[68birdfreak]

Looking to squeeze a little more hp outta the motor in my 69. Is it a reasonable expectation to gain some hp and better track times out of a properly tuned Q-jet ? I have a 800 cfm holley DP currently and it was just dynoed today at 399hp and 441 tq at 6100 rpm on mustang chassis dyno... combo is a 428 bored 40 over ...
camshaft duration @.050....251 int 259 exh
lobe lift....3533 int .3677 exh
112 sep
lift .530 in .552exh
40 degrees total timing
3640 total race weight
5 spd tko600rr
3.55 gears
edelbrock performer rpm
have no clue as to what else you guru's would need to help me make this decision but if you can help I will do my best to give you the info you need.
Car is streetable at current time..very streetable but experiencing some possible vapor lock... A/Fmixture @13.0 to 1

[BVR421]

399 wheel hp is nothing to sneeze at. Were you tuning or just getting a power check? Ive heard Mustang dynos are a little conservative compared to others but I guess that would depend more on the software and the dyno operator.

My carb preference for anything on the street is qjet. I wouldnt expect any gain from one carb to another if each is tuned properly.

Something doesnt seem right if you have to run 40º total timing with those heads? Not unheard of but I would have expected maybe 34º

thats a sweet looking Bird!

[screamingchief]

Both carbs being tuned properly to their ideal states of tune,there should be virtually no significant difference in power ouput between the two carbs.

Now might one exhibit better traits in one way or the other,sure can,one carb might get better fuel mileage than the other,or feel a bit "crisper" than the other,but rarely will that show up on a dyno,or at that track if both are "optimized" for peak power.

If a significant difference is indeed found,than there almost certainly was a problem with one of the carbs somewhere.



BP.

[Brent Flynn]

I would have to agree with everyone's posts on this topic. I believe i would run the q-jet, tho, even if it is a 750. If they are both setup for peak performance, the Holley may out-pull the q-jet(maybe) on maximum high gear run, but i doubt it would b very much. Also, you have enough power to blast the rear tires anytime you want, so you prob wont see the difference between the two. Ive had excellent results on the track with my 750q-jet. The only changes ive made to it since driving it on the street are the primary jets(71's to 74's) and richening up the secondaries. Nice car man!

[rtanner]

I bet your not putting all that down w zero tire spin at the track now!
So are you racing against other dynos? Don't get mad slot of people
do that now days I'm just asking.

[68birdfreak]

Originally Posted by rtanner

I bet your not putting all that down w zero tire spin at the track now!
So are you racing against other dynos? Don't get mad slot of people
do that now days I'm just asking.

Ha...well said RT....keep on smilin.....put ur $ where ur mouth is....whattya say?....slips or paper....ur call!

[68birdfreak]

sorry...alien invaded my body...

[77birdman]

Originally Posted by 68birdfreak

sorry...alien invaded my body...

That's ok as long as ashe was pretty and got the job well done

[Cliff R]

Considering the carbs being used (q-jet vs Holley) were correctly set-up for the application, and enough cfm for the power output, not really much power will be found, one over the other. The q-jets will prefer a spread bore manifold, and may give up considerable power bolted directly to a single plane intake. It typically takes a well blended 1" spacer to get a q-jet to work effectively on a single plane intake, at least from what I've seen in most of the tested we've done and been associated with.

On the dual plane intakes, the q-jets has a slight advantage over a square flange carb, being well centered in the plenum areas.....Cliff

[BruceWilkie]

Originally Posted by Cliff R

On the dual plane intakes, the q-jets has a slight advantage over a square flange carb, being well centered in the plenum areas.....Cliff

The original Torker is the only single plane Pontiac intake I'm aware of, that specifically incorporated changes that accomodated the qjet's throttle bore varience and the effects that varience has in a single plane manifold environment.

[Cliff R]

Bruce, I dyno'd a Torker I intake once. It was down over 50hp compared to my own ported iron intake.

It was a "box stock" intake, not even port matched, and no spacer was used on either intake for the testing.

The test engine was a 455 with ported 670 heads, 247/254/108 hydraulic cam, apprx 11.6 to 1 compression.

Yes, I couldn't believe it either.....Cliff

[BruceWilkie]

Originally Posted by Cliff R

Bruce, I dyno'd a Torker I intake once. It was down over 50hp compared to my own ported iron intake.

It was a "box stock" intake, not even port matched, and no spacer was used on either intake for the testing.

The test engine was a 455 with ported 670 heads, 247/254/108 hydraulic cam, apprx 11.6 to 1 compression.

Yes, I couldn't believe it either.....Cliff

In that article I've always wondered what they tested it against and the details of the build. Its quite conceivable that it really could make 20 hp over a stock intake at 6500 rpm with a cam favoring and putting the engines PEAK power at around 5000 with either intake. Of course they wouldnt mention that part. IIRC McFarland wrote for the car mags as well as worked for Edelbrock. They sold a lot of intakes though. Media bias??

