...

Go Back   Lateral-g Forums > Technical Discussions > Engine
User Name
Password



Reply
 
Thread Tools Display Modes
  #11  
Old 04-10-2015, 07:14 PM
bdahlg68's Avatar
bdahlg68 bdahlg68 is offline
Senior Member
 
Join Date: Apr 2010
Location: Northville, MI
Posts: 463
Thanks: 3
Thanked 11 Times in 10 Posts
Default

Quote:
Originally Posted by camcojb View Post
I know you can take inline 6 off the list for this site...
Hey hey hey. Not entirely.
__________________
Brian

1968 Pontiac Firebird
1989 Ford Mustang
Reply With Quote
  #12  
Old 04-13-2015, 10:19 AM
DavidBoren DavidBoren is offline
Senior Member
 
Join Date: Oct 2014
Posts: 189
Thanks: 0
Thanked 1 Time in 1 Post
Default

The inline six should never be scratched off the list, in my opinion. Between the 2jz and the 6bt, I think that platform has earned its place and proven its worth. I would love to see more inline six swaps, as even the all aluminum Atlas motor can handle boost and respond well.

Just something interesting I found on a big-bang-theory-esque forum discussing undersquare versus oversquare engines from a physics/math/nerd perspective;

Oversquare engines will last longer because the piston travels a shorter distance, therefore it creates less friction. The larger piston also transfers heat to the cooling system better than a smaller piston does. So an oversquare engine creates less heat through friction and transfers the heat to the cooling system better.

Apparently the heat created by friction in the piston rings increases exponentially with stroke length. So if displacement remains equal, the engine with oversquare architecture will waste less energy, every time.

It's kind of funny, or sad, that reading all the advantages of going with oversquare bore-stroke ratio does little to sway my decision to build an undersquare engine. But, I am sure I will find an excuse to build another one, and I will go the other way with it just for the sake of comparison.

Speaking of comparison, here are the two extremes of what is available using stock LS bores and strokes.

Undersquare:
359ci (3.78" bore X 4" stroke)

And

Oversquare:
353ci (4.125" bore X 3.3" stroke)

I think the difference of six cubic inches in total displacement is negligible, so it would be really cool to build and drive both to see if oversquare versus undersquare makes a difference you can feel.

PS. A "square" bore/stroke motor with a displacement of 356ci (the average displacement of the two engines listed above) would have a bore and stroke of 3.842", just to give you an idea of how over or under "square" each of those engines are.

Last edited by DavidBoren; 04-13-2015 at 10:58 AM.
Reply With Quote
  #13  
Old 05-06-2015, 03:01 PM
DavidBoren DavidBoren is offline
Senior Member
 
Join Date: Oct 2014
Posts: 189
Thanks: 0
Thanked 1 Time in 1 Post
Default

I mentioned that the oversquare engine will generate less heat due to the shorter stroke causing less friction. It also transfers the heat to the cooling system more efficiently because the larger bore cylinder will expose more surface area.

This is also a detriment to the efficiency of combustion in the cylinder. The flame has to spread across a larger surface. A greater portion of the combustion heat/energy is being transferred to the cooling system, rather than being converted into work. And there is a greater loss in pressure per angle of rotation with a shorter/wider cylinder, regardless of rod ratio.

It seems, in my limited understanding, that any benefits of going oversquare, just to gain larger valves, would be negated by the less efficient combustion characteristics. And oversquare cylinders make less efficient air pumps.

So in a naturally aspirated motor, I am going to build it undersquare to capitalize on the efficiency of the tall/narrow cylinders, both as better air pumps and as offering better combustion characteristics.

The small bores/valves can be ported to flow PLENTY enough for a naturally aspirated 359ci (6.0L) motor. TEA stage 2 flows over 300cfm @ .600, which will do just fine for anything less than 7.0L spinning at less than 7k rpm's.

Any thoughts? Am I missing something entirely? The obvious trend in OEM engines is oversquare, unless you count transverse motors which tend to be undersquare for packaging reasons.

You can't really say reliability or service interval is a determining factor in this case due to the fact that there are a lot of high mileage OEM motors still on the road with 4" stroke crankshafts.

And with compression ratios constantly on the rise, you would think that a longer conrod would be preferable to slow the piston near top dead center for less detonation issues. Undersquare engines tend to have longer rods inherent to their design.

