More valves means more curtain area at a given lift. Meaning you can run less agressive lift and druation and get the same power. I know LS7 heads can flow 360CFM. At what lift? Gas mileage is not emmisions. GM probably had a hell of a time getting the LS7 by the Smog ***** in getting it EPA approved. If they could run a lower duration/lift cam for the same power they could probably pass easier and get more power accross the board.

The sad fact is the OHC might be needed for emmisions reasons. Im hoping this MDS and DI stuff keeps that problem at bay.

 

Ok, I certainly don't understand why you can't read what is wrong with your original post, and I certainly don't want to give any more time addressing this at all, but here we go for matters of correctness. Your full statement was:

See it?? Guess what, with a bore of 3.55" and a stroke of 3.54", the 4.6 is slightly oversquare . Understand now? When did you actually address this as a mistake when it was brought up? You didn't, hence my comment about you ignoring your error. Look, this is a pretty stupid thing to be arguing about, and I have no inclination to waste any more time on it.

For all intensive purposes, the 4.6 is a square engine, but if one wants to really nitpick, it is oversquare, not undersquare.

 

chalk it up to oversight, it still doesn't change the fact that I neither ignored it nor does it change the point of my post. OHC takes up less space for a given displacement.

 

I'll assume this is a typo. I am really pro DOHC, but I can even bow down to the space argument.

But the space constraints have never really been an issue to me. Hell they put Northstars, Small blocks, LS1s, and DOHC V6s in the back of Fieros. Everything I ever need to change on the Fiero I can get to, except the timing belt. But if I'm due for a timing belt change, I'm probably do for a head rebuild and lower end inspection at the same time.

 

I agree; power:mass (for the whole vehicle) is much more meaningful.

 

So let's compare the P:M rates for the Suzuki 1300cc GSX-R motor to the GM LS7. I don't have the time to find the numbers then compute them, but I'm sure someone does.

I realize this is not a great comparison, as the two engines have VERY different objectives. But that's my point. The 1.3l is simply on a much higher performance platform than the LS7. But it doesn't mean anything, since the 1.3l would prove to be a very terrible powerplant in a Corvette. But a 1.3l pushrod, OHV motor with a LS7 specific output in a Hayabusa would be just as impractical, needing more cubic inches (Thus space and weight), to make the same amount of accelerative force.

 

GM does sell power, 85% of all Mustangs are V6's. 85% of all F-bodies were V8's. There's your power.

 

Physical space and weight taken by the powerplanet do come into play
and will affect handling and whether even said engine is able to be installed.

On the OHV vs OHC space constraint, the heads on the OHC are much larger making a 4.6L of Ford DOHC being physically larger than a big block ford and weight is close. All alum BBF is lighter than a 4.6L DOHC. Max cubic inches for a BBF stock deck height is on order of 600 or so cubic inch, max cubic inch of a 4.6L not using 5.4L deck is around 300 cubic inch. BBF of 600 cubic inch, can make around 1400-1500HP N/A with right heads. 300 Cubic inch of max done up 4.6L ford might be able to get close to 700HP N/A.

Physical space of the BBF is close and weight is lighter if you go all alum,
this is how the Space argument came up.

The other argument, was the LS1 was clean on emissions and produce good fuel mileage. Would a 2.3L OHC 4 cyllinder in say a vette produce better fuel mileage? ( Its not guaranteed ), its possible the smaller motor can put out less mileage!

The space argument was for X amount of space in a DOHC I can have quite a bit more space in a pushrod motor, have lowered cost and complexity and make more power without having to turn as many rpm.

Any amount of Cubic inch going from pushrod to OHC is going to take up more physical space and weigh more.

"Curtain area" - is even less relavant to rod ratio and might as well be something along the lines of a bogus equatio of "rod ratio vs oil pressure".

Case in point is two 1.1" intake valves would have a curtain area of 2.2" but would not even come close to the flow of a 2.2" valve, probably at any point on a flow graph. At max lift the single 2.2" valve maxed out ( prolly 450CFM ) would be double what two 1.1" intake valves of same 2.2" curtain area would do.

