Is that true? I don't know the answer to that. I do know that there are some 7L+ V8's that make your 8500rpm number. Ofcourse they have to be solid roller, but their piston speed is MUCH greater than the Ferarri's you listed. That Ferrari's cylinder's aren't that large at 4.3L and 8 cylinders. Don't just look at the displacement of engine, but the size of the individual cylinders. Those are pretty small pistons and not nearly the stroke of the 7L V8.

Don't get me wrong, the Ferrari engine is extremely impressive. I'm just curious as to how ohc's are capable of higher RPM's than ohv's of the same size? I honestly don't know.

I swear I didn't make this up. I thought it was mainly due to less moving parts. I actually think I wrote about it in a paper for school about 4 years ago. Maybe I'll be able to find it.

 

I'm gonna take a stab in the dark and guess you have been taking this discussion personally. As logically its the only reason I can think of for some of your comments.

eh?

HP is just an expression of torque at speed. HP WILL NOT exist without torque, but if torque exists then there is HP.

Ok you seem of be comparing a blender with dragster. I mean what sort of engine is capable of producing 1200lb ft @ 4200rpm? None that are streetable.

But alternatively what sort of motor are you using to claim 100lb ft from???

You seem to have sat down with the calculator and just inputted numbers until you've found something you can use to argue with.

Any chance you want to divulge what engines you actually had in mind?

Physically impossible is a strong word. Usable, reliable and durable are all important and this is where OHV is let down. Can you show me a single street going OHV motor using those rpms?

Also there's a thing called curtain area. I'll explane after your next quote.

Simply - YES!

Now this is more than just OHV and OHC. It comes down to curtain area.

Assume you had a 2v per cylinder engine. Now this could be OHV or OHC it would matter not in this instance. The combustion chamber has no idea how the valves are being operated.

Now due to curtain area the engine will have an operational rpm range. Say 1500-5500rpm. After that it basically runs out of puff/air. To increase HP you can run a wilder cam(s) and ported heads or even bigger valves. But suddenly your operational power range has changed. It's now 3000-7000rpm. This means it's a bit of pig down in the low rpms. Not very nice to drive, probably won't idle very well.

This is the same for ANY 2v per cylinder engine. OHC and OHV.

Also buy adding bigger vlaves and higher lift cam(s) it means you have to have much greater valve spring pressure. This means increased wear rate.

Multivalve setups like 4 valves per cylinder which are typically found in DOHC engines (but not exclusively, there are some SOHC and even OHV multivalve engines out there).

Such an engine may have an operational rpm range of 1500rpm-7000rpm. So the torque curve will look different anyhow, because it's doing more over the entire rpm. If you took a snap shot of the torque curve over a smaller rpm range (say same as what the 2v works in) then it would be identical. Assuming same bore & stroke of course.

To then gain HP you can do cams and p&p heads the same. But beacue you have double the amount of valves opening you generally won't need such a wild cam or heavy vlave springs so wear rate is reduced.

But you can get say 2000-8000rpm usuable rpm range with a good idle.

With an OHV a limitation is valve train mass. The higher the rpm the less suited it becomes compared to OHC setups.

Lastly, it's very easy to confuse bore & stroke, or more rather forget all about it.

Most OHV engines are long stroke. This suits the valvetrain and the large displacement. Thus making lots of torque low down but generally not liking high rpms.

OHC motors are generally short stroke which again suits the valve train setup, so you will generally see torque in the higher rpms.

This is not a direct function of valvetrain layout, it is merley a side affect associated with bore & stroke in combination with vlave train.

If you can find where I said that I'll buy you a C6 Z06!

What I said is:

HP = torque (lb ft) x rpm / 5252

Meaning the more torque you can make at higher rpms the more HP.

So to go back to your example:

12,000lb ft @ 4200rpm = 9596HP

Imagine if the SAME torque was produced 2000rpm higher?

12,000lb ft @ 6200rpm = 14,166HP

A massive difference. Using the equation its easy to see that small chances to rpm will have a greater affect on HP than small changes to torque.



Physics IS maths.

 

Physics is the application of math. I didnt take it personally, nor did I intend to personally insult your intelligence in any way.

I was making up theoretical numbers. What should be said here and now and always is that you can have a 3.0L v6 OHV and a 3.0L v6 DOHC, and both can make exact same HP numbers. Its all in the tune.