So if you can achieve adequate air flow with smaller valves, what is the advantage of being oversquare? I should say that we are staying below 7500rpm's for the sake of this discussion... I have no interest in tickling 10k rpm's.
Reply With Quote
  #14  
Old 05-06-2015, 10:25 PM
Che70velle's Avatar
Che70velle Che70velle is offline
Senior Member
 
Join Date: Aug 2012
Location: Dawsonville Georgia
Posts: 2,219
Thanks: 609
Thanked 157 Times in 109 Posts
Default

David, speaking only of naturally aspirated engines, the over square method of achieving a set cubic inch goal will be more reliable. Increased rod angle is the biggie, with a taller stroke. The more rod angle you have, the more wear you put on the cylinder wall, and the piston rings/skirt, and it also puts more heat in the engine from friction, which is a no no. A bigger piston will run cooler, all things being equal, due to more surface area for oil splash to cool piston from bottom.
These are things to consider if your building a high rpm endurance engine, which your not, so I say build what you'd like, and enjoy it.
Fun fact...in two absolutely identical engines, one having aluminum heads, the other having cast iron heads, the engine with cast iron heads will make more overall power, due to being able to hold heat in the combustion chamber longer...
Totally off topic, but worthy of discussion also. Logically, you'd want aluminum heads over the iron heads, due to weight, and where the weight is at in the vehicle.
__________________
Scott
---------------------------------------------------------------
70 velle' on custom chassis w/custom RideTech coilovers, RED sleeved 434” with Mamo 265’s, F-body Magnum, 12 bolt 3:73, wilwood 6/4's, bla, bla, bla...build. thread https://lateral-g.net/forums/showthread.php4?t=39631
New 434” engine build here https://ls1tech.com/forums/generatio...ved-block.html

Thanks Dad!!

My Chevelle is old school... It has a belt driven power steering pump.
They're 17's, but I keep em clean!
Reply With Quote
  #15  
Old 05-07-2015, 11:50 AM
DavidBoren DavidBoren is offline
Senior Member
 
Join Date: Oct 2014
Posts: 189
Thanks: 0
Thanked 1 Time in 1 Post
Default

Thank you for the input. I have heard that about iron heads making more power due to combustion chamber heat.

And given that this is a discussion of design theory, I see the inherent detriment of increasing stroke. The side loading and friction/heat increase presents a problem to be resolved, for sure. And is probably (obviously?) best left avoided.

In my particular case, I will have an oversized cooling system with electric water pump and fully boxed/ducted radiator, to handle the heat. And I am going to use the small bore block to capitalize on its thicker cylinder sleeves to address the side loading caused by the 4" stroke.

I also will be running an oil cooler, and I have a small quandary about oil squirters...

Are oil squirters piston coolers, or are they just oil heaters?

They use engine oil to cool the piston. Which puts the heat directly into the oil. Are the pistons cooled enough to really make a difference in detonation issues? Doesn't cooling the combustion chamber decrease power output (as discussed above with iron vs aluminum heads)? Doesn't squirting 75psi of oil UP at a piston that is traveling DOWN add resistance/drag that is otherwise not present?

Also, undersquare engines have better combustion due to small chambers, less surface area, blah blah blah. So if oil squirters do detract from the combustion efficiency, due to heat loss in the combustion chamber, this effect would be naturally counteracted by the undersquare small bore combustion efficiency.

If oil squirters are just to stem detonation, then the long rods inherent to an undersquare motor make them (oil squirts) unnecessary. As long rods slow the piston near top dead center, and naturally reduce detonation issues.

Said another way, do the characteristics of an undersquare motor counteract everything oil squirters are trying to accomplish? Or would the longer stroke, and the friction/heat that comes with it, be in a greater need for added piston cooling?

Last edited by DavidBoren; 05-07-2015 at 03:08 PM.
Reply With Quote
  #16  
Old 05-16-2015, 08:20 AM
Twoblackmarks...'s Avatar
Twoblackmarks... Twoblackmarks... is offline
Senior Member
 
Join Date: Jun 2013
Location: Norway
Posts: 261
Thanks: 0
Thanked 1 Time in 1 Post
Default

In my opinion, an short stroke high RPM engine is usually much more fun to drive than an long stroke grunty one.

3.78" Bore is very small for an 2 valve 5.8 liter+, it does not matter if you get "better" combustion chamber, because the valve probably is so shrouded by the cylinder wall that you get poor filling and "looses" combustion efficiency by that. So then you probably need to put in smaller valves to unshroud them. And that 300cfm is probably not flowed on a 3.78" bore, I would guess. But I may be wrong.

But it depends on if you want an 300HP truck engine or an 300+HP fun engine.

I would take the fun engine, a shorter stroke engine that survives some RPM and abuse much more easily than an long stroke grunty engine that runs out of rpm.

I dont think the heat and resistance is such a big deal, unless you are going to run a lot of track, rod angle this and that, the most important is the guy who put the engine together, like Warren Johnson says " The rod only holds the piston" but of course, there is more to it than that..

