LSOHOLIC

iTrader: (3)

Looking for IVC info or theories on a manifold limited setup.....heavy hitting 346's.

Talking about IVC at
47* @ .050 and later.

Only three constants
346"
Fast manifold
N/A

~Whats the latest you've seen ??
~Are there RPM gains by bring the IVC later (manifold limited) ??
~Or does the manifold dictate the RPM when you get to "these" IVC numbers ??

Would love to see graphs or track numbers to back up the IVC numbers.

Thanks...........
~

JakeFusion

iTrader: (7)

IVC of 48 degrees with the FAST is about as high as you want. The runner design of the FAST limits you to about 6400 RPM peak. By pushing the IVC that high, you create a "double hump" in the torque peak... at 4800 (which is about normal on LS motors with FAST) and again in the 5500 range.

What you do with your exhaust timing determines if your midrange peak is higher at the expense of carrying power past 6400 or if you give up some midrange for additional power past peak. Depends on what your application is, of course.

LSOHOLIC

iTrader: (3)

Agree for the most part......not sure what you mean by 6400 peak ??
peak what ??

Which brings me to the next logical question
1) Most, if not all of the quickest sbe 346" combos "seem" to run IVC's of 47 or later (by my calcs).
24x/24x....and as soon as the ICL brings the IVC back under 47* your having ptv issues, even flycut (Based on ptv calcs). So, are the running IVC's later than 47* or...... ??


Next question....or thought. Is there a hard/fast rule for overlap on a 346", Fast manifold, n/a application ??
Because when you try to bring the IVC into the "sweet spot", overlap is out to lunch.

Btw, what is the IVC on the latest version of the T-rex ??


Thanks......

Always2Slow

iTrader: (8)

Your manifold limited by the runner length. Your fighting engine harmonics when your having double dips in engine output. Horsepower will peak around 6400 or so with a fast always unless you modify the runner length, that is what he means. It's all about application of what your expecting out of the car. There are many events other than just saying ivc. You will also gain more et at the bottom of a gear change than top. A 240 cam will make more power up top, but doesn't mean it will et quicker.

LSOHOLIC

iTrader: (3)

Ok......couple of questions and statments.

That is why the opening statement of the thread is manifold limited and heavy hitters.

I understand that the 12" Fast102 runner, 4-5" head runner (17"-ish total), manifold volume, manifold harmonics, 4th wave tune is the limiting issue.

I have found evidence contrary to the peak hp @ 6400.....thats where the "heavy hitter" line comes in. Most 23x/24x cams or larger will peak from 6600-6800. Now I do agree than some smaller cams peak lower.

I agree that the 3 other events are important also.....next being the EVO...imo. Power to be had during the blow down event.

And I also agree that a larger cam is not necessarily faster without the entire combo being on the same page. And that shift recovery/rpm drop are critical in lining out a combination....just look what happens on the G-meter at peak tq and a couple hundred rpm after.

So, in a manifold limited environment (such as the Fast), what happens when you keep throwing IVC at it ?? The double hump was mentioned, is that it ?? Will it continue to make "power" in the same rpm range because now the manifold is dictating the rpm rather than the camshaft. Or until the total induction system and cubes can no longer support the air requirements @ rpm.



Thanks.....

98blueSScamaro

iTrader: (14)

peak of the fast from all the data i have is 6850 almost every time right on the money. it holds on till about 7000 to 7200 if valve train is up to the job and light. but falls and then no more power is made. Also look at a super vic to a fast. I must say vic has his casting spot on. i bolted up my super vic and had seen a nice clear clean runner rightto the head. no port shift. and the runner is much shorter.

But in every setup there comes a time where you meet the forkin the road. full race or street with great perf. your trying to max out some thing thats already maxed. time to step up or be happy with what you got.

ls6jay

My super vic had port shift. It was way off.

98blueSScamaro

iTrader: (14)

mine was spot on

LSOHOLIC

iTrader: (3)

[QUOTE=98blueSScamaro;17928347]peak of the fast from all the data i have is 6850 almost every time right on the money. it holds on till about 7000 to 7200 if valve train is up to the job and light. but falls and then no more power is made. Also look at a super vic to a fast. I must say vic has his casting spot on. i bolted up my super vic and had seen a nice clear clean runner rightto the head. no port shift. and the runner is much shorter.

But in every setup there comes a time where you meet the forkin the road. full race or street with great perf. your trying to max out some thing thats already maxed. time to step up or be happy with what you got.[/QUOTE]

Quoted for the truth....lol.

Well if I go single plane......time for an clutch change.......what a can of worms !!!

.

LSOHOLIC

iTrader: (3)

Jake, do you feel or know with certainty that the IVC is what causes the double hump ??

From what I have seen, most cams in the 47*+ realm have larger overlaps (do to the nature of the events). Could the double hump be from over scavenging via overlap or a low rpm reversion, maybe causing some stand off issues inside the plenum ??

Also, how does the double hump seem to effects 1/4 mile performance ??

The majority of the cam only record holders are running some version of the T-rex, which has IVC ranging from 47*-49*.

Thanks......

JakeFusion

iTrader: (7)

The overlap certainly helps. I'm not sure I know how much it actually drives the double hump in the torque curve that is common, but it helps with the total power output.

The later the IVC, the more compression you need as well. IVC that late really needs something close to 11.8:1 to get the dynamic compression up on a 346.

98blueSScamaro

iTrader: (14)

well said. and also the hump is not ever really a problem in the 1/4 mile as most the time unless leaving the line at a really low rpm your never in that area of the power band.

JakeFusion

iTrader: (7)

Pushing the peak torque higher is never a bad thing if you have the gearing/stall to make use of it.

LSOHOLIC

iTrader: (3)

Absolutely.......or be happy if it held on longer also.

When you say "higher"....are you referring to power or rpm ??

.

JakeFusion

iTrader: (7)

The peak torque shifts up with that second "peak RPM." Even if the power stays the same, shifting the peak torque RPM range up 600-700RPM will make you faster if you can take advantage of it.

Hemi horsepower

http://www.hotrod.com/articles/20-ls1-intake-manifolds-tested/

This is an interestingly good thread. In the above article, the test engine...a 6.0 with an IVC point of 48.5, the Wilson Fast LSX with it's 12" runners (the longest runners of the group) peaked at 7000 rpm. The Holley Mid Rise and it's 5.0" runners peaked at 7000 rpm. Out of the 20 intakes tested in efi form, the peak hp rpm ranged from 6900 to 7100.

A T-Rex cam has an IVC of 49°. I've read on this forum that anything over 47 with factory style long runner intakes was inefficient. That's what our computations say at least, however the fastest all motor stock bottom end 346s are using the T-Rex camshafts.

I've read on S.T. that camshaft grinders argued with head porters about what plays the most important role in rpm capability. The cam grinder argued and say camshafts while the head porters argued the induction system. Good topic of debate.