Are there advantages to running a destroked 7M?

[Ma70.Ent]

For both turbo and N/A purposes, are there any advantages? I'm not too good with these types of engine concepts so knowing this would be nice. I don't understand the whole high revving craze and I have no idea why it could be advantageous. What's the point of losing torque to gain revs, etc? If you could answer this in-depth, that would be great. Thanks for your time :D

[Doward]

# of putts per minute = more power.

Either more cylinders, or more revs.

[bmoss85]

it really depends on what you are using the engine for, and where you want to make your power. destoked engines usually lose some power on the bottom end, but make up for it on top with the extra rpms its able to turn. i cant say a whole alot about the turbo application of this though, as most of the engines i have built have been chevys.

[Adjuster]

In general theory, if you are building a motor, you can tailor the bore v/s the stroke for the vehicle the engine is going to be run in.

A "Square" engine is one where the bore and stroke are about the same. (Or are the same.) It generally results in an engine that is quite well rounded, depending on the displacement of the engine.

The 7M is a stroker motor from the factory. It has a longer stroke than bore, and thus was/is a good engine for making tourqe, but is somewhat limited in how high the engine speed can go without causing terminal damage to something. (Rods)

Destroked, and thus lower displacement 7M's have been built that made serious power at high rpm. (HKS did it on the 80's MK3 based drag race car.. 9 second or better IIRC on 2.8L and custom everything.)

The JZ engines are also shorter stroke, and more "square" designs than the 7M. They allowed for a shorter stroke by having a larger bore to keep the displacement ability of the design capable of 2.5 or 3.0L and still have a motor that can turn quite fast with less stress on the rods.

There are some long stroke engines out there making serious power at very high speeds, but they also tend to have very high quality internal parts. (Forged, Ti and other expensive yet strong moving stuff for the crank, rods and pistons.)

Valve weight is an issue too. Most larger valves are going to hollow stems, and other tricks to keep the weight down. (Lighter materials too.)

Ok, so all things being equal here is a good rule of thumb.

Same engine design. I6 in this case, and 3.0L for discussion.

Generally, the one with the large bore, and short stroke would make more high RPM power and have less off idle tourqe.

The one with the longer stroke, and smaller bore would make more low and midrange tourqe, and possibly less power on top due to reduced engine speed.

The way around this, is to build a long stroke, big bore, and higher displacement engine with quality parts that can handle the engine speed, and yet provide the best of both worlds. (IE: My stroker 7MGTE.. :) ) LOL

In the V8 world, look at the LS7 engine. It uses very high tech, and expensive parts to maintain the best of both designs, but now the new LS9 Supercharged engine has gone back to the displacement and design of the "base" engine with thicker cyc. bore walls, and less stroke to help keep this motor together under the stress of force feeding it.


BTW, turbo size, or SC ratio all play into how the tourqe curve is going to look on any motor, and with variable valve control, many engines that would normally be "gutless" down low, or on top can now have very broad power bands because the valve event timing is completely controlled by a computer. (Heck, some do not need throttle bodies, they are controlling it all with valve control.. You step on the "gas" and the computer decides to now start opening the valves more to flow more air v/s a "gate" like Throttle body that allows more air into the intake manifold.. ) As you might expect, this makes throttle response very fast, and reduces some other losses, so the fuel economy and power is further improved.. (BMW calls it "Double Vanos" IIRC.)

And that is totally another subject!

[3p141592654]

You mean Valvetronic, not Double Vanos.

[Adjuster]

Ok, whatever, vanos, valvetronic, and now I see Nissan has their version in the G37.

It works, that's the key :)

I would expect to see some sort of variable valve timing, lift and complete control like this on new motors along with more direct injection engines.

It would not supprise me to see 12.5:1 or higher CR with variable valve control and direct fuel injection become standard on most vehicles in less than 10 years time. (To easy to improve fuel economy, power and emissions performance with these new systems.)

