Race cam in autocross?

[Ponder]

I’ve autocrossed the car for years and have been trying to deal with the lack of low end power for a decade or more. I know… that’s a long time. The cam is an Elgin(?). I have the card that that has the lift and dwell on it somewhere. It’s very peaky. It worked very well at nationals except for getting off the line, but local events are way tighter than nationals and the car bogs down several times on a typical track. The leaving it in second and waiting is torment.

I’m working on shifting back up into first more often than I’m comfortable, but I’m not sure I’ll be able to make that work.

I’m thinking all of the peakiness is coming from the cam. The ztherapy carb be contributing.

Giving up some peak power in order to get a wider power band seems like something that should help. Does a milder/stock cam seem like the way to go? Would a stock cam work?

Thanks,
Steve

[david premo]

Sent you a pm

[Stick]

Which rear end gears do you have? A change there might also keep you in your sweet spot. If anyone can get you pointed in the right direction D Premo can

[theunz]

Obviously a cam that makes it power up high is not the hot ticket for a tight autocross course. I run a B cam with Solex’s and never seem to bog. I’m sure the 4:62 gears are a big contributor. The downside is that on some of the longer sections I’m buzzing redline. I’m in the process of changing to 4:10’s but that’s a story for another time. If you can get a B cam I think you will like it, and cams are easy to change.

[Gregs672000]

I'm sure you'll get good advice shortly... it would be helpful to have your current cam specs, especially if we get duration at "50 thousands"... duration determines most about where the engine makes power. Give us an rpm range for your current cam (describe the peakiness) and where/rpm you need it to work.

Many many years ago, as a twenty something I used to go bug a local Datsun Z car repair and former racer guy about my Roadster. He told me about a 2000 Roadster that dominated the local autoX circuit running a cam that was all about low end torque. Had nothing past 5500rpm, but down low it was a "monster" by his account that few could compete with.

Keep us posted, and good luck! I'm happy to share what works for me, but my engine is not stock. We'll find out how that's worked out... on the dyno Tuesday, hoping to not be humbled!

[Ponder]

Which rear end gears do you have? A change there might also keep you in your sweet spot. If anyone can get you pointed in the right direction D Premo can

Greg, I’m running a 5.13:1 that I got from Bill Wessel a few years ago. I had a 4.88:1 that came with the car. It didn’t seem too bad. I’m also running a stock 4-speed because second in the four speed is a better ratio than it is in the stock five speed. That seemed odd but that how I remember it. The one problem with the four speed is the huge drop in third. I think I sometimes think I need to shift to third at around 7000 instead holding second for longer. I didn’t have to shift to third at nationals except at the finish on the faster course.
Thanks.

[Ponder]

I’m out of town this weekend and doing this on my phone so I might have to dig into things more on Monday. Thanks for the help.
I feel like it runs between 4.5k and 8k rpm. I have an autocross next weekend so night to be able to pay more attention to the bottom end then.
A question that I think I should know the answer to by now: what’s a B cam?

[rwmann]

B-cam was provided with the Solex 44PHH-2 setup. Higher lift, longer duration. Made ~10% more power out of the box. A little lumpy idle, power comes on above 3000 rpm.

There was also a C-cam, a Racer Brown cam, and an Iskendarian cam, each with even longer duration and higher lift, said to require revised rocker geometry.

[Ponder]

Are these 2 liter cams exclusively? I assume there are cams out there for the R16.

The rocket geometry aspect worries me a bit . I broke a rocket shaft a few years ago and replaced it with a stock one. I don’t remember the stock cam looking different from the original, but I’m not sure it would be obvious. It’s running pretty normally.

I really need to find the specs of the existing cam. Monday.

[Ponder]

Are these 2 liter cams exclusively? I assume there are cams out there for the R16.

The rocket geometry aspect worries me a bit . I broke a rocket shaft a few years ago and replaced it with a stock one. I don’t remember the stock cam looking different from the original, but I’m not sure it would be obvious. It’s running pretty normally.

I really need to find the specs of the existing cam. Monday.

[Stick]

R16 Cam specs from the tech Wiki

http://www.311s.org/pmwiki-311/pmwiki.p ... n.CamSpecs

If you know what you currently have you might be able to determine which grind might offer different performance at the rpm you’re looking for?

Sounds like you have a nice set up! Best of luck.

Greg

[theunz]

For some reason I thought you had a 2000, anything I wrote about the B cam is irrelevant. You must have really tight courses if you’re bogging in second with 5:13 gears!

[Gregs672000]

^+1! I was thinking U20 as well! The R16 cam is much harder to swap out vs a U20...

[david premo]

Hi Steve,
I did note that your car was a 1600, and I would still be interested in seeing if we could find a cam or tune that would improve the throttle response much earlier on. I have a number of grinds to choose from, I think we should be able to wake up your engine.
Dave

[fj20spl311]

IF I had access to a dyno I would try advancing the cam timing for more low end torque.
2nd on the 4 sp and 5sp are very very close, if you were using 1st or 3rd then a 5 speed would be better because the rpm drop between gear is much less.