Camshaft theory question

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Blenderhead

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I was thinking about something as I was driving home tonight. Our cars have 2 separate intake runners, one of which is closed under 3K rpms, right? We also have separate intake valves for each runner, with separate cam lobes for each valve. Why then do we have the same cam profile on both intake runners? I don't know a whole lot about fluid dynamics and how it would effect the airflow when the IMRCs are opened, but it seems to me that on the runner that is closed off by the IMRCs, you could run a much more aggressive cam profile, and then maybe even tone down the profile on the other runner, and I would think it would really help smooth out the torque curve and help drivability. If you were to make the one cam profile have peak torque at say 3500rpms and the other have peak torque at say 5500, then when the IMRCs are closed, you have made the motor much torquier, and then I would think when they are opened, you would have slightly less air entering through the one runner, but then more air coming in through the other, so I would think it would balance out. Am I way off base with this thinking? I've never had a chance to mess with a dual-runner head on a flow bench, so I really don't know how it would react to something like this. Any thoughts?
 
I think because both valves operate all the time the IMRC valve opening would'nt allow the valve action of the secondary to have a lot of control (primary would open sooner to create torque) killing the effects of the secondary valves.(for good cyl. pressure) now if the primarys were on a electric controlled pivot point...... (oh yea its called v-tec)
 
That's not what I'm talking about. You are thinking of changing the cam timing, as in having one valve open first, then the other. I'm talking about having more lift and duration on the valve that is behind the IMRCs than you have on the primary valve, but leaving the cam timing alone. Still have max lift occur at the same time on both valves, just have the secondary one open faster and farther, and stay open longer.
 
Cams

There are a few company's that produce after market cam kits that do just that.
 
I believe Hitech Motorsports in Elk River, MN has experimented a little bit with this.
 
Any one else have ideas? Would this give a broader torque band? What all would be involved, just cams? I can't say I'm at a full understanding, just interested.
 
cams

With the DOHC 4.6L you have an intake cam and an exhaust, to increase low end torque Ford introduced the IMRC's they close of the second intake valve until 3K RPM then they open allowing full flow to both intake valves.
By having two different grinds on the intake valves you can take advantage of a short duration lower lift better center line grind on the primary cam giving increased low end torque and power, and use a higher lift higher duration secondary cam profile for high end HP and torque. Kind of the best of both worlds.
Mercedes Benz and various imports have been doing it for years. Problem is matching the cam characteristics so overlap is not a problem.
 
I like this idea and it seems to make sense to me. To bad a cam set up is $1200 for these motors.
 
Roadboss said:
The old story is who will buy it. Most are IMRC less now
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if it wasn't so costly you could count me in for sure, idea seems pretty sound and i should imagine it would make the engine one hell of a lot meaner.
 
The 96-98 Cobras have difference profiles for primary and secondary. IIRC the secondary has longer duration. I have also heard the secondary is a couple degrees retarded to promote swirl.

I have many different things as to what the Mark cams spec out at. From less lift and duration then the Cobra intake cam to it is the same just retarded 3 degrees to shift the powerband a little lower.
 
The Cobra cams are very very similar, I'd say that most of the hp rating diff fromt he Cobra to the Mark is in the intake, and in the politics of Ford....
 
kustomizingkid said:
The Cobra cams are very very similar, I'd say that most of the hp rating diff fromt he Cobra to the Mark is in the intake, and in the politics of Ford....
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I agree with you on that.

I did a lot of surfing around the internet looking for what the Mark cam specs were and could not find them. Max confirmed for me the exhaust cams are the same and intake are different but how so I don't know.
 
Rich88LSC said:
I agree with you on that.

I did a lot of surfing around the internet looking for what the Mark cam specs were and could not find them. Max confirmed for me the exhaust cams are the same and intake are different but how so I don't know.
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the intake cams are retarded 3 degree's to provide more top end HP.
Or the mark 8 cams were advanced 3 degree's to promote better bottom end, how ever you want to look at it.

now..before someone "thinks" cobra cams are BETTER, they are not.

Two drasticly different platforms

Cobra is a lightweight stickshift car witha different intake and cam strategy than a HEAVYweight automatic car.

And of course KK is right about ford politics and HP ratings.


and as mentioned before...
1200.00 for cams makes it the least "bang for the buck" mod you can do to a mod motor..for 20ish HP you would gain, it's just "not worth the money".

for half of that you could get an honest 100HP gain, and not have to take the valve covers off.. nor take a chance of screwing up the cam timing.

if I were gonna spend 1200.00 I'd put a 100 shot of nitrous on the car and save the other 600ish dollars for "bottle refils"....then go kick the dogcrap out of cobras with 1200.00 worth of "bang sticks"
 
Thats the most you can get out of a cam swap? What about some of the wilder cams with very noticeable idles? For one, a cammed up engine just sounds bad ass. I thought you would be able to get a little more than that.
 
XLRVIII said:
the intake cams are retarded 3 degree's to provide more top end HP.
Or the mark 8 cams were advanced 3 degree's to promote better bottom end, how ever you want to look at it.
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I have heard that but I have also heard different altogether.

XLRVIII said:
now..before someone "thinks" cobra cams are BETTER, they are not.

Two drasticly different platforms

Cobra is a lightweight stickshift car witha different intake and cam strategy than a HEAVYweight automatic car.

And of course KK is right about ford politics and HP ratings.
Click to expand...

Agreed. With gears, stalled and a Cobra intake you might see a couple HP with Cobra intake cams but I do mean a couple and it is completely not worth the time and effort.


XLRVIII said:
and as mentioned before...
1200.00 for cams makes it the least "bang for the buck" mod you can do to a mod motor..for 20ish HP you would gain, it's just "not worth the money".
Click to expand...
I think you would see more then 20HP probably 30-40 but I completely agree it's not worth the $1200 plus the extra $400 for valvesprings.
 
There used to be a technical article out on the web, before the web became so contaminated with bad information that showed the exact differences between the 4.6 Mark 8 Motor and the 4.6 Cobra motor.

They described the cams in detail...among other things.

It was called the 4.6 White Paper if I remember correctly
 
I'm gonna have to look for that. To bad the internet is so crowded with crap it's hard to find anything useful.
 
After I posted that.. I looked..and looked and looked..couldn't find it.

If my feeble memory is correct it was late 1999 or 2000 and was posted over on www.markviii.org in a discussion thread.

since I dont go to that site and haven't been back in 5 years, I didn't go dig thru the posts over there.

google and yahoo struck out.
 
cams

There's a great book called "Buliding a Max Performance 4.6 Liter Ford by Sean Hyland that has ton's of info on all of the 4.6 motors- not just cams but sleeving and overboring, intakes, etc. These motors can stand well over 1000 h.p when done properly.
 
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