NA Engines: Factors that increase torque

[NewbVetteGuy]

I'm picking up bits and pieces but I'd love to see a discussion with a full list of engine building decisions that can help to maximize torque and a rough idea of just how impactful each decision is.

Forced induction and increased displacement are the obvious gains, so let's leave them off of the table. In a naturally aspirated engine, for a given displacement, what are the design decisions that can increase engine torque output? (What do we start to see in nA engines with ft lbs:cubic inch ratios of 1.3:1-1.5:1 or even higher if that's possible...?)


Here's my starting list of things that I've heard increase torque (or prevent torque loss to ultimately result in more flywheel torque), but I don't have a great understanding of how impactful these are:

[*]Exhaust tuning -my understanding is this is always step #1 and the most impactful or one of the most impactful items
[*]Compression ratio- kind of obvious, right?
[*]Intake tuning- Long runner tuned lengths when you want to stuff the most air possible in an NA cylinder
[*]Head and intake design that focuses on flow VELOCITY
[*]Efficient fast burn, high swirl combustion chambers that burn quickly
[*]Piston & ring packages that prevent leakage AND minimize friction- [edit]just read an article that showed 10+ft lbs improvement across the whole RPM range from using zero gap seal rings-way more than I expected
[*]All engine friction reduction - less power loss
[*]Well-timed sequential port fuel injection events- improves low RPM torque, anyway
[*]Piston top shape? -I've heard whispers and rumors that dished pistons of certain shapes may make for a faster burn that enhances torque slightly (pistons that mirror the shape of the chamber above, for example) -I'd LOVE any assessment of how much this helps; I'd imagine its incredibly minor
[*]Rod Length?
[*]Cylinder height to width ratios?
[*]Colder intake air charge -improves torque across the RPM range, correct?

In the same vein: If faster burns increase torque does that mean that higher octane fuel, which burns slower, decreases torque?


Adam

[FC-Pilot]

You have to first decide on what RPM you want peak torque to be at. That dictates most of those details. 3500 or 7000?

Paul

[NewbVetteGuy]

You have to first decide on what RPM you want peak torque to be at. That dictates most of those details. 3500 or 7000?

Paul

If some of the factors in the list simply move torque around then call that out; if they maximize torque across the RPM range (like better sealing rings and colder air intake temps) then call that out to.

This is about learning about theory and just getting a "brain dump" about factors that impact torque, so no need to "choose an RPM.


Adam

[LCaverly]

having a cam with a very aggressive lobe always increases torque. when looking to maximize torque with a roller I like comps TK or HXL lobes but valve train has to be spot on. I'm sure there are other companies that have equivalent lobes,
Len C

[Zmechanic]

In terms of total charge density coming from intake, for a N/A engine that's TO THE MAX with 127% VE (as compared to pumping displacement), the rule of thumb breakdown is:
100% cylinder displacement
4% Fill of combustion chamber
18% Inertial ramming
5% Wave tuning
Note: Those are guidelines developed by those far more experienced than I, I'm just passing them along.
The heads, intake, and exhaust have to be tuned in each of the aspects for the RPM range you care about. There isn't a one size fits all approach.

A smaller chamber that promotes good fuel vaporization without compromising flow or pressure recovery will almost always require less timing. This shows faster and more efficient burn, which will yield more torque. Equalizing the flame front with good plug location helps quite a bit too, and allows faster burning fuel to be used without getting into end gas detonation. Piston dome "creepage" (which is actually an electrical term) matters as well. How far in actual distance does the flame front travel? This is why excessive valve reliefs are a two-fold killer. They bleed off C/R, and to make up for it, the dome must made bigger, increasing flame travel time.

[AMXstocker1]

So out side of a Hemi would a very small chamber and dished piston be optimal

[PackardV8]

So out side of a Hemi would a very small chamber and dished piston be optimal

If the discussion is about 2-valve OHV8s, then just look at current LS tech.

[digger]

id put cam events at top of list

[NewbVetteGuy]

having a cam with a very aggressive lobe always increases torque. when looking to maximize torque with a roller I like comps TK or HXL lobes but valve train has to be spot on. I'm sure there are other companies that have equivalent lobes,
Len C

Wow, I learned something new already! I did not know that. Can you give a super speedy explanation on why this helps improve torque? (more air flow sooner?!?)


Adam

[NewbVetteGuy]

In terms of total charge density coming from intake, for a N/A engine that's TO THE MAX with 127% VE (as compared to pumping displacement), the rule of thumb breakdown is:
100% cylinder displacement
4% Fill of combustion chamber
18% Inertial ramming
5% Wave tuning
Note: Those are guidelines developed by those far more experienced than I, I'm just passing them along.
The heads, intake, and exhaust have to be tuned in each of the aspects for the RPM range you care about. There isn't a one size fits all approach.

A smaller chamber that promotes good fuel vaporization without compromising flow or pressure recovery will almost always require less timing. This shows faster and more efficient burn, which will yield more torque. Equalizing the flame front with good plug location helps quite a bit too, and allows faster burning fuel to be used without getting into end gas detonation. Piston dome "creepage" (which is actually an electrical term) matters as well. How far in actual distance does the flame front travel? This is why excessive valve reliefs are a two-fold killer. They bleed off C/R, and to make up for it, the dome must made bigger, increasing flame travel time.

oooOOOO! I love this thread already!

Can you define "intertial ramming" for me? I'm surprised Wave Tuning effects are listed as so low...


The the stuff about Piston dome "Creepage" it sounds like what you've said implies that a flat top piston will produce more torque than a domed piston because the flame doesn't travel as far- is this part of what you're saying?


Adam

[NewbVetteGuy]

So out side of a Hemi would a very small chamber and dished piston be optimal

If the discussion is about 2-valve OHV8s, then just look at current LS tech.

Jack, help me wrap my mind around what I'm looking at; I've never seen a piston like that (not that I've spent much time looking at pistons...).

I see a huge flat area that's for the quench; and then a horseshoe-shaped domed dish/ exploded volcano ala Mt. St. Helen's looking piston? (Hard to tell what it looks like 3 dimensionally because it's so dang shiny!)


Adam

[PackardV8]

a horseshoe-shaped domed dish

I believe that's where the Direct Injection fires.

[Dan Timberlake]

Did I miss any mention of getting the spark timed just right for the situation at hand ?

[roc]

a horseshoe-shaped domed dish

I believe that's where the Direct Injection fires.

They're certainly aftermarket pistons for direct-injection (LT1?), in three different compression ratios. Nice!

[cab0154]

if an engine creates more power at a given rpm it will also create more tq at that rpm and vice versa. as far as airspeed, your target airspeed will come from your displacement and port cross section, and those partially determine where that will happen along with the camshaft. as a general rule, at an engines peak tq you are no where near your target peak airspeed. cylinder fill creates power. whether you want to measure as tq or hp, that doesn't really matter.