dyno test- Alum head Big car motor

From the "now for something completely different" file..


Have a local friend and customer, Steve Robin, whose into the big cars. Not so much a speed freak, but likes performance as much as the next guy.. He's a board member here who is also into the 65 sportwagons, and the older buicks as well.

Steve has a couple different big Buicks that this motor might end up in.. either a nice clean 75 electra or a 51K Mile 71 Lesabre.. both Big heavy cars, that will be daily driven with a stock converter and 2.73 rear gears.

He picked up a set of the TA Stage 1 SE alum heads a while back, and we used them to build a great all around performing motor for one of these cars.

Now, with the weight, converter and rear gear, along with Steve's desire to get something that at least resembles gas mileage, we set the following parameters for the build

• Use 87 octane regular unleaded
• maximize mileage
• responsive even with the highway gears and stock 13" converter

To achieve these goals, we followed the following receipe- we took the 75 electra's motor which was tired, and filled it with

1. Forged pistons for reliablity
2. stock rods, crank- completely machined and rebuilt
3. a premo 1970 SF 455 stock cam and lifters
4. STG 1 SE heads with the TSP bowl/port work upgrade (320/225 cfm)
5. Edelbrock performer
6. The 75 Q-jet, rebuilt, jetted and updated with an electric choke
7. Stock HEI ingition
8. TA shorty headers, for performance and mileage improvements.

Now, this cam is tiny, by any performance specs, but the use of a long duration cam is just not in the cards for this buildup. Not with the weight of the car, the gears, converter, and the desire to daily drive it..

Compression was held at 9.5-1, and the 70 SF cam is 200/225 duration, and .388/.423 lift.

Yes.. you read that right .388 intake lift... with just 200* of @.050 duration.

This is one of the few motors that when we rolled it into the dyno shop last night, and Ron, the dyno operator, asked me how much it would make for power, I just went.. "maybe 400 HP..".. don't really know..

He started laughing when I told him the lift of the cam, and said that he didn't think you could even buy a .388 lift cam.. for small block chevy..

But the numbers were great.. this thing idles at 600 rpm, with 20" of vacuum, and sounds exactly like an stock engine. Even with the headers it's very quiet..

And it don't run too bad either..



Now that's a flat torque curve, and we bested the vaunted 70 STG 1 Engine by 50 HP

Torque is strong down as low as 2500.. had a few lower rpm tests, with a different Q-jet that wasn't working as well as his, that were over 500 lbs down low.. we didn't pull the final combo that low, but it's there no doubt.

Stay tuned for how this works out in the car..

I know I have said this a thousand times, but it's worth mentioning again..

"It's all about the heads boys.."

JW

 

That's impressive.

Makes me wonder if with my setup I'd be better following your example and spending the money on a set of heads.

Good work Jim :TU:

 

That ought to be fun in that big car ....what a torquer- top end cruiser . J

 

Jim, can you comment on the A/F ratio getting leaner as the RPMs increase?

Seems like the holley's are pretty good at keeping a consistent A/F ratio
across different flow rates. But the Qjet seems less consistent.

Is there any easy way to get that under better control?

 

Thats awesome. Thanks for posting this Jim, I have always wondered about a "big car" engine, did not think anyone would ever really commit to it in this big way! Nice. This is what I should have done for the wagon.:TU:

 

What a cool experiment! I'm also quite surprised by the results.

Sorry, but I still prefer my 308S cammed "big car motor". :laugh: :beers2:

Devon

 

Very cool that it's going in a big car, I would of course like to see it go in the LeSabre. Any chance that you would have a price tag (more or less) on such a build, with the machine work, parts etc.

 

Nature of the beast with a Q-jet on the dyno.. Unlike in the car, there is not a static load on it, it varies, espcially at the start of the test. The rush of fuel when the secondaries open will momentarily flood the intake.. we see this all the time on the dyno with a Q-jet, this carb had a very smooth transition. As the rpm increases, it clears the manifold and the AF numbers lean out.

Holley's meter fuel better because they have secondary venturies, with independant secondary accel pumps, on the double pumpers. Therefore you have a quick pump shot to cover any lean stumble, and the jetting can be precise for fuel requirements vs airflow..

By the way, this q-jet outpowered a 950 Hp on this motor, even with the help of a 1" 4 hole spacer under the HP carb.

JW

 

Not if you drove it every day you wouldn't... unless your independatly wealthy and don't care about the 5 MPG :laugh:

I'm shooting for 17 MPG on the highway with this build.

JW

 

Your 4 speed car's motor is going to be a cross breed between the PSMCDR motor I just did, and this one Ted... an idea or two taken from the cam in each motor, mixed together to come up with a new approach to a street hot rod. I'm done with the noisy, won't barely run the brakes camshafts.. makes the car not as much fun to drive.

JW

 

Round figures, carb to pan.. about $8000 if you have good cores for the block and timing cover, and the sheetmetal. Headers would be on top of that.


JW

 

Of course, Jim...two very different animals for sure. :TU:

Devon

 

Jim,

Could you please tell us who makes or sells an electric-choke conversion for the early Q-Jets? I have a '73 Osborne carb on which I would like to have a working choke--can't do it with my Bulldog heads and no heat crossover.

Thanks!

Best,

Ranger/Craig Stangohr
Aiken, SC

 

Glad to see a big car build! Don't see many people dropping cash into one trying to make it run better.

 

Love this dyno test!

About the Q-jet lean out. Has anyone tried an 80 degree air flap opening as apposed to jacking them open to full 90, assuming more AIR is better.
I've read that full open blockes the nozzles, but seen no tests done.
I've asked this question more than once and never got an INFORMED/TESTED answer.

 

Gary, I don't have an aboslute answer for you, but I can offer up what's written in my old 1973 edition of the "Rochester Carburetors" book by Doug Roe & Bill Fisher (it's got about three times more info than the one sold today).

They mention airflow itself doesn't change at 90 5 secondary throttle position. They do mention that at less than 90, the front cylinders may tend to run lean. They demonstrate the method of compensating for this by setting the carb up for 95 plus if distribution is a problem.

If those few pages would be of interest to you, I can scan them for you.

Devon

 

Thanks Devon,
I have the Doug Roe book, and know about the trottle angle with a little foreward pitch, but the air valve (flap) and spring tension are both left to guesswork or bogg avoidance.
The factory air flap angle is produced in either 70 or 80 degree angles on the Buicks. The Ram Air Pontiacs used 76 and a Pontiac guy said he got deminishing returns after 81 degrees because it smothers the fuel tubes.
Everyone else I talk to said they opened the air valve straight down (90degrees) and then started testing and jetting and turning the spring tension.
I suspect this an issue that NO Buick guys have ever worked out. I have no A/F meter and would SURE LIKE TO KNOW the low down on the flap stuff. Could be the answer to leanout on Q-jets?

 

Ahhh...my mistake, thought you'd been on the subject of throttle blades!

Devon

 

Jim, is there any possibility of testing that combination with a GS-116 or T/A 212 cam before the motor finds it's new home? I would love to see what kind of torque and horsepower numbers one of those cams would make using the same combination of engine parts.
This is some great info I can use on my .030 over 455 build for my Riviera. Thanks again for sharing it with us, Randy

 

Sorry, that motor is in the car and down the road.. about a month or so ago..

I am sure we will do more of this in the future..

JW