Cam for a 512

Thought I had better start my own thread before I mess up another one.

I need to make a decision on a cam for my combo. The one I have might be just fine, and I've contacted a few cam grinders and received back two very different cam recommendations.

My combo is a 68 roadrunner, 3600 lbs with me in it, 3.91 gears, what should be a 4500 stall 9.5" converter, 512 low deck, 10.8 compression, Indy s/r heads with max wedge ports currently getting worked on at M&M, Indy single plane, AED 1000 hp. The cam I have now is a solid roller single pattern 292 adv 261@50 .648 lift on a 108 l/c installed at 104. The intended use here is street strip, hence the low compression and modest gearing. I only drive it in good weather and don't go too terribly far with it. I just want it to go as fast as possible at the track and I'm not too concerned with street manners. If I have to do maintenance on it every year, that's ok with me.

The first cam that was recommended was a solid roller 276&50 .660 lift intake, 284&50 .664 lift exhaust on a 112 L/c they didn't say where they wanted the cl to be.
the second one was another solid roller 263&50 .675 lift intake 269&50 .650 lift exhaust on a 108 l/c installed at 104.

Quite a bit different I would think. What would you guys do here ?

Your current cam seems fine to me for 512 inches with 10.8 compression. I wouldn't go much bigger that is for sure. The 263/269 cam that someone recommended for you would also work if your valve springs are good for the extra lift but I really doubt you would see enough difference to justify the cost of switching.

Thanks Andy, this is was what I thought to begin with, but it can't hurt to ask about these things while it's still on the engine stand. The cam I have now was what was recommended by muscle motors a long time ago for my 451.

Since the heads are off of it and in the shop. Maybe I could have them shaved a bit more to get the compression up. the 10.8 seems to limit what I can do.

Well at 10.8 you should be able to run pump premium. If you go much higher than that then you need to mix in race gas which gets to be expensive and a hassle. You'll be somewhere in the 650 hp range with your current engine which is pretty respectable. Not a lot of 650 hp pump gas cars cruising around so I'd put it together and run it.

My 517 C.I.(4.300 stroke in a 400 block) pump gas 3450 lb Duster with a similar motor and heads ran bottom tens(10.001) and high nines on Oregon 91 octane pump gas through the 3 inch exhaust at Wodburn Or. in the summer That cam was a Com Cams with 260@.050 and .420 lobe lift on the intake side, 266 @.050 with .409 lobe lift on the exhausts side with a set of Harland Sharp 1.65 ratio rockers Try changing one thing at a time so you can see real world results on your own Let us know what they are also

Ok then, well I guess I'll keep the cam I have for now. I think I'm still going to look into getting my dynamic compression up to about 8.5 though.

I think the first change I would make is higher ratio rockers.

Have you run the eng with the cam thats in it and if so how does it run ? Ron

How much is it raced VS street driving.. have
you done a compression test.. what is it... I
wouldnt waste the money on a new cam.. your
very close now

I did run it when it was a 451. It seemed ok then. No problems really and I drove the heck out of it on the street. Was a bit of a disappointment at the track, but it had other issues. Lets just say finding a good shop is not always easy.

I was just reading some of the things posted in Tex's 505 thread, and thought that perhaps a bit more cam would work out well for me, as now would be the time to do it. It's good to get feed back from people much more experienced with this.

I would say about 60/40 street to track. My house is literally 5 minutes away from the front gate at IRP.

No, haven't done a compression check.

Since it was a bit of disappointment at the track
I would ask what was your 60' time.. that tells a
lot

I don't have a time slip in front of me, and where they are now is a bit of a mystery.....getting married means not knowing where your stuff is now apparently. But as remember it was 1.65. It didn't dead hook.

Didn't miles an hour all that great either.
11.48 at 118.5

Something does not seem right. Seems like you might have another problem that you should find before replacing the cam.

Yes, for sure. This is a new motor though, not the one that ran the 11.48. I'd like to get this one right so I don't have another underachiever.

Besides issues with the exhaust (3" pipe attached directly to the 3 1/2" collector, poor muffler choice) the dynamic compression was pretty low 7.35. I don't remember what the cranking compression was, that was a while ago. The carb was on the small side too.

There isn't quite enough info to tell if you could/should run more cam than you have now or not.
Primarily, header size and the make up of the exhaust system.

My preference is to build to a targeted goal, then work towards that end.
As long as the goals and budget are on the same page, I find that to be a better way to approach it.

The headers are the TTI step headers for Indy heads. 2"x2 1/8" into a 3 1/2" collector. That goes into a Dr.Gas 3 1/2" X pipe that reduces down to 3" after the X. Then it's to the biggest case 3" Magnaflows and then it's 3" mandrel bent over the axle to the back of the car.

