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Thumpr cam on sbc?

I want to know some peoples opinion on this since I have no idea about this stuff and I’m very inexperienced. I have a 1987 sbc 350 that I’m going to put in my 1968 firebird. It makes 250 hp and 350 lbs of torque (its a truck motor because it was decently cheap from ATK). It has a carb so no worries about it not working with injection. I have patriot long tube headers to go in it and a wieand street warrior intake manifold. “stock” cam thats in the engine right now

  • Camshaft: Hydraulic flat tappet
  • Cam Duration @ 0.050 in.: Intake 194 / Exhaust 202
  • Cam Lift: Intake 0.390 in. / Exhaust 0.410 in.
  • Lobe Separation Angle: 112 lsa
  • Timing Chain: Single roller
    And here what I want to throw in it
    0.479 int./0.465 exh
    duration- 279 int/297 exh
    107 lobe seperation
    If I did buy this I do realize I need the better springs and I would buy some hardened push rods. This is what I don’t know, should I buy all new rockers that match the push rods as well? The engine hasn’t been put in the car even and came out of the crate not too long ago. Can I get away with the factory rockers and hardened pushrods and new lifters? This isn’t a race situation, I just want to be able to drive the thing for a decent amount of time with a nice idle. Bonus, I stripped some threads in the crank since i don’t believe the crank pulley bolt was long enough even though ARP said it was meant for a sbc, so I’m a little worried if I put a tool in there it’ll do some more damage. Should I helicoil it or tap it to metric? Im not putting a new crank in it since I’m not looking to break the bank and I want this engine done soon as possible. This is going to go into a 1968 firebird and I’m only looking to drive it. I’m not building a 1000 horsepower motor, and I actually don’t even care if I lose power because the sound matters more to me. Any help would be greatly appreciated

What crate did the engine come out of ? I’d call them and ask what cam gives what qualities… in fact all cam mfg’s will be able to tell you what cam profile produces what results. Its a known formula they are all familiar with.

We could provide you with generalities, but why? Just ask the cam people…or the engine builder if it was a crate motor. It’s illogical to ask people in a forum for this data as the mfg’s have it all at their fingertips.

Or you could research on the net and get this info easily enough.

If I was you I’d just asking the crate motor builders…and or the cam mfg’s both. You will get the data, quick, fast and in a hurry.


Alright I’ll try and ask comp cams. It was just weird because some people said it works great stock, no problems and that’s actually what summit says too just needs different springs. But there’s a couple people who say it bends pushrods and you need new everything. Also people say you need new rockers when you get new pushrods and I’m just a little confused on the whole matter. I don’t really know what I’m doing since all I have is highscool shop and youtube backing me up. This will be my first time modifying anything and I really don’t want to screw it up

They wont be confused at all… All this data is a known quantity…esp for the sbc 350. Its all right there in front of them backed up by hard facts and measurements. No confusion involved.

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What year is your firebird? I assume it’s not a 1968. So, what type of exhaust are you going to run? Stock manifolds? Single cat? Carb? Stock torque Conv? Stock rear end gear ratio? So , a cam designed for no low end power? Typical novice mistake.

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I apologize… I should have answered your original question in a better manner rather that given you the info I gave.

Instead of just trying to answer you by directing your attention to the information source…

I should have politely pointed out that you did not provide us with the information we need to actually try to answer you on the stats of what cam and what profile etc.

We… and you… need to know what exactly you are trying to do with this engine and vehicle… we dont know the vehicle either…

All answers that would be useful to you would be based on what you are trying to do… Is this engine going to power the worlds most powerful water pistol? Is it going into a Ski Lift ? Is it going into a Mazda Miata? Is it… well you get the idea at this point.

What is the engine going into…and what are you doing with it… The answers will dictate what characteristics the engine would require in order to serve your purposes…whatever they are.

SO… this is the Pre- Answer basically… Need to know all that before you can dial in the engine and its characteristic

This is what I should have responded with initially… and I am betting that many if not EVERYONE will agree with me temporarily…

THIS even would be an Exceedingly Rare and Joyous occasion believe me.


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The classic rabbit hole. That truck cam needs to go but be wary of picking out radical cams thinking it alone will make huge changes. A moderate version of the “car” motor will be best if you’re not also changing heads, intake etc because you won’t realize the increase and in fact the cam will be too big and actually hurt performance. I didn’t look up the cam you selected but you should carefully compare the specs and unless you’re ready to start stripping back to the quick and changing a whole bunch of stuff, just get rid of the truck version of parts on this motor and swap to the car version.

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The thumper cam is going to want better heads, higher compression and better exhaust. It is also going to need you to check for interference between the piston tops and the valves. The data you posted is apples and oranges…

You say the “cam lift” of your cam is 0.390/0/410… No, that is the valve lift. Compare that to the valve lift of the Thumper… 0.479/0.465. That might make the valve hit the piston tops. Probably not, but you should check.

The duration in your cam is measured at 0.050 lift while the Thumper is gross duration, usually measured at 0.004 lift. The 0.050 lift specs are 227/241. The cam might make a nice sound in the car but it will hurt low end torque and driveability. This is too much cam.

As @TwinTurbo says… classic rabbit hole!

Oh, and I’d guess you stripped the threads on the crank snout because you tried to pull the balancer on with the ARP bolt. The bolt you have is correct, the way you tried to use it is wrong. Use an harmonic balancer installer. You should be able to clean up the threads with a fine tap.


rabbit hole? ditch the old motor and get a LS. now you can spend more money. i think the carb intakes are only $399?

Keep in mind that valve lift mentioned is for the stock rockers. Change the rocker ratio and the valve lift also changes. There are also issues with pushrod length and whether or not you shave the heads. I assume you are not doing the latter and assume (right or wrong) it hasn’t been done before.

So it is a 1968, sorry I didn’t think the car would matter much because it’s just the engine. I have patriot long tube headers and a wieand intake. It’s with an m20 transmission with wide ratios with the 1987 truck motor. I also edited the original post and I should’ve said I’m not really caring about massive power gains and if it loses some power then so be it, I just want a cool sound because this is not a race car.

Alright thanks. Maybe I’ll try and find something less aggressive or just ditch the plan all together. I don’t really have the money or time to do a full build or something for lots of reasons. Also all I was doing was trying to tighten the crank bolt down once I got the harmonic balancer and pulley installed, so I’m a little unsure of what went wrong there.

Thanks for the all the replies everyone that did but it’s making me realize I think I’m in over my head. Thank you!

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I was guessing. I assumed you had a 91 with a small v6. Ala ricer setup. But you have 1968. Duals will fit fine. You have headers already. What muffs do you have now? Gotta believe you have everything you need to make noise. 68 firebird is nice. Or could be.

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I don’t actually know but the it sounded pretty good when it was running with the other 87 sbc.

you Have a real car. Vs a poser ricer Honda with a 4 banger. You don’t even have to start motor to look good.