Why was the Ford Med Riser 4v so weak at 2500 in TGFEIC ?

[WerbyFord]

Recently over on the old/new fordfe.com, a question came up about the Blue Thunder (BT) intake vs the Ed RPM intake. The OP decided to go with a BT, due to the torque loss with the RPM intake at eg 2500rpm in TGFEIC.

https://www.fordfe.com/which-blue-thunder-intake-for-a-390-gt-motor-c6ae--t161264.html

I hadn’t taken that much note of the issue, because I usually use 2000rpm as the Gonkulator’s “Bottom”, since that is in the range of stock FE converter stall. But on going back and looking at all the Torq in TGFEIC at 2500, some very interesting and hard to explain stuff seems to be going on.

For example, here is a list of the 2500rpm Torq as reported, for the good old 428cj410hp engine/mule.
UP=Unported
PM=PortMatch

406   Ed F427 PM
401   Holley SD UP
399   Ford “Z” c4se-a
398   Ed SM-PM
397   BT-UP ******************************* versus:
396   Ed F427-UP
396   Ed SM-UP
395   Ford “S” c6ae-g
392   Offy POS-PM
389   Ed Perf
385   Ford MR-8v-UP
385   Ford LR-8v-UP
384   Offy POS-UP
380   Ford 390hp
379   Ford Sidewinder-UP ********************* -18
379   Offy360-UP
377   Offy DP-UP
376   Ford 428cj-iron
376   Ford 428pi-alum
373   Weiand 7282-UP

343   Ed RPM ****************************** -54
333   Ford MR-4v-PM to LR heads ************* -64

Note that the average of all these intakes is about 390 ftlb at 2500rpm.
The BT intake does better than most at 397 ftlb.
But then there is the very popular Ed RPM intake way down there at 343 ftlb, a loss of 54 ftlb at 2500rpm.

Of course, for the RPM’s intended use, this doesn’t matter too much, as it is intended for combos that will never see full throttle much under 3000rpm where this intake comes to life. Still, at 2500, why does the RPM lose so *badly* compared to other intakes, whether dual or single plane?

It has been suggested that this loss of low end is due to lack of taper in the RPM’s intake runners. I don’t have a better explanation, so let that be the proposed cause. As we know, above 3000rpm the Ed RPM comes to life and is among the best street/strip single quad intakes. OK, problem solved, I guess. 

MUCH HARDER TO EXPLAIN is the dual plane Ford Medium Riser 4v (MR-4v) intake. It is the worst of the bunch at 333 ftlb at 2500rpm, down 64 ftlb vs the BT intake. And it is also down 48 ftlb versus its near sister, the even larger volume Sidewinder, at 379 ftlb. The MR-4v also loses badly to other near twins, the 428pi and 428cj intakes, both up there at 376 ftlb.

What’s going on with this intake? All I can figure is that as Jay notes in TGFEIC, this intake was “port matched” to the big somewhat lazy low riser head ports as received for testing. Still, it doesn’t seem like that would explain a loss of 50 ftlb give or take, but maybe it does. But other than “port matching”, all those Ford intakes look so similar, and they all put out near the same torq at 2500, except the MR-4v which is WAY down.

Comments/Explanations? Jay? 

[jayb]

Werby, you have hit on some data that has baffled me ever since I ran those tests.  I really can't offer an explanation.  Especially for the Performer RPM, which seems like it should work all across the RPM range, but for some reason, on that particular engine, was way down on torque at the lower engine speeds.

I don't think that the port match explains the poor low speed performance of the factory MR intake, at least not to the tune of 50 lb-ft.  Again, I can't explain this except to say that the engine wants what it wants, and that manifold didn't give it what it wanted. 

For what it's worth, I always ran two back to back pulls when doing those tests to make sure I had valid data, so I'm confident that the results are accurate.  However, please note that these manifolds were used, and could possibly have had a defect that explained the test results, although I'd think that would have showed up across the whole speed range, not just low engine speeds.

Go figure...

[machoneman]

You may have hit upon the reason (defect of some sort) the RPM did so poorly. Perhaps down the road you could test another out-of-the-box RPM against your 'best' performing intake on the same engine (not necessarily of course the test engine of long ago). Just a thought as the old test results are very odd.

Werby, you have hit on some data that has baffled me ever since I ran those tests.  I really can't offer an explanation.  Especially for the Performer RPM, which seems like it should work all across the RPM range, but for some reason, on that particular engine, was way down on torque at the lower engine speeds.

I don't think that the port match explains the poor low speed performance of the factory MR intake, at least not to the tune of 50 lb-ft.  Again, I can't explain this except to say that the engine wants what it wants, and that manifold didn't give it what it wanted. 

For what it's worth, I always ran two back to back pulls when doing those tests to make sure I had valid data, so I'm confident that the results are accurate.  However, please note that these manifolds were used, and could possibly have had a defect that explained the test results, although I'd think that would have showed up across the whole speed range, not just low engine speeds.

Go figure...

[Drew Pojedinec]

Can we really trust a dyno at such low rpm?

