Overhead cam VS pushrod design? Which is better?

[260DET]

That's funny, I thought you in particular had a thing AGAINST the L6. Didn't you go RB just for that reason? Just out of curiosity what does the RB weigh, and how much $$$ do you have in your swap, and how much hp does it have. I'm betting that you could have done better with an LS1 swap.

....................

Ah, I took the poll to be about OHC engines in general, not the L6 in particular. Which was a good engine in its time, the '70's.

Mine was fitted with a FJ20DET about eight years ago, now a VQ30DET would probably be the engine of choice. A mate of mine has a RB30ET in his, goes quite well.

[jmortensen]

Ah, I took the poll to be about OHC engines in general, not the L6 in particular. Which was a good engine in its time, the '70's.

Mine was fitted with a FJ20DET about eight years ago, now a VQ30DET would probably be the engine of choice. A mate of mine has a RB30ET in his, goes quite well.

EXACTLY MY POINT!!! Nothing wrong with an L6, unless you want the most power you can get for a given displacement. Suddenly it appears the L6 may not be the answer... OHC or OHV...

[speedyblue]

Who said anything about bigger engines? mine's a 1.3 liter!

but it's like a 2-stroke, so it converts to 2.6L.

When it comes down to it Torque is a measured figure, HP is a calculated one, something like HP = torque x rpm. Ramp up the RPM in the engine more and you can get more HP.

My Scout is rated at 150HP, just like the L28 in my Z, but it weight heaps more and is still almost as quick off the line. Why It has over twice the torque of the Z and the peak is at 1800rpm. The engine is a pushrod type, and can best be described as agricultural. Redline is at 3800rpm. :stupid:

Horsepower sells cars.

Torque moves them.

[260DET]

EXACTLY MY POINT!!! Nothing wrong with an L6, unless you want the most power you can get for a given displacement. Suddenly it appears the L6 may not be the answer... OHC or OHV...

The other point of course is weight. The VG30E is significantly lighter than the L28, the VQ30 significantly lighter that the VG Only problem with a VQ is working a gearbox to fit.

[240ZX]

Interesting comments all! I believe the only reason for the OHC vs OHV is to reduce valve train reciprocating mass to obtain efficiency and higher RPM. If you through enough $$$ at either design you will get the horsepower. Comparing one engine to another vs OHV vs OHC is just two separate issues.

[auxilary]

pft, it's not a two stroke! 4 stroke combustion process! suck squish bang blow happen in a circle! It just drinks oil like a 2 stroke...

[jmortensen]

Yes but it is two strokish in that it does a power stroke with every revolution.

[auxilary]

and if you want to have a really good laugh... for every 3 revolutions of the eccentric (crank) shaft, the rotor makes ONE

[CoastGuardZ]

sbc powered mustang

give me some time and I'll find you a hemi camaro

Who said anything about bigger engines? mine's a 1.3 liter!

I was thinking of going to the junkyard, finding a datsun 310, and making a 130Z badging for my car

I just got nautious! :sick:

Sorry aux, the bigger is better thing was in reference to Chevy's LS7-500hp with the Ford GT 5.4L-550hp rebutal.

Of course you could just make it a Mazda 130Z while you're at it

[thehelix112]

It seems to me that we are all assuming that V8s are all OHV and that these are the only ones you would consider putting in a zed.

To answer the question posed in the subject line: it depends what you mean by better. As has been mentioned by several people, OHV is cheaper and easier to make, and OHC is more efficient and allows higher RPM due to lower weight/inertia in the valvetrain. Does anyone want to discuss these two assertions?

Now if we start talking about putting a V8 into a zed, then it really becomes a matter of, do whatever you feel like. Depending on how much power you want and the drivability characteristics you prefer there is no real answer as to what is `worthwile', and less of an answer as to what is `better'.

People can *try* to justify their preferences based on cost, but really, not too many people who do up cars don't realise that its an expensive hobby (by my humble standards anyway). Personally I don't really care about cost, if it costs more, it just means it'll take a bit longer to get. I have made a few decisions for reasons other than cost, like keeping the L6 engine in an attempt to see how far it can be pushed reliably, and keeping the chassis and basic suspension design for the same reasons. Plus I love the way an L6 sounds on boost heading past 6500.

Do whatever you want, but don't expect everyone to like it. I don't know how many times I've heard: ``You're a fool, you should've just put an RB26 in it.''