 

No worries, I;m not insulted at all

I love these topical debates, its just sad if it reduces to name calling.

As for your example, then I'm afraid I'd have to disagree.

Assume 3 engines. Identical bore/stroke and heads (where possible). For all intensive purposes they are the same. Except on is 2v OHC, 2v OHV and 4v DOHC.

Now under this circumstance:

both the 2 valve engines will make very similar power across the same rpm range.

However the 4v unit will have a bigger rpm range and will not run out off puff at the same point. So it will by means ot making torque at higher rpms make more power at PEAK. But crucially MATCH the 2v setups below the curve.

for the 2v setups, if you made the stroke longer and bore smaller. You would see very little difference between them. The higher rpms would be restricted due to inertia of the pistons. But a 2v OHC would match the 2v OHV in torque and HP. The down side is the OHC isn't playing to it's strengths. It's using a more complex and liely heavy valvetrain to achieve what a OHV can do.

However if you changed them to a short stroke and large bore setup. The OHC would be more comfortable at higher rpms. And has the potential to make more PEAK HP. However the operational range of the engine would not change, so the advantage is somewhat limited.

A nice example is the ford 4.6 2v unit. It's OHC but for some reason uses a long stroke and really doesn't not make any use of it's OHC design. The DOHC engine adresses this nicely and is by far a superior engine over the 2v unit, although it is still not ideal.

Have a look at the attachment. It's not a particulary good example but I hope it gets the point across.

The left hand chart shows what happens on a 2v setup if you add a high lift cam or big valves, etc. It moves the torque up the rpms (pink line). so you get more HP but you loose out at the lower end. Remember this is the same for ANY 2v setup be it OHC or OHV.

The other graph is a represenation of what a 4v setup can manage. It matches the stock 2v in the low rpm and also in the high rpms. It is in many ways the best of both worlds.

It's never just as simple as OHV vs OHC because there's so much more too it. But ultimatley a multivalve engine capable of spinning high rpms will be able to offer the highest HP and the most driveable.

 

I live my life one liter at a time.

 

300bhp/ton-

I did some googling and everything I read pointed to DOHC's generally being more expensive than OHV's.

Another interesting thought I found from someone:

"Here's why GM OHV engines have higher displacement than their OHC competitors...BECAUSE THEY CAN...the absence of a overhead cam makes the engine MUCH smaller, so that the block can be bigger to support higher displacement...

Another by product of the absence of an OHC is LESS WEIGHT...therefore not only can an OHV have more displacement in less size than it's OHC competitor, it WEIGHS LESS...in fact a 5.7 Liter LS1 weighs about the same as the 3.5VQ and has similar physical dimensions, but also with, of course, more displacement..."

 

Here is your 1k+ hp N/A pushrod engine
You wont want to see this in your rear view mirror pissed off at you =)

 

Yeah I know, but what I can't determine is the truth behind the claims. It just seems to be internet folk lore.

Someone onced claimed it ws cheaper, they told two poeple who told two people and so on.

It's just like some of the mods we perform on our cars, like TB coolant by-pass. Everyone seems convinced it's there to prevent the TB freezing. I say bollox to that, the avaialble evidence and physics don't support that conclusion. However do a search and that's what you'll be told.

Now I'm NOT disagreeing on the costing of OHV compared to OHC. I merely state that I see no evidence to support the theory except for hear say from people who actually don't know. If I was a kjudge and this was a court of law based on the evidence I've seen I would not be able to rule that OHV is cheaper, infact there is more evidence to support that it isn't.

I would like to know though.

Yeah this is something I've heard before. But again I don't really know the truth, sure I know what a OHV looks like, got two different one on my drive at the moment. But I can't really believe OHC can't support the same displacement. Again I think this is very much folk lore spawned by the lack of a large displacement OHC.

I mean take the Ford 427 OHV, it was converted by Ford into a OHC engine for Nascar, known as the Cammer. It still retain 427ci and the block didn't get any bigger. Sure the heads where larger but it didn't double the size of the engine. Also had it been designed from the ground up then the block could have actually been made smaller because you wouldn't have needed room for the cam.

At the end of the day, yes a DOHC engine must end up a bit bigger and heavier, but you have 4 cams as opposed to 1 in the OHV. But I do honestly believe the size and weight difference is minimal under ideal circumstances.

