Cliff's Quadrajet Parts and Rebuild Kits
General Category => Quadrajet Carb Talk and Tips => Topic started by: Brian B. on May 02, 2021, 01:15:59 PM
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Hi. I was wondering if the more experienced strip tuners could kindly help me with some suggestions to improve. Just had my best 60 foot, ET, and MPH to date with this setup and conditions.
ET - 12.91, MPH - 104.98, 60FT - 1.82, 330FT - 5.333, 1/8 ET - 8.251, 1/8 MPH - 84.31, 1000 FT - 10.768
Air Temp = 50 degrees, Pressure = 30In Hg, Humidity = 57 percent, Water Grains = 38g/lb, DA = 600 Feet.
Mild Hyd Roller Cam @ .050 224 Intake, 230 Exhaust, Lift .552/.528 Lobe Sep 112.0 degrees
Car = 4000lbs, 455 auto 2800 stall, with 3:08 rear.
Stock intake, round port cast iron exhaust manifolds, x-pipe, and Flowmaster transverse muffler.
Launch at 2000rpm with dead hook.
Carb is #7044270 and is stock for my car. Only deviations from stock are jets, rods, accel pump, and choke pull-off.
Primariy Jets are #78 with 45B primary rods. Secondary Rods are DG with G Hanger.
Choke Pull-Off is 1.5 seconds with 3/4 turns on windup spring.
Total timing is 36 degrees all in by 2600 rpms.
Tried 76 jets and car ran slower ET and MPH. Tried CC and AX rods and car ran slower ET and MPH.
If I encounter similar good weather conditions next time, would any of you with more experience recommend any carburetor changes. Thank you for your help.
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Super Duty 455?
Tiny cam for a Super Duty engine so focus should be on short-shifting and improving 60' times to get the best ET's.
Did you raise the compression during the engine build?
What are the rest of the cam specs, duration @.006" and where is the ICL at?
Running huge jets in a SD carb will require pulling some fuel out on the secondary side. If you have access to them try a CV rod on the next outing.
I've drag strip tested SD carbs with 73-74 main jets in them and found best ET and MPH with rods n the .048-.055" range, but they were custom machined from the same cores and on a "L" hanger.
I used to do a LOT of testing/tuning at private track rentals figuring all this out. Super quick timing curves don't really help either, unless you have a pathetically "low" compression engine in place with too much cam in it.
Not too long ago I helped a customer with a pretty "basic" 455 build using a 276/284, 224/230 @ .050" cam and 9.3 to 1 compression. He was on the dyno and only making 428hp/516tq DONE at 4800rpm's. The heads were professionally ported to 250cfm (96 castings).
I suggested a cam change to a 289/308, 236/245@ .050" cam on a 114LSA with the ICL set at 110degrees. With no other changes made the engine made 514hp/559tq done at 5800rpm's. He also noted it actually idled smoother with the larger cam and improved street manners as well as there were able to put more initial timing in the engine without pinging and "bucking" the starter on a hot restart.
I've built at least half a dozen 455 HO's and SD's here, and the smallest cam I'd even look at using in one would be 230 @ .050 and nothing tighter than 112LSA and ICL not further ahead than 109 degrees. They are "sleeping giants" with those huge round port heads just sitting their waiting for someone to put some cam in them so they can come to life and really show their colors.....FWIW.......Cliff
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Hello Cliff. It is an SD-455. I know I went conservative on cam selection back during the cam swap. I was looking more for mid-range torque at the time. Goal was to comfortably drive back and forth 300 miles to a car show and have some fun track time. Compression is now 9 to 1. Vacuum at idle is 13 inches. .006 is 275 Intake and 285 Exhaust. ICL is 107 Degrees.
I really appreciate your insight. Next time I get weather conditions like these I'll short shift and use my CV rods and K or M hangers. Thank you!
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Here is a dyno chart from one I did here, 8.8 to 1 compression and 281/287, 230/236, 112LSA cam.
Makes 16" vacuum at 700rpm's....
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That's a sweet wide torque band! It must pull like a freight train. I imagine it would be fun with a 3:42 gear on the street.
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I also noticed above "launching at 2000rpms".
Are you "power braking" to 2000rpms on the starting line?
