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Next Gen HotRodder
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Discussion Starter #1
I have a 383 in my K2500 that's using TPI right now. Originally, I was going to turbo it, but I ended up having to buy another vehicle bc my daily died (13k+ out of pocket cash gone T_T). So instead I want to just carb it, and change out the small compu cam.

I have been reading a bit on this, and since it IS in a truck (6000+lbs mind you) that less is actually more? But I honestly don't have a true understanding behind cam design. I want to get as much as I can in this one cam swap. The trans is built and I have a stall and gears already.

My initial choice is a Lunati bracket master II 246/246 .05 dur, .515/.515, 108LSA. But apparently that might be a bit much. I calculated the overlap on that and it's like 84... A bit racey, but thats kinda what I wanted. This is not a daily driver, it's a toy, so drive-ability isn't to weighted in my mind. The engine can handle RPMs, fully forged bottom end. I want more high end power than the TPI craps out, but I guess I can't really loose to much low end or the truck won't get off the line at all. :/ I dunno. I can give detailed specs if needed. Thoughts, suggestions, personal experience? Thanks.
 

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Cars, Trucks, Boats, Motorcycl
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. What's your stall RPMs? Rear end gear? Rear tire size? Overdrive tranny?

. By "TPI" do you mean the 'Vette/Camaro/Firebird EFI setup that whacks off power above 4500 RPMs?

. Got the spec.s on the CompuCam? Is it roller cam/roller lifters? It will prolly have much more high RPM power with a carb. Even the stock TPI cams (~202/207 or 207/211) were kinda too big for the TPI setup, they usually wanted to HP out at 5,000 - 5,200 RPMs, but the TPI flattens the HP curve by 4000 or so in a 383... 4500 in a 350...

. Your 246/246 cam choice won't do much below about 3,000 RPMs, so need a 3,000 stall... power brake it up for a second and see what you have...it wants to make about 500+ HP at 6200 RPMs... needs 10-13:1 compression ratio... the higher, the better the drivability...
 

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Next Gen HotRodder
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Discussion Starter #3
My stall is a 2800 (give or take), the gears are 4.10 posi, and my rear tires are 245/75R16 (pizza cutters, I know. they're snow treads) It is an over drive 700R4. The TPI is off a 88' vette, so yes the restrictive turd. But I want to get away from that. I already have a dual plane carb intake and holley 750. The current compu cam has 210/216 .05 dur, .440/.454 lift, and 114LSA. It's hydraulic flat tappet. The engine has 11.8:1 compression, it runs on pump 93.
 

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Next Gen HotRodder
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Discussion Starter #5
Currently the engine uses a stock style '88 vette ECM with a custom chip and stock distributor. I am getting an MSD HEI dizzy and control box when I ditch the TPI. 11.8:1 is a rough calculation. It may be slightly less, but it IS certainly in the high 11s. The timing is at 10* advanced initial, 36* total. I never noticed what it is at idle. I haven't had any ping or det issues.
 

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Cars, Trucks, Boats, Motorcycl
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. C.R. looks way high for pump gas and a fairly short duration cam... cam prolly HP peak about 5,000 RPMs carb.'d... I think we're still missing what the heads are...
 

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Next Gen HotRodder
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Discussion Starter #7
The heads are old Trick Flow Twisted Wedge aluminum. 180cc intake runners, 76cc exhaust, 63cc chambers, 2.02/1.6 valves. 1.470 dual springs good to .600 lift. Crane 1.5 roller alum rockers. If I really should, I can get VP Racing fuel from my local engine shop. I just never bothered bc pump fuel didn't seem to bother it.
 

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Wrench Turner
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4,952 Posts
I believe you've made a mistake on the compression ratio.Even using a 4cc flat top piston,I can only get 11.2:1 out of your engine specs,unless,you're using some type of domed pistons.With the cam specs of your current cam,your DCR would be over 10:1.That's over 1 full point above what is considered safe for pump gas & aluminum heads.I can't see that engine running with any timing set [email protected] least not on pump gas.
 

