ctusser

Torque dips in that RPM range are usually an exhaust tuning issue. For some reason with your combination it is over-scavaging in that RPM range.

Kappa

That "dip" is pretty common on modded(ie cam, etc.) 'Vettes from I've seen. I'm pretty sure there's a way to tune it out but you can't feel it in the car. At least I can't.

SpinMonster

Well, I'm stumped. I cant think of anything else that could cause it. I've used your headers and they add Tq in that range with no dip. The two cams both do it and the heads were swapped so it wasnt the heads in either set-up. I havent seen the dip on other cars with this cam or the G5.

I didnt think a dip over such a short rpm range could be felt and it comes as no surprise to me that you dont report feeling anything there.

We agree on gears. ECS' dyno compensates for gearing changes so it doesnt drop the reading. Dynojets do.

SpinMonster

Anthony states that the G5 you had was a 112lsa. That makes it a 12 degree overlap cam. This 236 cam is an 8 degree overlap cam so it should be somewhat better mannered. A really great tuner can make either drive pretty good for most people.

Increasing compression will make up for the later intake valve closing point. The reason your old cam was as strong as it was in the low end TQ is because a narrower LSA closes the IV sooner than a 114lsa. If you had the 114lsa cam, the differences would have been greater. I wouldnt be surprised to see the cam do 10hp better w/higher compression which makes it drive better yet. You have plenty of octane protection and you dcr at 12:1 would still be fine for pump gas due to the DCR.

If anyone wants to use this at 11.5:1 then use it as a 112LSA. It will lift the low end TQ by closing the intake valve sooner and will still pull all the way to redline. If it were any tighter an LSA then add 4 degrees to the exhaust duration to extend the top end out more to redline.

Anyway, the cam is still designed to drive great. It hits 500rwhp/445rwtq at 12:1 compression and stock gears. 510/455 with meth.

If anyone wants max-effort with no concern for manners, the G6X3 is a proven leader but some may not like it in their daily driver. Its something like 18.5 degrees overlap. It has a violent midband to redline pull.

ctusser

Add some back pressure and I bet the dip is diminished in that range but max hp may be adversly affected. It's a balance b/t cam and supporting induction components and exhaust. A more optimized custom spec'ed cam would probably get rid of the dip as well. Bolt on header systems are good for most applications, a one size fits all, but may not be optimized for a certain combination. Many racing teams put a lot of R&D into optimizing thier exhaust tuning per application and intended use and would be an expensive or time consuming route to go for the average enthusiast to try and dial in.

Joe_G

I actually did test that theory. I happen to have cutouts and stock mufflers. Thus I can add and take away back pressure. I tried everything to eliminate that dip. My graph is scaled differenty so the dip is less pronounced and I have less power but it's there. I tried changing timing and fuel and nothing got rid of that dip. I wonder, but have no basis to say, if it's intake manifold related.

Here is my dyno sheet with cutouts open (top) and closed (bottom).

As you can see back pressure doesn't seem to affect the dip as the lower back pressure led to increased gains pretty much across the board.

HC Mechanic

I think you hit the nail on the head with the mention of exhaust as a limiting factor, but I don't think your ever going to get an exhaust runner/header combination to over scavenge. Race teams put a lot of resources into trying though : )

Dips in torque/power would be created when one side or the other of the combustion chamber is not flowing efficiently. Which is why Spin often brings up velocity

If you look at any race engine that is designed to run at various rpm's like Moto GP(unlike F1 or Top Fuel), they actually run through a pretty wide range of rpm's. So as a result a 4 into 1 designs are not generally used. I have seen some examples where a 4-2-1 header works much better on the LS engines. I'm pretty sure that the LM cars don't run a 4-1.

vague

What is the timing on the run without meth and what is the timing on the meth run?

mAydAy121

The dip is due to intake manifold resonance. As the engine goes through its rpm range, the intake manifold will hit different harmonics at different rpm's, causing increases and decreases in power along the way.

Where the harmonics hit is a function of runner length. If you ever watch F1 intake runners you will see them as they run through the powerband get longer, then snap shorter almost instantly, then continue to grow to the rev limiter. This is an attempt to maximize the 3rd harmonic as long as possible lower in the intake manifold, then maximize the 4th harmonic higher in the powerband.

Neumonic2002

The intake manifold makes sense, I noticed a small dip when I switched to a Fast 102 intake on my bolt-on only setup.

sthornburg

The first dyno sheet in Post #67 shows the base line pull before changing the heads, cam, and ported FAST 92 to a ported FAST 102. With the FAST 92 and other set up, there as a flat spot but not a pronounced dip....but it was also a completly different set up.

I assume that you just added the FAST and nothing else when you noticed the dip. What was your observed dip differential vs. your gains?

Mez

Here is my dynos of my 2005 LS2 MN6. Mods listed in my signature.

I noticed there is a flatting of torque in the 3200-3500 range. The differences between the three dyno's is the intake manifold. The highest torque curve is with a ported FAST 92 intake and ported throttle body. The middle is the ported stock intake and ported throttle body. The lowest is un-ported stock intake manifold and stock throttle body.




The dyno below is after the final mod which was install of Yella Terra 1.7 roller rockers. It now has a slight dip in this area. I tried timing and fuel changes and it made no difference.



I've noticed during dyno runs at the shop I visit, vitually all the LS engines have this flatting or dip of torque in this area but nothing as dramatic as the dip above. Another thing I noticed was the engine has more vibration in this area, so my theory there is something going on with harmonics either in the intake or perhaps mechanical in the design of the LS engines.

Neumonic2002

You are correct.

The dip starts at 3100 and carries to 3700, the Fast is stronger than the ported LS2 intake it replaced by 8/12 rwtq before and after the dip.
In the middle of the dip it almost touches the previous intakes curve but rallies for a peak gain of 21 rwtq @ 4850 rpm

The dip in the rwhp is much less on the front end but then just climbs off the ported stocker from almost touching @ 3400 rpm to a max gain of 25 rwhp @ 4850 rpm

Mattraffai

spinmonster you really seem to know your stuff! can you pm or give me your number for questions i have on a 402 stroker kit and changing cams,milling my trick flows,and if u sell them?

SouthTexasBully

OP,did you ever drive your car? How does it run,have you taken it to the track? Thanks

sthornburg

I'll be picking it up later this week.....I haven't had a chance to drive it yet.

SouthTexasBully

Good deal man,i bet u cant wait...my car will be done early next week with my h/c/i setup and i cant wait so i can only imagine how excited you are..keep us posted,thanks

Joe_G

Good for 9's. see Stanger383's times with the 4k converter.

UmX

Im currently looking at the trick flow 225cc heads ported. for my m6 c6 06

I currently have a vengance vrx5 cam, ar racing headers 1-7/8, 160therm, ported stock throttlebody, UDP, stock gears, fast 102 ported.


Car made 434 at the wheels before TB and intake was added. With a conservative tune.

Im curious what I could pick up with adding the heads.

So head gain and total with everything. Sorry to hijack didnt want to make a new thread.