Sadly people always then look at the Ford modular unit, this is not the pinnicle of OHC engines and should never be used as an example as one.

The Jaguar AJV8 is a much better example. It's similar sized to a LS1 ( a little narrower I think but a tad taller, due to 90 degree V and not 45 degree). It also weighs slightly less than a Ls1. So far maximum production capcity is 4.4 litres. But I have no idea what true potential it has. No where near what the displacement an LS1 can be taken too, but then the AJV8 was never intended for that kind of use. Had it been, who knowns. An extra inch in length would of allowed much bigger bores and thus more displacement.

Not sure I understand this, smaller engine can support higher displacement. Doesn't make sense. A cubic inch is a cubic inch and requires the same amount of space regarless of valve train. And as stated an OHV has to make room for the cam in the block where as OHC doesn't. OHC should in theory have greater potential to have a smaller short block but larger displacement. Becuase the block doesn't have to cater for any of the valve train. Th elong block due to DOHC heads maywell make it bigger overall, but that's not relative to your statement.

Well I think the above covers my views already on size and weight.

But also look at it this way, an OHC doesn't need the same displacement as a OHV to make the same or more power. This is again one of the key reasons why we don't see large displacement OHC engines. They simply are not needed for production road cars.

Example:

OHV to make 500bhp and be FULLY legal as a production engine. Which means noise and emissions complient, along with durability and driveability.

Currently the best is the LS7 which requires 7 litres. (specific out put of ~71bhp/litre)

Even "aftermarket" modified it will still only reach ~96bhp/litre in a fairly wild setup and produce ~675bhp.

DAMN IMPRESSIVE!!!!!

But potentially a DOHC V8 could easily achieve 100bhp/litre as a STOCK FULLY legal production engine. In which case the OHC would only require 5.0 litres to math the OHV on power.

And then if the "aftermarket" wanted to tune it up, 120bhp/litre would not be out of the question which would bring it very close to the OHV. At 600bhp.

And to be honest you would only need to get the OHV to 135bhp/litre for a 5.0 litre engine to actually match the wild cammed 7.0 OHV @ 675bhp.

Now it probably would end up being rather a revvy beast, but due to curtain area it would probably be smoother in the low rpms and more driveable. This is very a doable, as there are a few 4 cylinder DOHC in production as FULL legal engines making almost this specific output.


At the end of the day, I'm not claiming OHV is rubbish. Because I genuinlly like OHV's and have a personal preference for them. However as an ultimate performance engine DOHC is in concept technically and ultimatley superior.

It's like taking an F15 fighter and pitching it agains a F22 Raptor. You can add every hop up to the F15 with bigger guns extra rockets and so forth. But at the end of the day the F22 is technically superior.

 

Cool truck!

Is it yours?

Got any info on the motor, like displacement and fuel it runs on?

 

It isn't random people on forums claiming OHC's are more expensive, I'm finding this on sites with pure information on the various differences between OHC and OHV.

The only disadvantages they give for OHC's are more moving parts and more expensive. I don't see why that is so hard to believe - take a 4 valve/cylinder DOHC compared to a 2 valve OHV. Is it going to be cheaper to make 4 valve cylinders with more lobes that need to be actuated or a simple 2 valve design? And I don't need to give you scientific proof as to why 4 cams (and all of the parts each entail) are more expensive and will take up more space than 1 cam.

But I agree that if cost is no object, DOHC is king. That's why F1 cars use them. They can rev them to the moon and have more valves for breathing, yielding a lot of power with minimal displacement. Oh, I also had found exactly why DOHC's can be spung higher than OHV's, but I'll have to find it again when I get home.

 

GM bought Lotus in 1986 -- before the ZR1 was planned....Lutus = GM GM North America actually had a good deal of influence also. Every month during development, there was a meeting with GMNA/Lotus/Mercruiser to hash out design details. The fact that the motor could hold the endurance record for over 10 yrs only to be dethroned by a non-production prototype is a testament to how great it was.


Seeing as we only have a few of the 800hp+ engines from TVR -- it is hard to say how durable or drivable they actually are. Would one last 50k, 100k or 150k miles with just basic maintenance -- I seriously doubt it.

