SD-455 Qjet Clone
 

Some people wanted me to post this Ebay special.

It's an SD-455 clone made from a standard 1974 Firebird 750cfm.

The real SD carb is an 800 with the larger primarys so the builder of this unit figured he'd hack out the outer booster ring to match the CFM and leave the rest of the calabration stock.

Bad idea as it kills signal strength and proper atomization and unlike the 71' 455HO single booster which the single booster extends down about 1" this one is only about 1/2" long

I'm currently modeling, fitting & making replacement outer booster rings to correct this unit and here's a few pics.

Jeff, I didn't know you did Q-jets.

Steve,
I do them all.

I've had several of those sent here. They can be effectively calibrated and actually work quite well. I've had them on the dyno and followed up that testing at the track.

We ran within .02 seconds of my 1977 Pontiac q-jet, within .5 mph as well. They drive fine on the street, but the calibrations are WAY off what a standard unit would require. Seems to me it would easier to just replace the casting with another $30 unit than to go thru the steps required to put boosters back in it?....LOL....Cliff

Here's today's progress:

Outer rings fitted

That's fine,
We simply have the ability to restore this unit if nessary rather than replace it just like the three rare Qjets I also machined for you.

If you'd like to contribute and post your new calabration for the single ring that would be great as we are returning to the dyno Wed.

Also, I can set this unit up to test both ways...with or without outer booster rings.

Few people can look at that and appreciate the amount of tedious ,time consuming, out of the box thinking, and work that went into that.

Very nice job on that.

Thank You Sir!

That's very nice of you to say.

You are most welcome!

I have to get into "watchmaking" myself at times, but that is a little out there.

My guess is the guy that bought it spent many cubic dollars on it and just wanted to spend some more to come out on the upper end of the deal, after he found out it wasn't what it was advertised as to begin with??

Not exactly,

The owner knew it was a clone and the price reflected it.

Other than the booster rings the unit is clean and replated and every other 74' casting I have worked ran some of the best.

This timepiece took only a few hours to rework and now the booster are installed and on the dyno today.

Shaker does some of the nicest and acurate work I've ever seen. He's taught me alot about carbs and how they work, that alone puts him above many others.

I remember removing the booster rings from a 75-up 800 cfm QJ years ago just to see what would happen. That was before I truly understood the benefits of recalibrating the idle circuit. Surprisingly it idled and ran well, but the missing booster definitely affected throttle response.

Jeff, what did you use (or are you planning to use) to keep the boosters in place?

It's an SD-455 clone made from a standard 1974 Firebird 750cfm.

With enough time/funds I suppose we could restore anything? Problem is, the standard 1974 unit is a $35 core (or less), and there are PLENTY of them available.

For dyno runs I'd recomend running it straight off the jets, this will provide the cleanest fuel curve.

I would also machine a complete set of secondary rods from the same cores. Swapping around secondary metering rods on the dyno will have fuel curves all over the place unless the same hanger is used and all of the metering rods have the same taper, tip length, and included angle between the tapered section and the tip(s).....FWIW.....Cliff

Jeff is making this carb work for me until I can find and more importantly "afford" a real sd carb. I have no intentions on passing this carb off as real! We will be running the sd on the dyno tonight baring anymore ignition issues. It's a .040 sd455 with an xe274 cam. (Cliff's favorite!) Any guesses as to dyno numbers?

5


I never meant to say or insinuate that the owner was trying to pass it off as such, just that I figured the guy got so far in on the front end, I just figured ya wanted to make it at least functionally a good clone. I get distributor work like that all the time and the guy says make it work anyway. No big deal at all no offense intended or implied.

Those SD carbs that are legit bring insanely serious money... but then they don'rt makem any more either. I think I need a raise just to look at some of that stuff on ebay.

"(Cliff's favorite!) Any guesses as to dyno numbers?"

Assuming stock compression ratio, no porting of the heads, intake and factory iron manifolds: 411hp and 499tq.....Cliff

Update & Results:

We had a great time up Lenny Caverly's dyno tonight and will start a new post with that subject possibly in the SD forum.

I tested 3 of my Qjets on the SD-455 including the 74' unit I restored the removed booster rings.

This is peak numbers, keep in mind the numbers didn't drop off as much as I figured as I'm not a fan of the XE-274.

1st, Mid 70's 800cfm unit I built for general dyno use:
406 HP @ 4800
532 TQ @ 3400
A/F high 12's

2nd, SD Clone with outer boosters & recalabrated:
412 HP @ 4900
523 TQ @ 3500
A/F very nice fuel curve high 12's low 13's

3rd, My 71' 455HO factory single booster that I calabrated for my car in 04'
415 HP @ 5000
534 TQ @ 3400
A/F Low 12's

We concluded our break in/tuning and removed the SD off the dyno.

Once the car is finished I'm planning on extensive street tuning & testing, and at that time I may test with the outer boosters removed and machine up an extended center booster simmilar to my factory single ring.

The test results reflect my HO carb to be the best preformer.

Special thanks to Jeff Esmel, Len Caverly and John Gogeun for all their help and hard work.

Marc

Also, a special thanks to Jeff Esmel for the work he's gonna do soon on my 3-bbl custom watch.....hehehe.....

It would be nice to know the engine specifics, true static compression ratio, headers or stock iron manifolds, intake used and if it was ported, etc, etc, etc?

Peak torque is good for the combination of parts, and is occuring EXACTLY where it has with every XE274 cammed 455 dyno test I've seen, which is about 400rpm earlier in the rpm range than either the Crower 60919 cam or our "custom" HR cam of similiar specs.

What was the torque number at 4900rpm's?

Same thing with peak HP, 4900 is EXACTLY where every single 455 quit that used that cam, even with very good flowing heads on them.

FWIW, we built a stock 455 SD engine here couple of years ago. No grinder or sanding roll touched anything. It was zero decked, and aftermarket forged rods and pistons were used, but the owner insisted on all stock components otherwise without any "mods".

We were able to convince them to upgrade to a small HR camshaft, which I chose from Comp Cams. 230/242/112 with .361" lobes. That engine cranked out over 440hp and 550ft lbs torque. Peak HP at 5400rpms, and peak torque at 3900rpm's.....FWIW.....Cliff