What do you guys think a motor being bored .050 over would give it?
2hp?
its a total of 91cc so i figured it would give you alittle.
thoughts?
2hp?
its a total of 91cc so i figured it would give you alittle.
thoughts?
how much hp for boring?
- Thread starter 87supraturbo19
- Start date
Noting you can measure, unless you are running naturally aspirated. The amount of air we can squish into the cylinders is really dependant on the turbo and the valve size in the head, not the displacement.
Not saying anyone here did this but don't bore the cylinders for power or volume only if cylinders need it. Making the cylinders .050 will have very tiny affect on overall power if any at all. In fact I wouldn't go more than .020, .050 over your cylinder walls are very thin and a "good" scratch(in the cylinder wall) occurs, your block could be junked easily.
The general rule of thumb when overboring is to remove the MINUMUM amount of material to achieve a good surface. Overboring is not done for power, it's done to refresh the walls of the cylinders. By going with the minimum you leave yourself the maximum amount of material to do it again. If you do an .050 overbore, and then score a cylinder, you either have to scrap the block or sleeve it. If you do a .020, you've got room for a few more rebuilds. This becomes especially important with cars like these where they have been out of production for many years and there are no new blocks being produced. Value what you have guys, the supply won't last forever.
N
NDBoost
Guest
toyota should do something like nissan...
Factory Rebuild/Refurbs on the older z's :2ar15: :bigthumb:
Nissan did something crazy like remove all bolts and wiring etc re-coat redo all bolt holes and bolts and repaint/recoat the chassis as well as fully rebuild the motor..
Factory Rebuild/Refurbs on the older z's :2ar15: :bigthumb:
Nissan did something crazy like remove all bolts and wiring etc re-coat redo all bolt holes and bolts and repaint/recoat the chassis as well as fully rebuild the motor..
Turbo. Targa. Life.
SupraMania Shirt Slinger!
if you're trying to achieve more power you're better off stroking it (*giggles*). But I don't even know if anyone makes a stroker kit for the MKIIIs...do they???
Flatlander does.
Some good, some bad experiences.
Overall, not a great idea to stroke a stroker, but when the kit performs, apparently it's amazing.
Some good, some bad experiences.
Overall, not a great idea to stroke a stroker, but when the kit performs, apparently it's amazing.
Stroking a 7M is definitely not the best idea, and I'll show you why. There are several methods that you can use to determine tensile loads on rods, but the most simple and available to someone with basic mathematic skills is to use mean piston speed.
This is the average speed the piston travels at static engine rpm. Remember that. As we move through these calculations, realize we are talking about the "average" speed. Meaning that the speeds go much higher.
Next, we need to know good vs bad.
The industry "rules of thumb" for mean piston speed are:
Under 3,500 ft/min = Good reliability
3,500-4,000 ft/min = Stressful, needs good design
Over 4,000 ft/min = Very short life
You will find that auto manufacturers keep the mean piston speed below 3500 ft/min in 99% of their motor designs except for a few rare exotic sports cars. The reason? Reliability & warranty. In a few rare cases, manufacturers cross that line for "special" cars. The Supra (both MKIII & MKIV) fall into this class. But they don't go far over that line. But I digress...
Determining the mean piston speed is damned simple.
Stroke and RPM are really all you need to know.
The formula is Cm = 0.167 x L x N
Cm = mean piston speed in ft/min
L = stroke in inches
N = crankshaft speed in rpm
Take the stock 7M-GTE with a 3.582" stroke and a 6500 redline.
At 6500 RPM your stock motor has a Mean Piston Speed of 3880 ft/min. Based upon our chart above, you are already "pushing" it in stock trim.
In comparison the 2JZ-GTE has a stroke of 3.386". This doesn't sound like much of a difference, but do the math and at the factory redline of 6750 for this motor your mean piston speed is 3816 ft/min. At 6500 RPM it's only 3675 ft/min. Much lower stress at the same RPM.
As you can see the very slightly shorter stroke on the 2JZ allowed Toyota to raise the redline by 250 RPM, but lower the mean piston speed. Both motors are 3.0 liter, but the design change allowed higher revs with better reliability.
So now go back to our 7M-GTE and let's throw the Flatlander stroker kit into the mix.
The Flatlander kit has a 3.833" stroke!!! That's HUGE! Do the math and you come up with an impressive mean piston speed of 4160 ft/min at 6500 RPM. Take a look at our chart above. We are deep into the "very short life" area.
Now stop and think about how a 4 stroke gasoline engine works. Intake, compression, power, exhaust. That's your four strokes. But which one is going to do the most "damage" to our rods when we take mean piston speed into consideration? Lots of people would guess the "power" stroke. And they would be VERY wrong.
Think about this. Take our Flatlander stroker motor at 6500 RPM. During the exhaust stroke the piston is traveling upward at an amazing average speed of 4160 ft/min. What is there to stop it at the top of the stroke? The exhaust valves are open, there's no compression. The ONLY thing stopping that piston from slamming into the head is the connecting rod. Think about that. That rod not only has to stop that piston, but change directions and accelerate it downward as well. All of this loading is "tensile" loading. (i.e. - the forces are trying to STRETCH the rod) compressive loads (like during the power stroke) are easy for the rods to handle. Compressive forces are a cake walk for a forged rod. Tensile forces (stretching) is a lot more damaging.
When looked at in this light, is it worth the couple of extra cubic centimeters of cylinder displacement? Yea, a little more off idle pre-boost torque is there, but it's not worth it in my opinion...
