Grumpy

I've had dealings with many folks with many different cam head exhaust intake valve changes, and have really noticed first hand how some seemingly minor changes take lots of work to recalibrate. Hence my stand about to get things right means testing and doing your own chips.

Well, in my Black Car, I knocked the lobes of a cam, and replaced it will a cam of the same specs. Lift and duration were exactly the same, and just the overlap changed a few degrees. I caught the problem very early, so no bearings or any internal parts were changed other then the cam.

What an unbelieveable change.
While my last chip was about perfect for the old cam, it's way off on the new one. So far so that I'm going to starting with a virgin bin, rather then trying to get the old bin to work.

MonteCarSlow

Bruce,

When you get your new chip roughed in for your new cam - could you summarize what changes were required? I'm just curious what effect lope seperation has on timing and fuel curves.

Thanks,
Ernst

FastBroker

That's what happened to me when I went from a mellow Edelbrock 3702 cam (194/214) to the roller Hot Cam. It was so bad that I actually put a cam in that was in between the two, or so, to make the PROM learning process easier for me.

DM91RS

Bruce. I did what you suggested in "Tuning Tips" and went very conservative using the stock LT4 cam to learn with. The cam that I would like to end up running is the LT4 HOT version. Am I correct in understanding that after I get my present cam tuned that I should consider it a learning experience and return to my stock bin and start over after moving up to a hotter cam and intake? Thanks and take care!

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91 RS 350TBI VORTEC HEADS EDELBROCK PERFORMER INTAKE LT4 CAM 1.6 ROLLERS EDELBROCK HEADERS 3' EXHAUST 5SPD 3.08 GEARS

Damon

Interesting. So you basically either tightened or spread the lobe sep angle with the new cam and there were bigtime changes needed in the programming. Interesting. <scribbling notes furiously>.

I have always been aware of differences lobe sep. has on how and engine behaves, jsut from general expereience. But it sounds like tunign for FI is hyper-sensitive to stuff like this.

I GOTTA start burnin' my own!

MonteCarSlow

Bruce,

Any theories on why the '730 TPI 305 A4 and M5 bins are so identical even though the cams are very different? The VE tables are identical (at least in the bins I looked).

Ernst

Grumpy

If you look at the injectors sizes for the HP level that makes for a very forgiving set up. Doesn't take much of a BL change to correct.

As you raise the HP level and still use the stock injectors things get much less forgiving. That's why I say the .5 BMFC is get for aftermarket ecms, but falls apart when using oem ecms.

I'd say 90% of the people doing hop up work on their cars should have changed injectors, but it will take time again for this message to get out. If you had 20% more HP to your engine you should be running an injector 20% larger then the oem one.

I had run 40#ers on the GN, and went to the 55 on a lark, only to find the 55 were sooo much better drivibility wise. WOT is exactly the same, idle the same, MPG the same. Hot or cold humid or dry thou, the car runs really close to the same, and response is just that much better. Even after changing all the fuel stuff to being the same ratio wise as things were with the 40s. just the BLs can more easily compensate.
HTH

TRAXION

I remember when lots of people said I was crazy for switching from 22lb GM injectors to the SVO 30lb injectors. I got a bunch of crap from everywhere and almost everyone saying that the injectors were too big and that I would have a worse idle. I proved them all wrong. The 30lb injectors are perfect for my setup when you consider the power I am making at WOT and injector Duty Cycle at 6500rpms.

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

branz28

Funny traxion, i get the same responses when i say i burn my own eproms.

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89 IROC-Z 350 TPI

-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Gutted cat
-!AIR
-Gutted Air Boxes

MonteCarSlow

I can atest to the same results. I run 4.3tbi injectors in my 2.8tbi 4x4 truck with no loss in idle or driveability. I just scaled back the BPW till the BLM's lined up again.