A question that has often arised, in my mind, is why Ford went OHC? Chevy and Dodge are producing similar hp/tq with like displacements using the "cam in block" design. When it comes to low reving truck engines, what would be the benefit of OHC?

 

4v Heads would be the only thing I could see, if they used them more. I've often wondered the same thing.

 

Cost. Cars and trucks use can use the same pistons and heads with just different cam and intake profiles depending on duty. Other than that they are neither inherently better or worse than a pushrod motor.

 

I can see that being the case with the 4.6L. The 5.4L and 6.8L, up to this point, have been strictly a truck/van engine. To the best of my knowledge the 5.4 and 6.8 have been the same across the board in regards to cams and intake profiles. So there is no cost savings there.

[QUOTE=Blown330]Cars and trucks use can use the same pistons and heads with just different cam and intake profiles depending on duty. [/QOUTE]

Couldn't the same be done with a pushrod engine. Dodge is using the 5.7L HEMI in everything with minor hp/tq changes. The same with Chevy and the 5.3L. It will be heading into both cars and trucks.

I suppose cost and versatility may have been the underlying reason at some point, but it doesn't seem to be the case now. In fact the overhead cam design has a lot more parts. More parts equals more money.

 

IMO the two biggest reasons to go with ohc would be more than 2 valves/ cylinder and variable valve timing. Why when Ford started with ohc they didn't go straight to 3v/4v and variable valve timing, I have no idea.

GM now has pseduo varaible cam phasiing on pushrods and rumors of multivalve heads have been floating around. If this is true then pushrods may not lose those advantages to ohc engines

Other reason's to go ohc would be the ability to rev high as the valve-terain has less inertia than pushrods and with dohc you can vary the intake cam seperate from the exhaust cam

Per displacement a multi valve motor will be more efficient than a pushrod 2v which means for a given displacement it will most likely make more power. What people tend to forget is a higher displacement doesn't mean the motor is physically bigger. The ohc motors now have to take the cam from inside the block and put them ontop of the heads making the motor physically bigger.

I'm still not sold 100% on either design, they are both just different paths to the same goals

 

Cross-flow heads are an advantage for OHC. Ford thought that it would also give them a marketing advantage, which I don't think has really happened.

Ford's implementation of OHC technology is pretty lackluster, and the 5.4 motor reminds me a lot of the GM 305 thanks to the tiny, valve-shrouding bore and lousy stroke/bore ratio (at least the 4.6s are square).

GM and DC both have done amazing jobs with the pushrods - with lighter, physically smaller motors as the payback.

 

Not just costs in parts but costs in production. The production flow for OHC engines is much simpler and things can be shipped as preassembled affairs. One of the reasons that foreign manufacturers went to OHC designs decades ago. BMW had pushrod engines in the 1950's. For Ford's part it was also due to increasing emissions regulations. Small bore, long stroke mills produce less emissions. I think Ford's implementation was great, initially. I think it focused on developing the 4.6's for the Mustangs somewhat to the exclusion of the 5.4L and 6.8's. Now with the 3V heads have helped the truck motors quite a bit but at the same time made aftermarket work more difficult. Ford does need a bigger hi-po V8 in its stable and I think with the reemergence of the Hurricane motor we'll finally see that. Look at the stuff Aussies get for their Modulars...wondering were all the performance R&D for the trucks went...Dundee freaking got it.

 

All of these posts has given me a better understanding...thanks.