RussStang

Yo, you really have no idea what the hell you are talking about, do you? You do realize that Ford's pushrod 5.0L has seen 9k rpms so many times now it is probably impossible to count, right? You do also realize that at 9k rpm the 5.0 has a lower piston speed than the 4.6, right? Guess what, ultimately the 5.0 is going to be able to turn more rpms than the 4.6 can safetly, regardless of pushrods. I don't know who taught you **** about engines, but you obviously have not been keeping up on technology. You do know there are destroked pushrod small block Chevy's that have seen 12k rpms, right?

READ THIS : THERE IS FAR MORE TO MAKING AN ENGINE REV STUPID HIGH THAN WHERE THE CAM IS LOCATED. You stated something completely opposite from the truth in one of your last sentences; DOHC 4V engines have far more friction losses than a 2V OHV engine. I don't know who has filled your mind with this crap. Sure, a Ford 5.4 DOHC engine can spin to 9500 rpms, but guess what, it is likely the highest it is going to spin, because at that engine speed with its 4.17" stroke the piston speed is 6602FPM, which is dangerously high, even for a drag motor. Thats what happens with long stroke, undersquare motors. The fact that the motor is undersquare certainly doesn't help it breathe up top any better either, because even with 4Vs per cylinder, the small bore itself is going to be a limiting factor.

Look, the LT5 was a great motor for it's time. It can make tons of power, but it is hellishly expensive to modify compared to something like the LS1. I have read about 415CID LT5s making 620hp at the wheels, and I am sure some have put out more, but at the same time, the new LS7 is easily capable of that as well, and it only has 13 more cubes on its side.

RussStang

Look, I am not stupid. I know that take two engines, both with the same bore spacing, the same bank angle, and the same deck height, and make one OHC and one OHV, the OHV one will be smaller. My point is, using the Ford engine as the benchmark for all OHC engines is retarded. There are far more compact OHC engines out there. Every see a modern Ferrari engine? I wouldn't exactly call one big.

Regarding my previous statement to the Ford engines. The SOHC Ford engine is not as bulky as a DOHC Ford engine. Both the cylinder blocks of both engines are beefier up top to support the larger heads, but the heads themselves on the 2Vs are not as big. Ever see a new Accord V6? It is a 4V SOHC engine. Ever wonder why they would do something like that? I don't know for sure, but it could definelty be to keep the size down.

One final thing regarding your statement that HP/L is ricer math. I completely disagree. It is not the end all benchmark of engine design, I agree with you there, but it certainly has validity. Typically an engine with a high HP/L not only has high rev capability, but also high Torque/L output. Guess what? Torque production is directly related to engine volumetric efficiency. You know, torque, the thing that domestics pride themselves on. I find it interesting to see how all of these ratings come together to act upon the system. Engineers do spend time looking at this kind of criteria. Would you consider them ricers? When the LS1 was being designed, there was a power benchmark set for the motor. It was 1 HP for ever CID. Does that make GM a ricer company?

black_knight

iTrader: (1)

Okay. After the thrashing you gave 93LT1 up there, I can see maybe I overreacted to your posts.

I think that it's useful only in an engineering lab, and even then only within a very specific, narrow context. Do agree that ricers use it inappropriately as a measure of the better engine? Can the better engine be the one with worse hp/L? If yes, then of what use is it as a comparative measure?

If one engine is to be considered superior to another, the last criterion that anyone should be using is HP/L. Things like total output, total weight, size (for packaging's sake), and HP/lb of engine weight are useful for comparing engines. HP/L, as such, is not.

300bhp/ton

eh?

Buddy you need to check your physics before bashing. As they are totally related.

HP = torque x rpms / 5252

The more torque you make at higher rpms the more power - SIMPLE

It is for this reason Formula 1 race engines rev to 19,500rpm and most higher performance motorcycle engines also rev high. And precisley why most low reving diesels make great torque but relatively low HP by comparison.

300bhp/ton

Sorry but this is total BOLLOX!!!!!

Are pretty meaningless, espcially in LARGE American cars.

Come on think about it for a bit, if Jagaur, BMW, Mercedes, Ferrari can fit OHC V12's into their cars squabling over a OHV or OHC V8 for a large American car (most pony/muslce cars and even the Corvette by sports car standards) is pretty dumb!!!!

Again total rubish.

