technical discussion on the standard fuel rail

I've been looking around for information on this but can't seem to find alot out. So hoping we can have a technical discussion regarding pressures flow rates regarding injector pressure drop in the rail. Without "well mine has been fine" being the only feedback.

I'm mixed minds weather to fit drop in side feed injectors into my supra for my small single turbo upgrade or machine and make my own top-feed rail for the car.

Now alot of people have said the drop in's will be fine, and I'm not doubting this. But.

My technical knowledge on this comes from over 10 years experience in the 3sgte field where I pushed the engine to close to 1000bhp and did alot of expensive flow testing on parts while developing the engines to that level.

Now, the thing that troubles me with running 800cc injectors on the side-feed setup on the supra is as follows. When pushing the stock 3sgte rails to there limits, basically 100% duty on a flow tester with 63.75psi line pressure (equivalent of running 1.5bar + 42psi standard BFP) we found a huge pressure drop on the standard rail. To the regions of 0,1, 4.5, 7.5% from first injector to the 4th. Also tested that 7.5% pressure drop is almost an entire AFR point, so tuned to 11.5:1 the leanest cylinder could be 12.5:1 which is just asking for trouble.(just rough estimate as i fully understand that AFR taken from the exhaust is going to be a combination of all cylinders)

The 3sgte stock side-feed rail is almost identical to the supra unit with its 8mm internal bore (believe supra is the same), and added bypass channels around the injectors. Except the supra has an additional 2 injectors on the end. So if the trend continues pressure drop at the end would be very dangerous.

I have read about people dual feeding the supra rail, but assuming the supra rail follows a similar trend to the 3sgte rails the inside 2 injectors would still be a 4.5% pressure drop the starting injectors.

In my tests the machine was calibrated before use, fuel pressure from the pump monitored (did not falter during testing) and all injectors cleaned and flow tested before the tests.

So looking at this information I'm sure you can see my concern before purchasing drop in side feed injectors, because ideally I want as much consistency as possible. And on the 3sgte we fit a top-feed fuel rail system with Delphi 870cc injectors or even 1000cc + and there isn't a pressure drop issue again, other than that of pump in-ability but then all 4 injectors drop the same amount. Even if with 800cc injectors on my supra i'm only going to be running 75% of there capacity on a 4 cylinder car the end injector would see see 5.6% pressure imbalance, so again would increase by #6 if this was a supra application

Wandering what the more technical people of this forum think to this, differences of opinions etc etc. The information I posted, although I've only posted the basics is all correct and factual. Hopefully if there are counter opinions there is similar information

I'm hoping the side-feed setup is going to be ok as my fuelling setup would be alot cheaper lol, but going on what I know and looking at the supra rail, seeing its exactly the same just 2 extra injectors I can't see the results being much different.

Look forward to peoples opinions and replies

Tim

no-one?

I don`t think anyone has actually done any proper flow testing with the standard rail,however a number of people have gone to circa 600fwhp without issues, personally i have gone for a top feed setup because it came along at the right price.

what is your power goel tim?

I'd always plan for more, as it will happen eventually.

well Geo this if for future projects as well even if there not my own, remember why I bought the supra in the first place.

Personally I'm only looking for a fast response 550ish anyway on a gtx35 but as stated above even running 800cc at 75% duty if those trends continue your at 5.6% imbalance on #4 so guessing up near the 7-8% again by the time you get to #6

As you know when we've spoken Geo I plan on building most my own parts so I can use my own supra as a test bed, so thinking fuelling system might be something to add to the list.

Looking around the TT Rail has the same internal design and bore as the 1994+ 3sgte design just 2 extra injectors on the end, so i need no reason why the thread of the 4 cylinder version won't be escalated by the time you add another 2. Be very interesting to see how far out the supra design is, as the 3sgte one in my opinion becomes to imbalanced over 600cc so you might find the imbalance starts anything over the 550cc range with the 2 extra injectors.

Tim

Over here in Germany they rebuild the stock rail to dual feed. I think there won't be any pressure drop with that mod

Im still running stock fuel rail! drop ins and uprated FPR

I have a stock fuel rail with twin feeds that came off JohnnyGs big twins car, that ran around 800hp I think.

Over here in Germany they rebuild the stock rail to dual feed. I think there won't be any pressure drop with that mod

I've done this before. I milled a flat on the other end and drilled and tapped it out to m12x1.25mm and attached a -6 fitting. 1 of the cars I did this for made about 650hp at the flywheel with more to come.

I've done this before. I milled a flat on the other end and drilled and tapped it out to m12x1.25mm and attached a -6 fitting. 1 of the cars I did this for made about 650hp at the flywheel with more to come.

Yes that's the way it's done over her too. A friend of mine ran over 700hp with a S366 and 850(or 800?) drop ins without any problems

The wangan Supra, before it was imported made iirc over 800hp with a modded stock fuel rail and twin -6 feeds.

One thing I've always pondered is whether twin feeds are actually required unless your pushing silly numbers, say 700+?

I could well be wrong here, wouldn't the collision of 2 lots of flows of fuel colliding in the rail would create turbulent eddies which could cause some pressure inconsistencies in the rail?

see i know its been done but without individual AFR widebands on each cylinder which isn't possible you never know how close to failure you really are. I have seen 3sgte engines in that should have failed along time ago but on inspection were hanging on by the skin of there teeth, So seeing how close to failure they were and the own was under the impression it was all ok and fine.

again alot from Japan with high power setups and then doing individual EGT on cylinders were all over the place because of this imbalance.

I did look at the dual feel setup, but like i said in my previous posts the supra rail is almost identical to the 3sgte setups so assuming that your only feeding 3 cylinders at a time we were still getting 4.5% on the #3.

The turbulence inside the rail is a totally different conversation again.