I'm throwing around ideas for a custom cam for my 95 TA. I'm looking for an rpm range of 2000-2500 to 6500, give or take. Something with good power under the curve. Overlap centered about TDC to build power past peak and around 8.5 DCR. I chose a single pattern cam b/c I don't particularly want lope and from the heads to the tailpipe the exhaust is aftermarket. Here's what I've come up with:

@.050 232/232 .565/.575 111LSA +1
IVO 6
IVC 46
EVO 48
EVC 4
OVERLAP- 10*

@.006 284/282 ?/? 111 LSA +1
IVO 32
IVC 73
EVO 73
EVC 29
OVERLAP-61

Maybe asymmetric lobes. More aggressive ramp rates on closing than opening. This is mainly to help the overlap. That way the exhaust valve is shutting quicker while the intake is opening slower, to push overlap closer to TDC. Overlap is 6* exhaust stroke, 4* intake stroke @.050. Lift #s are with 1.6rr, btw. I think the tight LSA will also help with power under the curve. I come up with a DCR of about 8.38, a little lower than hoped for, but if I advance anymore, the overlap will move more towards the exhaust stroke.

Thoughts, opinions, suggestions are greatly appreciated. Thanks!

 

If it's a custom grind, what do mean? Ae you specc'ing it out yourself? Not a good idea. If you mean you are haivng someone design it for you, why not let them do what you are paying them for?

Anyway, to make an intelligent comment I would need to know your CR is and what you what kind of driving you do with the car. Also, just to be sure, it's a HR?

Rich

 

You want SCR or DCR? It's a HR. Car is not a DD. May see some 1/4 mile passes, but not many.

Not being a smart ***, but just look at the cam objectively. As if it was on a speed shop's website or something. What do you think about the cam as far as doing what it's designed for?

 

Not being a smart ***, but I think Rich was looking for SCR, because DCR will vary with cam timing, won't it?

With a 3600 stall (per sig) how are you going to need lots of 2000 WOT torque? What did I miss here? If it's not a DD and only occasionally does 1/4 mile strip duty, what exactly is the car used for? Wouldn't a cam designer want to know all this kind of stuff (plus more) to intelligently spec a cam for your needs/wants?

 

Let me take a step back for a second. What value should I use for piston head volume for an LT1? I'm having trouble calculating compression. Is an LT1 piston dished or domed?

Also, the car is used for occassional track use but will be driven on the street a little. I'm not concerned about street manners as far as emissions, but would prefer less lope. I don't need lots of torque at 2000. Maybe I should have said 2800-6500. I just want a cam thats has a broad torque curve. I was gonna go with the comp 280XFI, but it's just a little too peaky. Does this answer your questions?

 

ok..using 4.5 for piston volume I actually get 10.8 SCR and 8.2 DCR. My DCR calculation was off. So, I probably need to bump up compression some.

 

This cam was also suggested to me over at ls1tech(sort of-I tweaked it a little)
@.050 228/232 .576/.570 110+2
IVO 6
IVC 42
EVO 48
EVC 4
OVERLAP-10*

@.006 278/284 (? on lift at these duration values) 110+2
IVO 31
IVC 67
EVO 74
EVC 30
OVERLAP-61*

SCR is 10.8
DCR is 8.49

Again, hoping to accomplish the same goals as the cam I started the thread with. Would this work better?

 

@.050 232/232 .565/.575 111LSA +1
IVO 6
IVC 46
EVO 48
EVC 4
OVERLAP- 10*

@.006 284/282 ?/? 111 LSA +1
IVO 32
IVC 73
EVO 73
EVC 29
OVERLAP-61

vs.

@.050 228/232 .576/.570 110+2
IVO 6
IVC 42
EVO 48
EVC 4
OVERLAP-10*

@.006 278/284 (? on lift at these duration values) 110+2
IVO 31
IVC 67
EVO 74
EVC 30
OVERLAP-61*

I am making a couple of ASSumptions here. 1. It's a HR cam. 2. Heads are stock. The second cam will be better for a DD, up to 5,500 rpm.

But LT1's like a split duration cam with more exhaust than intake duration, due to relatively poor exhaust flow, especailly considering the entire exhaust system. And so on. My advice: stick with what is known to work or pay an extra $100-150 to get a "custom" grind. The people who know LT1 cams (Bret, for one) have this pretty well nailed. People seem to have an aversion for paying for advice, it's often the wisest investment you can make.

Rich

 

read sig. GTP LT4 heads and far-from-stock exhaust. AS&M LT headers, B&B Tri flow catback w/ elec. cut out. Would the exhaust really need more duration? If so, I saw a 227/233 .560/.569 110+2 that I liked. DCR of about 8.5 and 10* overlap mostly centered about TDC. What are your thoughts on that cam?

I respect yours (and many other's) opinions to go to a cam expert like Bret and just pay them to design a cam for my application. However, this is my passion. I would like to design and build engines for a living one day. The joy comes from helping become part of the process of building a performance machine, not just handing over cash and asking someone else to do it for me. I respect Bret's knowledge, but I'll never really learn if I just buy a cam without given specs. Again, thanks for your time and comments-opinions. Keep em coming!

 

try it and see how it works. if you don't like it, buy another and try it. repeat until you find what you want. OR pay an expert to get the right one the first time.