germeezy1

The LS7 is actually 72 hp/liter and we also know that with normal drivetrain losses the LS7 actually puts out more than 505 flywheel hp. I don't think you are getting what I am saying. GM isn't going to go to 4 valve/cylinder technology for the volume V8's just yet. There is alot more to the picture than just hp/liter. With the lower cost of pushrod engines alot of technology can be included in them to make impressive power out a compact light weight engine. My C5 is the first pushrod car I have owned in many years, compared to my previous DOHC cars, it has an amazing powerband and serves its intended purpose. The pushrod engine isn't near its development ceiling as most think it is. Most don't know this but there was a pushrod racing engine that made upwards of 200 hp/liter....it proved that good design and high revs is as much a recipe for power as DOHC and 4 valves a cylinder are.

engineermike

I'm not disagreeing here. I believe that GM is playing a bit of a strategy game now. They already know they can produce v-8 engines with much higher outputs than they currently do - even with the LS7. However, if they jump straight to a 1000 hp NA v-8, then you run into 2 problems: 1) suspension, tires, and people aren't ready for it and 2) they'd be cheating themselves out of future sales. I believe the car makers are intentionally releasing higher output engines to the public in small increments to they can sell more cars each year.

I think that's more a result of sheer displacement rather than the cam and valve arrangement.

I do agree that pushrods and 2 valve/cylinder has some more left in it. I believe that 90 hp/liter (a 427 cid making 600+ hp) is achievable with the current engine architechture. However, to make it much beyond that is going to require a 4 valve head. I'm sure the pushrod racing engine making 200 hp/liter wasn't smooth idling, tractable, pump gas, or long-living.

Mike

B T

Would these help at all?

http://www.coatesengine.com/products.html

black_knight

iTrader: (1)

(bold mine)

Sorry, but you have still missed my point: it is SPECIFIC OUTPUT itself that I am trying to tell you is irrelevant.

Here is where I responded to you before. Please re-read the below:

(emphasis in original)

Please excuse my frustration but I have said this many times and in many ways and you still seem to be missing my point. It isn't that you used HP/L as a measure of specific output. IT IS SPECIFIC OUTPUT ITSELF THAT I AM CRITICIZING.

The point is that specific output is not a valid performance goal, nor is it something that qualifies for bragging rights. Good overall power production and good power per size/weight are. Specific output does not make a car go faster - overall output and power/weight do.

StevensBikes27

haha what????? i thought only honda or bmw do this

black_knight

iTrader: (1)

See, everyone? This crap is where this HP/L thinking leads.

The OHC, 4 valve BMW V10 in the M5 has greatly superior HP/L than the LS7. And it's heavier, physically larger, and way down on torque. If you develop motors for HP/L and not HP per size/weight then that is what you get. And that is precisely why I am saying it is invalid as a measure of the worth of a performance engine.

2v pushrod technology isn't something "old" that GM must "upgrade" to 4v, ohc to be "more advanced" and attain greater HP/L while turning up the "suck" meter. The fact is that the LS7 is a better engine than the BMW one and thus it is by any sane comparative measure more advanced.

But no, HP/L is valid somehow. The ford 4.6 is a better engine than the LS2, by that measure.

germeezy1

Contrary to popular belief pushrod engines do high revs but you get the same tradeoffs you get in high rev DOHC engines. VVT and lift, and electronic valve actuation is the only way to get around the valve events for good high rpm power conflicting with low rpm power.

germeezy1

You know its funny OHV architecture is relatively new compared to the old fashioned OHC architecture

engineermike

Maybe we all understand your point, but choose to ignore it because we all don't agree with it.

Once again, specific output does not make a car go faster, but neither does BMEP, VE, peak rpm, cid, BSFC, etc. . . when looked at individually. [sarcasm]Hey, I guess it all just boils down to power/weight ratio in the end anyway, so why look at all that other stuff? [/sarcasm]

Read this paragraph carefully: Where hp/l thinking leads, is to look at other engine designs for benchmarking so that you can see just what it would take to reach your goals for an engine design. By looking at the previously demonstrated hp/l of sportbike engines, you can determine for yourself how far you're willing to go and what types of technologies you're willing to employ. As some have stated, GM isn't going to put a 4 valve head on the V-8. Okay, fine, maybe that's the right choice due to size, weight, and cost. But, we already know from benchmarking hp/l that the 2 valve head will be limited to about 100 hp/l while retaining other good characteristics. Now, by looking at hp/liter, we know that you can achieve 600+ hp while retaining a 2 valve pushrod design and optimizing port geometry, cam timing, chamber shape, intake manifold, compression ratio, etc. . . NOW do you see where hp/liter thinking leads?

If you were to scale the 10 year old 4.6 4-valve engine up to 6.0 liters, then it would make more power.

Mike

black_knight

iTrader: (1)

Did you read the post I was replying to? He clearly thinks it's a semantic issue.