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Next Gen HotRodder
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Discussion Starter #9
Well it's a forged Egale rotating assembly. 4.03 bore, 3.75 stroke. 5.7" rods, flat top pistons 2 valve reliefs, head gasket bore is 4.06 and the comp thickness is .04. Piston to deck height is .01, and the pistons are probably no more than 5cc with the reliefs. So you're right. My compression is most likely around 11.0:1, or less. That's my bad. :p But it's still fairly high. My original dumbness calculated with 0 piston to deck height and no compensation for the valve reliefs. Doh moment.
 

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Going with that much in a K2500, that is curious.

I didn't like any low end loss in a big truck, or any situation where you have to give it a ton of pedal. Yes, that is going to be a big limitation.

Those cams with big duration and lift will need a radical chassis in a heavy truck. Then soften the suspension and soften the low end, IMO that is gonna drive retarded.

Rather than stroker and cam.. IMO You want bore and boost.

edit- retarded is poor word. It will be a monster.
 

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Next Gen HotRodder
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Discussion Starter #11
Stupid power I suppose is the point. The engine originally was boosted slightly by a B&M 144, but that's since been sold. The truck was my late fathers, he built it. I restored it after it sat for 13 years following his death. I just want to make it what he couldn't, the red beast. Anyway, I still don't know what cam I need to be shooting for. Just assumptions. Lower duration? Larger LSA? I dunno the balance. Maybe I should just stick to the math and weigh it out? If my intial choice didn't look to great, what about the Comp XE284H-10?
 

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Stupid power I suppose is the point. The engine originally was boosted slightly by a B&M 144, but that's since been sold. The truck was my late fathers, he built it. I restored it after it sat for 13 years following his death. I just want to make it what he couldn't, the red beast. Anyway, I still don't know what cam I need to be shooting for. Just assumptions. Lower duration? Larger LSA? I dunno the balance. Maybe I should just stick to the math and weigh it out? If my intial choice didn't look to great, what about the Comp XE284H-10?
Take a look at this tutorial I wrote for the wiki. All the info in the charts was taken directly from the Crane Cams Master Catalog and re-written so that it would make sense to those of us who don't know everything there is to know about camshaft design and application....
http://www.crankshaftcoalition.com/wiki/Cam_and_compression_ratio_compatibility
 

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Cars, Trucks, Boats, Motorcycl
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. The XE 284 240/246 is prolly the very largest you should go with 180cc heads... I get around 11:1 compression ratio... your stall RPM and toy usage looks fairly compatible with that cam...

. Since it had a blower at one point, are you sure it didn't have dished pistons? Since it had a blower, it may have low enough max timing advance that it could run pump gas 91-94 at that compression ratio with aluminum heads... may need timing advanced more with bigger cam and no blower for proper power... just guessing so far...
 

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Next Gen HotRodder
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15 Posts
Discussion Starter #14
. The XE 284 240/246 is prolly the very largest you should go with 180cc heads... I get around 11:1 compression ratio... your stall RPM and toy usage looks fairly compatible with that cam...

. Since it had a blower at one point, are you sure it didn't have dished pistons? Since it had a blower, it may have low enough max timing advance that it could run pump gas 91-94 at that compression ratio with aluminum heads... may need timing advanced more with bigger cam and no blower for proper power... just guessing so far...
Well in its original configuration the engine had the blower. That was 13+ years ago. Before I was old enough to even really remember it. It destroyed 4 transmissions like that. I can't say if it ever had dished pistons or not, but the blower didn't stay on the engine long, and it's only been bored out once. I personally sold the blower when I did a refreshing on the engine about a year ago. (complete bearing replacement, fresh cam, so on..) The blower wasn't installed at the time. It's always had the TPI since I've been old enough to remeber. So currently at least, it does have the flat top. I think I'm going to try out the COMP. Maybe look around just a bit more, call them and see what they suggest. I'm joining the Marines soon, so I won't really have a lot of time to test and enjoy it. :/ Appreciate everyones cents on the subject!
 
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