TVR 7.7 litre DOHC V12 fitted in a car with similar proporsions as a Corvette.

And if you can acheive greater efficency you do not need as many cubes to acheive or even superseed the same level of HP.


Why oh why oh why do so many of you guys seem to believe the Ford OHC V8 is the pinnicle of OHC technology.

Next you'll be tellling me Mc Donalds produce the healthyist food in the world

black_knight

iTrader: (1)

I don't. I know it's crap. It just happens to visibly demonstrate the disadvantages that all OHC engines have over OHV motors. Even if all of them won't suffer to the degree that the ford mill does, they all do, to one degree or another.

As for packaging, what I mean is that for a given external dimension limit, the OHV will be able to stuff in more cubes. That's a major advantage.

Explain this comment. Why would one WANT to use less cubes to achieve a given level of HP? Remember this is a hot rod board, not save the earth.

300bhp/ton

bhp per litre is very useful and not just in a lab. Sadly many Americans owning large V8's try and claim it's BS and Ricer'ish. Which in turn makes them as stupid as the Ricers they are trying to insult.

Example:

If a 5.7 litre LS1 can acheive ~450rwhp which arguably is around 500-520bhp. We can work out it's specific output.

510bhp / 5.7 = 89.5bhp/litre which IMO is pretty darn stout for a OHV engine and in a street going LS1 would probably be quite wild.

(NOTE: I refer to rwhp as Mustang Dyno numbers corrected SAE, not Dynojet as these are generally highly inflated when compared to SAE Net figures).

As we have know calculated the LS1's spcific output we can use it to estimate HP on larger displacement setups.

Generally retaining specific output on larger displacements is harder, but the variation is likely to be minimal as the LSx has proven to be capable of producing good power.

A 427ci LSx or 7.0 engines specific output would be:

89.5 x 7 = 626bhp is it was running the same relative state of tune. And would probably be considered to be as streetable as the 5.7 variant. Thsi would likely be ~550-570rwhp on a Mustang Dyno (and around 600rwhp on a Dynojet).

So it is useful.

DOHC engines are generally capable of much better specfic outputs. And IMO a equiverlent state of tune to an LSx producing 89.5bhp/litre would yield a better specific output.

Most n/a DOHC engines are quite capable of making 115-120bhp/litre and often still remain totally legal from an emisison/noise point of view.

If we assume that the DOHC is making 115bhp/litre compared to 89.5bhp/litre for the OHV. This is a direct alternative in terms of streetability, relaiabilty, fuel efficency. But due to curtain area and probably rpms the DOHC is being more efficent.

Our target goal is 626bhp as that is what in theory our 7.0 LSx should be producing.

626 / 115 = 5.4 litres

So on a like for like setup (provided both engines are good enough) a DOHC 5.4 should match a 7.0 OHV in terms of HP. And again due to curtain area would probably have a broader and more progressive power band.


This isn't to say OHV is the underdog, because it simply isn't. But dymancially and technically a DOHC has it beat on every level.

If you prefer they are different solutions to the same question.

And again please don't use the Ford modular V8 as the best example of a OHC engine. Do you every sight the L98 or TBi Chevy as the best OHV? No, because quite simply they aren't and neither is the Ford Modular V8.

300bhp/ton

The Ford Modular DOHC V8 is certainly anything but crap. It just isn't the best. But there's a BIG difference.

Look at how many 4.6 DOHC 03/4 Cobra's are making over 600rwhp on pump fuel and with a supercharger. A blown 5.7 litre LS1 will hardly produce more power running a blower under the same circumstances.

Unless the engine is going in a go-kart it is not an advantage.

The Jaguar AJV8 is the same weight as a LS1 and a similar size, if not smaller in some dimensions. fair do it is only a maximum of 4.4 litres in production but I have no idea what it's full potential is.

I really doubt the difference in displacement for equiverlently externally sized engines would really amount to that much.

And to be honest in the majority of cars fitted with a V8 and extra few inches in width or hieght is not likely to make many odds. espcially if it is recognised from the beginning.


Why would one WANT to use more cubes to achieve the same given level of HP?

black_knight

iTrader: (1)

Nope, it's rubbish outside a lab, and often rubbish inside that lab.

You just don't get it. You're delusional if you think a 5.4L OHC motor will match the LS7 under the curve.