Where DOHC did make sense was in a 4.125" bore you might have DOHC arragnement of two 1.84" intake valves and two 1.47" exhausts. You might not be able to go much larger. Two 1.84" intakes might be able to max out close to 500CFM with a great port design. Can shut off one intake for running at low RPM and steady state.

Each vavles have their own springs. Lighter valves means float rpm is higher on the graph. Lighter springs can be used to control lighter vavles. Two 1.47" exhausts is overkill since we know for even a 2.15" head a single 1.55" exhaust can be more than sufficient. This is where 3V arragnement came in. Due to lack of need for more exhaust flow.

 

.85 of FBodies were not V8's.

W

 

They sold power, they don't anymore. That's because even when they did, they didn't really sell much of it, more offered it for sale....Ok ok, enough F-body bashing

 

No it is'nt I work for PTG we race M3's that's how much a complete crate engine costs. Hell our air boxes are $8,000, the altnater is like $1200. The valves from BMW if bought seperatley are $80 few doolars apiece. A M3 is 50k. And buy the after we race prep the we sell them for around 50k.

 

No not just the motor, but the whole vehicle (that's what I said); otherwise it's even sillier than HP/L.

 

Power:Weight comparison is my point.
Specific output comparison (HP/L) is useless.

 

"intensive purposes?"


It's "intents and purposes."

 

More cubic inches doesn't equal more space and weight. That's the whole point, which you're missing. If an OHV V-type engine will take up less space and mass than a OHC motor with the same displacement, then therefore you could make an OHV motor with the same space and mass as the OHC but run more displacement.

The advantage of OHV motors (besides the flow-velocity and thus "torque" advantage) is that for a given amount of weight and space to work with, you can run more cubes with the OHV than with an OHC. Thus it isn't ever meaningful to compare OHV and OHC of the same displacement since the OHV will always be able to run more displacement.

If different configurations of motor can run different displacements, then to compare equal displacement is totally useless. That's why, in this context specifically, the whole HP/L thing is so useless. (it's really useless in every other context as well, but that's another story)

 

It didn't take me long to find some from multiple BMW stores online for around $12k, advertised as brand new.

 

OK. Stupid mistake of phrase on my part. My points still stand though. The 4.6 is not undersquare, and OHC have not "lost" this debate. Funny how the thread started out as being nothing about this.

 

Anyone ever see that Hayabusa V8 motor? Bad *** motor. It is something like 210lbs, displacing 2.6L, and making 372hp. Assuming an LS7 is around 380lbs (all engine weights are dry without flywheel), that would give that little engine a better power versus engine weight than an LS7, and make it a smaller engine as well. Could be even cheaper than an LS7, given the LS7's price tag.

I know this isn't a conventional motor, but it does help to give some perspective. OHC engines can be compact. The Ford motors aren't the end all, be all of OHC engines.

 

Oh, come on - you guys are gonna argue about 10 thousandths of an inch and "intensive purposes", but nobody noticed the post with "powerplanet" instead of powerplant?

And apologies to the original poster, as this has gone

 

More cubic inches DOES mean more space and weight when you're talking a GSX-R motor that is already at it's limit of displacement. The bores are already so close that the motor can't be bored more than .020, which won't make any difference in power. Same goes for stroke. The LS7 makes approximately 430whp, based off 505chp and a 15% drivetrain loss (Feel free to add a proven stock WHP number). This translates to about 61whp/l, whereas the Gixxer motor is at 125whp/l. Thus in order to make the 163whp that the 1300 does, the pushrod motor with a LS7 specific output would need about 2.7l of displacement. Once that big, it'd probably be beneficial to add cylinders, since most motors over 2.5l are 6s. Now you can sit here, and tell me, with a straight face, that a 2.7l V6 is the better engine because it's smaller? My a$$.

While this may be the case most the time, don't draw that line straight across the board, as I just proved above. Have fun taking your Nissan Frontier's 2.7l pushrod and fitting it in a motorcycle. But make sure you put a nasty cam in it, CNC port the heads, use titanium everywhere you can, and so forth.

The GSX-R uses the highest level of factory tuning ever known to man to cram 163whp in an engine that I can curl...With one arm.