Thompson can do anything you need.

I used them with my 370 build.

 

sounds to me like your happy with the displacement you currently have.

so throw "science" at your 'current' engine.

I image you have an older steel block 5.3L. Why not...swap to a newer aluminum L33 5.3.


since an engine makes peak torque at peak efficiency, work on maximizing that...which will inturn give you more power(towing) and gas mileage. The weight savings is also good for the above (maybe negligible).

the easiest way to increase efficiency is raise the compression ratio. the L33 is already 9.5:1, I'm not sure how much higher but I'm sure this could be bumped. If you bump the compression through pistons or maybe longer rods this keep your chambers flowing well.

Add free flowing intake, exhaust, mild cam, and head work if you desire. I believe the L33 has 243 heads so they are pretty much ready to go as is.

I think this would be the best combination for your needs. I don't see how increasing the displacement(either bore or stroke) would give you some of your requirements unless you are doing mostly interstate driving and even then it may not.

 

Agreed, and which each comes trade offs. By adding bore, you will increase piston size which in turn adds more mass to the little end whereas stroke will also add addition frictional losses due to side loading. Of note though, by adding stroke you are essentially creating a longer lever which would create more force acting upon the crankshaft given equal forces being applied to the piston, so theoretically given a proper setup, the stroked motor/same bore should make better overall power and in most cases the valvetrain would be the limiting factor in RPM given the availability of quality rotating assembly parts. I'm sure some of the additional friction loss can be absorbed with skirt coatings as we have seen as well as perfect Ra finish on the cylinders walls however I haven't myself see emperical data that directly correlates a proportional value between the two.

 

Interesting reading! In my old school engines, they always run the best at the track with more stroke it seems, throttle response and low end grunt seem to be where it makes the difference.

 

Heads, intake, cam, that's why.

The bottom end is he bottom end and to many think that's where the power is made, power is made by camshaft heads and intake the bottom end only holds it.

Edit:
I truck pulled for many years the best performing motors we had were short stroke big bore yeah we had to twist them 3-500 rpm more, but they also made more power. Point being you pick the rpm you want and the power you want and build to it.

 

If you change absolutely nothing other than Bore and Stroke...and you keep the Engine Cubic inches the same...meaning decrease one and increase the other...

you will always gain more power from increasing Bore

in classes in limited Cubic Inch dimensions...where bore and stroke can be anything they desire as long as it hits "X" cubic inches...
they always elect for more bore and less stroke...
it makes more power, and the shorter stroke has benefits as well allowing you to turn higher rpms equating to more potential horsepower with the right parts.

at the lower level...bore size is determined by your wallet...
in hard core racing, the wallet doesnt matter so they can afford big bore with short stroke

 

 

In this build, should I use the LSX block, the block will be the only seriously high dollar item I have to buy. Higher compression on 87 octane gas is supposed to be one of the advantages of a big bore engine. I knew I had read this years ago in a HR mag article. However... If this is repeatable, why don't more people do it? Here's a link the old article:

http://www.purplesagetradingpost.com...%20engine.html

Long rods were an essential part of their build. They used 6.209 inch ford rods. I can go a little longer using the stock 4.8L rods (6.275) and still use standard pistons. Their engine started producing 400+ ft/lbs of torque at 2800 RPM. They used an old comp cams H270 flat/hydraulic lifter cam. I'm sure I could do better with a mild roller/hydraulic lifter cam. I've used the Comp Cams H260 in a truck, H268 in a firebird, and the H270 in a 71 Chevelle. Some kind of roller cam equivalent to the H260 would likely be what I would use. I have no doubt there are much better cam options today. The H260 was a great cam for a 350 we put my dad's 1-ton truck. It got relatively great gas milage and pulled anything he hooked up to it.

 

As others have stated; dynos measure torque (twisting force) and horsepower is just a mathematical computation of where (rpm powerband) the engine produces those forces. 5252 being the denominator in the equation. Racing classes typically use the big bore/short stroke combo for a number of reasons. As mentioned the larger piston will unshroud bigger valves being fed by larger runners to get more air in and out of essentially an air pump. Roughly 60% of and engines reciprocating friction is from the piston rings. Increasing the bore does add more surface area (contact) however this can be off set by thinning the rings from the old 5/64 to 1/16, 1.5/1.2mm and even .043 or less yet for all out applications. A 3" stroke V8 engine has 8 less inches of piston travel per single crankshaft revolution than a 4" stroke. Dramatically reducing piston speed and pumping friction, which is another of many reasons why short stroke engines can be safely revved so high. Racing classes also don't care about mileage or torque because they can adjust the trans and/or rear gearing to multiply the torque the engine makes to suit their needs. I wouldn't say that a shorter stroke engine makes more peak power but all things equal (cam, heads, inches, induction) it should make more average power through efficiency although the power band will shift upward (where it makes it's torque). Obviously for a big heavy vehicle where mileage and response/drivability is a concern then a square 4"/4" combo or 4.125"/4.125" will tend to have what you need when the heads and cam are appropriately matched. More than overkill for your wife's daily.....