Now this is all a gross oversimplification (I could [and probably should] write a book on this stuff) there are MANY other factors involved.
For example, the mass of the pistons. Compare a JE brand piston to it's Ross branded counterpart for the 7MGTE. Ever looked at the weights quoted by each manufacturer? JE forged pistons for the 7M are 293 grams. The Ross model is 357 grams! Which one would you rather have your rods trying to stop from 3880 ft/min? Now I'm not saying that a Ross piston is bad, it's not. But it's a heavy son of a bitch. Imagine that mounted on the top of your stroker rod!
We haven't even talked about crank angles, pistion accelleration, etc, etc... There's a ton more.
I had to make myself stop here because I can think of about 5 tangential directions I could go off on from here and I could write multiple pages just on internal motor geometry alone.
But I guess my overall point is that engine design is a science. And there's a ton of information needed to make intelligent design choices. And in my opinon, a stroker 7M isn't the best bang for the buck.
Damn - I'm a long winded SOB these days... LOL
This is the average speed the piston travels at static engine rpm. Remember that. As we move through these calculations, realize we are talking about the "average" speed. Meaning that the speeds go much higher.
Next, we need to know good vs bad.
The industry "rules of thumb" for mean piston speed are:
Under 3,500 ft/min = Good reliability
3,500-4,000 ft/min = Stressful, needs good design
Over 4,000 ft/min = Very short life
You will find that auto manufacturers keep the mean piston speed below 3500 ft/min in 99% of their motor designs except for a few rare exotic sports cars. The reason? Reliability & warranty. In a few rare cases, manufacturers cross that line for "special" cars. The Supra (both MKIII & MKIV) fall into this class. But they don't go far over that line. But I digress...
Determining the mean piston speed is damned simple.
Stroke and RPM are really all you need to know.
The formula is Cm = 0.167 x L x N
Cm = mean piston speed in ft/min
L = stroke in inches
N = crankshaft speed in rpm
Take the stock 7M-GTE with a 3.582" stroke and a 6500 redline.
At 6500 RPM your stock motor has a Mean Piston Speed of 3880 ft/min. Based upon our chart above, you are already "pushing" it in stock trim.
In comparison the 2JZ-GTE has a stroke of 3.386". This doesn't sound like much of a difference, but do the math and at the factory redline of 6750 for this motor your mean piston speed is 3816 ft/min. At 6500 RPM it's only 3675 ft/min. Much lower stress at the same RPM.
As you can see the very slightly shorter stroke on the 2JZ allowed Toyota to raise the redline by 250 RPM, but lower the mean piston speed. Both motors are 3.0 liter, but the design change allowed higher revs with better reliability.
So now go back to our 7M-GTE and let's throw the Flatlander stroker kit into the mix.
The Flatlander kit has a 3.833" stroke!!! That's HUGE! Do the math and you come up with an impressive mean piston speed of 4160 ft/min at 6500 RPM. Take a look at our chart above. We are deep into the "very short life" area.
Now stop and think about how a 4 stroke gasoline engine works. Intake, compression, power, exhaust. That's your four strokes. But which one is going to do the most "damage" to our rods when we take mean piston speed into consideration? Lots of people would guess the "power" stroke. And they would be VERY wrong.
Think about this. Take our Flatlander stroker motor at 6500 RPM. During the exhaust stroke the piston is traveling upward at an amazing average speed of 4160 ft/min. What is there to stop it at the top of the stroke? The exhaust valves are open, there's no compression. The ONLY thing stopping that piston from slamming into the head is the connecting rod. Think about that. That rod not only has to stop that piston, but change directions and accelerate it downward as well. All of this loading is "tensile" loading. (i.e. - the forces are trying to STRETCH the rod) compressive loads (like during the power stroke) are easy for the rods to handle. Compressive forces are a cake walk for a forged rod. Tensile forces (stretching) is a lot more damaging.
When looked at in this light, is it worth the couple of extra cubic centimeters of cylinder displacement? Yea, a little more off idle pre-boost torque is there, but it's not worth it in my opinion...
Now this is all a gross oversimplification (I could [and probably should] write a book on this stuff) there are MANY other factors involved.
For example, the mass of the pistons. Compare a JE brand piston to it's Ross branded counterpart for the 7MGTE. Ever looked at the weights quoted by each manufacturer? JE forged pistons for the 7M are 293 grams. The Ross model is 357 grams! Which one would you rather have your rods trying to stop from 3880 ft/min? Now I'm not saying that a Ross piston is bad, it's not. But it's a heavy son of a bitch. Imagine that mounted on the top of your stroker rod!
We haven't even talked about crank angles, pistion accelleration, etc, etc... There's a ton more.
I had to make myself stop here because I can think of about 5 tangential directions I could go off on from here and I could write multiple pages just on internal motor geometry alone.
But I guess my overall point is that engine design is a science. And there's a ton of information needed to make intelligent design choices. And in my opinon, a stroker 7M isn't the best bang for the buck.
Damn - I'm a long winded SOB these days... LOL
A truly wonderful write-up Mike. It's good to see somebody bringing this information here. Long winded? Not really, information like this shouldn't just be skimmed across and turned into cliff notes. The information contained here is important, and people should take the time to read it. And I hope they do. It provides a very good image of the kind of conditions our engines must endure.
I actually found that very very informative and interesting but was saddened by it's short-ness. I think you should write a couple of pages of the basics of engine geometry. Very nice