[Navy Horn 16]

Last year, I put a "fresh" 469 in the Trans Am. It's a 1970 455 block, 40 over, forged everything, just a hair over 10:1 compression, with an uncut RMP Performer Intake, 800cfm Q-Jet (from Jet Industries). 1.75 inch headers, into 2.5 inch exhaust, TH350 and 3:42 gears. E-Heads from Kauffman, ported to flow 320. This cam with 1.65 roller rockers:



That made 379.82hp and 384ft/lbs of torque. (all numbers listed here are rear-wheel) Since then, I've made the following changes:

Added a HSD intake that is within .010 of port matching the heads (and a 1 inch spacer). Both intakes require the WFO-1 drop base air cleaner.
Replaced stock HEI with D.U.I. unit, 14 initial, 35 total degrees of timing.
Replaced TH350 with an Art Carr 200 4R
Swapped the Chevy Truck Q-Jet for Pontiac unit from a 1970 GTO, performance built by Quadrijet Performance LLC in Texas.
Installed 3 inch exhaust cutouts (Doug's) behind the headers.

I did three different types of runs at the Dyno (the same chassis dyno as last year, same settings).

I started out on pump gas, 93 octane with the exhaust dumps closed. I've got full dual exhaust with X pipe and flowmasters. That put up 389.91hp and 391.45ft/lbs. That was an increase of 10hp, and about 6ft/lbs increase over the previous year.

I followed that by opening the exhaust dumps and the numbers jumped to 403.15hp and 407.11ft/lbs of torque. I made the exact same torque at 4000rpm which was the previous peak. That continued to climb to about 4400rpm which was the new peak. I made more torque than the previous peak all the way from 4K-5500rpm. So I didn't pick up a spike, it was a broad increase.

Finally, I added 4 gallons of 100LL to the tank. I had filled up before I made the trip to the dyno, and 4 gallons is all that I could get in. That bought me 4hp up to 407.33, and half a foot pound of torque to 406.62. The run with 100LL was consistently about 5hp (and up to 10hp) higher than the 93, though the peak only showed a gain of 4. I don't know if that is a function of octane, or displacing some of the 10% ethanol with 100% gasoline. We all know the "power penalty" of ethanol. I'm pretty sure this proves it.

For a street car that makes a couple trips to the strip a year, I'm pretty darn happy with those numbers. I know that I gave up some power going to the overdrive transmission, but I more than made up for it with the upgrades in intake and exhaust. The D.U.I. has really made the acceleration and power band smooth, and starting a lot easier. I'm probably cam limited at this point, and I'm traction limited on the street as it is. Chasing extra hp in a street car is kinda pointless when you can't hook up with properly inflated drag radials.

I'm looking forward to getting it back to the strip later this summer.

[ta man]

Good stuff! My favorite type of thread! Are you using 1.5 rockers? Any results with different total timing?

[Sprocket]

Nice. Thanks for the info.

[surfsama]

It's a nice build and if you're happy with it that's all that really matters.

If you're still looking for some more and heading to the dyno, experiment with the timing. My engine dumps 40 HP either way from 37 total (I'm using the older e-heads so mine might be extra sensitive) but it's well worth it to find the sweet spot. If you can swing it, I'd get an A/F gauge installed (preferably one with a sensor for each collector. It is one of the most valuable tuning aids and engine monitors IMO. Your engine might lean-out a bit when you open the exhaust dumps.

Depending on how much you want to (or if you want to) experiment (1 7/8 headers, ported Torker II/RPM, Holley carb, etc) I think you have some untapped power in that combo.

Thanks for sharing!

[Navy Horn 16]

Originally Posted by ta man

Good stuff! My favorite type of thread! Are you using 1.5 rockers? Any results with different total timing?

1.65 roller rockers. I didn't fool with timing at all. Pretty much everyone I've spoken with says that 35 total is a nice safe sweet spot. I also had pretty much as many variables that I wanted to throw at it today. As fun as it is to hear that car rev to 6K with open headers, I get nervous that pieces are gonna fly all over the place or out the exhaust.

I sent an e-mail to Butler Performance, and they got back to me within minutes. They think I could benefit from a little more carb, like a 950. I doubt that I'll change anything. I like my setup as is.