Piston squirters are good for piston cooling, an 100HP VW engine from the 80s has that, then I would think an 3-4-500+ HP V8 SHOULD have it, it`s almost only just american V8s that dont have it for some reason. Any engine that is going to run continually at high speed/load likes piston coolers. Before people often cut a groove in the rods to get piston cooling, and lubrication.

I dont think there is anything wrong with a 4" stroke, but team it up with an bigger bore than 3.78 and it would be better. Cubes work, that I have experienced.. I have an 4.25 stroke engine.. But is it made for endurance racing, probably not so much..

If you can I would just go for what you think would work and try it, on a side note, most european engines are long stroke - small bore, but they are small engines that "need" the stroke. They often have short rods to, sometimes because of not much room for long. If you are used to US V8s, many european engines seems not so smart put together, from an performance view....
Reply With Quote
  #17  
Old 05-16-2015, 12:03 PM
Ron Sutton's Avatar
Ron Sutton Ron Sutton is offline
Senior Member
 
Join Date: May 2013
Location: Folsom, CA
Posts: 2,422
Thanks: 45
Thanked 35 Times in 26 Posts
Default

This is a cool thread ...

IMHO, the I think the key goals are:
A.
Wide powerband ... to reduce or eliminate shifting
B. Smooth, non-peaky powerband ... to eliminate surprises to the tires
C. As much power as we can actually use

Concerns:
* The problem with big stroke engines is they build so much torque ... right at the corner exit rpms ... it's hard to not blow the tires away.
* The problem with short stroke engines is often ... not always ... they low end lack torque for optimum acceleration off the corners ... and with the wrong cam, can have a useless, narrow, peaky, high rpm power band.

From my racing experience, if you are in a series with no cubic inch limits, what is both fastest ... and EASIEST TO DRIVE ... is a big bore/medium stroke engine ... designed for a wide, smooth powerband. When I raced in West Coast NASCAR Modifieds, there was no cubic inch limit ... just a carb & tire limit. So we saw every combo including 355"/358", 372/377", 383"/388", 400"/406" & 434" engines. The story went a lot like the 3 bears & porridge.

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.

The engines that were "just right" were big bore (4.125"-4.185") & medium stroke (3.750-ish). These 400"-410" engines were dominant. They had optimum torque for the best corner exit on the narrow slick we ran. With the right wide lobe centerline camshaft, they had a wide, smooth powerband that was easy to drive fast & consistently. And the top end power was awesome ... pulling all the way down the straights. In my experience, the 383" & 434" combos are just two different sizes of the same long stroke strategy. Both build their torque down low & run out of stem too early. The 377" & 410" combos are also two different sizes of the same big bore/medium stroke strategy. The 410" just builds more power throughout the entire curve.

For road courses, this is even more critical, as the 10-12 corners are all different. Making the need for a wide, smooth powerband even more critical. I built all of our winning road race engines the same way ... big bore/medium stroke. Getting this strategy right will be even more critical for autocross on TW200 tires.

As over simplified as this sounds ... determining the stroke length you want/need for just the right amount of torque ... is a good starting point. Then design the whole engine around that. I have several versions of a 409" LS engine in development currently. The "tame" versions build 750 hp & the "mean" version will make 900hp. All very drivable on track with a smooth, flat, wide powerband. So that tells you my preference.





__________________
Ron Sutton Race Technology
Reply With Quote
  #18  
Old 05-17-2015, 03:03 PM
Matt@BOS's Avatar
Matt@BOS Matt@BOS is offline
Lateral-g Supporting Vendor
 
Join Date: Oct 2008
Posts: 2,036
Thanks: 2
Thanked 37 Times in 30 Posts
Default

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.
Reply With Quote
  #19  
Old 05-18-2015, 10:38 AM
DavidBoren DavidBoren is offline
Senior Member
 
Join Date: Oct 2014
Posts: 189
Thanks: 0
Thanked 1 Time in 1 Post
Default

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?

Last edited by DavidBoren; 05-18-2015 at 10:48 AM.
Reply With Quote
  #20  
Old 05-18-2015, 12:36 PM
Rod P's Avatar
Rod P Rod P is offline
Senior Member
 
Join Date: Nov 2008
Location: Thompsons Station, TN
Posts: 977
Thanks: 0
Thanked 2 Times in 2 Posts
Default

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
__________________
Rod Prouty
My websiteAuto-cross 101
I'm not a Real Racer but I did spend a night in the Pozzi's motor-home
Bangshift Stories
I’m not the smartest guy at the track … but when he goes home … I’m still there testing, tuning, learning & getting faster.
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 02:07 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright Lateral-g.net