Supersquare idea?

[Sparky12]

Alright, so how would this setup sound, experienced Z gurus?

 

L28 block, bored 0.40 over

L24 rods

L24 crank

L28 flattop pistons 0.40 oversized

 

on a shaved P90 head with 1mm headgasket, with a hot street/mild race cam and 44mm mikuni's? The Lengine calculator gives me a displacement of 2629cc's, with a stock (0.080mm) deck height, with an 87mm bore and 73.7mm stroke (stroke/bore ratio of 0.85). I put an N47 head on it (close to the same compression ratio a shaved P90 would give?) and it gives me a 9.72:1 cr. I'm looking for a rev-happy, high-rpm street engine...would this be a step in the right direction?

[Brad-ManQ45]

I wouldn't give up the displacement if I were you - the L28 crank will rev just as high as the L24 (for all practical purposes) and you have more power under the curve.

[naviathan]

Sounds like a fun little rev happy L6. I thought about that setup one time, but I don't have an L24 crank to try it with.

[JMortensen]

With a street cam I'd say you're headed in the wrong direction. As Brad-Man says you'll have less power because of less displacement, and you'll have more theoretical rpm capability that you won't use because the cam is too small. If you were trying to wring it out to 9000 rpm I'd say this is probably a good way to go because the rod/stroke ratio will help out, but that doesn't sound like your plan.

[Sparky12]

With a street cam I'd say you're headed in the wrong direction. As Brad-Man says you'll have less power because of less displacement, and you'll have more theoretical rpm capability that you won't use because the cam is too small. If you were trying to wring it out to 9000 rpm I'd say this is probably a good way to go because the rod/stroke ratio will help out, but that doesn't sound like your plan.

That's actually more or less exactly what I was aiming for. I was thinking about a 300deg (intake and exahust) cam with 560 lift which, if I read right, is about as big a cam as anybody would want to try and drive on a stret car. Would this cam be about what I need? Also, would you shoot for a higher compression ratio? I'd like to stick to 93 octane if I can.

[JMortensen]

My opinion is that to run a cam that large efficiently you'd need a compression ratio high enough that pump gas wouldn't do it.

 

I think you have your wires crossed a bit. You're going from "I want a race engine that revs to 9000 rpm" to "I want to drive it on the street and I'd like it to run on pump gas."

 

To me those seem mutually exclusive for an L series engine. Have you thought of what would be acceptable to you in terms of durability? Most L's that rev that high have a lifespan measured in hours.

[evildky]

I know a guy that did a similar build, big bore long rod but only .020 over pistons and an E31 head with the L7 cam, felt liek a sportbike powerband, it came on strong about 2500 rmp and was constant up to 7000 rpm, put about 180whp IIRC

[Sparky12]

I think you have your wires crossed a bit. You're going from "I want a race engine that revs to 9000 rpm" to "I want to drive it on the street and I'd like it to run on pump gas."

 

To me those seem mutually exclusive for an L series engine. Have you thought of what would be acceptable to you in terms of durability? Most L's that rev that high have a lifespan measured in hours.

 

 

I think I know exactly what you mean. I guess what I'm looking for is the most rev-happy engine that would still run on pump gas and would hold together for more than a few hours. Obviously, a 13:1 12,000rpm 300whp 2.5 liter wouldn't be able to satisfy the other requirements. What do you think would be the limits of compression ratio, engine speed, and cam duration where it would still be durable and not require a trip to the local airport for fuel?

[JMortensen]

Probably about Dan Baldwin level. Search and you should find build info on his stroker. I think he has some dyno posts either at zcar.com or classiczcars.com. 255 whp, I think redline was 7000 or 7500, triple 45s, cam is a funky Sunbelt unit with single valve springs. I want to say compression around 11:1. Not sure about that...

[Sparky12]

Sounds fun, except I wasn't really thinking of a stroker at all. My idea would be more like an L24 that's been bored waay over. I like the short stroke idea because it would be able to rev quicker (i.e. from idle-redline sooner than an L28 or an L31 would) because the piston speed at redline would be lower. Only downside I see to this is that I'm basically taking out the torque from an inline 6 (which is naturally torquey)...am I thinking in the wrong direction?

[JMortensen]

Sounds fun, except I wasn't really thinking of a stroker at all. My idea would be more like an L24 that's been bored waay over. I like the short stroke idea because it would be able to rev quicker (i.e. from idle-redline sooner than an L28 or an L31 would) because the piston speed at redline would be lower. Only downside I see to this is that I'm basically taking out the torque from an inline 6 (which is naturally torquey)...am I thinking in the wrong direction?