Personally, I don't like mongrel cars, and I don't see the need for it.

Dave

[ecp48]

And then came Chevy's latest rendition of the pushrod V-8. The LS-1 is as light, or lighter that the L-6, though when combined with the BW six speed the package is slightly heavier with about 1% more weight on the rear wheels. It's about as high tech as a pushrod V-8 can get. Revs very freely and depending on computer programing 350 to 450 HP.

Yes I voted for an overhead cam engine, but in the real world that LS-1 fits nicely, a touch expensive, but an enviable package.

My next step. Although I will keep one of the cars with the L-6 at about 190 RWHP, just because I couldn't do it in 1979, when I had my 75 280Z (didn't know how).

[jmortensen]

It seems to me that we are all assuming that V8s are all OHV and that these are the only ones you would consider putting in a zed.

The most common swap is the 350, followed by the LS1 or the 302, so that's probably why we're talking OHV V8s. I believe the Ford 4.6L OHC V8 is too wide to fit in the engine bay, not to mention it's a dog anyway so it would be a waste of time/money. Not too many other options for OHC V8's that would be readily available IMO. I haven't heard of anyone swapping in a BMW M5 engine, but that's probably because the engine would cost 5 or 6 times the price of a decent Z.

To answer the question posed in the subject line: it depends what you mean by better. As has been mentioned by several people, OHV is cheaper and easier to make, and OHC is more efficient and allows higher RPM due to lower weight/inertia in the valvetrain. Does anyone want to discuss these two assertions?

I thought we already did on the other thread. The 350 has a higher potential redline than an L6. OHC in theory has more potential for higher rpms, but the L6 in particular can't handle the extreme rpms. I don't know whether that's because of the non crossflow head or the crankshaft harmonics issue or what. Regardless of why, V8s actually can do better than an L6 at high rpms and that's the truth. If you're going to push either to that kind of limit you're already talking about a high dollar engine.

Most people use these arguments when talking about relatively stock engines, where the V8 might have a rpm limit somewhere in the 500-1000 rpm slower than the L6. IIRC my original L24 had a redline of 7000, and the L28 I replaced it with had a redline of 6500 from the factory, my new Sierra pickup has a readline of 6000. So then you're talking about the relative benefit of another 1000 rpm and 150 fewer hp than the V8, which again leads me to believe that the advantage still goes to the V8. Now we're talking about a displacement thing more than anything else, but the power advantage is there for a rpm disadvantage that's pretty minor.

Now if we start talking about putting a V8 into a zed, then it really becomes a matter of, do whatever you feel like. Depending on how much power you want and the drivability characteristics you prefer there is no real answer as to what is `worthwile', and less of an answer as to what is `better'.

People can *try* to justify their preferences based on cost, but really, not too many people who do up cars don't realise that its an expensive hobby (by my humble standards anyway). Personally I don't really care about cost, if it costs more, it just means it'll take a bit longer to get. I have made a few decisions for reasons other than cost, like keeping the L6 engine in an attempt to see how far it can be pushed reliably, and keeping the chassis and basic suspension design for the same reasons. Plus I love the way an L6 sounds on boost heading past 6500.

You're talking boost, so are you swapping in an L28ET or are you driving a ZX Turbo? If you're swapping the motor into an early Z, then I really don't see the distinction between doing that and putting in a V8. Is it a Nissan thing? If someone swapped in a Nissan V8 (the old 70's pushrod limo engine for instance) would that be "better" than a 350? If so why? Just trying to understand.

The L28ET is a MUCH better match up to a V8, and it makes a lot of sense to do a turbo swap IMO. Obviously you've seen the limitations of the NA L6 and chosen to do something about it. In that sense we're in agreement.

Do whatever you want, but don't expect everyone to like it. I don't know how many times I've heard: ``You're a fool, you should've just put an RB26 in it.''

Personally, I don't like mongrel cars, and I don't see the need for it.

Your taste is your prerogative. Taste is subjective, and there certainly is no need for anyone else to tell you how to build your car. You like the L series, build an L series. I would still argue that an early Z with a ZXT engine is also a "mongrel" in technical terms. If it ain't stock, it's a mongrel, right? Isn't that the purists' credo?

I followed Auxilary into the argument on the other thread because I used to argue the purist case until I realized that ALL of my preconceived notions about the pushrod V8 were incorrect. It took me years to rid myself of the prejudices I had built up.