(latter bold is mine)

Don't you see? You're doing it again. Ignoring the important factors and focusing on a disconnected metric that isn't a good basis for comparing engines.

black_knight

iTrader: (1)

You can't just do that. That is one of the worst fallacies of HP/L. First, if you scaled it up, it would be a different goddam motor! Second, things do not just "scale up." Try "scaling up" one of those tiny thimble-sized motors that make huge hp/L and see what happens.

And what's the point of your "10 year old" comment? I was making a comparison with HP/L. That comparison says the ford 4.6 is a better motor. Clearly, it is not.

black_knight

iTrader: (1)

Nah, what I mean is that it didn't "scale up" to 6.0; it's not like you shined a raygun at it and it got bigger. You changed the bore and stroke, which is sometimes possible, sometimes not. But the laws of physics mean that you can't just enlarge a small engine to make a big one. The proportions don't work on larger scales. So it's particularly useless to compare small engine HP/L to large V8 HP/L and say that the latter are lagging behind big time in the "advanced" department.

I think there's a lot of confusion in this because people talk about increasing HP/L and imply that they don't mean to change the number of L's involved. But mathematically, that cancels L out of the equation. It's just a really convoluted way of saying you want to increase the HP. Well, duh, that would be good. But why did you just go in a big circle to get there? Why twist yourself in knots to involve HP/L?

As before, the purpose of an engine is to make a car move. Displacement-specific output is not the purpose of an engine; just plain output is.

If you're going to compare engines from a performance perspective then you need to use a performance-related metric. It is false to say that if one engine has better HP/L than another that therefore it is "better," "more advanced," etc. From the perspective of performance, HP/L is entirely null. It means nothing.

Let's say that we have a car and want to decide which engine to put into it. We are concerned entirely with performance. We'll take two engines of relatively similar size, weight, form of aspiration, and power output. These two engines are the LS7 and the BMW V10 from the M5.

The LS7 is physically smaller. It is 71 lbs lighter, despite BMW's use of exotic materials. It produces more power, especially under the curve.

And it has less HP/L.

Did HP/L tell you which engine was the better one? No. Did it even contribute positively in some way to that decision? No. Is HP/L a useful or valid metric of a performance engine?

No. Which is why I'm saying it shouldn't be used for that purpose.

The original poster called HP/L a "lofty goal;" presumably something that performance engines should strive for. Why? Why should they strive for that? It doesn't make the car go faster.

Stang's Bane

iTrader: (22)

I agree with wht you are saying 100%
The only time any output/displacement is a valid arguement is when everything is equal. Meaning physical size, weight, etc. You could even go as far as when displacement is equal, however at that point, it turns into a hp/configuration arguement.(pushrod vs ohc, inline vs V config etc..)

Given two equal physical size/weight engines, in a street/race car, I will take the one with the higher displacement everytime. Honestly, I don't know of many that would not.

engineermike

Question: How much further can we take the production LSx engine, hp-wise NA?
Stipulations/assumptions: 427 is the max cid, keep cam-in-block and 2 valves/cylinder.
Answer: Around 630 hp using demonstrated technology. (I'll give you one guess as to how I arrived at that answer).

My question for you, black-knight, is: what is your answer to this question and how did you arrive at that conclusion?

Okay, reality check here. Powerplants are scaled all the time. A few examples come to mind:

- The 4.3 liter v-6 chevy is a 350 minus 2 cylinders. It makes 75% the power of an equivalent 5.7, just as expected.
- The Ford modular v-10 is a modular v-8 plus 2 cylinders.
- The 150,000 hp gas turbines produced by GE were scaled up in some way, shape, or form from the earlier 15,000 hp units.
- Heck, the LS7 is basically a scaled up LS6. Larger bore, stroke, valves, ports, runners, throttle body, etc. . . and guess what? Strikingly similar specific output (dare I say, hp/liter?).

Of course, when you scale up a powerplant while retaining the same number of cylinders, considerations and debits have to be made in some areas, but the concept is still valid and used frequently in industry.

Mike

DanO

lets face it.. black night is correct..



the automotive industry doesnt know what its doing.. somebody better inform them!

FieroZ34

iTrader: (1)

Looking at GM's sales figures, I'd have to agree (But without the sarcasm).

DanO

.. that doesnt have anything to do with their engine designs though.. GM is one of the leaders in the fuel consumption arena and has very powerful engines.

FieroZ34

iTrader: (1)

You'd think with all these great engine combinations, there would be funds to spare for little things such as interior and exterior styling. But alas, BMW has the funds to build these exotic 100+hp/l engines, and yet still build a car that people will actually buy.

got-a-ls1

iTrader: (12)

thats just stupid... BMW charges 3 times more while they do it! you cant even compare because of the cost difference. you think any of these car companys are in business to make people happy? its the bottom line that matters to them.

If GM can sell their cars with their "cheap interiors", why would they spend more on them if they are meeting their sales goals.

Id hate to show you how many more cars GM sells then BMW.

black_knight

iTrader: (1)

That's what I was getting at. You really glossed over that part. Also, the LS7 has totally different heads than an LS6.