[MikeEC]

Here's the plan. 1972 SS El Camino auto, 60 over 402 w/ 119 cc heads. Headers and 2.5 inch free flow exhaust, high-rise dual plane intake w/ Edlebrock 750 carb. I want around 1900 RPM cruise at 65 MPH. My calculations say that with a .7 OD 700R4 and 26 inch tires I will need a 3.23 gear. My objective is to build a fuel efficient (read as least 20 MPG, pump gas), torque engine for an everyday driver. I would like to have as flat a torque curve as possible w/ around 400 lb. ft of torque at cruise RPM. Any experience out there with building a torque engine? Do I need to modify my objectives?

Questions:
1. How much compression should I go for. My calculations say that 30cc dome pistons w/ .005 deck will give me 9.5 to 1. Is this too much or too little? Engine must be decked so I have something to work with here. Piston choices are limited.
2. Presently the 292 casting heads have small valves. Should I go with larger valves or would this hurt because I intend to run headers and a 2.5 exhaust?
3. Cam recommendations? I have three cam catalogs and there are some significant differences in their "off the shelf" torque type cams. I called Edlebrock and naturally their Performer Plus cam is the greatest. Their lobe center line is 114 degrees where the "off the shelf" torque cams for Comp and Lunati are 110 degrees. I am not sure about using a dual pattern cam because of the headers and exhaust.

Looking for some real life experiences in doing something like this. I will also be calling Lunati for their recommendations too as they can custom grind a cam for me.

Have A Great Chevelle Day and TIA

Mike Crosby



[This message has been edited by MikEC (edited 12-11-99).]

 

[68Malibu Blown 406]

Mike, I'd be surprised if you could achieve 20 mpg with a BBC even at 400 inches.

I think what tends to kill the mileage on a BBC is the weight of the reciprocating parts, the parts that move back and forth.
That said, for a high mileage piece, I think the lighter you make those parts the better. Look for lightweight pistons and see if you can get the small end of the rods as light as possible. Light valves and pushrods will require less valve spring pressure, and could free up a bit more friction.

I feel the 9.5:1 is about maximum and is about right. I would use the Peanut port heads (not large ovals) because with a small displacement, the smaller ports would tend to fill the cylinders better at low speed. I would install large valves in the heads because I feel that the restriction at the valve seat, could be reduced, and take away some of the vacuum in the cylinder that is working against the piston on the intake stroke. This may also help the mileage.

Camshaft in the 200 - 204 range intake 210-214 exhaust, Elgin makes one that is 204 214 .476 .501 on 112 LSA. That would be about right. For a little more low speed TQ try a 190/200 .450 .465 114 from Federal McGoo.

Use a 750 cfm vacuum secondary.

Mileage????

On my simulator this eng makes 468 TQ at 4000
and 430 HP at 5000.

A camshaft

 

[Ian]

Mike,

I would tend to agree with 68Malibu. It makes sense about the vacuum acting against the piston, however I have been told by a couple of machinists that if torque is the main priority, then leave the smaller valves in.

My 2 cents,

Ian

 

[von]

Mike, For mileage and torque, I would go with a Quadrajet carb. The small primaries and precise metering (for a carb) are the key. von

 

[Jimmy P]

I built a 468 with pocket ported 049 heads, big valves, TRW 2399 pistons (~9.0:1) and a Crower .224 @ .50 cam. Installed it with a 700 R4 and a 3.73 rear gear and a 29" tire and got 19 MPG cruising @ 60-65 mph. Also in the mix was a Jacobs ignition, Super Comp headers and a flowmaster exhaust. It can be done!