[hal101]

sounds good do you have any track times that can be compared with the dyno pulls
sounds like a very nice car im sure you are very happy

[ta man]

Originally Posted by Navy Horn 16

1.65 roller rockers. I didn't fool with timing at all. Pretty much everyone I've spoken with says that 35 total is a nice safe sweet spot. I also had pretty much as many variables that I wanted to throw at it today. As fun as it is to hear that car rev to 6K with open headers, I get nervous that pieces are gonna fly all over the place or out the exhaust.

I sent an e-mail to Butler Performance, and they got back to me within minutes. They think I could benefit from a little more carb, like a 950. I doubt that I'll change anything. I like my setup as is.

Gross valve lift works out to .594/.619 with the 1.65 rockers. There should be extra horsepower in adding a few more degrees of timing so that's good to know. I probably would have left the race gas at home and concentrated on tuning total timing.
I don't think your carb is too small. I also think your 1 3/4 headers are fine. There may be gains with the exhaust. Where are the cutouts?

[Navy Horn 16]

Before all of the changes, I had run a best of 12.75 at 107.9. And I spun a little on that run. I've got a much better convertor now, and more power, and better gear ratios. I'm hoping to get under 12.5.

I've got about 18 inches of 3 inch header extension before my cutouts. It's basically open headers with the dumps open.

My plan is to play with the timing at the track. That will be more fun anyway.

[ta man]

A good goal would be to add 10mph and get into the 11's. What is the fuel system on the car?

[TCSGTO]

Originally Posted by Navy Horn 16

I sent an e-mail to Butler Performance, and they got back to me within minutes. They think I could benefit from a little more carb, like a 950. I doubt that I'll change anything. I like my setup as is.

The 950 flows about 830 so I doubt it would make a huge difference. In the low 11 range a850 Holley gained a tenth and 1 mph over a Q-jet for me but that’s within the margin of error and more tuning could have changed the result.

[hal101]

did you get any grafs showing air fuel ratio from the dyno

[Cliff R]

During one of our dyno sessions we back to back tested a Holley 4781-2 850 DP carb and a very well set up HP950 against my 1977 Q-jet. They all ran within 1-2hp of each other with the Q-jet making highest HP but not quite a "clean" thru the mid-range. We carried the 4781-2 to the track and the Q-jet ran .02-03 seconds quicker in ET and about .5 MPH faster. We repeated that testing several times, all documented as part of either an HPP "Shootout" or witnessed by representatives from HPP/Popular Hot Rodding magazine for the KRE head testing articles that followed.....FWIW.

With that said your earlier Pontiac Q-jet is not nearly the CFM as my 1977 model nor is it as much as the HP950. This will cost you about half a tenth and 1mph or so at your power level, at least from the testing I've done here with that sort of thing.....Cliff

[Steve C.]

Cliff Ruggles was kind enough to let me try one of his Q-jet carbs for interest for back-to-back testing with my 'worked' Holley HP950 carb.. We only tried it on the one outing, this was with my old 462cid pump gas combo after a change to a small 248 @ .050 solid roller from the previous 254 degree roller. The Q-jet performed well. I only ran that motor once with that cam and then retired it for my current 505cid build.

Q-jet / 8 psi at reg / 41 degrees timing
5400 rpm shift point
1.67 60-ft
11.64 @ 115.59

HP950 carb / Same fuel pressure & 41 degrees
5400 rpm shift point
1.66 60-ft
11.65 @ 115.38 mph

Side note. With the new smaller cam we had no idea for the shift rpm, on the first run with my carb it was shifted at the same 6000 rpm as with the previous cam which would run high 10's and low 11's. The first run was very slow indicating the obvious, the new cam made peak power at a much lower rpm. So on the next run we tried using the only shift chip on hand at the time, thus the low 5400 rpm shift point used for the testing. Due to limited time we did not try other shift points but I know for a fact both times would be MUCH improved doing so.


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[Formulajones]

Here's an interesting dyno session on the 950hp.

I reworked this carb years back with my own tricks and dad ran it for years on his 455. When he built this 571 he used the same carb with just a jet change.

What's interesting is that Tony thought the carb might now be too small and tried one of his dyno 1050 dominator carbs. Turned out the dominator only picked up 6 peak HP but the 950 had better torque throughout the pull with a better HP average overall.