This bold part has been discussed ad infinitum (usually in the V8 forum where someone wants to build a Chevy 302 because they think it will rev faster than a 383) and yours is an incorrect assumption. You're right about the piston speed, but wrong about how quickly the engine will rev. More power will accelerate the engine faster, so the more power you have the faster the engine will rev, and that is true regardless of the rod/stroke ratio.

 

Your engine will have a higher potential top speed because the piston speed will be slower during the period when the piston changes direction, but you still have to figure out what the next weak link is. I personally think it's the crankshaft. If you start looking around you'll see that when guys get into really high rpms they start breaking vibration dampers, flywheel bolts start coming loose, etc. You mentioned a 12K rpm L, I've never heard of such an engine in reality. It's entirely possible that they're out there and I'm just not aware, but the highest rpm L engine I've ever come across is 9500 rpm, and that was an L16 built by Rebello with all the tricks. Dennis Hale owns that motor and if you spend more than an hour with him in person he'll end up telling you how much he spent on it. It was hyper-expensive. I want to say he had $20K in the shortblock.

[PanzerAce]

The highest rpm L engine I've ever come across is 9500 rpm, and that was an L16 built by Rebello with all the tricks. Dennis Hale owns that motor and if you spend more than an hour with him in person he'll end up telling you how much he spent on it. It was hyper-expensive. I want to say he had $20K in the shortblock.

 

All of a sudden I don't know if I feel like trying to get an 8k redline on my three liter.

[JMortensen]

All of a sudden I don't know if I feel like trying to get an 8k redline on my three liter.

There are differing opinions on this issue. The "old standard" info is that pushing a stock shortblock beyond 7500 is a bad idea because of crank vibrations. Then you have guys like preith and gramercyjam (this is memory talking, could be I have those two names wrong) who ran their engines to 8000 with no issues, and guys like Dan Baldwin who had his flywheel bolts come loose on his stroker with a redline of 7200 if I recall. I think Tony D has had some ideas on this issue in the past as well.

 

There is more than one opinion on the issue for sure. Mine comes from reading others' statements more than anything. I did personally have an old, high-mileage, stock 280ZX damper come apart after running over 7500 a couple times and that ended up screwing up the snout on the crank, but I've never experienced a broken crank or any other really bad ill effects. Seems to me from what I've read that your engine will last longer if you keep it under 7500 rpm.

[Xnke]

I thought Tony D was shifting the Bonnieville car at 9300?

 

I could be mistaken, but I'm pretty certain.

[josh817]

Theoretically it sounds like a good plan but I'd take it from everyone else here. The L engine has is unique spots. Generally speaking the logic behind high revving is short stroke and big bore. Short stroke allows more revolutions because of well... obviously the small travel distance. Large bore to compensate for the short stroke would be my best guess. Big bore is more horsepower while big stroke is more torque, thus the reason why you see strokers. People love torque but torque doesn't like top end. If you really wanted to go ape **** on your project then get liners/wet liners, bore that thing out as much as you can without running into problems, and run the l24 bottom end. Don't take it from me though, I just base my thoughts off of F1 info and such... Thats the only reason why they have 3 liter V8's and V12's. Make 700hp but only 370ftlb, tiny tiny tiny stroke with a huge bore. I don't have the numbers in front of me but I think it was something like 25mm stroke with 97mm bore. Something crazy.

[Sparky12]

Theoretically it sounds like a good plan but I'd take it from everyone else here. The L engine has is unique spots. Generally speaking the logic behind high revving is short stroke and big bore. Short stroke allows more revolutions because of well... obviously the small travel distance. Large bore to compensate for the short stroke would be my best guess. Big bore is more horsepower while big stroke is more torque, thus the reason why you see strokers. People love torque but torque doesn't like top end. If you really wanted to go ape **** on your project then get liners/wet liners, bore that thing out as much as you can without running into problems, and run the l24 bottom end. Don't take it from me though, I just base my thoughts off of F1 info and such... Thats the only reason why they have 3 liter V8's and V12's. Make 700hp but only 370ftlb, tiny tiny tiny stroke with a huge bore. I don't have the numbers in front of me but I think it was something like 25mm stroke with 97mm bore. Something crazy.

This was, more or less, exactly why I thought of this to begin with. But I think maybe I should embrace the inline-6 L-series engine's torquey nature instead of trying to fight it.