 

OHC engines may make peak power but f1 cars only weigh around 1500 pounds and they idle at around 4000 rpm. Try putting that in a street car. I dought the engine would even have the torque to move the car. Horse power is the measure of the amount of work an engine can perform. therefore horsepower is directly related to rpm's to the point of which the engine becomes inefficeint due to mechanical limitations (ussually thte heads or valve train). Torque is the actual twisting force of the engines crank shaft. f1 cars have great heads and valvetrain but lack torque very much so. So you should really rethink the idea of DOHC being king. Maybe king of the road corse. But for sure not king of any drag strip. I see no DOHC on the topfuel funny cars or dragsters. I don't see too many of them even setting world speed records. So they're king? Not really. When you get down to it both setups have pros and cons like anything and you have to decide which one suits your aplication best. Just because DOHC works great in a 1500 pounds f1 car that'll never have to sit in traffic at a stop light and only has to accelerate a few times in a race doesn't mean it is the hot ticket for everyone.

 

Yes, you are correct because very few Corvettes are actually imported to the UK and the import tax is very steep. Regardless, the Z06 out performs the Sagaris handily regardless of engine design. I pointed out price to show what American consumers would be paying for a car like that -- I imagine well over 100k (if imported here). When you buy an American car in the UK, you are still getting a car that is made around the American price point. In the case of a Z06, it is a car built for $65,000 or £35000. Another example is the Mustang -- the base price is ~£300 less than the cheapest Vauxhall Astra (a 4cyl econo car similar to the base Saturn Ion ) in the UK.

If us people living in the US had to pay the same import tax and VAT -- a $93,000 Sagaris would cost us $110,000 --That is $17,000 flushed down the drain. Even with the extreme tax on the Z06, it still smokes the Sagaris for a little more money.

I don't think they're bad. It has yet to be seen if Honda can just double the displacement and double the power at the same time. The biggest question is can they do it and compete price wise with OHV alternatives, namely the Viper and Corvette. So far the most HP we have received from Honda was the NSX (I believe) -- $95,000 290hp 3.2L...performance similar to a '96 C4. Currently, the 290hp 3.5L is the HP king.

 

Can you give the price of the cars that will outperform the Z06 in both £ and $ amounts? Please exclude things like Catherham, Radical, or Ariel as they are more purpose built for racing. From what I've seen, UK buyers are paying ~58,000 GBP for a Z06 On-The-Road and ~33,000 GBP for a regular C6.

In comparison, something like a Noble M15 cost £75000 and ran a tenth slower around Top Gears track. That is $32,000 extra to match the handicapped Z06 with about $30,000 in taxes added to it. A 911 Turbo is £96000+, M6 is £82000, Marcos with performance pack is £58000 (462hp LSx pushrod engine )

The Corvette and Viper have plenty of refinement and quality for their price/performance combination. In comparison to something like a TVR I'd say they are leagues ahead in quality and reliability. If you want more, you'll have to step up about $70,000 and get a Porsche -- but hey, even they aren't perfect(and the 911 TT is outperformed).

 

The truck belongs to a customer.
It used to be his high school truck and was 2 wheel drive and lowered.
It has since morphed into the monster you see it as now.
The engine is a merlin alum tall deck, with dart big chief heads, Lunati crank, oliver rods ect ect ect.... it is just shy of 600 inches.... you can se more photos of it at www.offroadfabrication.com
The engine just makes STUPID power

I work with Darren @ fulcrum fabrications and he built most of the truck before I started working with him.... I did the front engine cage from the a pillar downtubes forwards, as well as bunch of other things =)

 

I hear what you say, but I can't help feeling its a rather naive viewpoint.

1. If you wanted to use a DOHC large displacement V8 for Top Fuel use, which engine would you use?

Well you see there aren't any in production. So that's the real reason behind it. Lack of availability not lack of ability.

2. Where is top fuel drag raving most common?

America, and what engines are plentiful and affordable in the USA? Yes large displacement OHV engines.


Not too sure where the world speed record comes from? I mean piston engines haven't been used for such attemps in decades. Jet and Rocket powered vehicles like the Thrust SSC are the current record holders.

But that aside, again where does this high speed attempts take place? America (Bonoville) so what large displacement engines are readily avialable at affordable prices? Yes OHV. And if you wanted to use a large displacement OHC which one would you choose?

