53.9 ABDC @.050 
DRC With 408, please help me figure this out!
Thread Starter
Joined: Nov 2004
Posts: 425
Likes: 1
From: Jacksonville, FL
DCR With 408, please help me figure this out! I know, everyone hates these threads so I'll make it quick.
I've got a 408 with -8 cc Diamond pistons, 64cc PRC Stage 3 heads and will be using the TSP Giant cam. I will have 11:1 compression after the head gasket and just wanted to make sure I will be in the safe zone with this cam and will be nice for my set-up.
Would anyone be willing to help me out and show me the DCRC calculations with my specs as an example? I'm not an idiot but never could really grasp the x times 4 squared to the million power of Pie, apple pie is good, plus the square root of fried chicken...anyone?
I've got a 408 with -8 cc Diamond pistons, 64cc PRC Stage 3 heads and will be using the TSP Giant cam. I will have 11:1 compression after the head gasket and just wanted to make sure I will be in the safe zone with this cam and will be nice for my set-up.
Would anyone be willing to help me out and show me the DCRC calculations with my specs as an example? I'm not an idiot but never could really grasp the x times 4 squared to the million power of Pie, apple pie is good, plus the square root of fried chicken...anyone?
Last edited by 02BlackBullet; Apr 19, 2006 at 10:42 AM.
I found this for you.
Originally Posted by Patrick G
Typically, you advance a cam that's too big and retard a cam that's too small. If you choose your cam carefully, you will not need much if any advance. 5 degrees of advance on your cam is going to severely exhaust-bias your cam and it will run out of breath too soon. Ideally, you want to choose your intake valve closing point to where it makes best power on a 408. From what I've seen, that means it should be around 48-50 degree ABDC IVC to work best with the FAST intake. Anything later than that will peak later than the FAST intake is trying to force.
The duration is going to be around 8 degrees bigger than what works with a 346. If a 234/242 G5X-3 works great in a 346, then a 242/250 would be close to equivalent in a 408. Too often though, I see mistakes being made by running too wide of an LSA in these larger motors. Truthfully, to get the DCR up into the 8.5-9.0 level, it's better to narrow the LSAs some and not advance the cams so much. This will center the overlap closer to TDC and will allow the motors to rev better past peak hp. An ideal street/strip 408 cam in my view would be something with LSK lobes like a 243/251 .653/.660 110LSA (+2). You get an IVC under 50 degrees ABDC and your overlap is exactly centered over TDC.
The duration is going to be around 8 degrees bigger than what works with a 346. If a 234/242 G5X-3 works great in a 346, then a 242/250 would be close to equivalent in a 408. Too often though, I see mistakes being made by running too wide of an LSA in these larger motors. Truthfully, to get the DCR up into the 8.5-9.0 level, it's better to narrow the LSAs some and not advance the cams so much. This will center the overlap closer to TDC and will allow the motors to rev better past peak hp. An ideal street/strip 408 cam in my view would be something with LSK lobes like a 243/251 .653/.660 110LSA (+2). You get an IVC under 50 degrees ABDC and your overlap is exactly centered over TDC.
Thread Starter
Joined: Nov 2004
Posts: 425
Likes: 1
From: Jacksonville, FL
Originally Posted by gollum
I found this for you.
Thanks for that. I'm still confused with the whole DCR topic. I have actually read that exact post before but it's all greek to me.
My cam specs are as follows:
248/254, .611"/.613" 114 lsa
Bore: 4.06
Stroke: 4.00
Heads: 64.5 CC PRC Stage III
Compression: 11:1 with proper head gasket
Pistons: -8cc valve relief
Intake: Fast 90mm w/ hand port
Is there anything else that I need to compute the DCR and to see if this is a good cam selection for my needs?
Last edited by 02BlackBullet; Apr 19, 2006 at 10:41 AM.
Thread Starter
Joined: Nov 2004
Posts: 425
Likes: 1
From: Jacksonville, FL
Haven't got it yet. I knew it was DCR. I just had a brain fart. Sorry, it's been a long day at work. (over 12 hours)
Rod length is 6.125
I'm trying to dig something up right now on the Giant cam.
Rod length is 6.125
I'm trying to dig something up right now on the Giant cam.
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http://cochise.uia.net/pkelley2/DynamicCR.html
Download file at bottom of page and plug in your numbers.
Download file at bottom of page and plug in your numbers.