Fast forward to about 13 minutes, when the 950 is put back on to compare to the dominator pull just prior at the 10 minute mark. Tony in the video was shocked and impressed with how well that 950 was working on an engine this size. That says something considering all the various engines this guy has his hands on searching for HP.
https://youtu.be/5WswK-m-zIA

[Formulajones]

Originally Posted by Navy Horn 16

. Pretty much everyone I've spoken with says that 35 total is a nice safe sweet spot. .

It's crazy how much timing affects the engine and almost every combo I've ever dyno'd showed me the best timing setting wasn't what I thought it would be.

In the case of the engine I posted above, it uses old Edelbrock bathtub chamber heads. Now if I listened to everyone on this forum about best timing setting they would all tell me it needs to be 40 degrees.

That was simply not the case. We tried various timing settings and 34 was the best place to be. Oddly, the engine size had no affect. These same heads were also on dad's previous 455 and again, on the dyno it made best power at 34 degrees. Move the timing even 1 degree on either side of that and power fell off. Timing is the first thing I want to play with before I get into too many carb changes.

Using the dragstrip as you mentioned is also a good place to experiment, and more fun.

[Steve C.]

Numbers assigned to a carburetor often mean very little. I have a custom carb built by Brad Urban at the original Carb Shop, his catalog stated it was his Stage III 750 Holley. On a previous 4.125 stroke / 450 cid combo with a Victor intake that 'little' carb supported 680 hp at 6900/7000 rpm. On back-to-back dyno testing that same engine made 699.9 hp at 6900 rpm with a Dominator style Victor intake and a 1050 Dominator carb using a 1-inch cloverleaf spacer.


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[Navy Horn 16]

Originally Posted by ta man

A good goal would be to add 10mph and get into the 11's. What is the fuel system on the car?

It's a Holley Blue to a Q-Jet. Pretty simple.

My cousin has a 77 Monte Carlo with a 427 that made the exact same power numbers (well, 2 less HP actually, that I'll never let him forget). He has run a 12 flat, but he had 4.11 gears and would run out of gear at the top end. He's also a couple hundred pounds heavier than me.

[Formulajones]

Originally Posted by Steve C.

Numbers assigned to a carburetor often mean very little. I have a custom carb built by Brad Urban at the original Carb Shop, his catalog stated it was his Stage III 750 Holley. On a previous 4.125 stroke / 450 cid combo with a Victor intake that 'little' carb supported 680 hp at 6900/7000 rpm. On back-to-back dyno testing theat same engine made 699.9 hp at 6900 rpm with a Dominator style Victor intake and a 1050 Dominator carb using a 1-inch cloverleaf spacer.


.

Used as a reference point only. Once reworked that 750 number is likely out the window if you get deep into changing things. I don't know how extensive Brad gets. I didn't get into booster mods or swapping throttle plates, smoothing/polishing the bore, things that would affect CFM, so the 950 rating from Holley, if accurate, didn't change. I merely got into the fuel circuitry with metering block mods, imulsion and air bleed changes using a wideband to dial it in nicely.
I assume since the 1050 is Tony's dyno go to carb, he's made extensive changes to it as well. It only needed a minor .003" air bleed change to bring the AFR where it needed to be, so it was pretty close right off the bat.

[Formulajones]

Adding to that, if you get someone that really knows what they are doing, there is quite a bit of power to be found in carb tweaks.

From what I've seen, Jeff Koerner is one of the best with Holleys. He used to run a well known carb shop with a partner (name escapes me) but Paul knows more of the details. He did a bunch of work in Nascar for Michael Waltrips team when he first started out in Toyotas, and started winning more races with Jeff's modified carbs (before Nascar went fuel injection)
He still offers his carb services at the machine shop and Paul has witnessed first hand what his carbs will do on many dyno sessions where a very mild engine with a basic carb can see as much as a 30 HP gain with Jeff's carb, and a more rambunctious engine gained 100 HP. Paul could elaborate more.

Very cool stuff though.

[ta man]

Originally Posted by Navy Horn 16

It's a Holley Blue to a Q-Jet. Pretty simple.

My cousin has a 77 Monte Carlo with a 427 that made the exact same power numbers (well, 2 less HP actually, that I'll never let him forget). He has run a 12 flat, but he had 4.11 gears and would run out of gear at the top end. He's also a couple hundred pounds heavier than me.

The fuel system may be costing you power at the track. I had the same fuel system years ago stock lines Holley Blue..I picked up almost 4mph in total going to a half inch pickup, Mallory 140 and all 8an lines.