BIG Low End TORQUE

broncr

broncr

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It 's Saturday, so I'm in mood.

It seem a bit quiet here at HC Tech (no offense) and I thought I'd throw this out and see if anyone cares to comment. I've noticed the last few weeks that under normal driving conditions, I'm shifting between 2-3,000 rpm. What might I do to bump up my LOW END TORQUE ?

I know there is a lot of discussion about high rpm horses & mods, but what if you just wanted some low rpm mega pull? I'm talking about engine mods...I like my 3.50's and don't want to change front AND rear gears.

Broncr
 
Actually there's another few words: "positive displacement blower"

The only way to increase torgue is to increase BMEP. The way you increase BMEP is by getting more mixture into the cylinders and/or by burning it more efficiently. If you port the head perfectly (tough to do without a flow bench and/or lots of experience), select the correct camshaft and re-work the fuel and exhaust systems as req'd, you can pick up at best a 20% increase in VE at low RPMs which translates more or less directly to an equivalent torque gain. The problem with this approach is that when you build an engine for a specific RPM range, you necessarily sacrifice performance in other ranges. This is equally true whether you're building a 2000 RPM tractor engine or a 14,000 RPM race engine.

If you stick a positive displacement blower on an otherwise stock engine running at 8 PSI, you'll see an approximately 30% gain in torque across the entire RPM range of the engine. The bad news is that the boost is always there whether you need/want it or not and fuel consumption, and sometimes drivability, suffers accordingly.

What you get from a turbo is greater efficiency, therefore more power produced for fuel consumed, and the fact that boost is "on demand." You can cruise forever at zero boost but have it readily available when you mash the stupid pedal. Really the best of both worlds.

The fact that turbos are simpler to implement is just icing on the cake.
 
bring your compression up to 9.0 and shave the block down to get zero deck on your piston. I rebuild my 300-6 with 275,000 miles on it and I noticed the that the pistons sat .020 down in the hole, and my new 0.030 overbore pistons also sat .018 down in the hole. I took the block in and had them shave .018 off the block. That brought the pistons to +/- 0.000 in the hole and the headgasket compresses to about .042 which is very close to the Ideal .040 piston quench area which creates ALOT more turbulance in the combustion chamber allowing for better air/fuel atomizsation and complete burn. It also allows for more timing advance without ping, I got to run 2-3* more that stock even with higher compression and still using 87 octane. This REALLY gave it a kick in the lowend, and the 4bbl and headers I added after 5000 miles helped again. I have no trouble turning my 33" swampers with authority with 3.55 gears in my 83' bronco (had a NP435, now has a C6 with V8 converter for a bit more stall)
 
instead of having the block decked why not just have the crank turned offset by .015 and take it down to .040 under stock that would even give you a 4.010 stroke and go with a 4.030 bore and get a 307ci 5.0L
or 4.060 and get a 311ci 5.1L inline six
 
Turbos are great for torque. My inline 5 cylinder volvo has max torque at 2500 RPM of about 260 ft-lbs. Not bad for a 2.3L 5 cylinder engine. The non turbo version of that engine has max torque of 170 ft-lbs at 3300 RPM. That's the beauty of the Turbo, the ability to increase your torque and lower your torque band (along with flattening it) to a more usuable RPM. Even with a 2100 RPM stall speed on the automatic, I can get about 90% of available torque by power braking to 1800 RPM. It's also so cool to hear the turbo winding up like that and just sucking air in. and when you let off the brake, bye bye traction. hehehe.

Slade
 
I like the previous points in the discussion. Peak HP only means something If you drive at near WOT at around max revs. I still dont understand the logic in having an engine capable of high power ouput at high revs and never venturing to go near the point of its max power.
What really doesnt make sence is to do this at the expence of low end drivablity and the never explore the upper limits of an even a moderately cammed up engine. Most drivers fall into this catagory (normal driving). A lot of the newer cars with their double overhead cams and multi valves are all good for high rpm that most users dont use.
I guess a lot of consumers dont ask the question "what do I want to do with it first". In the end it might be worth trading off a small amount of low rpm power to gain up high in the rpm but only if I go there occasionally. Ford sixes have heaps of low rpm power, mine growls like a tiger wanting to get out of a cage at low rpm and I definitely could trade off some low end power by camming it up a bit. but just the same it goes like nothing else I driven at low rpm as it sets it appart from a lot of the new stuff out there (the question should always be power at what RPM). I Cant Imagine what some of the turbo sixes on this forum must be like. They seem to have the right Idea.
The manafacturors will keep trying to increase the trend to higher peak Hp at ever higher rpm because it looks good on paper and it helps them stay competative while many consumers are probably confused about what it means, especially for daily driving.
Cheers Tim
 
British car engines took a different approach to the US motors, tending to be seriously undersquare, low revving lumps. You'd then team that up with a gearbox that had a tall overdrive on third and top, and a 5.something:1 diff. Lower operating RPM must've meant lower CFM requirements, and better possible control of airflow. Anyhow, they were sometimes torquey to the point of being axle-snappers.

