I was expecting 10-15 HP gain, were those high hopes? I gained a little and lost a little, here is a link to my previous dyno post for details.

Motor: 350/Edelbrock Performer 60cc heads 2.02/ Comp XE268H/Harland Sharp rockers/Performer intake/ HEI (36* @2300)/ long headers. The motor did not change.

Below are the results and the corresponding changes made. Blue run is previous (see link above) Red is today's run after the following changes. Red is what has changed.

Blue= 269.45 RWHP 315.96 Max Torque
Red= 273.38 RWHP 314.12 Max Torque

QuadraJet to Holley 600
3.08 rear to 3.55 rear
TH400 w/stock converter to 200-4R w/D5 converter I thought this would have helped.
Stock exhaust pipe size w/turbo mufflers to 2.5 pipe size, w/straight through mufflers and H


Since this is a chassis dyno, the rear gear change probably dropped me a little. Perhaps the 200-4r brought me back up a little.

The loss of 2 points of Torque was disappointing and I assume it has to do with the larger exhaust.

I have an A/F gauge and determined that the dyno a/f reading is within 1 whole point of my gauge. (ie gauge=13 dyno=13.7) My WOT at the gauge is between 12.5 and 13:1 with the Holley.

Mathematically, a 600 cfm carb should be fine for a 350 bored .060. Did the loss of cfm from the Qjet hurt me?

I think I significantly reduced the exhaust back pressure with the 2.5 pipe. Did that hurt me?

 

Put the Quad back on for your next test.

 

I don't think it was the exhaust. I believe it was the switch from a Quad. to a Holly 600.! A properly set up Quad. will outbeat a Holly 600 any day.

 

It's very likely you are experiencing just the real side of performance upgrades: They often don't amount to much unless you are replacing compromised parts or making big, dramatic changes. You rarely pick up much on the intake side, and the factory 2.0" exhaust ain't all that bad at your power level.

Few actually put their car or engine on a dyno for A-B testing to see if they got anything for their money.

 

No need to be disappointed, you picked up 4 HP. Torque can change with every run with an auto trans unless you are amazingly consistent, as the converter multiplies torque throughout the rpm range. I think the Quad would have given a little more HP also. The gear change does not affect chassis dyno numbers, a 3.08 or 4.11 will produce the same numbers; the 4.11 just does it faster.

 

This is good to hear. I thought this was going to be my final dyno. However, now I am thinking a 383 and Holley 670 might "match" the exhaust a little better. Perhaps that will be the next long term project.

The Qjet was set up pretty good but I relate to the Holley design better. Again, based on those carb size formulas, a 600 was suggested.

The car has great acceleration and is fun to drive.

 

What is a "D5 converter"? Also, going to a lower rear gear (higher numerically) will suck some HP up on a chassis dyno.

I agree with the others, the Holley 600 is a step down in every way from the QJet, although the AFR numbers the Holley is posting are better than what the QJet was posting. (easily fixed)

 

A D5 converter is performance rated converter used in stock Buick Grand Nationals. It is rated between 2000 and 2200.

Maybe someday I will go back to my Quadrajet. Thanks.

 

I like the Holley design carbs better, too. I would go to a larger(perhaps 750 cfm) version to match the capacity of the Quad.

 

So are these cfm calculators bs ? I used http://www.summitracing.com/expertad...cfm-calculator

plugged in 5250 redline and 360 cid and it suggested 600 cfm for a racing carb none the less. I don't understand why they would want to sell a smaller carb.

 

Hi,

The carb and exhaust changes will have an effect on the dyno numbers; the gears and trans/converter changes won't, but will make it feel better on the street. Dyno numbers sometimes don't translate directly to 'real' street driving.
Most Q-Jets are rated at 750cfm, so going to the 600 was a step in the wrong direction. A 750 vac-secondary Holley would have been a better choice. It'll act like a 'small' carb at low rpm and a 'bigger' one as rpms climb. Also, in messing with small-blocks, I've found that you can go bigger than you think on carb sizes and still have a nice driveable car. The vac-secondary will help response at low rpm and still work at higher rpm. And, if your fuel will handle it (pinging, detonation, etc), more timing may also help.
It seemed to dropoff at a pretty low rpm on the dyno. Is it a stock HEI? How about valve springs?
Remember that tuning for response on the street is different than tuning for big numbers on the dyno.

Good luck.
walt

 

You used the carb formula for the size of the carb ? WOW ! I cringe ever time hear about that formula, you need a 750 Holley.

 

I'd agree with others on the carb.

