EFI Question for Dave re: individual runner intakes on 510" FE

[dieselgeek]

Dave -

This past weekend I went to Minneapolis to help a FE-fanatic friend, Jay Brown, finish a year-long test of intakes for a 510" SOHC FE combo.  Background: he was testing as many intake manifold combos as he could get his hands on, including some rare old tunnel ram used by Dyno Don, all the Ford racing pieces, and lastly - a Hilborn MFI intake with individual runners and throttles.  This Hilborn setup was converted to EFI, with the electronic injectors in the same position as the mechanical units, aimed towards the intake (see pic).

Now, this was *far* from optimized; we didn't play with runner length, all we did was get it running the best we could for WOT pulls on his dyno...  i.e. find best timing and AFRs for peak power and torque.

What I observed was interesting...   there was a HUGE dip in the VE of this engine, I was able to map to it and achieve flat AFRs in the 12.8:1 area, our EGTs were even across all cylinders, but for whatever reason - there was what I would describe as some kind of "pressure phenomenon" happening right around 4800RPM that required dramatic reductions in fuel delivery to maintain consistent AFR, until about 5000RPM where things picked up dramatically.   

I noticed on some of his other intakes, a similar dip in power - his carb combos had a much more wildly sweeping AFR curve, but smoother power output.  With the EFI/Hilborn setup I was able to nail down smooth AFR but came up with the below power curves (EFI/Hilborn in red):




One thing that I observed, after a pull we'd remove the airbox & velocity stacks, and observed fuel stains ABOVE the throttle blades!!  this is well above the placement of the injectors - is this some kind of standing wave or pressure pulse going on?  how would fuel get spit back up into the intake?   The engine ran perfectly smooth, no misfiring or backfiring or any events that would cause this - it was definitely happening during the power pull.


other pics of the setup:







This is an early AFR log, as I tried a smooth fuel curve, and yes I externally verified that fuel delivery at the injectors was as the EFI system (FASt XFI) was commanding.  I.e., fuel pressure was even, injector opening times & duration was as commanded, and the sequential operation was properly configured (although I didn't play with phasing)




However, I notice some of his other intake tests, showed a tendency to "dip" in power at the same RPM as the EFI/Hilborn combo, see below:







I have tuned a number if ITB intakes before, all but one of them were Forced Induction engines; the other was a Cosworth DFV that had "optimized" stack lengths already.


What do you think was happening?  And now that his testing is over, how would you suggest optimizing this combo?  It's probably going in a fun street car, not an LSR effort, but I figured your intake experience could guide us a bit here.


thanks,
-Scott

[dieselgeek]

We've gotten some interesting feedback on other forums, other builders/tuners are suggesting that to optimize this combo, we should be playing with runner length, injector placement, injection event phasing, and exhaust collector length.


Sounds like Jay wants to put it in a car this way, he is very happy with the throttle response, idle characteristics (when we adjusted the TBs for even EGTs at idle, I was able to get a 750RPm smooth idle which he really liked).

I'm still very curious what Dave has to say though!

[ddahlgren]

I have run this before same engine same IR setup...
send me the graphs as I can not get them to come up here..
Dave

[dieselgeek]

I've sent our info to Dave for evaluation, in case others were wondering what's going on in this thread.   huge thanks for Dave taking his time to offer suggestions!!! 

[ddahlgren]

I wish the graphs came across or maybe everyone can see them but me lol.. Anyway we shared some info some important and some not..
Valve size of 2.4 a bit big for the 4.13 or so bore but if unshrouded ok. The cam lift of .665 is way short to take full advatage of the valve size.. 0.800 is closer to correct. Problem is low rocker ratio and low lift.  the real question at times is..what is the valve lift or flow around 76 degrees ATDC that is where peak airflow is required and why a lot of people are running high ratio rockers. It is not just for lift but lift at 76 ATDC give or take a few degrees..
Intake size of 2.437 butterflys are smaller than the port.. 2.75 minmum and a big problem  2.90 probably spot on.
Headers right size wrong length 28 to 30 inches is what I would shoot for and avoid the different sizes between them an 8 inch difference from longest to shortest is an issue. The collector seems short to me a drag race piece rather than something with a broad torque range. A couple of pulls with both longer and possibly an H pipe might have been interesting.
The rods..sigh do you have the room physically to go longer someday.. 6.7 with a 4.375 stroke is painfully short and just makes the intake problem worse. How tall is the deck height??? you really need around 10.562 or more to get a decent rod in this thing...11 would be even better..
Sorry for all the doom and gloom LOL but ya asked so here it is. It didn't take the time as I don't have it to do a peak and mean airspeed calcs but the dyno shee shows the problems at around 5500 to 6000 rpm..
Oh well off to work for me....
Dave

[dieselgeek]

doom and gloom?  no worries!!