I'd try leaving off idle instead if that's the case instead of loading up the drivetrain and suspension and taking the "hit" out of the converter.
Also curious who's converter it is, diameter, etc? I can't get past 1700rpm's with my 10" converter without the rear tires starting to spin and it flashes to 3600rpm's on a full throttle start with traction.
Also, what RPM's are you seeing at the finish line at 104mph?
Something else I noticed was running 78 main jets in the carburetor. Not sure why or how you ended up with that much jet? Also a mention of it running slower with 76 jets.
We tune the primary side separate from the secondary side for drag racing/WOT performance. I've set up scores of 73-74 Super Duty carbs and you don't need or want that much jet in them. I'd back that down some and go to smaller primary metering rods as well. Also remove the triangular cover over the adjustable airbleed screw and gently seat it, but leave the cover off for fine tuning if/as needed.
You mentioned 36 degrees timing all in by 2600rpms, how much timing is the vacuum advance adding?........Cliff
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Cliff I have a 13" Continental converter. My stock brakes barely hold on the starting line but I can power brake it to 2000rpm. With the exception of Bilstein front "racing" shocks My suspension is very slow. I typically leave as soon as the 3rd amber lights up without red lighting. RPM at finish line is 4000 with my 3:08 rear end. Transmission shifts into 3rd gear approximately 100 feet or so before finish. Accel Adjustable Vacuum Advance can adds 12 degrees without pinging or black specks on insulators of NGK 2771's, which are one step colder than stock and are NGK's recommendation for my application. As far as 78 jets go, car always seemed to run best times with those with no drive ability issues or fouling.
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Sorry..I forgot one other suspension mod. I clamped the front half of my leaf springs. I am sure this sounds like a lot of backyard engineering but I do most of my testing at the track rather than a dynamometer. Amateur for sure.
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Those are excellent converters but I'd leave at or just above idle speed. When you "load" the converter that hard it softens up the hit to the suspension and tires and can hurt short times.
I'd drop back the jet size at least 3 numbers and same with the primary metering rods. Don't forget about the air bleed screw in the airhorn under the cover. Then you will be able to tune more effectively on the secondary side of the carb at the track.
Clamping the springs is fine, but you need sub-frame connectors on those cars to effectively transfer weight. An adjustable pinion snubber will also be required to control wind-up of the center section.
"Old School" mods but they work. My car is set up the same way, and don't forget to weld the axle tubes to the center section. 8.5 diffs are only "spot" welded and known for spinning axles in the housing when hit with big power and good traction.
It's been at least 20 years now but I helped a customer set-up his Super Duty T/A pretty much the same as yours other than running an old HO Racing (may have been a Nunzi cam) flat cam. It was 240 something @ .050", and topped with Rhoads lifters. Motor was pretty much stock otherwise.
He used a TH400 with 3.08 gears and we ended up getting him to 12.0's in the 110-112 mph range. In addition to a LOT of carb tuning it took a lot of suspension work and good tires but those engines are a factory "hot-rod", just waiting to be exploited........
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Cliff...thank you for your insight and thumbs up on my converter. I should have added it is what was called the "Jim Hand Converter". I will try the carb modifications soon. Just curious about the customer's SD that ran 110 to 112mph. Was it equipped with headers? I'm trying to do all this without tube headers. So far I've taken a stock and option loaded 14.0 second car to 12.91 and don't want to use headers or a gear swap. Thank you!!!
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I'm familiar with that converter and used one for quite a few years before moving to the 10" version which is still in the car today. Below is a run leaving at 1000rpm's and most runs are typically 1.59-1.61 60'.
https://www.youtube.com/watch?v=6zVdoLR-VzM
That isn't the kind of converter that you "load" against the brakes, too efficient. It LOVES leaving off idle or less than about 1100rpm's and will "hit" the tires much harder, wind up the suspension, transfer weight and 60' better.
It's been so long ago I don't remember all the details, but I do know that he was using 3.08 gears and a TH400, and the smaller 10" converter from Continental.
