View Full Version : Larger power band? 5sfe

Razors_Edge

07-24-2009, 07:54 PM

How would i get a larger power band out of my 5sfe?

I already have 294 cams and lightened flywheel planned for top end power. Im wanting to get more acceleration on the bottom end. I currently have a short ram, header, 2.5" exhaust from the resonator back and i do not have a CAT on my car. God bless Oregon!

Murgatroy

07-24-2009, 11:39 PM

Squeeze it.

joe's gt

07-25-2009, 12:26 AM

The only way I could think of doing it is staggering the cams. You'd have to make a custom intake manifold such as MrTurrari for anything else that would be effective. Can't really have both. Everything is gonna be a compromise.

If your header and cams are tuned for high rpm, then that's where your going to make your power. I assume staggering your cams is the only way to get some of the low end back. Not too familiar with the 5s tho.

nuclearhappines

07-25-2009, 01:02 AM

timing advance

higher lift cams

intake manifold spacer plate

more compression

more stroke

more bore

ported throttle body

Razors_Edge

07-25-2009, 08:20 AM

ok thanks guys. I have tons more research to do! LOL! Great info and a very good starting off point.

joe's gt

07-25-2009, 08:12 PM

In case your wondering about Nuke's suggestions and why he suggested them.

Timing advance is a great starting point. It ignites the fuel a littler sooner and gives you higher cylinder pressures for more power. You'll have to look at previous threads for how much is perceived safe.

The high lift cams will of course allow more air in the cylinders without changing duration. However, depending on how high you go here, you might need stiffer valve springs so you have to be careful with that.

The intake manifold spacer is a good idea for increasing the runner length. This is better for low rpm performance I forgot why. lol. I believe it has something to do with stronger pressure waves.

nuclearhappines

07-25-2009, 08:39 PM

1000 rpm is 1000 revolutions per minute.

There are 60 seconds per minute

1000 rpm = 1000/60 = 16.6 hertz (rounds per second)

Period = 1 / Frequency = 1/16.6 = 60 milli seconds between two valve openings at 1000 rpm.

At 6000 rpm you do the math again and that comes out to 10 milliseconds.

The speed of air in the manifold is the speed of sound...343 meters per second

In 60 milliseconds, a pressure pulse travels 0.060 * 343 = 20.58 meters

In 10 milliseconds, a pressure pulse travels 0.010 * 343 = 3.43 meters

Since the pressure pulse has to travel all the way to the end of the intake and reflect back , it has 30 ms to go and 30ms to comeback, the intake length has to be a subset of 20.38/2 = 10.19 meters for an intake tuned at 1000 rpms.

similarly for 6000 rpms the total intake length has to be a subset of 1.715 meters.

For example

10.19/1 = 10.19 meter intake first reflection

10.19/2 = 5.095 meter intake second reflection

10.19/3 = 3.396 meter intake third reflection

10.19/4 = 2.548 meter intake fourth reflection

10.19/5 = 2.038 meter intake fifth reflection

Similarly for 6000 rpms

1.715/1 = 1.715 meter intake

1.715/2 = 0.875 meter intake

1.715/3 = 0.571 meter intake

1.715/4 = 0.428 meter intake

1.715/5 = 0.343 meter intake

These distances are from the valve to a reflection point and back.

Reflection points include:

where the runner meets the plenum

where the plenum meets the throttle body

where the intake system ends (with your air filter)

If you dwell on those numbers for a bit you can see why a cold air intake (with a long pipe) boosts low rpm power more than a short ram intake (with a short pipe)...

Let's assume just now that both intakes (the cold air) and the short ram are fed the same temperature air (like a short ram ending in a boxed filter with a snorkel to the front grill).

These are really crude reflection 'ram air intake' maths done as early as the 70s on chrsytler.

The other maths come from fluid dynamics on some thing called a spring dampened mass system (or some BS like that) ... I'm not a mechanical engineer.

Ideal intake manifold runner length = 13inches +[-1*(6,000 rpm - desired peak VE RPM)/1000*1.7"]

That is if i recall this correctly.

so a manfiold optimized for 1000 rpms would have a runner length of:

13 + -1*-5*1.7 = 21.5 inches (from the valve to the plenum)

A manifold optimized for 6000 rpms would have a runner length of:

13 + -1*0*1.7 = 13 inches from the valve to the plenum

Thus a change of 0.5" from a spacer brings down the target rpm range by about 294 rpms ...so if your peak torque is at 2500 then with a 0.5" spacer look for peak VE at 2200 and at 1900 for a 1" spacer... (this is also neglecting any positive effects having a cooler / colder manifold has on torque delivery).

That's the math... now you can optimize your intake manifold and intake system.

Of course one last thing to say.

If you have an intake optimized for a 1st reflection at 6000 rpms, then at 3000 rpms you also get a slight VE bump because at 3000 rpms , air has twice the time to go and come back so you get a 2nd harmonic reflection at the valve as it opens... a 2nd reflection is weaker than the primary reflection, but you still get a tiny VE bump at 1500,2000,3000,6000...etc for a manifold tuned for 6000. (with each reflection getting weaker and weaker and becoming negligibale really).

joe's gt

07-26-2009, 01:47 AM

^^ Thanks Nuke. Excellent Info. I'm actually at the point where I can finally understand what you write. lol. Although I think that equation with the 13 inches is actually for an intake pipe and not the manifold runners.

nuclearhappines

07-26-2009, 09:16 AM

if you've seen the AEM V2 cold air intake, it has a hump / transition in the middle

They have it tuned for 2 different lengths... one as a 'short ram' and one as a 'cold air'

cool stuff when you see companies try to apply science rather than just sticking a filter on a stick : )

joe's gt

07-26-2009, 06:59 PM

Troof. Just getting in to all the theories and stuff and finally understanding how engine tuning REALLY works. Thanks for the info man. I love your informative posts and in depth explanations. They are very helpful to mine and many other people new to cars understanding the science and engineering behind the results

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