I own a 92 ZR-1 Corvette and an M3 and am fascinated with DOHC motors. Why did Ford choose to go this route with the Cobra?
WHy Did Ford Go DOHC in the Cobra?
- Thread starter Lowflight
- Start date
:shrug:
![AMD[H]unter](/data/avatars/m/62/62604.jpg?1479576167){kind=avatar}
AMD[H]unter
Banned
Because that's just how they roll.
I'm gonna say that Ford chose the DOHC configuration because it was able to make more power than the SOHC 4.6 is a mass produceable trim. It was just an easier and cheeper way to make power, than an engine reconfiguration. They have used the engine for a while now, I believe that the Mark VIIIs were the first. The DOHC heads have seen many changes in the decade that they have been put of Fords.
This is similar to how Ford chose the supercharge the Terminators instead of upping displacement. It was the best way to keep production processes constant, and meet the customers needs with more power.
This is similar to how Ford chose the supercharge the Terminators instead of upping displacement. It was the best way to keep production processes constant, and meet the customers needs with more power.
Last edited:
:banana:yay! because its two import motors in one :??:
That's funny because I was wondering the same thing about the ZR-1 and the M3.
Maybe someone "in the know" will speak up :shrug:
Maybe someone "in the know" will speak up :shrug:
Bore spacing and overhead cam geometry did not permit any larger valves in the 2V heads. So, to increase the flow they decided to go with 4V twin cams. If you will notice the 05 up 4.6 and 5.4 V8 has a 3V system that is one intake and two exhaust.
Rumor has it that the next Ford V8 will not be OHC but OHV similar to the previously successful 5.0 motors of 12? years ago...
Last edited by a moderator:
I can't speak for the M3...but in the ZR-1, it was the best way to get the most power out of a V8 given 80's technology and ability to stay within EPA regs etc...In the mid-80's, General Motors and its Corvette Division approached Group Lotus in Great Britain with the idea of developing the world's fastest production car. From that collaboration came the LT5 engine, an aluminum-block V-8 with the same bore as the standard (L98) 350ci displacement unit, but with 375 horsepower. To accomplish this power boost, the new block featured four overhead camshafts and 32 valves. The LT5s were built by Mercury Marine in Oklahoma and assembled into the ZR-1 vehicle at Bowling Green.
A unique computerized engine control module provided "bi-modal" characteristics. This dual personality was a logical outgrowth of the appeal of the twin-turbo Callaway conversions. The ZR-1 could be used for routine street driving or convert to a race car with speed and handling available on demand. The computer system directed fuel mixtures through an upgraded injection system that allowed for low-, half- and full-throttle modes and kicked the engine up to 375hp. And, a key-operated "valet" switch locked out the upper speed ranges, limiting power to a normal 250 horses to prevent inexperienced hands from taking advantage of the car's outstanding power.
A unique computerized engine control module provided "bi-modal" characteristics. This dual personality was a logical outgrowth of the appeal of the twin-turbo Callaway conversions. The ZR-1 could be used for routine street driving or convert to a race car with speed and handling available on demand. The computer system directed fuel mixtures through an upgraded injection system that allowed for low-, half- and full-throttle modes and kicked the engine up to 375hp. And, a key-operated "valet" switch locked out the upper speed ranges, limiting power to a normal 250 horses to prevent inexperienced hands from taking advantage of the car's outstanding power.
01cobravortech
Banned
They were probably bored. They probably figured it was too easy to make 500hp on the old 5.0s and said hey lets make it more challenging by trying to make 500hp out of a 4v motor to impress those Chevy guys. Naturally, Ford probably has rid themselves of the geniuses that came up with the idea. But now they're stuck with the problem.
Not quite………actually not quite at all. The valves in the Modular Ford 2V engine has plenty of room for larger valves (see link)
http://www.musclemustangfastfords.com/tech/0302MMFF_MixMatch/photo_21.html
This is a PI head
The heads on 2V engine are designed primarily for emissions, to promote high velocity intake charge and have plenty of room to accommodate larger valves. If you look at a 351 Cleveland head you can see what an engine with oversize valves looks like (the valve seats actually merge with one another.
4 valves flow better then 2 valves at lower lift and have a lighter mass to promote higher RPM's using less valve spring force. 2 valves actually flow more at higher lift then 4V that is why all the top fuel dragsters still use 2 valves.