The really cool thing is with turbo charging and these designs, the ability to overcome lean detonation and pre-ignition is very possible. (The fuel is added only when the computer wants to burn the fuel, and depending on load, could run lean under low load, and rich enough to avoid excessive heating of stuff when making power.)

Also more diesel engines, and possibly even engines designed mainly for E85 that can run on pure gas, but will run best on the higher octane E85.

It's going to be fun, no matter what ;)

[madseacow]

weird, I was just looking this up last night, and came here to ask about 5m crank swaps. I'm not done reading aaron's thread, so forgive my ignorance. I don't know much about the subject, but I enjoyed reading this Wiki page. (http://en.wikipedia.org/wiki/Stroke_ratio)
If anyone feels like commenting, I'm thinking I could sell my current 7m crank/bearings and get closer to square with this. (http://www.rpmrons.com/toyota,cranks.html) I havn't come across the stock 5m stroke, stock 7m is 91m, I believe I can get 84mm max out of the stock block's bore correct? It'll be damn close to square. I'm interested in square for the throttle response benifits, and reliability at sustained high rpms (nothing crazy, 7-7.5). Is that a bad idea?

If this is answered in "high revving 7m" or "Bigaaron's" threads, I'm sorry... I'll get to it.

[annoyingrob]

If you picture your piston movnig up and down, it's obviously experiencing acceleration forces as it's being pushed up and down.

Now picture two motors, one with 10mm of stroke, one with 20mm of stroke, both spinning at 1000rpm. Both pistons are moving up and down 1000 times per minute, however the piston with 20mm of stroke must move much faster, as it has twice the distance to cover in the same amount of time as the motor with 10mm of stroke.

What's happening is the more stroke the motor has, the faster the piston is moving, and the more force it being exerted on it. If you were to look at a 7M revving to 6000rpm, the pistons would be subjected to the same amount of force as say a 2JZ would experience at 7 or 8k (That's not a mathematical calculation, just a wild guess used so you get the picture).

By de-stroking the motor, you're decreasing the stress you're placing on the pistons and rods, effectively allowing them to spin faster. By decreasing the stroke, say 10%, the motor can spin I believe about 19% faster (just doing some math in my head, I may be way off)

For de-stroking a 7M, I wouldn't bother with a 5M crank. Too much custom work to be done to it to fit properly in the block. What I would to is take teh 7M crank to a machine shop, and have them re-grind the rod journals offset to decrease stroke. Then it's just a matter of getting some custom rods with the right length and cam diameter, as well as right bearing size.

[madseacow]

Cool, thanks for the input. It seemed like I could just drop in a new crank with new bearings and be ready to go. But I guess not, if there's no easy/painless (Relatively speaking, without gobs of machine work) method then it's not really worth it for my build. Thanks again.

[Keros]

What's happening is the more stroke the motor has, the faster the piston is moving, and the more force it being exerted on it. If you were to look at a 7M revving to 6000rpm, the pistons would be subjected to the same amount of force as say a 2JZ would experience at 7 or 8k (That's not a mathematical calculation, just a wild guess used so you get the picture).

By de-stroking the motor, you're decreasing the stress you're placing on the pistons and rods, effectively allowing them to spin faster. By decreasing the stroke, say 10%, the motor can spin I believe about 19% faster (just doing some math in my head, I may be way off)

Just to add a comment here, that on a 4 stroke engine, it's the exhaust stroke (where the exhaust valves are open and the piston moves from bottom to top), that is most likely to cause catastrophic failure at high RPM's. When the exhaust valve is open, the pistons are pushing exhaust out, and there is therefore, no compression to slow the piston down as it approaches the peak of its cycle, this causes the rod (and only the rod) to slow the piston down and prevent it from rocketing through the hood of the car... however, this puts the rod under immense tensile stress, and like all metals, tensile stress is where it is weakest.

On two of the strokes the piston is moving down (compressing the rod) and the other stroke the rod is aided by compression in slowing the piston.

[Adjuster]

Thus the reason I have Pauter forged billet rods on my stroker...

