Restricted Airflow - ***?

[DrumrBoy]

I'm running John H's headers, no cats, no resonators and no mufflers but seem to have an airflow restriction since my HP curve shoots right up like it should until 3800 rpm and then is flat (except for a small increase at 4400 or so).

The A/F starts at a nasty 16:1 and ends up 11:1 at the higher rpms. Either too much fuel (not likely) or too little air.

I've checked the throttle cable to make sure that it pulls all the way to the mechanical stops when the pedal is depressed and it does. Checked the easy stuff like air filters and don't see anything wrong.

Any ideas out there for chasing down the elusive airflow restriction?

 

[Russ M]

You are going to have to get alot more detailed if you want any help.

Any and all mods, dyno numbers, etc.....

 

[DrumrBoy]

Sorry, got a little lazy with the post.

The cam is a 3/09-3119HR112 Comp Cam ......hydraulic roller with 112 degrees of lobe separation, 275/280 advertised duration, (220/224 @ 50) with 547/563 lift.

The heads are mildly ported with 1.7 rockers. The valvesprings are Manley Comp 925's but I didn't install them so I can't vouch for their integrity.

John H's airbox, K&N elements, Fidanza flywheel.

I have a VEC 2 on the way which will undoubtedly help with the fuel and spark, but several knowledgable folk suggest an airflow restriction. Unless its in the heads, there must be a dead possum in my side sills.....where else could I be restricted?

Any thoughts on where to look would be appreciated.

Here is a dyno sheet that is almost exactly representative of what happens today (even though this is last spring's sheet).

 

[Mr Hemi Head]

Drummer during the VEC2 install be sure to wire the MAP and TPS sensors into the VEC. Provides more data to help diagnose your problem.

 

[Russ M]

I would say that if you are running all those mods with stock tuning than that is your problem.

Also dont forget the factory injectors are only good for 480 or so rwhp. With your mods your car should make alot more when tuned.

 

[STUGOTS]

VEC 2 is worth its weight in gold bro TRUST ME

 

[Dave R]

You state "too much fuel or too little air". I would guess your main problem is just the opposite: FAR too little fuel before 5000, and a little too much after.

No restriction, just the tune.

 

[DrumrBoy]

Sean just sent the VEC 2 with a card designed to give me a decent baseline. I know this'll help but with absoluteness of the change at 4000 I'd be surprised if tuning is 100% the answer. We'll see when I get 'er in.

The injectors are a good idea to check - thanks for that suggestion. I assumed that John H put bigger lb/hr injectors in for a 650R but they may have been changed along the way. However, the amount of fuel up high doesn't seem to be lacking unless its in combination with less-than-sufficient air.

Thanks all.

 

[Jack B]

DrumrBoy:

There is a little confusion, your torque is what is peaking at 3800, not your hp, that is approximately where all vipers peak. What is bad is the way the torque declines so quickly. This is relatively simple, the torque cannot maintain itself because the car is so lean at that point. If you were to to maintain 12.5 up to about 4750 and then transition to 13.0 above 4750, you would see the torque maintain itself and the hp would increase. As has been stated, you have nice mods, but, without the VEC2 you are enjoying about 50% of them.

You might want to think about fixing the a/f before trying any more WOT. For the heck of it, pull the plugs see what they tell you.

 

[DrumrBoy]

Pulled the plugs....pretty consistent, tan/gray....lean.

The VEC goes on this weekend....Sean sent it with a starter-program based on the dyno.

Thx