Quote:
Originally posted by Don Shillady
Tech1, while you are thinking about cams, let me ask a question. Unfortunately I did not take your short course until my 350 engine build was past the assembly point. Anyway I did not deck the block so I assume the deck height is about 0.025" and I have used the standard gasket for about 0.039" with shaved 882 heads to give 73 cc pockets and flat top eyebrow pistons as 4.030" bore. I am satisfied the C.R. will be low enough that even without much quench I will be able to run with 87 or 89 octane. My question is the cam I chose does not seem to be in the Crane catalog anymore (at least I can't find it online) and the box had two numbers on it. The old number on the box is #10010 but it has a pasted-on label marked "10010" AND in larger numbers "140072", 0.050 DUR I 194 X 204. The card that came with the cam says:
Intake @cam 0.265 @ valve 0.398"
Exhaust @cam 0.280 @ valve 0.420"
@0.005
Intake 22 BTDC 58 ABDC Adv. Dur. 260
Exhaust 71 BBDC 19 ABDC Adv. Dur. 270
@0.050
Intake 10 BTDC 24 ABDC Adv. Dur. 194
Exhaust 39 BBDC 15 ATDC Adv. Dur. 204
I realize this is a very conservative low rpm torque cam, but (!) when I run the rpm numbers for cruisin' on two lane black top roads in the local area with a 3.55 rear ratio and a 700R4 4th OD gear of 0.7, I get 1446 rpm at 50 mph and 1591 rpm at 55 mph (235/75/R15 rear tires). It seems to me that I need torque in the 1500 rpm range to avoid downshifting to 3rd or lugging in OD. I am hoping the low gear of the 700R4 will give a good launch since the 700R4 has a lower 1st gear than the TH350, so the problem is to maximize torque in the 1500 range. Now here is the question. I have both 1.5 and 1.6 roller tipped rockers of the simple type from Speedway. IF I RUN 1.6 ROCKERS ON BOTH INTAKE AND EXHAUST WITH THE 882 HEADS I WILL GET 0.424" INTAKE LIFT and 0.448" EXHAUST LIFT. This is still a very conservative lift and the 882 heads seem to offer little flow beyond 0.400" valve lift, so the question is whether it will help or hurt to use the 1.6 rockers? Will the extra lift and short duration and lack of quench lead to detonation on 87 octane? Bottom line, should I use the 1.6 rockers to get a little more torque or will this lead to worse detonation on cheap fuel? I have both a Performer RPM manifold which I am going to remove and a Performer EPS which I think is better for low rpm. I guess I can start out with the 1.5 roller-tip rockers and then experiment with the 1.6 rockers, but I wonder if the 1.6 rockers will help much with only 882 heads or lead to worse detonation on cheap fuel? It also would be easy at this point to replace the head gaskets for the thin set you mention above. Overall I wonder if most folks realize how low the rpm gets in OD? In retrospect I guess I should have gone to a 3.70 rear gear but I can't afford to make that change unless I find out the OD really bogs with the 3:55. I had a terrific ride recently with a guy about 3 miles away who has just finished a Gibbons '32 highboy and he seems to get good mileage over 20 mpg with a 3.23 rear and a TH350 which only has a 1.0 high gear. Maybe there is no way around expensive trial and error but maybe the light weight of the '29 will make this no problem after all? Sorry to test your patience. I just have to get the car on the road because all this speculation is uncertain, but you are the closest I know to a "brain dyno".
Don Shillady
Retired Scientist/teen rodder
Well in edit mode it was good for me at least to go over all of this and now I realize that I probably will not be in OD at 50 mph but in 3rd with a pretty zippy 3.55 overall gear so probably I should have installed a 3.7 rear gear but I am just going to have to live with the idea that the OD will only be useful for the Interstate! Still that leaves the question for Tech1 as to whether the 1.6 ratio rockers will do me any good on this setup?
IF THIS IS FOR YOUR( PARADE CAR) JUST PUT PREMIUM GAS IN IT AND DON'T WORRY ABOUT IT.