Exhaust stroke stresses at stock rpm seems to be no problem.. :)

Even on a few over-rev moments into the 7150rpm range, it has not broken anything up to this point...

No need to rev this engine higher either, it's very powerful down in the 3.5k to 6k range, right in the sweet spot of this combination.

[Doward]

Also why I'm running Eagle Forged rods here. Hell, it's the big reason to go aftermarket forged rods - it handles the loads much better ;)

[turbodriz]

I see in the begining of the thread that the conversation was about rev. I just wanted to say that it has been proven time and time again that the 7m can be reved at it's standard stroke. There are many guys here on the site who's 7m make power in the 7.5 8.0 grand range.

[supradjza80]

For what it is worth the 2jz is perfectly square at 86 x 86 (bore x stroke). I believe the 1jz is 86 x 77. From what i have seen I think square motors have the most desirable characteristics, the best of both worlds design.

A formula one car for example has a really large bore and an extremely short stroke, (Ill see if i can find the exact numbers when Im not at work). So a formula one V-8 (2.4l) makes about 300 ft-lbs of torque maximum but since it revs to 19000 rpm it makes 750+ hp.

More interesting info is the equation for hp and torque and how they are related.

Hp=TQ*RPM/5252, so basically at 5,252 rpm horsepower is always higher than torque. This is also why making your torque curve go into higher rpms produces more power than the same torque curve at low rpms. And for what its worth, more HP is always better than more torque in terms of vehicle acceleration.

[annoyingrob]

^ 1JZ is 86x71.5mm

Random fact, RB26 is 86x72mm

[figgie]

A formula one car for example has a really large bore and an extremely short stroke, (Ill see if i can find the exact numbers when Im not at work). So a formula one V-8 (2.4l) makes about 300 ft-lbs of torque maximum but since it revs to 19000 rpm it makes 750+ hp.

more HP is always better than more torque in terms of vehicle acceleration.

F1 motor specifically.

the Bore is double the size of the stroke or put another way. the stroke is excatly half the bore size.

As for your last statement.

WRONG. HP = work but without Torque, nothing will happen (Hp= Work,TQ=Force, RPM = Time). Torque is a force that without TIME (very very important) is does not produce any work (put a 1 lbs weight on your breaker bar that measures 1 ft, means 1 ft/lbs. Problem is the weight is hanging there and not moving. A Force but no work is done). HP and Torque are related. You can have torque but no work done. But you CAN NOT have HP without the Force * time (simple work equation).

[Poodles]

Hp=TQ*RPM/5252, so basically at 5,252 rpm horsepower is always higher than torque.

Nope, it's the crossover point and they're equal.

Take two exact cars (assuming they have the ability and aren't already on the edge of max flow) and spin one up higher than the other. The one that revs higher makes more HP. These cars would be equal until they had to shift and the higher reving car would win as it would be higher in the powerband where there is more torque/horespower.

On a side note, the WRC cars run restricter plates and are tuned for the most power at 5252 RPM. They run out of air and getting more under the curve is the way to more power in their application as their max flow is limited.

[figgie]

Nope, it's the crossover point and they're equal.

Take two exact cars (assuming they have the ability and aren't already on the edge of max flow) and spin one up higher than the other. The one that revs higher makes more HP. These cars would be equal until they had to shift and the higher reving car would win as it would be higher in the powerband where there is more torque/horespower.

Just an FYI

More revolutions per minute equals more work done in the same amount of time (Second, minute, hour). That is of course taking into consideration that the head can flow the the amount of air for the given RPM.


On a side note, the WRC cars run restricter plates and are tuned for the most power at 5252 RPM. They run out of air and getting more under the curve is the way to more power in their application as their max flow is limited.

