece mixing plate deck
( both with an O ring seal each )
( the lower part with twin mixing plates,, one turned up against the airflow )
and you can build these up with 2 rubbers,, or one if retaining the top piece as a spacer
what is important is you have the top o rings seating properly into the fuel rail
myself i pick the marren modded import injectors as they are hassle free fit to unmodded fuel rails
( twin 11 mm top O ring seal and very good base rubber, blueprint paired )
i wrote this just yesterday somewheres elses on the webz---
the real plastic atomisers usually sit below the injector ,, spacing it up
you can delete these too,, as they are only to help atomisation at low airspeeds for economy and emissions
- in conjunction with air bleed to injector base ( air bleed to primary only on s4, but also secondaries in s5 )
when deleting this atomiser cup ,, you simply add a extra injector base rubber to build the injector up to sit in the fuel rail correctly
as for those add in injector bosses,, i ran two of those for many years on the rx2
( so i ran 2 primary, + 2 secondary + 2 auxillary 550's )
-- they dont need the atomisers either to seat properly,, your injectors will fit as is
myself ,, with ported engines ,, i chuck the real atomisers far away
- not required for the original purpose,, they pose an inlet spoil/ restriction and also a risk to the engine as they are very brittle when old
you can delete these too,, as they are only to help atomisation at low airspeeds for economy and emissions
- in conjunction with air bleed to injector base ( air bleed to primary only on s4, but also secondaries in s5 )
when deleting this atomiser cup ,, you simply add a extra injector base rubber to build the injector up to sit in the fuel rail correctly
as for those add in injector bosses,, i ran two of those for many years on the rx2
( so i ran 2 primary, + 2 secondary + 2 auxillary 550's )
-- they dont need the atomisers either to seat properly,, your injectors will fit as is
myself ,, with ported engines ,, i chuck the real atomisers far away
- not required for the original purpose,, they pose an inlet spoil/ restriction and also a risk to the engine as they are very brittle when old
Last edited by bumpstart; 03-07-10 at 10:38 AM.
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