 

4.125x4.125? LOL! That would achieve everything but MPG and long term reliability.

 

Why all the discussion about race motors that idle higher than the OP needs this build to start making torque?

Without getting too technical I wonder why when Furd developed the MOD motors and GM built the LS1 and later the truck engines from the LS1 BOTH shrunk the bore and lengthened stroke? To me what the OEMs do with their VAST R&D budgets far surpassing any racing team do would mater to me more than what they do in F1 or Cup or anything like that.

Comparing the gen 1 SBC to the LS1 we saw smaller bore and longer stroke, then when they developed the 5.3l as the most common 1/2 ton truck engine it got a smaller bore and the same stroke as the LS1, presumably the displacement decrease was done for the miniscule fuel savings.

The Ford MOD motors too shrunk the bore and got longer strokes too??????????????????????????????????????????????? ???????


OEM have a lot of non-racing concerns but among their top concerns are fuel economy and low rpm off idle performance both of which racing could not care less about.

Far as fuel economy IMO the commonly held beliefs that gear and displacement are the big factors are grossly overstated. I have a 500hp 5.7l 4200lbs car with a final drive of 2.87 and a 300hp bone stock 5.3l 5200lbs truck with the same tranny and axle but a final drive ratio of 2.39 and the car gets better mileage under all conditions even pure highway where the truck's weight is largely taken out of the equation. Now yes I understand the truck has a transfer case and front axleshafts to turn which hurt mileage, but the car has a cam on a 108LSA puking raw fuel out with the exhaust, 3800stall and 4.10s, 60% more HP, roughly 8% more displacement, older injection with distributor not multicoil, but IMO what really makes the biggest difference is that looking at it headon it is what 2/3rds the size? Yes the car is in the neighborhood of 12:1 and gets 92-93 octane and the truck gets 87-89 depending where I go. But still with the drastic final drive difference greatly "favors" the truck by conventional thinking.

Point being I think the OP is too hung up on limiting displacement.
You sound like one of those all too common engineers who can't figure out the theory behind something so you completely ignore the physical outcome in front of you.

If you really want to spend the coin on the LSX block go for it and then use the stock 5.3l crank, maybe find a set of 243s don't bother porting them and get one of Tick's new "truck" cams. Order pistons to suit the compression ratio you are comfortable with for whatever fuel you will run. Porting or larger aftermarket heads are going to shine more at higher rpms and the often pushed AFR stuff needs roller rockers which are substantial extra cost as well it all makes no sense for a truck build that likely rarely sees 4000 much less the 6000 you mentioned earlier.


I know that puts you over your self imposed 5.7l limit and part of that limit was probably the GM 6.0l trucks being considered bad on gas vs. the 5.3l but most folks fail to consider other things the 6.0l usually gets like the 4l80E and 14bolt axle both of which are more mass to turn and make the truck heavier. The 4L80E also has a worse first gear and less overdrive and often sees 4.10s behind it which makes for a worse final drive than my car with the same gear but shorter tire and better OD of the 4L60.

 

first off...
stock OEM motors arent built around power...
they are built around Emissions and Fuel economy

if they can make some power...great...but power is not the priority...

there are actual fuel economy laws that dictate what has to happen with an engine...
and unfortunately, it means that we have to have cars that reach a certain fuel economy and emissions rating, and in general, they improve upon emissions by making a smaller engine and then using technology to improve the fuel economy and power as best as they can for that engine



secondly...your 500 hp vehicle is lighter...
and your heavy truck makes less power..
just because it makes more power doesnt mean it will be less fuel efficient

small motors are less fuel efficient by nature if they dont make enough power to overcome the weight.

I can take a prius around a racetrack and get 17mpg...and then take an M3, and just keep up with it(going the same speed following along) and get 23mpg.....
the prius is grossly underpowered....yes it has potential for better gas mileage, but only if your driving habbits yield those results to begin with... the actual Engine portion of it is not very fuel efficient...its the electric portion that allows it to get great fuel milage

 

I saw the TopGear they tested the Prius vs. M3, that was awesome.

Far as comparing my vehicles I understand the truck is heavier which is why I specifically stated The truck has a more advanced injection system, much lower final drive ratio and an engine not spitting fuel out the tailpipes. I get it it is not an apples to apples comparison.
You are right about emmissions and economy being paramount to OEMs but at the same time the HP wars are still on and the engines still have to move the vehicle well under normal low throttle low rpm conditions and tow capacities in trucks have grown substantially while the trucks got heavier and the engines smaller. So I think it narrowminded to completely dismiss what OEMs do because as I said, they have a bigger budget for R&D than anyone else and are more concerned with the under 3000rpm range this poster should be concerned with than racing is.