To be more exact. The restrictor plate is exactly a 34mm opening for Group A cars, 32mm for Group N cars. The Restrictor plate must be within 5mm from the turbos Impeller and is attached via a tamper proof mechanism by race officials. Once installed, it can not be removed or bypassed. That is why WRC Cars have ALS on thier systems so they are always in positive intake pressure. IF by chance they fall of boost, the motor is sucking wind literally to try and produce power.

http://foo.is/~baldur/wrcevo1.jpg (http://foo.is/~baldur/wrcevo1.jpg)

Restrictor on the right hand side attached to turbo inlet.

[annoyingrob]

^^ Are they feeding air into the exhaust manifold too?

[figgie]

^^ Are they feeding air into the exhaust manifold too?


Glad you "caught" that :)

Actually that is the new version of the anti-lag system based on EGR. It works both ways for them ;)

The NEW ALS system that particluar car uses (EVO) is actaully pretty intresting. The "valve" you see on the exhaust manifold serves as the basis to bypass air into the exhaust system while the ECU adds fuel. But instead of the old style where you are dealing with pumping losses to get the air through the engine, this way, unrestricted air is injected directy into the exhaust stream while the unlit fuel comes into the exhaust, at the right time the valve closes, the mixutre lights and you have an ALS that reduces the EGT, is less destructive to both turbo and exhuast parts but still able to maintain race level boost when off throttle with less fuel consumed.

It is actually pretty f'ing brilliant. :) Also notice no BOV ;) All that work the turbo did is used to keep the turbo spinning off throttle. So no venting to atmophere for them anymore and if you think about it, why would you when you can keep all that nice pressurized air in the system and help in keeping the turbo spinning.

[JtWo]

this thread is so informational and gets me in trouble at work.

[tekdeus]

Glad you "caught" that :)

Actually that is the new version of the anti-lag system based on EGR. It works both ways for them ;)

The NEW ALS system that particluar car uses (EVO) is actaully pretty intresting. The "valve" you see on the exhaust manifold serves as the basis to bypass air into the exhaust system while the ECU adds fuel. But instead of the old style where you are dealing with pumping losses to get the air through the engine, this way, unrestricted air is injected directy into the exhaust stream while the unlit fuel comes into the exhaust, at the right time the valve closes, the mixutre lights and you have an ALS that reduces the EGT, is less destructive to both turbo and exhuast parts but still able to maintain race level boost when off throttle with less fuel consumed.

It is actually pretty f'ing brilliant. :) Also notice no BOV ;) All that work the turbo did is used to keep the turbo spinning off throttle. So no venting to atmophere for them anymore and if you think about it, why would you when you can keep all that nice pressurized air in the system and help in keeping the turbo spinning.

Essentially a BOV into the exhaust to keep the turbo spinning?! If this works, why isn't it seen more often? Any street cars doing this? Or is a huge Tial BOV "good enough"?

[Supracentral]

Just to add a comment here, that on a 4 stroke engine, it's the exhaust stroke (where the exhaust valves are open and the piston moves from bottom to top), that is most likely to cause catastrophic failure at high RPM's. When the exhaust valve is open, the pistons are pushing exhaust out, and there is therefore, no compression to slow the piston down as it approaches the peak of its cycle, this causes the rod (and only the rod) to slow the piston down and prevent it from rocketing through the hood of the car... however, this puts the rod under immense tensile stress, and like all metals, tensile stress is where it is weakest.

On two of the strokes the piston is moving down (compressing the rod) and the other stroke the rod is aided by compression in slowing the piston.

Correct. I did a pretty extensive writeup on this very topic (http://www.supramania.com/forums/showpost.php?p=180719&postcount=18) quite some time ago.

[gofastgeorge]

The rod length/stroke figure is used to determine maximum piston acceleration at top dead center.
(when the piston changes from going up, to when it starts to go down)
Sorry, I am too tired to go dig through my books to find the actual formula.

The accepted limit is 140,000 ft/sec/sec.
A stock stroke 7M with stock length rods reaches this at about 8500 rpm.
Above that point, the G-force of the upper components,
even with top of the line parts,
will exceed the strength of the parts them selves.
It will also cause the rings to lift of the bottom of the ring groves, and allowing pure fire (on the ignition cycle) to pass by the rings.

