When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
If you opt to advance the cam 4 degrees (8 degrees total advance from where you are now) you should pull a head, degree the cam, and check the piston to valve clearance.
My concerns align with scottyp99, that advancing the cam too much would cause a higher dynamic compression ratio. I plan to leave it at neutral
Most NOS cams have wide lobe separations. Why try to reinvent the wheel?
Working on engines is a hobby and I enjoy it.
when this motor goes I’ll try something different next, maybe supercharger or solid rollers. Who knows.
It was more fun to experiment with cam timing instead of just reading about it.
same with lobe separations.
If anyone’s curious I had a performer cam in it before which I absolutely hated. That was definitely a wrong cam choice. But it was the first time I’d picked a cam.
if y’all are curious, this is the dyno graph with the cam installed 4 degrees delayed.
28 degrees total timing
No NOS, this was tuning before spraying.
I never did a pull with 36 total timing, but I’d imagine it’d be an extra 10-15 or so hp.
I know the X axis is in speed not rpm, but for my trans and rear gear 120mph is just over 5k rpm 276rwhp, 326rwtq
It actually takes smaller than 64 cc heads or domed pistons to make above 10.5 compression in 355 motors.
Randal, please tell me about your NOS system, transmission mods, and rearend.
I agree on the CR, I think I’m right near 10:1.
trans is just a stock TH400 with a high stall converter, at 2800.
rear end is the stock 3.08
NOS is a 125 wet shot, push button activated.
Bigger rear gears would make a huge difference in times, my 60 foot is pretty bad at 1.96. Or even a higher stall converter. But as of now I don’t worry about breaking any components.
Like you said, those 3.08s are really hurting you. When I changed from 3.08 to 3.73 in my car, it took about 4 tenths off my 1/4 mile ET.
My car runs a little less 1/8 mile MPH than you but 2 tenths quicker ET due to better 60 ft times.
See the 1/8 mile (660 ft) data on time slips below. (Right lane).
Are you using drag radials?
Way back when my vette had a H-flat cam and 355 ci, built up th350, 3500 stall 9.5 inch vigilantly TC with 3.55 rear gears. I used Goodyear drag slicks. I was into the ET bracket points series division 7. (Arizona, California, Nevada)
Consistency is everything. So I bought the Pro and 5/10ths practice tree. Highly recommended. One other item that I kind of evolved into was how to do consistent launches without a trans brake? When you power brake at the tree and you are attempting to hold your gas pedal just below the rpm where your power can overcome the rear brakes and actually start to push the car forward. So when the lights come down you are releasing the brake and going to WOT. to get as near to .000 reaction time. I figured out that turning my idle up to 1600 rpm in the pits really helped. Same rpm launch every time with left foot braking. I installed a front brake line lock for consistent burn outs. Very easy to install a TCI roll control on our vette M.C.
Like you said, those 3.08s are really hurting you. When I changed from 3.08 to 3.73 in my car, it took about 4 tenths off my 1/4 mile ET.
My car runs a little less 1/8 mile MPH than you but 2 tenths quicker ET due to better 60 ft times.
See the 1/8 mile (660 ft) data on time slips below. (Right lane).
Are you using drag radials?
Thanks for that, that’s a really good data point for future plans of the car. You can see it, 2 tenths faster from 60 ft on.
and yes I run Mickey Thompson drag radials, no slipping at launch.
If only differentials weren’t so expensive lol
Last edited by randallsteel; Apr 1, 2023 at 11:14 AM.
Way back when my vette had a H-flat cam and 355 ci, built up th350, 3500 stall 9.5 inch vigilantly TC with 3.55 rear gears. I used Goodyear drag slicks. I was into the ET bracket points series division 7. (Arizona, California, Nevada)
Consistency is everything. So I bought the Pro and 5/10ths practice tree. Highly recommended. One other item that I kind of evolved into was how to do consistent launches without a trans brake? When you power brake at the tree and you are attempting to hold your gas pedal just below the rpm where your power can overcome the rear brakes and actually start to push the car forward. So when the lights come down you are releasing the brake and going to WOT. to get as near to .000 reaction time. I figured out that turning my idle up to 1600 rpm in the pits really helped. Same rpm launch every time with left foot braking. I installed a front brake line lock for consistent burn outs. Very easy to install a TCI roll control on our vette M.C.
that’s a really good idea with the idle launch. I do the power brake launch around 2000 rpm. I do have a line lock installed to make burnouts easy, it works great.
You used to be able to buy rebuilt iron vette rearends for about $1500 ready to run with your choice of gears and just install two super 17 spline yokes for about another $600. Add a HD rear end cover and tap the bottom for an oil drain. I actually later bought an additional vette rear diff from a guy parting out old vettes and rebuilt it so I would have a ready spare.
You want to limit your rear tire vertical travel. Squatting on launch puts a terrific load on the yoke ends and posi central cross pin.
