Suggestions For Next Drag Strip Testing Day

[Brian B.]

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.

[Cliff Ruggles]

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

[Brian B.]

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!

[Cliff Ruggles]

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....

[Brian B.]

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.

[Cliff Ruggles]

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

[Brian B.]

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. 

[Brian B.]

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.

[Cliff Ruggles]

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........

[Brian B.]

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!!!

[Cliff Ruggles]

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.........

[Cliff Ruggles]

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......

[Cliff Ruggles]

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......

[Brian B.]

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!

[Brian B.]

Oops.  I just saw your comment about headers above.  No need to reply. Sorry for the redundancy.