With ultra light weight components, this can be exceeded a little.
(titanium pins, only one compression ring, etc.)
And the use of a dykes (L style) ring will also help.

F1 pistons from a few years ago (pre-2 race engine rules)
used only the compression ring, no oil ring.

You can also increase this limiting rpm point by:
shorter stroke and/or a longer rod.

And........
Increasing the stroke, and/or shortening the rods will decrease the RPM limit.

Interestingly,
Crower used to show a rod that had the same upper & lower bearing diameters as the 7M, but was a few millimeters longer.

[figgie]

Essentially a BOV into the exhaust to keep the turbo spinning?! If this works, why isn't it seen more often? Any street cars doing this? Or is a huge Tial BOV "good enough"?

Well funny that you ask,

the EVO IX has that built in. It is not operational though, but the piping is all connected to allow for this type of system on the street. Remember, they (WRC) must use ALS as they are breathing through a 34mm opening. Not even in the most restrictive street car is the opening ever that small.

[Keros]

Correct. I did a pretty extensive writeup on this very topic (http://www.supramania.com/forums/showpost.php?p=180719&postcount=18) quite some time ago.

hehe. Sorry SC, but where do you think I learned it from ;)

I should have noted your thread initally. Atleast your wisdom does not fall upon deaf ears :icon_bigg

[supradjza80]

F1 motor specifically.

the Bore is double the size of the stroke or put another way. the stroke is excatly half the bore size.

As for your last statement.

WRONG. HP = work but without Torque, nothing will happen (Hp= Work,TQ=Force, RPM = Time). Torque is a force that without TIME (very very important) is does not produce any work (put a 1 lbs weight on your breaker bar that measures 1 ft, means 1 ft/lbs. Problem is the weight is hanging there and not moving. A Force but no work is done). HP and Torque are related. You can have torque but no work done. But you CAN NOT have HP without the Force * time (simple work equation).

I know the equations, this is why i said hp is the important value. Knowing HP implies that you know the Force*time...knowing just the force tells you nothing. So i believe everything written above is correct. If you know you have x amount of HP you know you can always gear the thing for the appropriate torque. If all you know is torque, you really don't know anything because of time...

Furthermore, If you have 500 hp, you have 500 hp. You can gear the torque output of the device producing the horsepower to put out the torque that you need. In a car this is the change in torque at the motor to torque at the wheels.

For example you take the motor out of the semi and properly gear it. This motor produces 425 hp peak in a completely linear fashion, but it only revs to 2000 rpm so the motor produces 1800 lb-ft of torque (i didnt calc this - Im lazy, but its just an example). You put it in a vehicle that weighs 5000lbs total.

Now in the other test vehicle you have a V8 that makes 425 hp in a completely linear fashion and only produces 425 lb-ft of torque (motor revs to 5252 rpm). This motor is properly geared as well and you put it in a vehicle that weighs 5000 lbs.

Now you race - and guess what, since the hp is the same they go the same speed...guess torque is not what really matters and horsepower is really what matters. As long as the vehicle has gears in it, and they are appropriately selected torque means nothing, and HP is what is going to determine how quick the vehicle is.

I know you understand the principals here figgie so I am just guessing any disagreement we have here is semantics based.

[supradjza80]

Nope, it's the crossover point and they're equal.

Take two exact cars (assuming they have the ability and aren't already on the edge of max flow) and spin one up higher than the other. The one that revs higher makes more HP. These cars would be equal until they had to shift and the higher reving car would win as it would be higher in the powerband where there is more torque/horespower.

On a side note, the WRC cars run restricter plates and are tuned for the most power at 5252 RPM. They run out of air and getting more under the curve is the way to more power in their application as their max flow is limited.

yeah looks like i mis-typed that, at least i wrote the equation right, but yes hp and tq are equal (HP and lb-ft units) at 5252 rpm. After 5252 hp is always higher than torque, and below the opposite is true.