[Stangman]

So can we trust the f427, not that I dont like that manifold cause thats what I had on my motor before the duel quad setup, and with the 428 crank in my 427 that manifold worked great and I had it on my 427 before I stroked it and it was great.  That RPM intake aint to far off the f427 if im right   

[jayb]

Can we really trust a dyno at such low rpm?

What's not to trust?  As long as the dyno can brake the engine and hold it at a specific RPM, and the torque link is calibrated, there's no reason the data wouldn't be valid.

[Falcon67]

Fun question that shows how much you can test and still not know "what".  Could be that the engine combo just didn't "like" that intake - carb signal hurt due to wave tuning in the runner, or pulsing in the intake at that RPM with same effect, etc.  Air does weird things.  I ported a set of 2V 351C heads, did pretty good for just a guy with a grinder and not trying to rule the flow world.  Ports did great, running close to 250 CFM @ 28 in/hg at .450 lift.  Went to wind the intake opening to .500 and just past .450 the flow bench made a noise like a firecracker and the flow dropped 30 CFM.  Air could not make the short turn and abruptly changed direction in the valve pocket.  Got back to the 250 range by .550 then no more.  On the motor, the heads worked fine and the motor with a mild 226/230 cam made a honest 400 HP depending on weather.  Never acted like there was a dip in power at any particular RPM on the strip. 

[Drew Pojedinec]

Can we really trust a dyno at such low rpm?

What's not to trust?  As long as the dyno can brake the engine and hold it at a specific RPM, and the torque link is calibrated, there's no reason the data wouldn't be valid.

I’m fairly ignorant about dynos. Thus why I asked. I didn’t know if it could brake well at that rpm.

[TomP]

I ran an F427 on my 428 ramp truck before getting a new Performer RPM when those came out. The Perf RPM certainly had more low RPM torque than the F427. My truck would lug down to 1200tpm on hills in high gear and still pull. I could mat the pedal at 2500rpm in second and blaze the dual rear tires more easily than with the F427.

[WerbyFord]

I ran an F427 on my 428 ramp truck before getting a new Performer RPM when those came out. The Perf RPM certainly had more low RPM torque than the F427. My truck would lug down to 1200tpm on hills in high gear and still pull. I could mat the pedal at 2500rpm in second and blaze the dual rear tires more easily than with the F427.

Tom, That is encouraging. What CAM was in that ramp truck?

It seems the torq "dip" in the Ed RPM didn't show up in a milder engine like Jay's "428 Tbird". With a bigger cam like the "428cj410" the dip at 2500 then showed up.'

[TomP]

A Crane HMV272. It was 10.5 compression so too big a cam makes it more tolerable for gas, I ran 94 octane but sometimes there wasn't any around so on 91 or 92 it would ping unless I retarded the timing.
http://www.cranecams.com/product/cart.php?m=product_detail&p=24124

[WerbyFord]

A Crane HMV272. It was 10.5 compression so too big a cam makes it more tolerable for gas, I ran 94 octane but sometimes there wasn't any around so on 91 or 92 it would ping unless I retarded the timing.
http://www.cranecams.com/product/cart.php?m=product_detail&p=24124

OK that would still jive with Jay's data in TGFEIC. The 428Tbird mule ran that cam 216-228-112 and did NOT show the anomaly. The RPM intake actually made more Torque at 2500rpm than the BT intake - with that smaller cam.

The anomaly, where the RPM intake is down 50 ftlb or so vs the BT intake, shows up with the bigger Ed RPM cam at 236-236-108. That cam sounds WILD with open headers. The first time I heard one open at Milan I almost thought it was a Ford "B" cam. Then again it's pretty close, as hyd cams idle about 10 degrees rougher vs a solid cam.

I think there's some strange, almost unstable, things going on down there at 2500rpm and below with big cams - the engine is running backwards down there so it may be that little changes result in combos that deteriorate in a hurry.

[machoneman]

I think there's some strange, almost unstable, things going on down there at 2500rpm and below with big cams - the engine is running backwards down there so it may be that little changes result in combos that deteriorate in a hurry.

You are onto something as we've all run various 'hot' engines way below the usebale rpm range (often accidently) and felt rough running, bucking, loss of hp/torque. Perhaps the dyno, with the throttle always wide open at all rpms, showed a real loss not quite 'felt' as if the engine were installed in a car and actually moving.

[Falcon67]

That sounds about right.  The 351C in the Falcon is a 10.5:1 motor.  I used a hydro roller (Howards) 233/241, 106 ICL, 110 LSA.  It's a bit grump below 3000.  No problem staging at 2000 and the converter wings to 4800 so not a lot of time spent at low RPM LOL.  And it probably would not hurt to have another 10 degrees duration or so in that motor.

[BattlestarGalactic]

Werby,

Was watching some Hogans Heroes last night and had to laugh.  They were screwing with the Germans with their rabbit trap "Gonkulator".   Was this where you came up with the name for your system?   This was the first time I've heard that term used any place but here.