"Dynamically and technically" are measures that engineers use to circle-jerk each other. Meanwhile the OHV designs continue to produce motors that are smaller in size, lighter in weight, and make more power (especially under the curve). For any kind of comparison that means anything in the real world, OHV wins.

That's why it's ricer math. You win on paper, you lose in reality.

black_knight

iTrader: (1)

1) Why the f*%(*#&)(&@#)(&*@#)%& not?

2) Torque and HP under the curve.

black_knight

iTrader: (1)

You need to do your homework.

300bhp/ton

Now you just sound like ,the typically PIG headed neanderthal that usually posts up about OHV/OHC comparison.

Still children will be children.

Try and think what you are saying.

An LSx in the state of tune we/I was talking about (89.5bhp/litre & 626bhp SAE Net). The LSx will not be making MASSIVE under the curve numbers.

Go look at serious cammed & heads LS1's generally they make very little below 3000-3500rpms in this state of tune. It's only once they come "on cam" they start to shine. But the rpm range is still pretty similar.

A stock LS1 is out of breath at ~6000rpm. A serious setup allows this range to be extended to 7000rpm+ but you loose equiervlent rpms off the bottom of the range. Also high spinning OHV's face other issues such as they may continue to make power but the valve train really isn't going to support the rpms to actually see the power.

Increased curtain area from multivalves will alow DOHC engine to have a broader rpm range. so in fairness it would be much closer than you think.

And also don't just be a typical or should that be stereo typical moron. You need to note that most DOHC engines (not all!!!! But most) are short stroke motors as this is better suited to high rpms which is where DOHC valve trains work well and again because HP = torque x rpm / 5252 is how to make more HP. Most OHV engines don't like revs and the valve train certainly doesn't cope with them so well so you''l find that by compariosn OHV motors are usually long stroke. And long strong motors as a trend will produce more low end torque. So don't let this OVERLOOKED aspect cloud your judgement when you make sweeping statements about under the curve.

Antoher thing to consider is gearing. If a cammed OHV looses it's low end then there is a limit to how much gear can be run or how high a gear (numerically lower).

So for the same gearing if a DOHC motor can spin 1000rpm fast it will also allow higher top speeds.

Only in America.

Go and look at the rest of the world.

A V8 works no differently to a V6 or in basic terms even an in line 4 cylinder engine. Yet how many V6's and S4's the world over are OHV and which valve train configuration produces the most power?

Do you see Formula 1 engines being OHV? No, because they just wouldn't make the power.


Yes OHV works very well on the street and due to the American automakers there are plenty of cheap mass produced OHV V8's of large displacement.

But again don't let the lack of mass produced LARGE displacement DOHC engines cloud your technical judgement.

For any given displacement on a like for like basis a DOHC will out perform a OHV V8 and with only a slight penalty in size and weight. Bore spacing and deck hieght have no relavance because the shape and design of each engine is specific to it's own layout. With a DOHC engine the block can be smaller due to no need for a cam or pushrods within it. The heads evidently need to be larger to accomodate the cams, but probably not that much larger as a OHV engine heads still have to house the rocker arms anyhow.

And another ORVERLOOKED fact is many DOHC engines have a different angle Vee (45 compared to 90) due to the fact of not needing to house the cam and push rods. This means they will be a different shape, either taller or wider but often not both.

Are you serisously trying to make this personal???

please grow up for pitys sake!

300bhp/ton

See post above.

And please prove to me that a OHV in a radical state of tune can produce more under the curve HP?

Why not find a dyno graph of a stock displacement 5.7 running 450rwhp (MUSTANG DYNO) and compare it to a similar displacement DOHC. Even a V10 or V12, as with DOHC these will tend to be short stroke motors so even though they have more cylinders low end torque will not be their best attribute.

Go on then I'm waiting??

300bhp/ton

Ok then.

How much HP does a stock displacement LS1 (5.7 litre or 346ci) produce on 93 octane street tune running a supercharger (preferably a twin screw for comparisons sake).

I guess to be fair you really need to find one running ~ 8.5:1 SCR.

There are many examples of Terminators making 620-650rwhp (admittidly I think on dynojets) with a 2.2 twin screw blower and bolt ons STOCK internals and on 93 octane fuel.

Only about 10 days back there was a turbo 5.7 LS1 running 9.1:1 SCR and 15lb of boost in the FI forum, I believe they where making high 500's although with a better exhaust it should have been high 600's. But isn't it amazing how close the DOHC 4.6 gets to the 5.7 LS1 considering it is giving away 1.1 litres.

