Secondary butterflies without secondary runners is a gimmick.
4k RPM activation
- Thread starter svtnos
- Start date
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Secondary butterflies without secondary runners is a gimmick.
Power Surge
SHO Member
You're right. I'm sure Ford put all the R&D into them and put them into production in a mass attempt to trick the general public.
You're right. I'm sure Ford put all the R&D into them and put them into production in a mass attempt to trick the general public.
That's what they did to the V8 SHO.
NiNeTy Fo SHO
No-mo-SHO Man
JustinSane
SHO OFF
from looking at the fuel tables it seems some top end power is to be had if you set them a tad leaner, from the factory they are a tad rich.
What do the fuel tables look like under 3800 rpm?
Racer X
SHO Pilot, Retired
On topic:
Paul is right... without secondary runners, the benefit to having secondary butterflies is negated. The butterflies opening at 4k effectively increases the intake runner length; the whole purpose of a secondary intake system. If there's no increase in the runner length, what's the point of the secondary butterflies?
According to Wikipedia, the Ford mod motors use a variable length intake manifold, however we all know to take everything wiki says with a grain of salt...
Off topic:
Sal, is your shop open on Saturdays? I'm down port pretty regularly during the summer on the weekends, and I want to see what numbers my car will be putting down once all the work is completed.
That, and my good friend with SCPD want to see what my top speed is as much as I do.
Paul is right... without secondary runners, the benefit to having secondary butterflies is negated. The butterflies opening at 4k effectively increases the intake runner length; the whole purpose of a secondary intake system. If there's no increase in the runner length, what's the point of the secondary butterflies?
According to Wikipedia, the Ford mod motors use a variable length intake manifold, however we all know to take everything wiki says with a grain of salt...
Off topic:
Sal, is your shop open on Saturdays? I'm down port pretty regularly during the summer on the weekends, and I want to see what numbers my car will be putting down once all the work is completed.
That, and my good friend with SCPD want to see what my top speed is as much as I do.
Power Surge
SHO Member
On topic:
Paul is right... without secondary runners, the benefit to having secondary butterflies is negated. The butterflies opening at 4k effectively increases the intake runner length; the whole purpose of a secondary intake system. If there's no increase in the runner length, what's the point of the secondary butterflies?
According to Wikipedia, the Ford mod motors use a variable length intake manifold, however we all know to take everything wiki says with a grain of salt...
Off topic:
Sal, is your shop open on Saturdays? I'm down port pretty regularly during the summer on the weekends, and I want to see what numbers my car will be putting down once all the work is completed.
That, and my good friend with SCPD want to see what my top speed is as much as I do.
The idea behind IMRCs with no secondary runners (like 3 valve Mustangs) is the same as the dual runner design. The closed butterflies allow air to pass through a smaller hole. Air passing through a smaller hole has a greater velocity. Higher intake velocity promotes more low end torque. Dual runner setups do the same thing, they just use a second set of longer runners to increase velocity, and then switch to the shorter runners up top for higher rpms. It does work, although a dual runner setup is preferred, but also costs a lot more to produce.
And yes, I am open on Saturdays (just not THIS Saturday as I have a tuning seminar to host).
I say the smaller intake hole is solely for better mileage or driveability at very low rpms and throttle angles. It is only a valid point in 1st gear or if you are lugging the motor.
You most certainly, at least on the V8 SHO, will not loose torque if you eliminate them. Mainly because the OEM tune is as flat as an Illinois corn field below the secondary opening point.
If the 4.6L is follows the 3.4L, the larger the displacement the sooner the secondaries open. You got to ask yourself just how long are you below the secondary opening rpm? With an automatic it is less than a 1/2 second as the TC takes 2800 rpm or so before you even start to move.
What are the sub secondary opening stock fuel and timing tables like on the 4.6L?
And on the V6 SHO it is the long runners that are open all the time with the shorter ones opening above 4000k correct?
You most certainly, at least on the V8 SHO, will not loose torque if you eliminate them. Mainly because the OEM tune is as flat as an Illinois corn field below the secondary opening point.
If the 4.6L is follows the 3.4L, the larger the displacement the sooner the secondaries open. You got to ask yourself just how long are you below the secondary opening rpm? With an automatic it is less than a 1/2 second as the TC takes 2800 rpm or so before you even start to move.
What are the sub secondary opening stock fuel and timing tables like on the 4.6L?
And on the V6 SHO it is the long runners that are open all the time with the shorter ones opening above 4000k correct?
