Guys: I have a 69 vert with a std 350, 47 heads, modified with a q-jet on a Pontiac cast iron intake, and cam specs .407/.411 and 200/210 duration. This combo is bolted to a TH350 and 2.78 open rear(AC car) I have an offer for a pair of #18 heads(350 HO from 68). I feel that my carb is already on the rich side, so it might work without rejetting? Should I get a bigger cam? What about advancing it to get max low end torque? What ignition curves are needed? Any opinions are very welcome!!
Step up for a bigger cam at the same time, not much extra work when you have everything apart. The 068 cam is a very good street cam, and the extra overlap may drop the octane requirement down to run straight premium pump gas (at least at my altitude).
Just an FYI. I'm using a set of 67 heads on a 350 I'm building. These have 2.11 intakes and 1.77 exhausts and with a .030 overbore on the cylinders the exhaust valve will hit the cylinder wall at about than .500 lift. Make sure you check for valve clearance before you torque them down permanently.
-=>Lee<=- Due to budget constraints the "light at the end of the tunnel" has been turned off!
Where are you in Wisconsin? One of my plans for the winter was to put a set of #16 heads on my 350 and your tip about the exhaust valves has me spooked.
John, I'm near Green Bay (little town called Algoma.) Where are you? Right now my block is at the machine shop, but they should be able to clearance the top edge of the block to make sure the valves don't hit (per the machinist.) The 400 block these heads came from had a much larger bore. I put the heads on the block (NO gasket) and measured. At .490" lift (at the valve) the valve would contact the side of the bore.
Sorry, don't want to steal the thread. Lee
-=>Lee<=- Due to budget constraints the "light at the end of the tunnel" has been turned off!
Tom(and everybody) As you might know gas is some close to $7 a gallon over here, so I kinda want to emphasize the mileage in whatever I decide to do. The 2.78 will stay, and I hope to be able to beef the low end torque as much as possible. No need for hard revving. My thought is this: Swapping the heads as is, get a new cam(067 or similar; is there a 066?) tinker with ign. curves and maybe jets/rods. How about advancing the cam? In theory it will bring up low end tq at the sacrifice of high end hp, which I really dont need?? Anybody with experience on this? Also, shouldn´t the intake valve size be good enough anyway as long as the rpm is kept down?
Well Hansi you asked for opinions: If you want gas mileage, get an overdrive transmission. The short first gear of a 700-R4 will make up for your tall rear end. A 200-4R is another nice option for OD.
Yeah, I know! :p But I can live with the gas mileage I got for now, or a tad worse if needed; I just try to minimize the mileage damage while getting as much as I can out of it
A rough rule of thumb: if you want more power, open up the intake side of things, if you want better gas mileage, clean up the exhaust. The shorter the cam, the more cylinder pressure you'll get. An RV type cam uses "faster" ramps on the lobes and manages to lift the valves a decent amount with less overlap. Porting will give you more power and gas mileage when done with that in mind. Free flowing exhaust manifolds or medium sized headers with a decent exhaust system including an H-pipe will also give the best of both worlds.
Proper tuning of the final combo is critical. Getting the right mechanical advance curve will give you the best power, and a properly adjusted vacuum advance curve will give you the best mpg. Jetting the carb (as you noted) is very important as well, gotta be lean to be green (or save as much green as you can) under light-medium throttle.
Next, the right gear will get you off the line and rolling more efficiently, and a lock-up convertor in an overdrive transmission should make you the mileage champ!