[NHRASuperStock455SD]

Agree with what is said here. I have dynoed a 850 holley against my race Q-jets and the Q-jets beats the holley every time. However it is only usually 5 to 7HP. Last time we tried a Super Tricked out 1150 and the 455SD got about 10HP. The Q-jet I believe is much more forgiving on tuning and is much easier.

Lynn

[grandville455]

Lynn
I sure would like to know How tweaked that q-jet is of yours ...

[Bruce Meyer]

Hmmmm. Interesting info here!! Do you think someone should tell the guys running Pro Stock cars that they would be better off with a couple of Q-jets on top of their motors?
Same with the Nasacar boys. They are all missing out!!

[Cliff R]

I see the same thing as Lynn, however the q-jets do NOT like to be bolted flat on any of the single plane intakes available for Pontiac engines. I have found that a 1" custom blended spacer is necessary to make the same numbers as a Holley carb on those intakes.

On the dual plane intakes, the Q-jet will typically be 2-3 hp better at peak power than any Holley or Holley clone I've tested them against. This leads me to beleive that being well centered in the plenum areas is an advantage of the spread bore design over the square bore when used on those manifolds.......Cliff

[grandville455]

Originally Posted by Cliff R

I see the same thing as Lynn, however the q-jets do NOT like to be bolted flat on any of the single plane intakes available for Pontiac engines. I have found that a 1" custom blended spacer is necessary to make the same numbers as a Holley carb on those intakes.

On the dual plane intakes, the Q-jet will typically be 2-3 hp better at peak power than any Holley or Holley clone I've tested them against. This leads me to beleive that being well centered in the plenum areas is an advantage of the spread bore design over the square bore when used on those manifolds.......Cliff

Cliff
What do u mean custom blended if its a open spacer? what are u blending? I still think to be fair one would have to try the holley on a single plane as thats what they like and vice versa for the q-jet. Also I would bet your carb is way different than most of ours out there...Cause my carb hates the higher letter hangers now. and i can only run the richest one any of the others i get a stumble? use to be able to run them ,but not anymore? I am testing again tomorrow, weather isn't going to be record breaking ,but i will be testing three different carbs,2 holleys and my q-jet, plus other stuff ,like open header etc..

[68birdfreak]

Originally Posted by Cliff R

I see the same thing as Lynn, however the q-jets do NOT like to be bolted flat on any of the single plane intakes available for Pontiac engines. I have found that a 1" custom blended spacer is necessary to make the same numbers as a Holley carb on those intakes.

On the dual plane intakes, the Q-jet will typically be 2-3 hp better at peak power than any Holley or Holley clone I've tested them against. This leads me to beleive that being well centered in the plenum areas is an advantage of the spread bore design over the square bore when used on those manifolds.......Cliff

Cliff,
How about on an Edelbrock performer rpm intake?

[Cliff R]

I haven't done much back to back testing with that intake, at least at the track. Actually, I hate the RPM intake for my set-up, and it's coming off my engine this week. It's a fine part, but will NOT work with the stock Shaker set-up, and I'm tired of the hood clearance issues and not being able to run a stock Shaker base, top and factory air filter assembly.

A good customer has donated a fully ported HO intake for testing, already port matched for my SD Performance 290cfm KRE heads, so back to the "stock" parts, FINALLY!

As for the RPM intake, I've tried them plenty of times on the dyno, with all sorts of carburetors. Tyically it's pretty much a "wash" with any well prepared carb. Never to date had a Holley or Demon make MORE peak power. At times the peak torque number has been just a tad better, probably due to design of the carb, 4 jets feeding 4 venturi vs the q-jets spread bore deal.

The RPM shows no advantage anyplace in power output compared to my "stock" iron intake on engines to apprx 500hp. It was actually down 6hp on a stout 428 we built a couple of years ago, 491hp for the RPM vs 497hp for the iron intake, same carb and no spacers on either one.

It still amazes me that those ugly q-jets make MORE HP, and runs MORE MPH at the track. I've back to backed my own 4781-2 850 Holley against my 1977 Pontiac q-jet more times than I can count (and before anyone cries "foul", both are dyno tuned EXACTLY for my engine), on several intakes, and the ugly old q-jet posts more mph every single time.

I've thought about contacting NASCAR about testing one, but they couldn't handle the extra power as they are restrictor plating most everything these days anyhow!.....LOL.....Cliff

[grandville455]

Originally Posted by 68birdfreak

Cliff,
How about on an Edelbrock performer rpm intake?

68
thats the intake I have been running . the only difference is i will be using a 1" open spacer on top for the holleys.. the one Holley is a custom tuned true 830 from shaker455.. the other is my 830,but still has the smaller 750 throttle plates!