 

I'm still not convinced. I've read a lot of these articles and non ever talk figures or have any references. It's like the EGR myth, do a search on Google and you'll find plenty of info out about how harmful it is to HP. This is all bollox, but to find the truth you have to dig deeper.

REMEMBER - I'm not claiming either way. I merly seek proof rather than non-fact based opinions.

But not all OHC's have 4 cams. I still think its pretty even.

SOHC - 2 cams, 2 sprokets & timing chain
OHV - 1 cam, followers, lifters, push rods, 1 sproket & timing chain

A DOHC only requires a few more components. A cam is not expensive to make, sure we may pay a lot for aftermarket ones, but that's due to R7D as much as anything.

 

Well did GM own 100% of Lotus? I’m not sure they did, as part of the company is still privately owned today. The rest being Proton. But regardless, Lotus Engineering is/was a British company based in Britain.


Personally I think the LT5 is fab engine. And after a little research it appears that it actually weighed pretty much the same as the LT1.

No I agree, we don’t know what they would be like long term. But looking at the only available data we have from smaller displacement engines producing high specific outputs then one could surmise that reliability should be very good. Although any issues would likely be due to other design flaws and not directly related to the basic valve train setup.

2.0 Honda VTEC engines have proven to be very reliable.

But realistically, if GM sold the Ls1 with a huge cam and all the trimmings making 450-480rwhp would it still be reliable for 100k with services every 20k or so?

Sadly comparing costs is not really possible. The easiest way I’ve found is assume $ = £ so if someone in the US earns $35,000 a year then in the UK for the same job they would earn £35,000 and vice versa.

I hear what you say, although a Mustang is actually about £23-26k here. So the same numbers as in the US just a different currency. It all goes back to not really being able to compare prices trans-Atlantically.


I don’t think it’s a question on whether it’s physically possible or not, such tasks have been undertaken in the past. Radical make their own V8 based out of 4 motorcycle engines. And for the state of tune it pretty much retains the same specific output.

On price I have no idea. But performance wise it’s hard to compare the NSX. Remember when it was launched in the early 90’s it had more power than a Corvette (TPI was it, 250bhp?) and was well on par with Porsche and Ferrari.

Also Japanese BHP numbers are mis-leading as for a long time legally they where not allowed to claim anything above 280bhp, regardless of the actual figure. The last of the NSX’s must have had a lot more power. Autocar Magazine clocked one 0-100mph in 10.6 seconds, they are also capable of running low 13’s @ 108mph. Very comparable to a manual Corvette C5.


For £ or $ per HP you CAN NOT beat American muscle. Hence I drive one

But in the UK cars such as Caterham’s are comparable to the Z06. The Z06 is designed to be extreme and track able. So for many it would be a weekend toy or a plaything. Caterham’s would fall into this category quite nicely. And believe it or not some people do DD them all year round.

Prices vary quite a bit. But for £35,000-£40,000 you could have a new car capable of beating a Z06. Maybe not in at the ¼ mile although it would be close. But certainly on the road and a circuit.

I think a C6 will setup you back about £45,000 not £33,000 in the UK.

I agree FULLY.

Generally exotica cost more money over here. The Noble is getting more expensive all the time, but then it is hand built and very exclusive. Price does not fully reflect performance, and there’s also the thing called FUN.

That was my point, not everyone wants outright performance.

 

We've been over this. No, they're not. Not even when money is no object. They have advantages and disadvantages. That's it. They're superior only if you're racing in a displacement-limited class. Or your idea of superiority is less NVH.

OHV engines are, all other things being equal, smaller, lighter, and less expensive.

 

Yes and no.

What is dismissed, rightly, as "ricer bs" is the idea that a HP/L is a meaningful measure of an engine. In fact, an engine could have less HP/L and yet be smaller, lighter, cheaper, and make more power. It could be in every meaningful way better and still lose in a contest of HP/L. (This is no abstract "well it could be" discussion, either. There are actual engines out there that fit that scenario)

Nobody dismisses that OHC can make more power per liter. What is dismissed is the idea that that statement is in any way meaningful outside of displacement-limited racing classes.

In other words, specific output is not a useful, meaningful, or intelligent way to compare engines. Anyone who does so, outside of a very limited context, is revealing their ignorance.

Thus, "Ricer Math."