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Actually, I'll just assume it's 297 at .006" intake and is on a 112 ICL. The ABDC is 80.5 degrees in such a scenario.
As for as 11.1:1, -8cc pistons with 64cc heads on a 408 is more like 11.4-11.5:1 with a .040" Cometic.
The DCR is barely 8.0:1 with such a low SCR and would result in less than stellar power. Mill the heads .030" down to 59cc to get over 12.0:1 SCR and the DCR up around 8.4:1. That's a big cam and can take a lot of compression easily. It'd still be pump gas friendly and would make a lot more power everywhere.
Also, look here for a description for choosing the optimal cam I wrote a little while ago: https://ls1tech.com/forums/showpost....61&postcount=3
As for as 11.1:1, -8cc pistons with 64cc heads on a 408 is more like 11.4-11.5:1 with a .040" Cometic.
The DCR is barely 8.0:1 with such a low SCR and would result in less than stellar power. Mill the heads .030" down to 59cc to get over 12.0:1 SCR and the DCR up around 8.4:1. That's a big cam and can take a lot of compression easily. It'd still be pump gas friendly and would make a lot more power everywhere.
Also, look here for a description for choosing the optimal cam I wrote a little while ago: https://ls1tech.com/forums/showpost....61&postcount=3
Originally Posted by 02BlackBullet
I'll be spraying a 150-250 shot.
Do I want it that high?
Do I want it that high?
Thread Starter
Joined: Nov 2004
Posts: 425
Likes: 1
From: Jacksonville, FL
Originally Posted by JakeFusion
Just retard the timing or mix in race gas when you spray if you want ultimate NA results. Otherwise, you could do a cleanup mill of .010" or so and get the compression upped a bit and still provide a nice cushion for the nitrous (though, you'll still need to pull timing).
I haven't even got the motor yet and I've already fucked up.
Looks like I could mill my heads and shave another -2 cc's off of em and with a .041 head gasket I would have right around 11.8:1 SCR and it would pull a lot better right? I'm just concerned with the Florida heat and detonation when spraying.
I wouldn't spray a stock LS1 without pulling timing, let alone an 11.1 or 12.1:1 stroker. Race gas is optional, but at the track, you might as well mix in some for safety.
Heat is going to be your major enemy with a high DCR anyway... Cylinder pressure creates heat. I wouldn't run in the summer down here without a big radiator/engine oil cooler.
Heat is going to be your major enemy with a high DCR anyway... Cylinder pressure creates heat. I wouldn't run in the summer down here without a big radiator/engine oil cooler.
Thread Starter
Joined: Nov 2004
Posts: 425
Likes: 1
From: Jacksonville, FL
Originally Posted by JakeFusion
I wouldn't spray a stock LS1 without pulling timing, let alone an 11.1 or 12.1:1 stroker. Race gas is optional, but at the track, you might as well mix in some for safety.
So the best set-up for me right now would be to get the heads milled to about 62cc...right?
I have plans for a bigger radiator and a Meziere Water Pump. I also have a 160* stat and 3 jugs of water wetter (like it does anything
)You think I'll have trouble with the 12:1 in the heat? Think maybe I should keep it where it is?
If you do a standalone system, I'd suggest a propane kit. High octane, cheap, and will allow you to hit a 200 shot on the street (though, to be honest, I don't think you'll want to hit a 200 shot on top of a 408 on the street unless you are racing a Hayabusa.)
Just do the clean up mill to .010" and that'll be nearly 62 cc (.012" would shave off 2cc).
And no, 12.1 is not where the problem is. The DCR determines KR. If you keep that below 8.5:1 on 93, even the FL humid heat won't cause you too much grief (but you'll be pretty close to the edge at 8.5:1.)
Just do the clean up mill to .010" and that'll be nearly 62 cc (.012" would shave off 2cc).
And no, 12.1 is not where the problem is. The DCR determines KR. If you keep that below 8.5:1 on 93, even the FL humid heat won't cause you too much grief (but you'll be pretty close to the edge at 8.5:1.)
Thread Starter
Joined: Nov 2004
Posts: 425
Likes: 1
From: Jacksonville, FL
How much power do you think I will leave on the table with my current set-up verses a .012 mill on the heads?
Also, if you have a formula for the DCR or a calculator, could you let me know where to find it so I can stop bugging you?
Thank you for your help by the way~!
Also, if you have a formula for the DCR or a calculator, could you let me know where to find it so I can stop bugging you?
Thank you for your help by the way~!
