Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

1903 Won't Respond to Tip-In Procedure

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tayto:
I unfortunately only put 1000 miles on it last summer, had some issue with lifter bores and am only now getting it back together (waiting on exhaust). I will keep you posted during the next month.Hoping to get it on the road by the end of the month

bry593:
Still waiting on the cam.  Continued disruption in supply chain due to C19 response?  Gates, Xiden and the CDC certainly want to extend the pain until everyone receives experimental gene therapy.  Incremental destruction of your constitutional rights.  Not to mention, I still don't have a cam.   >:(

tayto:
My vote is still for the GM cam i posted above even though a few less degrees duration. Than the howards cam. I have been waiting dor a missing piece from my flowmaster exhaust kit for over 3 months now. also helping a friend with his 1950 dodge and we bought a parts carb for it and have been waiting over 6 weeks. Yet my rockauto orders are delivered in 3 or 4 days.....

bry593:
Finally received the cam end of June.  Got it installed and running a few days ago.

Before I removed the 395 cam, I measured cranking cylinder pressure.  It was 210 psi which is too high for 87 octane.  Why did one of those HotRod magazines claim it was 195 psi?  I haven't measured the pressure of the Howard's cam, but shutdown run-on and WOT detonation are no longer an issue (Cliff, thanks for recommending the cam swap!).

My guess is the new camshaft will slightly reduce gas mileage since I no longer have "beast mode" torque right off the line.  It used to almost always chirp the tires on initial acceleration.  I'd guess the power band has moved up about 500 rpm. 

New cam definitely idles smoother with 112 vs 109 lobe separation, even though intake and exhaust duration are increased about 10 degrees.

Exhaust note is quieter under normal driving conditions.

Still running the same carb tune and it seems okay so far.

Overall, I believe the 395 cam would work great in an EFI daily driver, but it is a poor match to an old school carb and HEI.

Cliff Ruggles:
Good news.  You really didn't give up any power, it's making more power.  Wider LSA simply spreads it out some and doesn't spike it nearly as high.  This reduces octane requirements at the same time.

I'm NOT surprised idle quality is improved with more seat timing.  The longer seat timing and wider LSA will also make for a nice improvement in upper mid-range and top end power.

The engine may not "feel" quite as strong IF you are judging improvements by the "seat of your pants".  Do NOT be fooled by this.  Smooth/strong power over a broad RPM range will trump throwing all the power at you early and in a narrow RPM range. 

This simply happens because you are applying more power to the pavement on a full throttle run vs throwing ALL the power at you quick and early.  When this happens the quick blast of power "feels" like a shot of nitrous and we evaluate it as an improvement over the "locomotive" power from a smooth/flat/strong power curve.

I've tested camshafts on the dyno and it also reflects the same thing.  Tight LSA and shorter seat timing spike peak torque high and it happens early. 

One test I did back to back a few years ago was testing a Pontiac RAIV cam against a custom ground Comp cam with their "best lobes" (at that time). 

The factory cam was 304/316, 231/240 @ .050" and 113 LSA.

The Comp cam was 284/296, 240/248 @ .050" and 112LSA.  We had it ground to replace the Crower RAIV clone cam thinking the bigger Comp cam would make more power and improve both ET and MPH at the track.  The Comp cam also had a LOT more lift than the short lobed RAIV cam.  Even with high ratio rockers the RAIV cam was only .516" lift.  The larger lobe Comp cam was over .560" lift. 

EVERYONE involved in the swap was betting the "modern" Comp cam would outrun the old RAIV grind everywhere.

Well, NOTHING went well that day on the dyno.  We made great power with the RAIV cam, right at 500hp/570tq.  Once we dialed in the best numbers I installed the custom ground Comp cam and we fired up the engine.  Immediately I noticed that the engine idled a little better and it was really "snappy" right off idle whacking the throttle quickly.

I checked the timing and we started making pulls on it.    My heart sank as it printed out the first dyno sheet.   The larger Comp cam was down nearly 15hp and 25ft lbs torque....WTF?

I made several adjustments, timing, fuel, and it just got worse.  I even went in and move the cam ahead 2 degrees and then retarded it 2 degrees and things just got worse with everything I did.

I finally returned everything to the initial settings and fine tuned it to perfection and we were still off 10hp/22ft lbs torque that we just were NOT going to get back.

The engine also made peak power 400rpm's LESS in the RPM range with the larger cam, or done at 5200rpm's vs 5600rpm's with the RAIV clone.  I just couldn't figure it out?

So I changed directions and installed a HR cam (we had one ground just in case this testing didn't go well). 

The HR cam was a LOT bigger than in lobe lift than either of the flat cams.  It used .361" Comp XFI lobes, 284/296 @ .006, 230/242 @ .050" and 112LSA.


........Continued

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