[MRSUPRA]

Generally, when destroking, you are losing displacement. And when you lose displacement, you lose power and torque, especially the amount of power you can make on pump gas. Also, when you have less displacenent you lose the exhaust energy to spool a turbo. So not only will you get less power and torque with a destroked 7M, you will make for a laggier turbo setup. There is a reason why so many guys with domestic V8's use stroker setups to get more power (which do include turbo and supercharged V8's).

And if I recall, Milbrum is reving out his stock stroke 7M to 9500rpm's.

[gofastgeorge]

Not really, since higher RPM will make more HP
if the engine is built to opperate in the higher RPM range.

Just look at HKS's sub-8 second 7M powered Mk3.
It used a destroked crank (5M stroke),
and it was making low 8, and sub 8 passes back in the early '90s.

They were turning it to 9000 rpm.

Very few Mk3s are even doing this these days.........

[figgie]

I know the equations, this is why i said hp is the important value. Knowing HP implies that you know the Force*time...knowing just the force tells you nothing. So i believe everything written above is correct. If you know you have x amount of HP you know you can always gear the thing for the appropriate torque. If all you know is torque, you really don't know anything because of time...

Furthermore, If you have 500 hp, you have 500 hp. You can gear the torque output of the device producing the horsepower to put out the torque that you need. In a car this is the change in torque at the motor to torque at the wheels.

For example you take the motor out of the semi and properly gear it. This motor produces 425 hp peak in a completely linear fashion, but it only revs to 2000 rpm so the motor produces 1800 lb-ft of torque (i didnt calc this - Im lazy, but its just an example). You put it in a vehicle that weighs 5000lbs total.

Now in the other test vehicle you have a V8 that makes 425 hp in a completely linear fashion and only produces 425 lb-ft of torque (motor revs to 5252 rpm). This motor is properly geared as well and you put it in a vehicle that weighs 5000 lbs.

Now you race - and guess what, since the hp is the same they go the same speed...guess torque is not what really matters and horsepower is really what matters. As long as the vehicle has gears in it, and they are appropriately selected torque means nothing, and HP is what is going to determine how quick the vehicle is.

I know you understand the principals here figgie so I am just guessing any disagreement we have here is semantics based.

and incorrect. Assuming a MATCHING torque curve for each car with the SAME wieght and everything else matching. They should be the same. The problem is that even within the same model cars you have manufacturing variances that effect the torque curve which effects the acceleration curve.

500HP = 500hp. The difference is HOW you get those 500HP. Your hypothetical situtation does not exist on this plane but what the hell. If HP is Flat through out the RPM band then the Torque will have to decrease as RPM increase. This means that there is less force available to accelerate the car. In the situation you supplied, you have alot of missing infomration, what is the area under the curve like for both vehicles? If the gearing is such that both have the same MAX MPH. It still will be difficult to say which does what as we do not know the area under the curve.

The very principle applies to electic motors, There torque is greatest at ZERO rpm when a current is applied and have a linear fall off as they reach their max rpm (almost to zero).

I am not in the mood to debate this point today so in my corner, i Will let my good friend Paul Yaw explain it to you with Gearing graphs why HP is what matters in the end.

http://www.yawpower.com/tqvshp.html


Read up, if you have any questions after practicing those equations. Then lets hear them, you are on the right track but making some odd hypothesis.

[supradjza80]

http://www.yawpower.com/tqvshp.html


I don't know what else to say. I have been trying to say this and I guess you just don't get how I am saying this. For the last time horsepower>torque.

[Supracentral]

I don't know what else to say. I have been trying to say this and I guess you just don't get how I am saying this. For the last time horsepower>torque.

Incorrect.

Horsepower equals torque times rpm, divided by 5252

[gofastgeorge]

Incorrect.

Horsepower equals torque times rpm, divided by 5252

But why use know formulas, and fact,
when guessing, and forum bull S#it is so much easier to post............
:naughty: