The near-stock 401 build I did for my red '66 spec'd out at 9.8:1 CR with a 0.015" thick steel head gasket. Heads were 126 cc, Zollner piston dome 46.5 cc, head gasket 4.5cc, deck clearance of 0.45"= 10.25 cc, and a bit for ring land clearance. Using a 0.045" head gasket would drop it to 9.15 CR, and a 0.036" gasket would result in 9.4 CR. The 9.8 I got seems consistent with others have reported on near stock builds. To get the advertised 10.25 CR, items like deck height and head chamber volume would need to be machined to the minimum NHRA permitted spec. See those specs on the NHRA site. I don't know where TA got their rocker ratios from, but I measured much different.... My stock '66 401 cam had 0.267"(I) and 0.261"(E) lobe lift which at the valve resulted in 0.448" and 0.425" valve lift. Do the math and it's a 1.63 to 1.68 ratio rocker ratio at max lift. This is measured with a solid lifter and about 0.002" valve lash. Tom's roller rockers produced 1.9 ratio, and the old Buick adjustables were about 1.5 ratio. TA 25 cam looks good on paper for mild performance use. Joe had some bigger cams made by Comp that worked very well for him, take a look at those. In general, a milder cam will make more low rpm torque, a bigger cam will lose some there, but have gains in higher rpm's. Your choice should be based on how you drive it and where you want the power band. If you want to try different cams on a computer, Dyno 2003 is a fun program that can get very addictive! (right Andy?):laugh:
Bob - The car sounds awesome! I am really digging the sound you got out of it. I may have to go for something like that. It just has that nice performance/muscle sound. Me likey! Thanks for the info Walt. I new I could count on you to chime in, lol. I think the stock rockers were advertised at 1.4 were they not? And maybe that is were TA got their number. It's funny you mention how your stock rockers measured out. Working on Don's engine the other day we measured the lift he was getting out of the stock rockers on one cylinder and found he was getting around a 1.6 ratio as well. We didn't take the time to measure them all yet, but checked the one cylinder out of curiosity. Was a pretty interesting outcome. That 1.9 out of Tom's rockers is huge. And I hate to ask this, but who is Joe? I would like to hear about the cams he has made. I am not going for anything huge, I am just looking for a mild to moderate cam that is going to work well for running a 10:1 compression on pump gas. But it also needs to sound and perform well. Just cause a cam sounds good doesn't mean it performs well. I know I want to have my cake and eat it too. Or at least be able to touch it and smell the buttercream frosting. :TU:
Thanks Peter! I am familiar with the username, just didn't know him by first name. But now I do, lol.
Walt - I think I figured it out with the TA thing. I pulled up their catalog and it makes a little more sense. Kinda disappointing but it does make more sense. Here is what their catalog says about the TA-25. Stock Ratio 1.4 - .415/.433 Rollers 1.6 - .474/.459 Dur @.050 - 218/228 Dur Adv - 280/288 LC - 110 Info on the site appears to be jacked unless they recently changed the grind.
Wow Now you guys have me wondering what's in the replacement engine I purchased already rebuilt and ready to go. What piston, cams, etc. Guy couldn't find the paperwork on the rebuild and parts. Figure it all out Johnny, get it running and let me know. I may have to copy a few things. Sure wish dad was still here to help me out with this car. He was a car/motorhead from way back.
Very addicting Walt! :grin: The stock rockers are suppose to be a 1.6 ratio. Supposedly, with higher lifts from a more aggressive cam, the geometry is as such that they loose some of their advantage, thus resulting in something closer to a 1.4 ratio. I haven't looked at the geometry or measured it for myself, so I can't say that's 100% accurate. Perhaps Tom can chime in, I think I remember him discussing it before.
you are right saying that just because a cam sounds good , dont mean that it runs good.....:Brow: A lot of guys buy too much cam... dont overcam your engine,,, it is far better to slightly undercam one than to overcam....The old 091 factory cam was designed by Duntov and I ran it with a 950 holley 3 barrel and it ran just fine.... I have seen it run with every thing from a single 4 to 3x2s to 2x4s and my beloved 3 barrels and it ran good with all of them... sadly it has gone to the great engine factory in the sky... but you can find cams out there that is close to it or better.... just dont over cam.....:Smarty:
Yeah, I did that.... Built the engine in my blue '66 when I was 16 with a big ole Isky cam. Sounds awesome, low-end torque is a little lacking, but comes on strong over 4000. Runs strong in the 1/4 tho. Back then ,we didn't have the internet (or even computers!!) to do research.... just Hot Rod magazines and the guy at the local speed shop. Someday I'll make another vid to post here.....amazing that we can do that with a phone the size of a wallet..... that was unthinkable in 1977.
I called and talked to Don on the way home from work yesterday and were discussing all the good information that has come out of this thread. Since I am new to this engine building thing I am still trying to wrap my head around it all, but am making large strides. So basically this is what transpired from our conversation. After talking his ear off and voicing my concerns and opinions I received this response: "You make my head hurt. Here is what we are going to do. I am going to pick a cam and you are just going to like it!" All I could do was bust out laughing. If you know Don then you understand his humor. But he is probably accurate in his statement. Keep the info coming fellas. This is all good stuff. You can't speed learn Nailhead building 101 without the input from those that have been doing it for years. I appreaciate everyones input about the ignitions and the concern in helping me make sure I get this right as far as dynamic compression and all. If you can think of anything else, lets keep this thread rolling.
Todd - I wouldn't worry about it too much man. More than likely however the guy built it, it probably put the engine in the 9.? : 1 ratio so you should be safe. If he bought pistons off the shelf somewhere I would bet its probably close to 9.5:1 due to the pistons and that he probably used composite head gaskets. And if you are just trying to get your car back like new for the most part, then you should be set. The main concern here is that I want to go with a true 10:1, so I am playing with that fine line of having too much compression and not enough cam to run it safely on pump gas. Starting out I was planning to build a fairly stock Nailhead, but the more I get into it some small details are changing. Especially since I want this 10:1. So what I may end up with is a bigger cam and a switch pitch that stays in high stall all the time until I get out on the highway or to the track. Lol.