You got this one backwards. The three valve engine uses 2 intake and 1 exhaust valves (nobody does it the other way around) The reason Ford went to three valves is because it's a cheaper alternative to 4 valves.
An OHV engine is even cheaper to produce then an OHC because you only need 1 cam shaft rather then 2 or 4, is a lighter and a more compact design. The 4.6 (281 cid) 4V engine is physically larger (or pretty close) then a 426 hemi for this reason.
Engineering choices always involve compromises. The DOHC 4V setup is designed to allow better flow at high revs, resulting in higher power without increasing displacement (like F1 engines that put out 800hp from 2.4 liters because they rev to 18,000 rpm). Also, OHC valvetrains are lighter than OHV, allowing higher revs. They also tend to allow straighter ports and less valve stem obstruction of the ports than OHV designs (except if you go to the hemi concept).
Another factor is bore/stroke ratio. Newer engines (like Modular Fords) are square or under square, which makes it easier to achieve good emissions. This results in a smaller bore, which limits breathing if you only have 2 valves. For a while Audi went to really undersquare engines and used 5V technology. Older small blocks have larger bores and short strokes, allowing large valves even if they're 2V.
GM and Chrysler have held out with OHV engines only on their large motors where they can put in large valves, and cost and size advantages outweigh any high rpm flow advantage.
Another factor is bore/stroke ratio. Newer engines (like Modular Fords) are square or under square, which makes it easier to achieve good emissions. This results in a smaller bore, which limits breathing if you only have 2 valves. For a while Audi went to really undersquare engines and used 5V technology. Older small blocks have larger bores and short strokes, allowing large valves even if they're 2V.
GM and Chrysler have held out with OHV engines only on their large motors where they can put in large valves, and cost and size advantages outweigh any high rpm flow advantage.
Went to edit my post to fix my punctuation and lost half the content so I nixed the rest of it.
Last edited:
Considering they haven't achieved 500hp naturally aspirated after 12 years is pretty sad. I can't ever see Ford going back to a Push rod technology. Yeah they are stuck with this mess.
just like john force said at an interview once quote (FORD IS REALLY INTO RACING)end quote. (SVT)&(FRPP) NEED I SAY MORE!!!! henry ford started out racing his cars in the beginning!!!
Last edited:
I think the better question is why did Ford choose an OHC configuration at all for the modulars? I seriously doubt it's cheaper and it's not like a pushrod engine can't make the same power. I really appreciate all the tech info but my gut says that they just wanted to do something completely different with the mod motor. Somebody probably figured it would be good for marketing if nothing else being that a OHC has a kind of high end/tech image.
It's ridiculous to assume that Ford invested millions into modular engine just for image. Interchangeability of parts, multi valve variations (2v, 3v, 4v) as well as the limitations of the ohv engine performance at that time (late 80's - early 90's) all factor into the decision. I'd say for the time, it was the right decision. The versatility is amazing - look at the 3v now. Slap a blower on and it competes with engines with almost twice as many cubes - with just a compression change (2003 cobra - mach I). Anyone now can look back and say - hey, the ohv can do it cheaper and easier but the electronic engine management was not available to the degree it is now. Hindsight is always 20-20.
Last edited:
ya
Just wait and see when Honda brings back the CX500 (the worlds only Honda Motorcycle wit pushrods). Any day now!
Just wait and see when Honda brings back the CX500 (the worlds only Honda Motorcycle wit pushrods). Any day now!
your soooooo wrong.... It is impossible for 2v's to go even 1mm oversized with out boring the block aswelll.... and 20over at that....
You don't think so, huh? Companies spend HUGE amounts of money for promotions and image. Why... because image is perception and perception is reality. That's what sells products. But I don't doubt that someone sold it to the brass as having some technological advantages but you can bet your ass that the promotions dept was thrilled to have the new V8s being OHC.
Aren’t you contradicting yourself.
You state that it's "impossible" without boring the block yet when you do, it is possible......correct?
I guess I'm not "soooooo wrong" as you claim but I'll give a nod to your statement. 1mm oversize valves is hardly worth the effort. I was looking at the spacing beween the valves. I didn't realize Ford pushed the valves out so far in the bore. Too bad :nonono:
Users who are viewing this thread