My 13" Continental unit flashed to right at 2800rpms (leaving off idle) behind my old 428 engine topped with 6X heads (about 8.8 to 1 compression and HO Racing HC-01a cam), and 3200rpms behind the RAIV cammed 455 topped with the same heads that replaced it. Loaded hard against the brakes you couldn't get past 1700-1800 for any reason. It was locked nearly solid on top end and the car ran deep into the 12's with it. I saw a solid .2 and 2mph with the 10" converter and no other changes with that old combo.
For your combo you have some room to grow. MPH is down for one of those engines so there is some additional power lurking in there someplace. I just hope it isn't the small cam pinching off some upper mid-range and top end charge.
If you looked at the dyno chart I attached the larger HR cam made 1hp/CID but still finished by 5200rpm's. At 1hp/CID it would push 3900-4000lbs DEEP into the 12's closer to 109-112mph with good traction and a well chosen converter.
The 3.08 gears hurt NOTHING behind the 455 Pontiac engine. I've seen several cars run well into the 11's and one car I know of runs hard into the 10's with 3.08's in a 455 powered T/A.........
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If you don't think a 455 Pontiac LOVES a lot of cam take a look at the attached dyno chart.
The first cam was chosen by the "tech" at Comp Cams. It didn't make chit for power and pinged at 9.3 to 1 compression.
The second cam is the one I picked for the same engine.
The overlaying dyno charts indicate only the cam swap, no other changes were made. I'd add that with the larger cam the engine idled better, smoother off idle and made more power (torque) at every RPM, plus a BUTT-LOAD more upper mid-range and top end power......
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Forgot to add that the 455 above was topped with #96 heads ported to 250cfm, not the excellent 73-74 Super Duty heads. They would have made even more power in the same build......
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Good Stuff!!! I've viewed your pass on YouTube several times in the past and even gave you a thumbs up and commented how well your carburetor performed! Did your customer run headers on their SD car that ran 110 to 112? Thanks!
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Oops. I just saw your comment about headers above. No need to reply. Sorry for the redundancy.
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The excellent iron manifolds only add weight, they don't slow them down.
I have customers running in FAST well into the 10's with "D" port heads and "log" manifolds on them.
The Pontiac HO and Super Duty 455's are "sleeping giants". They are just sitting there waiting for someone to squeeze them a little harder (tight quench and raising the compression a tad) and the right cam to unlock the power.
I've ran several different cams in them and dyno'd each one. The 281/287, 230/236, 112 HR was the smallest one and a little disappointing. Done at 5200rpm's even though it made 1hp/CID it was too "mild".
I have another cam with bigger .361" lobes that specs at 284/296, 230/242, 112LSA that makes another 20hp and at least 20ft lbs but still pretty "mild".
I really like going up to 236/242 or 236/245 and pushing them out on a 114LSA with the ICL at 110. This pushes them over 500hp with ease and gives up NOTHING from idle to the shift point over a small cam on a tighter LSA.
Look at the dyno chart closely, especially up around 4800-5200rpms. A small cam is DONE way before that where the larger cam is making more torque up there than the smaller one made in the mid-range! Even if you shift at 5000rpm's the car will run nearly a second quicker in the 1/4 mile with the larger cam in it as it makes a LOT more average power, and power from where the converter stalls to the shift point.
HO Racing pushed many of their cams out on a wide LSA and so did Nunzi, maybe they knew something that most folks don't these days.......
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Cliff...you've given me great tips throughout this thread. I really appreciate your time and the depth to which you went to help. I saw some you made some early morning posts too. We're fortunate to have you as a resource and your firsthand experience to utilize. Thank you!
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You are most welcome.
One of my goals is to help customers obtain the best performance possible from their combination.
I still remember my first track outing with the Ventura decades ago in Richmond VA. At that time it was powered by a 400 engine with 6X heads and about 7.7 to 1 compression. The cam was a Crower 60240, 210/221/112LSA. Backed by a TH400 with a stock converter and 2.73 gears it still managed 14.0-14.20's at 98-100mph.
I was able to "tweak" that combo to a best of 13.87 @ 101mph. Since then I've powered the car with two different 428 engines and two different 455 engines. Each engine was a step up in power and required changes behind it to effectively use the power. I've had 3.23, 3.42 and 3.73 gears in the rear as well.