Jay is reworking the thing per most of your instructions.  Sadly, no room for longer rods - and he has to go with this intake initially until he can fabricate a larger one...   but he is thankful for the advice and is going to try to take care of the rod issue on his next build...

thanks a lot Dave!!  just wanted to make sure there wasn't something I was doing wrong (i.e. I'd be more concerned if there was some glaring tuning mistake I was making - just want to make sure I'm doing the best that can be done in the EFI dept.)


thanks a ton for taking your time to help us!!

-scott

[Stainless1]

Diesel, wow, talk about getting professional help, you hit the jackpot. 

Dave, it is great to have you here 

[dieselgeek]

I can tune.  I can even design an EFI system, but I have exactly *zero* experience "outside the box"  (haha).   I am thankful Dave spent as much time as he did, probably 10 emails back and forth, sharing his experience with us.   Which is what makes this particular sport so great.  Try finding that kind of knowledge sharing at the drag races...

[wolcottjl]

I had a hard time seeing them as well so I put them in my photobucket account.  I hope they show - If not let me know and I can try something else.



What I observed was interesting...   there was a HUGE dip in the VE of this engine, I was able to map to it and achieve flat AFRs in the 12.8:1 area, our EGTs were even across all cylinders, but for whatever reason - there was what I would describe as some kind of "pressure phenomenon" happening right around 4800RPM that required dramatic reductions in fuel delivery to maintain consistent AFR, until about 5000RPM where things picked up dramatically.   

I noticed on some of his other intakes, a similar dip in power - his carb combos had a much more wildly sweeping AFR curve, but smoother power output.  With the EFI/Hilborn setup I was able to nail down smooth AFR but came up with the below power curves (EFI/Hilborn in red):



One thing that I observed, after a pull we'd remove the airbox & velocity stacks, and observed fuel stains ABOVE the throttle blades!!  this is well above the placement of the injectors - is this some kind of standing wave or pressure pulse going on?  how would fuel get spit back up into the intake?   The engine ran perfectly smooth, no misfiring or backfiring or any events that would cause this - it was definitely happening during the power pull.


other pics of the setup:





This is an early AFR log, as I tried a smooth fuel curve, and yes I externally verified that fuel delivery at the injectors was as the EFI system (FASt XFI) was commanding.  I.e., fuel pressure was even, injector opening times & duration was as commanded, and the sequential operation was properly configured (although I didn't play with phasing)


However, I notice some of his other intake tests, showed a tendency to "dip" in power at the same RPM as the EFI/Hilborn combo, see below:

[Rex Schimmer]

It is probably a case of harmonics, i.e. the natrual frequency of the headers and the inlet air horns. These two could be very out of phase with each other at your 5000 rpm "dip" and then come into phase as you get to the higher end. The standing wave of fuel above the Hilborn ram horns is pretty common, and is usually a result of the combo of the exhaust headers and the rod length:stroke ratio. Your combination needs lots more time on the "pump" and you need to look at Dave's suggetions. Doing things like increaseing the dia of the inlet butterflys and ram tubes will raise the rpm that their natural frequency occures and shortening the headers and increasing their dia will do the same for them. If you are looking for a broad torque and hp curves then you need to have the headers and inlet be different frequencies but overlap each other, for absolute hp you would want them to both be at the same frequency.

Related to headers you might want to look at stepped headers as they tend to have several natural frequencies each related to the length and diameter of the tubes from one step to the next. Stepped headers take advantage of a sonic trait that when ever a fluid is traveling down at tube and there is a sudden increase in the tube area,  the step, there is generated a negative pulse that travels backward in the tube.

Great looking motor!! Good luck  and thanks Dave for more great info. BTW Dave what is the basis of the 76 deg ATDC?? that you mention.

Rex

[ddahlgren]

76 degrees ATDC peak piston speed give or take a couple of degrees..
Dave