Racer X
SHO Pilot, Retired
Correct, however when the secondary runners are open, they are increasing the overall length of the runners, not shortening it. At least that is how it was explained to me...
Power Surge
SHO Member
The secondary runners are short, seperate runners, they do not add to the length of the primary runners.
A short runner intake makes more high rpm power, while a long runner intake make more low end power. That's why a 5.0 truck motor has a tall long runner intake and a 5.0 Mustang motor has a short runner intake. Going even more extreme, race Mustangs that are solely high rpm power use bread box intakes (no runners at all, just a plenum chamber).
hawkeye18
Sorta cares
to get optimum airflow (and thus optimum power), you want the pulses caused by the valves snapping shut reflecting back and hitting the valves just as they open again, thus creating a pseudo-ram air effect. When the engine is running at lower RPMs, the time between those pulses is longer, thus you want a longer tube to reflect those pulses.
Above 4K rpm, the time between the pulses shortens significantly, and the longer tubes cause the pulses to start crashing into each other, neutralizing each other and robbing torque. The shorter tubes alleviate this, eliminating pulse collision up 'til about ~7-7.5K RPMs. That's why the torque drops off so much around there. Porting and polishing increases volume, effectively slowing the pulses down; that's why that mod makes the top end up so much. It also greatly reduces the number of secondary pulses off the ridges formed by the pipe unions; this also allows a stronger pulse to hit the valves, ramming more in.
Everybody understand now?
Above 4K rpm, the time between the pulses shortens significantly, and the longer tubes cause the pulses to start crashing into each other, neutralizing each other and robbing torque. The shorter tubes alleviate this, eliminating pulse collision up 'til about ~7-7.5K RPMs. That's why the torque drops off so much around there. Porting and polishing increases volume, effectively slowing the pulses down; that's why that mod makes the top end up so much. It also greatly reduces the number of secondary pulses off the ridges formed by the pipe unions; this also allows a stronger pulse to hit the valves, ramming more in.
Everybody understand now?
jedhead
New Member
Correct.
However one point that is getting overlooked is that the intake runner design on the V6 SHO allows VE to exceed 100% at two rpms. This happens because of a slight supercharging effect that happens at the two rpms ~2900 and ~4900 rpms. The air in the runners bounce between the surge tank and closed intake valve. The velocity of the air bounce between the valves and surge tank is at its maximum at the two torque peaks.
If you don't have the indivual runners you won't have this supercharging effect at two rpm ranges.
Bob
Racer X
SHO Pilot, Retired
The effect that jedhead and hawkeye are talking about is called the Helmholtz resonance.
VE can be manipulated by math and the MAF curve.
Obviously you cannot exceed 100% VE on a NA motor. I can tune your MAF then data log the load and exceed 100% but is it real or just number fantasy?
HotRodKid
mmmmm ... turbo
when the secondaries are open you still have 6 long runners which say the same length, it just gives you 6 shorter runners also
oh, and there would be an even greater supercharging effect at the 2nd power peack if the car switched from 6 long runners to TWELVE short runners
because having a short runner and a long runner going to the same cylinder means that your only getting 1/2 as many high rpm reflective pulses as you COULD be getting
2nd reflective pulse FTW
other people talking about reflective pulses FTW (usualy im the only one)
please try again .... after researching properly
ve has nothing to do with load readings
Last edited:
ritmusic2k
wears a tux.
Long runners only = good for velocity
short runners in addition to long runners after secondaries open = good because raw volume of air is much more important than velocity effects at these rpms.
short runners in addition to long runners after secondaries open = good because raw volume of air is much more important than velocity effects at these rpms.
HotRodKid
mmmmm ... turbo
^^^ velocity matters at all rpms, slow air does not fill a chamber effectivly. this is why a monster intake port kills low rpm power
a "perfect" variable intake system would be able to change port size AND length across the entire rpm range, keeping velocity high and staying in the "sweet spot" of the 2nd reflective event
a "perfect" variable intake system would be able to change port size AND length across the entire rpm range, keeping velocity high and staying in the "sweet spot" of the 2nd reflective event
93rev2sev
SHO Member
Performance is not always the reason for some settings and tuning features. Fuel economy is important to consider also.
I would think that opening the secondaries a LITTLE sooner would help.
Better yet, opening them a little bit at 2000 and a little bit more at 3000 and the rest of the way at 4000 might provide a flatter power curve...especially if you have airflow mods...y-pipe, MAF, BBB's, and of course a tune to utilize the extra flow.
Fuel economy would of course, suffer.