[1 fast z]

I run a 12-1 compression 89mm bore, 83mm stroke, .590" lift and 288 duration on the street, as my daily driver (while the Twin turbo car is down anyways). I run it to 8K daily, and it makes power to 7500 or so. Car runs HIGH 12.50's in the 1/4 mi, in a 2680lb 280z on pump gas. Like many others have said now, a 3.0 that revs to 7k, compared to a smaller motor that revs to 9300 with all the other "same" components, as far as cam, compression, head flow etc. the Stroker will always be faster, plain and simple.

[1 fast z]

Also for reference, My 24 valve engine I have run to about 9k before, that is a full 3.1 liter engine as well. Although I have a "bit" more flow than your regular ole L series to support that RPM range. This is with a VO7 stock crankshaft by the way.

[Dragonfly]

Thats the only reason why they have 3 liter V8's and V12's. Make 700hp but only 370ftlb, tiny tiny tiny stroke with a huge bore. I don't have the numbers in front of me but I think it was something like 25mm stroke with 97mm bore. Something crazy.

 

I believe you have some of your math a little backwards... most of the 3 liter V12's have very small pistons as well as short strokes, the primary reason is because the rpm's they run causes the piston speed to "outrun" the flame front. The fuel can only burn so fast so a smaller bore allows a more complete combustion at a higher rpm therefore making the engine more effecient.

 

found on a different forum:

F1 engines use very small cylinders (300 cc each) but that's a little extreme. Most manufactures of NA engines with high power/weight ratio make them with cylinders around 500cc each. This is an example of what I'm talking about:

 

Honda S2000: 9,000rpm 2-Lt I4 120hp/Lt, 500cc/cyl

Ferrari Enzo: 8,000rpm 6-Lt V12 108hp/Lt, 500cc/cyl

BMW M3: 8,000rpm 3.2-Lt I6 104hp/Lt, 533cc/cyl

Ferrari 360 : 8,000rpm 4-Lt V8 100hp/Lt, 500cc /cyl

BMW-Williams F1 : 19,000rpm 3-lt V10 ~300hp/Lt, 300cc/cyl

So from that we can see that a V12 will have even smaller bores in order to maintain only 3 liters.

 

A square engine will certianly have a higher rpm range and rev quicker but a well balanced and lightened stroker will have more torque, more HP and rev suprisingly quick. Just my opinion but I think there really is a reason you see a lot more stroked L engines than you do squared L engines.

 

Dragonfly

[josh817]

Ah I just pulled up the numbers and I was stating the maximum allowed figures for the 2006 season rules. My mix up there.

 

"For 2006, the engines must be 90° V8 of 2.4 litres maximum capacity with a 98 mm maximum circular bore, which imply a 39.7 mm minimum stroke."

 

 

Last night though I was trying to think of any ideas on how to make maybe a high revving lawn mower engine/pneumatic motor using actual pistons. Yah I COULD go out and buy like a go cart motor but it would be fun to design all the parts yourself or to do a mix match of parts. Anyways, after playing paintball and such, one thing you worry about when shooting quickly is if the air can recharge fast enough for the next shot, otherwise that ball would just roll out of the barrel or go 20 ft. At 35 balls per second the air can barely keep up with the speed and sometimes it will fall behind.

 

Basically where I'm going with this is that when dealing with a pneumatic motor it makes sense to go small. Less mass for one thing but the amount of air used to force the piston back down is much lower than with a big bore. Keep in mind that the motor I would like to build will be pretty much like a gas motor, valves and everything, but you would use air to move the piston. With the given amount of time for the valve to stay open and the PSI of going into the motor, you can only go so far. If you run into problems with recharge rates than you either lower the volume of the cylinder or do PORTING.

 

So yes a small piston/cylinder is probably better off BUT the problem which I explained about the air motor can be fixed by doing what motor builders do today and increase the flow of the head. Lastly, and most obvious when building a hot motor, make sure numbers are exact. Any unnecessary free play in the rotating mass will not only throw off balance but will put a choke hold on the RPM's. The perfect example is below.

 

Here is a little air motor my dad built when he was a teenager:

Notice how in the last 2 pictures I moved the crank in and out but only slightly. This motion limited the motor to about 8000RPM. If we were to make another one but with finer specs, I'm sure we could hit 12k. the way it works is the cylinder moves with the piston. It wobbles side to side and when the ports align it draws in air, and then when it moves away from the ports the air flows out. You can find videos of it on Youtube.