Non inigition controled throttle Body Injection Woes

[UNO_RACING]

I purchased a non ignition control TBI system through Howell Performance out of Michigan. Timing is controlled via vacuum from the Holley 670 cfm throttle body itself. I'm running an HEI distributor.

Since running this set up, I've had engine performance issues. I have a built 350 and the thing is weak beginning at 4,500 RPM. I'm running an RV cam, roller rockers and motor is bored 40 over. I have dual exhaust with rams horns.

Despite having the chip reprogrammed multiple times, I'm still having troubles at higher RPMs. I can't seem to figure this out. The truck drives well at lower RPMs and is a torque monster, but gives out at higher RPMs.

My local speed shop suggested that I change to ignition control because it could be directly related to timing at higher RPMs, as a non-ignition controlled TBI can have problems controlling timing at higher RPMs because lack of vacuum. I have about 10 inches of vacuum.

Does anyone have suggestions?

 

[Trollhole]

Yes, With a torquer cam (depending on which one) expect to hit a brick wall at around 4500 rpms.

Also you could have the wrong MAP sensor. I thought you had to change it out if you went with a performance cam?


Have you done any datalogging? Do you have acess to a laptop?

 

[Pin_Head]

I'm running an RV cam,

That is an important piece of info. You are running out of cam. RV cams are optimized for low end torque. All the other performance stuff you have on there is pretty useless with this cam.

 

[UNO_RACING]

Yes, With a torquer cam (depending on which one) expect to hit a brick wall at around 4500 rpms.

Also you could have the wrong MAP sensor. I thought you had to change it out if you went with a performance cam?


Have you done any datalogging? Do you have acess to a laptop?

I have access to a lap top, but no access to the software. Not sure about the map sensor....

 

[UNO_RACING]

That is an important piece of info. You are running out of cam. RV cams are optimized for low end torque. All the other performance stuff you have on there is pretty useless with this cam.

I'd be that's my problem. What would you suggest changing the cam to for a more linier peformance?

 

[inkpot]

Howdy! It's a trade off on the cam. You can't get max performance on both hi and low end from the same cam. What do you need all that hi rpm for? Mud bogs or racing? Other wise keep the low end, as it is a lot better for crawling, and usually it will give you the best mpg. John

 

[Downey]

I won't open my big mouth publicly about what I think your problem is, but I'd spill my guts in a heart beat on a PM!!!

 

[Pin_Head]

I'd be that's my problem. What would you suggest changing the cam to for a more livlier peformance?

I don't know what type of "RV" cam it is, but my understanding is that they typically have low duration and low overlap to maintain relatively high cylinder pressure at low RPM. This is for low RPM performance and far from ideal for high RPM power.

High performance cams are high lift, long duration and long overlap, which is the opposite of RV cams. My experience with these cams is the engine may barely run at low RPM, but they sure sound cool with that lopey idle. Chugachug chug...Chugachug chug...Chugachug chug...Chugachug chug...
You sure wouldn't want this type of cam for rock crawling, but it would be ideal for mud bog racing and other wide open applications.

You could split the difference and go with a stock type cam which will give a more moderate performence over the entire RPM range.

Once you decide what kind of power curve you are after, you can talk to cam vendors to find out how to get what you want.


PS. It would help to evaluate the possible contribution of the cam shaft to your problem if you knew specs for your RV bumpstick: Lift, Duration and Overlap

 

[Trollhole]

I have access to a lap top, but no access to the software. Not sure about the map sensor....

Software is free.
WinALDL - 160 baud ALDL reader

The cable is not.
ALDL OBD1 OBD cable OBDI OBD2 engine codes

At least with this you will see what is going on. I'm not an expert with reading the logs though. But I'm betting others are.

Also what is the condition of the fuel filter? A clogged filter will restrict flow at high rpms.

 

[UNO_RACING]

Great info. Thanks guys!

 

[malcb]

My local speed shop suggested that I change to ignition control because it could be directly related to timing at higher RPMs, as a non-ignition controlled TBI can have problems controlling timing at higher RPMs because lack of vacuum. I have about 10 inches of vacuum.

Didn't really understand this part. I am assuming that at 4500+ rpm your more or less wide open throttle (WOT) so vacuum in the manifold is going to be minimal anyway?

Turbo or Supercharger needed?

 

[FJFOOL]

Come on, Jim, open your mouth !! I wanna hear too !!