I'm looking for some good advice from Nailheaders. Long story short, I had a race engine builder rebuild my motor last year. He didn't do much to trick it out, but he zero decked it and had Elgin Cams grind a cam to his specs. Please bear with me as I don't know much about the numbers and I'm reading off the card. .484 lift in/ex, 0 clearance in/ex, in opens -1, in closes 39, ex opens 47, ex closes -9, duration 272, checking clearance on the ex side 110, corresponding number on the in side 118. Then there are a couple numbers without reference; 114 near ex opens, and 218 @.050 near ex closes. My main problem with the result is that I've lost much of my punch (low end torque) off the line (but it's great from 3-5k). This is for a strictly street application but I would like tire smoking power off the line - I know it's possible. I have a 3spd ST 400 with Switch Pitch (my only saving grace right now) and 3.08 gears which put me at about 3000 rpms at 75mph. I have thought about lower gears but it would be nice to keep it freeway friendly. Btw, it's a 65 Riviera. Thank you for your time and consideration, Zach
If you want , ya ain't gonna get it with 3.08 gears, IMHO. If you want to do 75mph at 3k, use the 3.08's, but you can't have it both ways without overdrive. -Bob
Well, that's not always strictly true. I have a fairly stock 401 (SP Trans, 800 QJet, Qjet intake, 3/4 inch open hole inch carb spacer and a HEI converted Distributor, spiral core 9mm leads) and the stock 3.07 rear gears. Admittedly it is an open (peg-leg) rear and not a posi but when I 'mash' it this normally happens. Between the Nailhead Group and this board you should be able to work out what's going (wr)on(g).
I think I'm getting there on carburetion and timing. Advance is set at 34 at 3000 rpms. It started to get a little erratic at 35 so I backed off. Idle mixture is pretty lean (I'm not fouling) and my vacuum is decent 16-17. With this I can peel one tire up to 5000 rpms in first. The next step appears to be degreeing the cam and possibly advancing it depending on where it's at. Above and beyond that, I'm considering a low gear set to lower my low gears and maintain my highway gears. With a 2.75 and a 1.57 I would effectively have 3.38 gears in first, 3.22 gears in second, and 3.08 in drive. Sounds like a pretty good combination to me. Any thoughts? Thanks, Zach Btw Bob, I'm in SF.
I'm thinking if you were happy with the engine before it got rebuilt and now it doesn't have the same punch, gears may not be what you need. I would contact Elgin if your builder doesn't have very clear specs on the cam and find out what you've got. Mr. Elgin has been around a LOT of engines and should be able to let you know if you have an appropriate cam for what you want to do. I've talked to him on several occasions, he is very approachable.
I am not doing the official math, but I think your data indicates a cam with 272 total duration, 218 duration at 0.050 valve lift, 0.484 total lift at the valve, and 114 lobe separation angle [(110 + 118) / 2]. This should be a pretty mild cam, it is not that big in terms of a "race" cam. Actually should be a pretty good street cam. You can advance the cam a bit to improve low-end, 2-4 degrees is common, I would not go more than 4, or you risk valve to piston interference. Advancing the cam does boost the low end at the expense of high end. Your cam already has pretty good vacuum, which tells me the engine is running good. A bigger cam would not reach 16-17 inches vacuum. I agree to check the ignition and carb so they are all working corrrectly before tearing into the engine. Your cam is a little bigger than a stock grind, but still should be plenty streetable. BTW, burning rubber may be fun, but your car is quicker if it is hooked up. For comparison, my blown nailhead has a Poston NH400 cam with 272 intake/282 exhaust duration, 0.486 intake/0.495 exhaust total lift. So yours is pretty similar to mine, just a hair smaller. I just got my heads back form the machine shop so I need to get my engine back together and then i can see for myself if the cam is a good choice. I got the car from my friend with the engine broke, so I have not actually ran the engine to know firsthand. He never said anything about lack of low-end, but then it also has a blower. I just thought of something on your car. Do you run a single four carb? Or dual fours? You might check your secondaries are fully opening, and when they open.
Thanks Bob and Terry, I'll reply to both your posts here. The motor had a flat cam when I bought the car and was only hitting on 6 cylinders so I do have more power now, but it's been a hard won battle - mostly because I have a lot to learn about engines. I just received a very comprehensive email about adjusting my timing curve and vacuum advance (which isn't currently hooked up), so I think I still have some playing around to do. Once I get the motor tuned as best I can, then I think I'll call Mr. Elgin. The general consensus has been that the cam is wrong for the engine so I'm debating whether to degree the cam or just replace it. TA now offers NH grinds and would probably have a good idea of what's best. It's just the labor involved in replacing it - more than I can handle myself. I guess it won't cost me anything except time to degree it. And I'll learn a lot. I have a single Edelbrock 600. A lot of people have said it's a bit small, stock was 625 I think. One guy recommended I find a 66 spread bore intake and use a Qjet. It's also been recommended that I need headers in order to realize the full potential of my cam (now offered for NHs btw). So many variables! Terry, I've been thinking my next car might be a 66 or 67 GTO with a Buick 455. What do you think? Thanks again, Zach
Hi George, I actually do like the look of 67 GS, especially the hood line (very menacing). But I'm in love with the look of the 66/67 GTO - from front to back. The GS definitely seems more unique looking though. What does the 400 designation mean? Not beyond the realm of possibility. Are they hard to come by? Thanks, Zach
Hey Zach,the `67 definatly looks awesome,i think you can find one for a good price,but if u have ur heart set on a GTO its hard to overlook it,the 400 means 400 cubic inches. Thanks
Cool. Just out curiosity, how much does the 67 GS weigh? Are manual trans common or are they mostly autos? Autos, I assume... Zach
They must weigh about from 3600 lbs and up depending on the options and they were on a conv`t frame (boxed)unlike other GM a-bodies,i mostly see autos around,i guess u can find a 4-speed but it wont be easy. Thanks
They must weigh about from 3600 lbs and up depending on the options and they were on a conv`t frame (boxed)unlike other GM a-bodies,i mostly see autos around,i guess u can find a 4-speed but it wont be easy but it should`nt ne the hardest either. Thanks
