What is everyone's engine design preference?

[Matt@BOS]

I think I prefer big bore and stroke engines for autocross and higher, faster revving smaller cube engines for road courses, at least in terms of fun factor. autocross is a lot more stop-turn-go. I have a Camaro with a 454 cube LS7, and it never lugs out of corners versus my Coyote powered Mustang. However, put the two cars on a road course, and the less powerful Coyote motor is way more fun, despite being slower, simply because you can put your foot down and hold on almost all the time.

[DavidBoren]

I am not trying to argue with anything anyone has said. I think Ron nailed my objectives perfectly. I do have a question about using a 4" stroke and this phenomenon that has been brought up multiple times called "running out of steam"...

From what I have seen, on this forum and other places, the LS7 is a staple of the pro touring community. It has been put in plenty of performance cars that have never had a single complaint about running out of steam.

How many rpms do you use on a road course? The obvious answer is all of them. But seriously, is the 7k redline associated with the LS7, and it's 4" crank, not enough?

Ron says, in "C", to build as much power as you can use. I am building a S-10, it's going to weigh 3000# race weight, I don't think I can use a whole LS7. But it's the go-to engine for pro touring and I am building a pro touring S-10. So I am going to subtract one liter of displacement, but keep the things I like (4" stroke = torque, I like torque). And, at the same time, it provides me with an opportunity to test some design theory that I have for some reason attached myself to.

As for what is more fun to drive. I favor torque here as well. I would rather spin my tires rather than spin the crap out of my engine. I don't roast my tires, and I know spinning tires isn't fast. But I prefer the feeling of taking off in a 500hp duramax diesel truck more than the feeling of "launching" with a 500hp evo8.

I would rather have a car that I have to drive with respect, more than a car I have to abuse. Hunter S. Thompson said that men like big guns and fast cars because they push us to our limits, rather than us pushing the machine to its limits. And with rpm motors, it's like you have to keep them at the upper limit for them to be any fun. But with a torque engine, you have to respect the machine.

Maybe I am just retarded. But I'm under the impression that using a 4" stroke crankshaft will in no way limit my useable rpms.

Is 7000rpms not enough?
Are LS7's hard to drive?

[Rod P]

cool discussion...I'll bite..
engine RPM and to me drive ratio go hand in hand and is very dependent on the track, for the few PT style cars I have built or advised on what I shoot for is an 70-75 mph speed at limiter in second gear..in order to have this i looked at having a 7200RPM limit on my engine, this allows the car to run small events such as Goodguys tracks in first or second only, for example the track in Nashville this weekend was a first gear track, and the finals track in scottsdale is a 1-2 track because it has a long straight that I just reach limit 7200 in second at the end of it....and for larger tracks like Las Vegas motor speed way or Michigan international...I spend a large amount of time in 2-3,,and forth on large straights.....so to me function over form in the engine department

[DavidBoren]

That's the whole point of this, though. I'm trying to make the form of the motor fit the function of the vehicle.

I am trying to get everything working in concert. Engine design theory and architecture, cam profile and useable powerband, transmission gearing, rear axle ratio, suspension and brakes... Isn't the purpose of starting over to do everything over? Everything, for the most part, on the S-10 is set up from the factory to work as a system. Even though it's made from GM's leftover parts bin, some amount of engineering went into making sure that the parts selected meshed together for its intended purpose.

So, for me to change anything, I need to adjust all things. And since there is no single redeeming quality of the original S-10 worth saving (other than its compact chassis/body), I might as well design a whole new system, including an engine specifically designed for the rpm range and powerband I want, and a suspension set up for exactly how I feel a vehicle should handle.

When I see a 10k redline, I think "why" because I know it's possible to make the power sooner. And if you can't make enough power to do... ANYTHING you want... before 7500rpms, then you need less mass, not a higher redline.

My idea of reinventing the 6.0L with a 3.8x4.0 architecture vs the 4.0x3.6 bore and stroke is to shift the powerband left, favoring early torque production. The exact same crankshafts are used in OEM engines that spin to 7k rpms. I have no doubts, whatsoever, that any engine built using this crank will be in any way redline limited.

So, it's up to proper cam selection, valvetrain components, and transmission/axle gearing to best utilize a powerband that both comes on early, and can extend to 7k rpms.

Mind you, the torque will come on early compared to a 6.0L with the 3.6" crank. But it won't subtract from the upper limit of the same mid-stroke 6.0L, given proper valvetrain and cam selection... So I literally do not see a downside to building a undersquare 6.0L motor.

All that needs to be done is porting the heads to provide adequate air flow for six liters of displacement spinning at 7k rpms... Which I know is possible, even with the little valves.

Little valves and little pistons are easy to move, so the rotating mass will be able to rev as high as the big LS7 components, even with the LS7 using titanium.