Some of the driveline aspects here might help manage a stump-puller motor get to highway speeds without too much effort.

Adam.
 
addo":2hwcnyot said:
British car engines took a different approach to the US motors, tending to be seriously undersquare, low revving lumps.
Click to expand...

Addo, that's because by the time they get to 60 MPH, they are at the end of the island and it's time to slow down... ;)

Slade
 
addo":1ps7558x said:
British car engines took a different approach to the US motors, tending to be seriously undersquare, low revving lumps. ......
Click to expand...

That design philosophy was actually an economic decision. In 1921 the British enacted something called the Motor Taxation Act which taxed private motorcars on an arcane Royal Auto Club formula. The RAC figured that 1 HP was equal to 2 square inches of piston area. This was known as the "treasury rating" and (4-wheeled) cars were taxed accordingly. To reduce the taxation, the engine designers went to undersquare designs in order to keep displacement up. This bizarre formula stayed in effect until 1947. You will see cars up until the 50's rated in terms of RAC hp (8, 10, 12, 14hp).

In the deep south, we once did a similarly dumb tax thing by taxing buildings based on the number of windows they had. Consequently you will see a lot of post Civil War buildings with bricked up openings....... :roll:
 
If on a buget, there are a few things I would try. First I would reduce friction by using roller rockers. This will help at all rpms just the same.
I think also porting the valve bowls a little, not going for larger size but smoothing out the transition between the valves and the ports. there are a lot of sharp edges in there. I would leave the valves sizes stock for the rpm you are wanting improvment.
The third thing I would do is use a different cam. something about 204 -
210 at .050' crane and comp have good 260 cams that would work well.
Jim
 
IIRC, Henry VIII taxed windows first. :P A British crack at the Windsor would have had a 3" bore, 5¼" stroke, bevel gears driving overhead cams, 7:1 compression and a magneto. They always seemed to fall down somewhere in the "whole package". I wanted to present another way of looking at the limitations, and what was done.

Hey Slade, have you heard of the "Land's End to John O'Groats" run? It's literally from one end of the place to the other. Rains all the way. Naturally, it's popular with the enthusiasts whenever run. :lol:

Adam.
 
At the risk of restoring the subject, the original question was about BIG torque. All the fiddling about you can do with a normally aspirated engine won't get you close to what a mild boost from a Whipple or a turbo can do for you at low revs.
 
For low RPM torque there is nothing quite like a long stroke. My sister had a Studebaker Lark with a 170 ci flathead six that had a 3" bore and 4" stroke. That little engine idled like a sewing machine, you could actually balance a nickel on it while it was running. I deliberately lugged it down to 10 mph in high gear and it accelerated up from there nice and smooth without bogging or jerking.
Joe
 
MustangSix":p53uqlnd said:
In the deep south, we once did a similarly dumb tax thing by taxing buildings based on the number of windows they had. Consequently you will see a lot of post Civil War buildings with bricked up openings....... :roll:
Click to expand...

really?
i never knew that... i'd always wondered why that was though, i figured that they were just abandoned (most i've seen look like they are at least) and some state agency had done it to prevent people from going in
 
I know this is a bit late in the conversation but I had a question. If I were to boost the cmpression to 9 to 1 then deck the block to zero piston deck wouldn't it raise the compression even more?? I understand the need for quench and I can see the point but I think I got lost somewhere. :wink:
 
addo":1nngeasx said:
IIRC, Henry VIII taxed windows first. :P

Adam.
Click to expand...

I think that's where the Reconstructionists got the idea......rich folks got lots of windows.....it didn't last long.

I just noticed, this has NOTHING to do with torque.... :oops:
 
Well, that was an interesting ride...

I was offline most of the weekend, and it's interesting to see where this thread has gone.

I appreciate that boost is the best way to get BIG TORQUE, which is what the original question was. The nice thing is that there are suggestions for both my current engine (10+:1 CR), which I'd rather not risk boosting, and my spare block, which I do intend to boost.

My rebuild came out of an '80 F250 Crew Cab. It was the FIRST time I had torn down a 300 & it had flat top pistons, so I had it rebuilt with the same, not being "turbo savey" as I'm BECOMING here (Thanks to the many who are willing to share their wisdom).

I'll probably be looking primarily at valvetrain improvements with this engine. That's about all I have left with it. I've ported, polished, mated, 4bbl'd, EFI'd - just a cam(?) & rollers to go with it.

When I pulled the head off of the original engine I was a bit surprised to see the dished pistons. Had I rebuilt with them, I'd be looking at BOOST now... but that gives me something to look forward to.

Wow, I had never heard of HP or window taxes... :roll: ( no offense, it was interesting - sort of) but, back to the point -

I have one question - is there any benefit to zero decking a block that will be turbo'd?

Broncr
 
broncr":2tij53ro said:
I have one question - is there any benefit to zero decking a block that will be turbo'd?
Click to expand...
Not for a boosted engine being built for low end torque. Decks are normally cut down to help the pistons exploit quench, which won't be as much of a factor with a turbo.
 
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