I need more Low End Torque!

[Pat n Pat]

I need some advice on how to improve low-end torque in our ’31 Buick racer. The car pulls very strong from about 2,000 rpm, but is weak off the line and requires a lot of clutch slippage to get going. The car was originally built for high speed. The car will be run in the 2011 Hemmings/Coker Great Race, which means we need more quick acceleration and less top end.
Here are the details (as best I can tell):

· 283 ci
· 8:1 Compression ratio
· John DeLong cam; IO @ 8 degrees BTDC, IC @ 42 degrees ABDC, max @ 107 degrees
· 1970 Olds Distributor (no vacuum advance)
· Two Winfield SR carbs (two are blocked off) on a single plenum log manifold
· 3.54 rear end
· ’31 Buick 3 speed trans

The engine will not idle below 950 rpm and has a big flat spot on initial acceleration.

I plan to add a vacuum advance (adjustable), change carburetion, and advancing the cam a few degrees to help low end. I also have the original 4.45 rear end gears, but they are a little lower than I want. By changing tire size I can get an effective 3.80.

I am looking at a pair of the new Stromberg 97s, Edelbrock 94s, or Rochester 2GCs. I am concerned that these options might provide a little too much venturi for low-end torque. Would a pair of single throat carbs be better? If so, what?

My cam theory is pretty rusty as I have not played with it in over 40 years. Any suggestions on cam timing? I was thinking of advancing it about 4-5 degrees. Too much? Too Little?

Any comments, recommendations, or other suggestions would be great!

Pat

[theoldguy]

How much total timing are you running ?? That is a lot of cam for a straight eight I would think you need 10-12 degrees initial and 34-36 at 2500 RPM to make the car move . advancing the cam will help bottom end .

[Pat n Pat]

We are running 12 degrees initial, and 32 degrees at 2500. Any suggestions on cam advance? Carburetion? Rear end ratio?

Pat

[pmuller9]

John DeLong cam; IO @ 8 degrees BTDC, IC @ 42 degrees ABDC, max @ 107 degrees

Are these specs @ 0.050 lobe lift?
What are the specs for the exhaust?

[Pat n Pat]

All measurements are at .050

There is some confusion in the documentation as it says that the duration for both Intake and Exhaust is 230 degrees at .050. However, in a couple of places it appears to be 234 degrees.

IO 3 BTDC
IC 47 ABC
EO 46 BBC
EC 8 ATC

Pat

[pmuller9]

All measurements are at .050

There is some confusion in the documentation as it says that the duration for both Intake and Exhaust is 230 degrees at .050. However, in a couple of places it appears to be 234 degrees.

IO 3 BTDC
IC 47 ABC
EO 46 BBC
EC 8 ATC

Pat

I would tend to believe that the intake duration is 230 and the exhaust is 234. This would put the intake lobe center at 112 and the exhaust center at 109. The cam would then be 1.5 degrees retarded from a straight up position. You could certainly advance the cam so it is 4 to 6 dgrees advanced.
I would put a timing tape on the harmonic balancer and actually find out where the cam is at and check the specs.
What engine is your 283 based on? 273?

[pmuller9]

Would sidedraft carburetors be allowed?

I am looking at a pair of the new Stromberg 97s, Edelbrock 94s, or Rochester 2GCs. I am concerned that these options might provide a little too much venturi for low-end torque. Would a pair of single throat carbs be better? If so, what?

The holes in the throttle plate for the Edelbrock 94s measure 1.25 inches.
Is that close to the intake port diameter in the head?

[Pat n Pat]

Sorry about the delay in responding. I have boxes of documentation to go through. Originally we were building a '32 Buick for the Great Race.....then this car became available (with about 5 years of sorting it out!). It just needs to be modified to meet our needs.

First, as to the cam. Just ran across another set of info that sets the IO at 8 degrees BTDC, and sets the intake fully open at 107 degrees. Apparently that is how John DeLong designed it. DeLong was one of the truly great pioneers in cam development. He passed away in late 90's, and the business was passed on. That guy passed away a few years ago, and the business is now known as Spiro's Cams. I know my cam was the prototype, but it is shown on their list of cams. I have written to Spiro to see what info I can get on the cam.

I am going to hold off on any cam re-timing until I confirm my info.

As to carburetion, the existing Winfield SRBB's have a 1-3/8 inch single venturi. Intake valves are 1-5/8. Not sure of intake ports, but they are Siamesed. Side-draft carburetors are allowed if they appear period correct. I would prefer down-draft as It is a lot easier to modify the current log manifold instead of building an entire new setup!

I need to improve my initial throttle response. It is just flat, and have to feather and slip the clutch. I am concerned that two 2BBL carbs will only exacerbate the problem by reducing airflow during initial throttle opening.

My wife is the driver during competition, and I want to make it as responsive as possible for her.

Pat

p.s. Just noticed your question on engine. It is a 273, .060 over.

[pmuller9]

First, as to the cam. Just ran across another set of info that sets the IO at 8 degrees BTDC, and sets the intake fully open at 107 degrees.

This makes the intake duration 230 degrees at a 107 lobe center and the exhaust 234 degrees at a 109 lobe center.
If this is correct then the cam is 1 degree advanced already. You should be able to advance another 4 degrees.
As you advance the cam the cranking compression will increase. I usually see 5 psi increase for every 2 degrees advance.
There are several other things to be aware of as the cam is advanced.

If the engine has high dome pistons to get 8:1 compression ratio, as the cam is advanced the intake valve gets closer to the piston just after TDC. It is a good thing to check if you don’t know how much clearance you have. I keep at least 0.080 inches of piston to valve clearance.

As the cam is advanced the intake valve opens sooner in the exhaust stroke. At low rpms the intake charge can be reversed back into the intake port diminishing the gain by closing it sooner.

The exhaust valve also opens sooner dumping cylinder pressure earlier.

Altogether as the cam is advanced, low end torque increases to a point then there will be a decrease.
Ultimately a cam with less duration would fit your needs better.

I can’t tell what the log manifold looks like from the picture. Long tubes between the log and the head ports would create a ram effect that would certainly help.
If you decide to go with 2 two barrel carburetors, I would consider using 4 long tubes that slowly turn upward 90 degrees, one for each barrel of the carburetor. The Edelbrock 94s have smaller venturi than the Winfield.
The reason I suggested the sidedrafts is they would just need 4 long straight tubes.

As far as the gearing, unless you can add an overdrive you are stuck with gearing for the max mph needed for the race.

Hope this helps.
Paul

[Pat n Pat]

Thanks Paul:

The info on cam advance is just what I needed. I knew it would work, but just how much was a concern. I appreciate the guidelines. I have not heard back from Spiro Cams for documentation (if there is any) on my camshaft. All of the documentation I have is in hen scratches on the back of cereal box cardboard!

What would you recommend for duration?

Yes, we do have domed pistons and I definitely would not want the valves and pistons to meet!

I would love to keep the Winfield carbs (although there are 4 on the manifold, 2 are blocked off). They are definitely period correct. This car was built as a "tribute" to the Red Shafer 1931 Buick Indy 500 Racer that finished 12th in 1931 and 11th in 1932. I have been trying to find someone who really knows Winfields.

The Great Race, Hemming's Challenge, and VCRA events are time-speed-endurance rallies that are timed to .01 seconds. Speed is not as important as accuracy and consistency. Rarely will we ever go over 55 mph (and then only when you get lost!). If I put the 4.45s back in, I will still only be turning a little over 2600 rpm at 55.

I would love to put in an overdrive, there is just not enough room; besides, this car has an enclosed driveline.

The info on cam timing really helps!

Thanks, Pat