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So I called Thompson motorsports and bought a can based on there sugestions. Just want some more opinions because I'm kind of scared lol.
I have a 98 camaro that I have completely gutted and I'm puting a 5.3l lm7 in it. The cam I have is a 236/250. Will I have piston to valve clearance issues or will I be Okay? It's a race only car and won't ever see the street again. It's getting a healthy dose of nitrous as well. Not sure how much yet but I'm starting at 200 and going up from there
I can't afford that yet. Heads will come after the 9" rear is finished though. I just bought the 5.3l and the cam. Also bought all the gasket, electric water pump, billet timing set, melling oil pump, arp bolt set, and mls head gaskets.
I have an ls6 intake and all of the stock ls1 stuff still. Something is very wrong with the ls1 though. It lost oil pressure in the middle of a run and seized up.
Next year I will buy a forged rotating assembly and have the block bored to ls1 spec.
Car has a built 4l60 and a 3200 stall. Might go up in stall to 4000.
I'd do something like a 222/234 112+3 or so for good midrange power while still being happy on the gas.
Or a little more top end would be a 224/236 113+3.
Both would drive well, thump a bit at idle, and make good usable power with the 3200 stall in the 5.3 but pick a ton on nitrous. The added exhaust duration would carry the power after peak pretty well NA.
Race only changes things a bit. Closer to your original cam...
But not quite.
234/246 111+3 would be where I'd go. And I'd move to a tight 3600 or 4000 stall.
The 236/250 115 has a lot less overlap than the above cam, so it'll make less power. It also has a very late IVC for a 3.622" stroke, so it'll be lazy in the midrange until the very top of the curve. And even then, it'll be fighting the harmonics of a plastic style intake manifold. You'd rather your IVC be closer to 45 degrees with the 3.622" stroke... which the above cam gives you. And the added overlap will make a ton of power uptop.
But you need more stall to take advantage of it. At least 4000. But with nitrous, you need a 3600 or tighter 4000 stall. So maybe an SS4000 from Yank would work? Or the PA3800.
Race only changes things a bit. Closer to your original cam...
But not quite.
234/246 111+3 would be where I'd go. And I'd move to a tight 3600 or 4000 stall.
The 236/250 115 has a lot less overlap than the above cam, so it'll make less power. It also has a very late IVC for a 3.622" stroke, so it'll be lazy in the midrange until the very top of the curve. And even then, it'll be fighting the harmonics of a plastic style intake manifold. You'd rather your IVC be closer to 45 degrees with the 3.622" stroke... which the above cam gives you. And the added overlap will make a ton of power uptop.
But you need more stall to take advantage of it. At least 4000. But with nitrous, you need a 3600 or tighter 4000 stall. So maybe an SS4000 from Yank would work? Or the PA3800.
Honestly, even with the other cams Jake recommends, I think you'd benefit from a shorter runner. You're setting it up to require RPM to run good, you need to set up the rest of it to support the RPM.
Honestly, even with the other cams Jake recommends, I think you'd benefit from a shorter runner. You're setting it up to require RPM to run good, you need to set up the rest of it to support the RPM.
MSD short runner you are thinking? 48 IVC with those? Or 50? If that's the case, the original cam may work. Still a dog until you get to 6k... especially if stock 9.5:1 CR with only 328 cubes.
You'll probably want a short runner intake, which will help move the power band to the right, If you're going race only, you thinking carburetor? That will open up your intake options. If you stay stock style, there aren't many options. At a minimum, you'll want the TBSS intake or possibly even the LSXRT. I don't think you have enough displacement for the MSD to be helpful for you
Second, you're going to want compression. LM7 is only around 10:1 iirc. (Edit - 9.5:1) When you cam it, it gets lazy quickly without compression to support it. I would suggest milling to 57cc combustion chambers and running a 0.040" head gasket. And the bigger the cam, the more you'll want the heads milled.
Maybe this will help a bit - your intake valve close (IVC) is typically the best determining factor in where your RPM will peak. On a 3.622 stroke, that tends to be right at 43 degrees after BDC for an IVC that will result in peak HP at 6300 RPM. You can cheat the HP peak to the right by delaying that IVC - think old school retarding the cam a few degrees to gain top end power at the expense of low end torque. However, the intake runner length is ALSO optimized for about a 6300 RPM peak HP in the factory and factory-style intakes. So, if you cheat the IVC too far past 43 degrees, the intake starts fighting you. You get to about 46 degrees, and the shorter runner starts to really make sense. Now, that howards cam you picked has IVC at 44 degrees, so it'll peak around 6300-6400 rpm. And the overlap will help it carry past peak (not fall over) like JakeFusion said. If you want to run that 236/250 cam, even at +5 advance, your IVC is 48 degrees, so you'd need short runners, and you'd need to mill your heads quite alot to get back some compression.
Honestly, cams are cheap enough, so I'd get one that works for you now and then go back in later when you do heads upgrades. Don't by your heads based on the cam - Buy your cam based on the heads. If you're not wanting to remove the heads at all, I would go 232/240-112+4, but being very honest, that would still work best with a 57cc combustion chamber. if you are not wanting to mill the heads for now, I think most cam upgrades are going to "feel" bad, unless you stay on the small side, like 214/224-112+4. But that'd be all torque and no top end, and counter to your goals int he first place.
If you're REALLY feeling froggy and race only, try 232/240-114+4 and go low lash solid roller. The solids will help greatly with the throttle response that you'd otherwise be giving up. And you don't need adjustable rockers for those. It'll drive like a 227/235, but it'll RUN like a 232/240. The kit is no different in price than any other cam and lifter kit.
03-19-2017, 02:32 PM
236/250 cam 