Everyone always says that they want a broad powerband, and yet it seems no attention is ever paid to broadening it to the left. People go through great lengths to expand the powerband to the right, ever increasing the redline. And engine design and architecture reflects the chase for higher redlines with oversquare engines. Yet you can achieve roughly the same effect starting power production earlier.

3000-8500 powerband is 5500 useable rpms...

So is... 1500-7000...

Things that make you say, "hmm..."

[DavidBoren]

As a side note, using head flow numbers from TEA's website regarding their stage two ported 5.3L heads, and an online calculator provided by Wallace racing, the projected redline where head flow can no longer support the displacement at any higher rpms, is 8000. Playing with different VE inputs got readings between 7300 all the way to 9000. So, no matter what, with properly ported heads, the small bore can support six liters of displacement spinning all the way to 8k...

I have no intentions of spinning it that high, but for the sake of this discussion, I thought it to be relevant.

For comparison's sake, the 353ci oversquare engine proposed earlier, 4.125" x 3.3" bore and stroke, using stock LS7 head flow numbers, gives a max redline of 8,300 to 10,900... depending on what VE values you use.

@RodP, I can get 74.5mph in 2nd gear @ 6500rpms with a 1.88:1 second gear and 3.55 rear gears with a 25.7" tire. All of that is theoretical using the Wallace racing online calculator. Rims are based on 2006 z06 18x9 fronts and Toyo R888 275/35R18 tires. Transmission ratio is from the TKO600RR. I would like to use a 5spd transmission and stay around the 3.5:1 range for the rear. So the road race TKO and relatively mild rear gears archives the 70-75 mph in 2nd gear rule.

Same calculator, same tire diameter, same rear gear ratio, same 6500rpms, just changed to the .84:1 OD gear of the TKO600RR, and this predicts a top speed of 166mph. I think that will do just fine.

[Flash68]

Originally Posted by Ron Sutton

While the 434" engines made the most power ... torque & horsepower ... they were too hard to drive fast. With 4" of stroke, the drivers were always struggling to get them off the corner optimally. They had to drive them with the proverbial egg under the throttle. That's doable occasionally ... but not consistently lap after lap when your adrenaline is up. The 355"-377" engines had way less tire spin challenges ... but just didn't make enough torque to accelerate the car off the corner optimally. The 383"/388" engines came of the corners hard, but laid over on the straights.

That's funny Ron. I started with a 377 and quickly discovered that was a big issue on both AutoX and road course. So, I decided to go overboard and skip all steps in between and go with a the big bore big 4" stroke 437"!

Originally Posted by Ron Sutton

The engines that were "just right" were big bore (4.125"-4.185") & medium stroke (3.750-ish). These 400"-410" engines were dominant.

So, what you're saying is.... Sprint Car engines FTW.

I really wanted to go with a 3.8ish stroke but decided to reuse all the parts with my used SB2.2 "deal" I found... smart? Maybe not... fun? Should be!

Originally Posted by Matt.A

I have a Camaro with a 454 cube LS7, and it never lugs out of corners versus my Coyote powered Mustang. However, put the two cars on a road course, and the less powerful Coyote motor is way more fun, despite being slower, simply because you can put your foot down and hold on almost all the time.

You shoulda bought a Miata like that Weld guy.

Originally Posted by DavidBoren

Maybe I am just retarded. But I'm under the impression that using a 4" stroke crankshaft will in no way limit my useable rpms.

For 99% of what are people are doing around here, I would have to agree with you.

Originally Posted by DavidBoren

Everyone always says that they want a broad powerband, and yet it seems no attention is ever paid to broadening it to the left. People go through great lengths to expand the powerband to the right, ever increasing the redline. And engine design and architecture reflects the chase for higher redlines with oversquare engines. Yet you can achieve roughly the same effect starting power production earlier.

3000-8500 powerband is 5500 useable rpms...

So is... 1500-7000...

A true 1500 to 7000 rpm range sounds very difficult to achieve. What would the specs of this engine look like?


Oh, and this is a winner:

Hunter S. Thompson said that men like big guns and fast cars because they push us to our limits, rather than us pushing the machine to its limits.

[DavidBoren]

What would a true 1500-7000 motor look like? I don't know. Hopefully it has a 3.78" bore and a 4" stroke. Lol.

But nobody knows what that motor looks like because nobody is working on extending the powerband to the left. We all know what it takes, or at least have an idea of what the motor with the 3000-8500 powerband looks like... if I had to take a guess, I would say it is probably oversquare.

[Sieg]

Originally Posted by Flash68

A true 1500 to 7000 rpm range sounds very difficult to achieve. What would the specs of this engine look like?

Something like this.........



....but you start at zero RPM.