If I'm wrong please go and find some dyno graphs of stock displacement blown LS1's.

black_knight

iTrader: (1)

Deja vu. Every point you make in that post has already been answered and refuted earlier in this thread. And yet you bring them out again. It's tedious and I won't play into it.

I'll answer your new points:

That's due to the intake design, not OHV.

Aren't they displacement limited?

It's nonsense to compare a given displacement. How many times must that be said?

Gee, you think?

You just keep thinking that.

All I said is that ricer math was flat retarded. I didn't say anything about you. Unless you're saying you embrace ricer math and are by implication insulted. In which case, them's the breaks because ricer math is, in fact, retarded.

black_knight

iTrader: (1)

Post above doesn't explain why I would want to run less cubes if given the choice.

More. Cubes.

For the millionth time, NO. It's nonsense to compare like-displacement OHV and OHC because the OHC engine is bigger and heavier. You give me an OHC and OHV engine with like external dimensions and weight, both fully bored and stroked (maxing their cubes for a given external dimension), and THEN you can compare their power curves.

I've said that over and over and over and over and yet you still come back at me trying to compare same displacements. To quote my Scottish buddy, "GET IT ROUND YOU!"

stik6shift93

First off i wouldn't compare a motor that's built from the factory with lower compression built for a blower to an ls1 somebody just slaps a blower on, and many a ls1 see 600rwhp stock bottom end. Most people just don't push them that far because with that much boost the stock bottom end it's a time bomb. Slap in forged pistons and lower the compression and guys will make more than 600rwhp no problem, but it's really comparing apples to oranges comparing a car that comes with fully forged internal meant for boost from the factory to one that was designed na with cast internals.
Secondly I'll tell you why people don't like insane hp/liter number, lets go purely hypothetical and say gm builds a 2.5liter v12 dohc for the vette that's na and revs to 12 grand and makes the same 500hp the zo6 does, it would be no fun to drive whatsoever. Torque if fun on the street, go ride a 600cc sportbike and go ride a 1000cc, the thousand is about 10x more fun to ride on the street, guess why? Nobody wants a crappy little motor that revs to 9k to make power and has no torque, they're simply not fun to drive.
Engine size plays a huge roll too, i think it's pretty unintelligent for someone to say that it doesn't. It determine how much frontal area you have, the length of the front control arms and geometry of the front suspension. Also lets not compare several hundred thousand dollar supercars to 40k production cars. Sure you can make a ohc motor into a small package, but you're almost always going to be able to make an ohv motor into a smaller one with more displacement for a lot less money which is a huge factor in the production world, i mean how many people on this forum do you think are going to ever own a tvr12, how many a vette.

RussStang

Then you can't really compare factory bhp levels with mustang dyno numbers, because the engine dynoes used to get the baseline numbers for the engines by the OEM more accurately reflect dynojet numbers. Nowadays, extremely healthy LS1s have been approaching the 500rwhp with more regularity. That it pretty damn close to 100hp/L at the crank.

RussStang

I really don't agree with. What are "the same circumstances"? Typically LS1s don't run 22psi from a 2.2L twin screw blower. A LS1 motor built specifically for FI application would have no problem exceeding the Ford 4V hp levels. However, the practicality in real life of building a full boost engine is such that only a few guys do, and really on simply strapping an aftermarket blower on the car, keeping the boost down enough to not damage anything, and calling it a day.

RussStang

[QUOTE=300bhp/ton]

OHC engines are just as capable of trading off a good bottom end for a great top end as well. You make it sound like it is OHV specific, which it is not. Even with VVT, there is only so much it can do. Even with the F22C, the S2000 still has a soggy bottom end, DOHC and all.

What are your examples on this? Most DOHC engines are undersquare 4 bangers in small cars. All OHV engines I can think of nowadays are oversquare.


300bhp/ton, you sound like a smart guy, but you also seem to skew just enough of your facts to be able to talk up OHC engines all that much more. Very similiar to what many on this site do for OHV engines as well. I am not saying any of your specific facts and observations are wrong, they are just not always totally accurate. I am trying to keep this from being a personal attack as much as possible, because there are more than enough guys on here that are biased enough to think that pushrod engines are the finality of engine developement, but it is just some things I noticed.