The first 455 was pretty "basic", just nicely cleaned up 6X heads, 9.97 to 1 compression, Crower RAIV cam, Rhoads lifters, and 1.73 ratio rocker arms. That engine was AMAZING and very difficult to hold on the starting line. After busting up a driveshaft, a transmission, two diff's and testing a half dozen different types of tires I managed to get it to run into the high 12's at 107-108mph. Two more seasons tweaking the suspension, welding in sub-frame connectors and wham went right to mid-12's at 108-109mph. It still felt a little "soft" past 5000rpms but rock solid otherwise, and running solidly in the 12.40-12.60's with a best of 12.37 @ 110mph.
Over one Winter I upgraded the fuel system, sumped the tank, 140gph pump behind the tank and 8AN lines/fittings everywhere. The first two runs with the new fuel system was 12.10/12.11 @ 112mph! I actually over-revved the engine as it spun past my 5500rpm's shift point and on past 6000rpm's so quick I didn't move the shifter fast enough! I caught on quickly and the next runs were 12.02, 12.03 @ 112mph shifting at 5500rpm's.
That was a solid .3-.4 seconds and 2-3 mph improvement over the previous set-up. I had no idea at that time that I wasn't keeping up with the engine. I had even tried (on the advice of many non-believers) running a Holley 850dp carb and with the old fuel system it ran no quicker than the Q-jet. That pretty much debunked the myth about not having enough fuel bowl capacity, you are either keeping up or you aren't.
Anyhow, made some more changes and right into the 11's we went. I continued to exploit that 455 and got hooked up with KRE to test their new aluminum heads. That made HPP and Popular Hot Roddings Engine Masters edition and the car ran in the 11.60-11.80 range for several more years with a best every 11.52 @ 116mph.
In 2009 I built a 428 with a 4.21" stroke crank topped with CNC ported KRE heads and it's still in the car. It's WAY too quick for 1/4 mile tracks (runs under the roll bar rule) but typically good for 7.20-7.25 @ 95-97mph in the 1/8th mile. On 1/4 mile track I add 200lbs in the truck, retard the timing 4 degrees and short-shift at 5000rpm's and that usually keeps the officials from visiting my pit-sight and giving me my walking papers!
....continued
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The learning curve with the Ventura (I also help out with 4 other cars raced out of the shop) has been a long one and I've tested just about EVERYTHING that's out there. This includes distributors, intakes, all sorts of spacers, air cleaners, exhaust systems, mufflers, and scores of carburetors. I've also tested some camshafts, hydraulic flat tappet, solid flat tappet, and hydraulic roller, camshaft timing, and a truck load of converters, plus at least 6 different types of tires.
I also dyno'd just about every engine we built here, and have a nice learning curve from the dyno as well. So if anyone has any questions don't hesitate to ask, but I'll warn you that I don't hold back when it comes to giving advice. There are a LOT of parts out there that don't make the grade, TONS of "propaganda" to go with it, and folks have vested considerable money in some of it. So wear your big boy panties if you are wanting me to give straight advice based on direct testing with parts you may be using........Cliff
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Cliff do you still use and recommend Rhoads lifters? I've heard good things, and was thinking about trying them in my roller SBC one day.
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I always use Rhoads on flat tappet camshafts as there are no negatives anyplace.
With the right cam you cam mimic the power of a very well chose Hydraulic Roller cam at much less cost.
I did a back to back dyno test on my last 455 engine between a 304/314, 231/240, 113LSA cam and a Comp HR cam with 284/296, 230/242, 112 specs. The roller cam had .361" lobes and a LOT more lift than the flat cam.
The roller cam only made 3hp/4ft lbs more power than the flat cam and done at 5400rpms where the flat cam made peak power at 5600rpms.
At the track the roller cam was worth more than the dyno showed, running about a tenth or so quicker for most runs and a solid 2mph faster.
Best run ever with the flat cam was 11.64 @ 116mph. The roller cam went 11.52 @ 118mph.
What the Rhoads lifter do is allow us to use a relatively large cam with less negatives, and have a variable valve timing set-up in an older engine design.
I've back to back tested them on the dyno against HT-951-R lifters and there is no power loss whatsoever from the fast bleed design.......Cliff