I really don't have a set time I want to see, so I'm probably not approaching this the right way. I just want fast within the limits of pump gas and 3.91 rear gears, and I can go to e85 as that's pretty easy to get here.

Without a specific goal in mind, about the best I can offer is the cam you have is appropriately sized for pump gas and 3.91 gears.
Since you already own it, I'd just try it and see if it runs well enough for you to be satisfied.

What carb...........that can make or break good 60`s and overall driveability............

That makes sense. The general consensus seems to be run what I already have as it's not bad, make sure everything else is good, see how it runs and go from there.

So that's what I'll do. I will be checking where this cam is installed at as I don't trust anyone anymore.

On that 451 motor I ran an old Holley 950 HP, which I still have. I also have a Quickfuel 950 with downleg boosters, and an AED 1000Hp with their new wazoo annulars.

And if you do need a cam you can regrind the roller you have up to another ~8-10 degrees @.050 and generally +/- 2 degrees on the lobe spread. you'd have to send the core to be sure but generally you can get at least one regrind on a roller Billet...for about a third the cost of another new one.

Any mods done to the carbs to clean em up down low and transition into the cruise then wot?

Thanks....I will keep this in mind if, or when, I decide to go to a bigger cam.

The holley and quickfuel haven't been worked on in those areas. The AED I'm not sure. I contacted them and they asked me a bunch of questions about my car, and said we can make something for you. What all has been done to it I honestly don't know.

Gotcha................

4500 stall isn't what I would predict from such a big converter.
Where does it actually stall, and flash?

Targeting a specific DCR isn't a useful goal, what you want to determine is your knock limit - but that varies quite a bit depending on too many things to pick a specific ratio.

About all I can tell you is on the 10" behind my 451 I never saw less than 4500rpm at full throttle. The 9 1/2" I have now I haven't run yet, but I'm kind of hoping for similar results. At least that's what I tried to tell them when I ordered it.

OK..........So I decided to be a jacka$$ and disregard all the really good advice I got here from everyone and got a new cam based on the recommendation of the local shop here in Indy ( No NOT Indy Cylinder Heads !)that went through my heads. The flow sheet looked really close to what Dwayne Porter gets out of a set of S/R heads so I felt good about the results, and that his bench is probably fairly accurate.

Intake Exhaust
.100 73 60
.200 149 116
.300 214 167
.400 275 192
.500 319 224
.600 336 240
.700 350 255
.800 365 265
.900 360 269

Cam is 276 intake 284 Exhaust @ .050
.682 Intake .667 exhaust
110 lobe separation.

Just to add a bit more, the heads were shaved a bit to get the C/r up to 11.1

Should work well imo.............

Just a wild guess, but IMHO your converter is going to make or break the performance of the motor with this cam.
I suspect it will need to be at least a 5000 stall to get the best out of the car. A 9.5 can be set up to stall that high with a motor that big.
In the end, testing will tell the tail. I would start with a shift loop and see what it does, and if it is soft on the bottom you have a couple of options. You can try the old cam, or loosen the converter, or both, but not at the same time. If it runs a good MPH I would loosen the converter first.
That new cam sure looks to be plenty big, at only a couple of degrees at .050 short of what made 847 hp in my 15/1 528 alky motor, and that motor pulled to 7,000 hard, till it went fat and nosed over.

Where are you planning on installing the intake lobe centers?

gregsdart.....I agree, converter will be critical. Like you said, need to see what kind of miles an hour it gets to decide what to do next.

Cab....I was thinking about 104.

Another question here.

I have an old set of the Comp chrome moly rocker arms that I used on my old roller cam. They worked fine and I had zero problems with them.

I'm running the PAC 1226 springs on it now.

Are those rockers going to be ok with this cam and spring ?

Unless things have changed, no..........

I have a Comp 264/264 HXL lobes 0.446" lobe lift 112 LSA cam that was in the 500" stroker when I was planning on doing more street driving.
It ran pretty good for a dual purpose cam.

That's what I was afraid of. While they worked fine with my old solid roller, I think I was one of the few who had good luck with those in that kind of application.

So.....I can take these to work and install a bronze bushing in them without too much trouble.

I'm thinking a .030" wall bushing would be fine for this.

Would 4640 aluminum nickel bronze work ok for this application ?

Can`t help ya there but it seems the bodys are not as beefy iirc so maybe it`s more that just bushings to fix em..........

I can't verify this with any actual measurements, but other than the bushing and a black oxide finish they sure look to be the same.

At this point I'm not really thrilled with throwing down more money on a new set of rockerarms when my old ones really are pretty decent. I'm going to bush the old ones and run em.

Go for it..............