I had a friend give me a Holley 600...I never bothered to put it on the car. It wasn't nearly as nice as the 4150 frame Holley 750 that was on the car even though it was brand new.

I am a smidge confused by the thought of a vacuum secondary being better. Dunno.

I've been through the carb thing backwards and forwards and my understanding is that the Q-Jet is a "self regulating" 750 that won't overwhelm the engine.

I had, as I mentioned, a Holley 750 on my car (vacuum secondary) and it never seemed perfect. Putting the HEI helped with the low-end bog a lot, but it was always just "the carb I had", not the carb I wanted.

My understanding is that a "massaged" 350 can handle a 750 carb, but it really is a high-end thing. Unless you're drag racing and care MORE about what is happening at 6,000 RPM than at 3,500 RPM, you aren't gaining a thing and are actually giving up some "snappiness" or "crispness" at the bottom end. Personally, I think a 750 Holley is too much.

After having gone through all this, I purchased a QuickFuel 650 Double Pump with Annular Boosters. It gives you the tight control of good atomization, the smaller size so it doesn't overwhelm the engine, and of course the fuel dump when you really want it.

This is going on a fairly built 10.2:1 engine with a 0.590 lift cam, 200 cc heads, and numerous other go-fast parts, so the double pump was a decision to marry up to a pretty good breathing engine that is on the 'extreme' side of streetability.

I'd be willing to bet you'd pick something up with a better carb, but I also bet you'd need to do something more extreme to get any massive gains.

If I'm being honest, 270+ RWHP isn't anything to sneeze at. You're going to have to get pretty serious to start to see real improvement on that. Bigger cam, maybe solid roller, which may require more head to clear the lift...blah, blah, blah. If you've already put money into nice parts, it may not be worth it to you.

 

Clearly I didn't get the memo.

It looks like ,short of a few hp here or there, I have reached a personal limit because I am not interested in a bigger cam or heads and my red line is at 5250.

I do have another small block waiting in the wings that I could make into a 383. That should probably get a roller cam.

Now that I have an A/F gauge, the Qjet may give me something to tinker with. I have plenty of time to knock that little pin out and pull the air horn every time I want to make a change other than Idle.

 

Run an M4M quadrajet and you'll only have to pop the airhorn for primary jetting, float, or idle circuit modifications.

The secondaries (which should have significant to major control over the AFRs shown in your dyno chart) can be changed easily; pop the air cleaner lid and remove a single screw to lift the rods and hanger out.

 

You didn't state what your cam specs were, but judging by the kind of HP numbers you're seeing with either carb the 600 Holley is hurting you on the top end. I have personally felt the top- end difference between a 600 and a 650 on smaller- displacement engines than your 350.

MY recommendation if you insist on running a Holley on a moderately- cammed 350 is a 670 Avenger. The vacuum secondaries will work better with an auto trans than a double pumper, which will literally do just that- pump double the amount of gas down the intake when you stomp on the pedal, and the 670 cfm rating is perfect for a 350 without going overboard (unless you're racing this thing or compensating for something a 750 is just overkill on any 350).

The key to making a Holley perform properly once you've got the correct one bolted on there is tuning- you have to get the floats set properly, use the right power valve, secondary spring, and finally the right main jets. Once all those elements are correct and the ignition curve is dialed in I think you'll see a noticeable jump in both horsepower and torque.

Or you could just bolt that forlorn- looking Quadrajet back on...my $1.380

 

BINGO!!!

I love me some QUAD! I went to Holley 750 on my car and now it's sitting on my work bench collecting dust. I don't think RQ ever made anything smaller than 750cfm unless it was professionally modified. So, you practically went back -150 cfm just in cfm size. According to cfm calculator, stock 350 will push out 560 cfm at 6500rpm at 85% so with little mod you got going on may push u over 600cfm.

 

i dont care what charts and others say, a 600 holley on a modified 350 is a waste. you have a set of heads that should be pretty good compared to stock and then with the increased airflow from the heads you put a smaller carburetor on it? I'm surprised you made that much power. put the quadrajet or a bigger holley on it. i think you will be pleasantly surprised.

 

Your Red line is only 5250? I have the same cam with stock heads, and my red line is 5800. My buddy says I can even go a little more to 6000, But am afraid of pushing it to that. Have you re-adjusted your valve springs?

 

Its a self imposed red line, more like a pink line. The bottom end is a stock 4 bolt main block but nothing special. The transmission gov. shifts at around 5250 and its just a street car not a race car. It will go further I just don't want to wind it that high out of fear of breaking something.