 

Hasn't the EMC taught us anything?

 

All that nonsense about the GM & Ford engineers... These are the same guys that gave us the Cadillac 4100, the Northstar (a money pit), Ford Interceptors that are slower than the civilian equivalent, the 4.3L odd fire v6, the 305, the Fiesta, DoD, the Cobalt, etc. BTW, I met one of the engineers who designed the 4100. Nice guy, but not a rocket scientist.

I've been working on small blocks since the late 70s. I've built 4 engines, all small block chevy 350s. One of them has never been started so I don't consider it a complete build. I've helped roughly a dozen people with their engine builds. Yeah... I'm one of those dumb engineers who can't deal with reality.

I owned a garage for a short time but I quickly grew tired of geniuses bringing their car to me to fix what they screwed up while trying to tell me how to fix it. That's why I got a degree in computer science. IT customers (usually managers) know they are too ignorant to tell you how to fix their problems.

Why am I here? Because I've never had to build an LS engine. I've been pleased with the feedback I've received until now...

Did you read the topic? Do you have proof that torque is tied to stroke? If so, please give me the links!

Displacement has a direct impact on fuel economy. Air/fuel ratio must be at or near 14:1 for all engines. The more air required to fill the cylinders, the more fuel is required to make it operate correctly.

My truck has 3.73 gears and I'm not changing them to get better economy out of a 6+ liter engine. It gets roughly 17mpg on the highway with the stock 5.3L. The 4bbl carbed 350 I built for my father got 19mpg with 4.10 gears and no overdrive. Why am I limiting the displacement? Because I got pretty close to what I am looking for using an old gen 1 350! With all the high tech advances in induction, ECMs, etc. since then, I SHOULDN'T NEED MORE THAN 350 CUBIC INCHES!

Lastly, I've read the comments in the forums talking about how you need to stay under 10:1 compression on these LS engines to run on 87 octane gas... Seriously? None of my old Gen 1 350s ran less than 10:1. My LT engines' stock compression starts at 10:1. What is wrong with the LS engines that they can't do better on pump gas? Maybe it's those expertly engineered small bore blocks that are the problem. Then again, maybe it's because they can't use reverse cooling on the LS engines because the idiots at GM tried to steal the design from the original inventor when they made the LT engines and they got their butts sued.

 

ROFL! What!? I thought we were talking engines, not fiber channel RAID arrays!

http://en.wikipedia.org/wiki/EMC_Corporation

 

I'm NOT saying to spin a 450+ inch engine to 7000 rpms. For what you're asking from a combo it will make more torque at 2200 rpms than a 350 inch engine with a 3.25" stroke crank. Torque is twisting force and increasing the mechanical leverage (stroke) will do more low end work. All the OEM engines designed for low end torque have had long arms as a constant. 292
chevy and 300 ford sixes had big stroke. 455 buicks at 3.9", 400M and 454 had 4", 472 caddy at 4.06", 455 pontiac at 4.210", 455 olds at 4.25", and 500 caddy at 4.3". I'm not trying to talk you outta your idea but since you brought the big bore LSX block to the conversation my suggestion for an idle to 5000 grunt master would be to square that thing up and let it loaf along while effortlessly moving a heavy vehicle with the aerodynamic properties of a barn.

 

Personally, I think displacement is all that really matters when trying to produce torque. I wanted to see someone PROVE me wrong. I think people love strokers because they are cheap and easy to build. I think the reason you don't see a big bore engines with lots of low end torque is because people build them to take advantage of the higher RPMs that they are capable of maintaining. I'm sure it will drive someone crazy if I build an engine that could do 8k RPM but I put an RV cam in it. That's life...

What I would love to see is a comparison of a standard 5.3 or 5.7 LS motor to a big bore equivalent. It would be even better if the two were built to their maximum potential for a given RPM range and no forced induction. If cams, heads, etc. are all the same, one of them will likely not fare well. I'd like to see the maximum compression ratio that will work with 87 octane gas for each build. I'd like to see the effect of various camshafts and cam timing on each build.

I'm just amazed nothing like this has been done before. If it has, please reply with links.

 

Your comments are appreciated. A 7.2L would certainly make me smile if the liberals weren't driving gas prices through the roof. My wife spends about $50 a week in gas, I wouldn't mind it if she had to spend $80 a week for a better running truck, but the continual nagging about turning her truck into a gas hog would suck all the joy out of my life.

 

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