Cam swap size and springs help needed
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Joined: Feb 2008
Posts: 488
From: Las Vegas, NV
Cam swap size and springs help needed
Its a long one, the question is at there somewhere though.
Doing the bottom end with better bearings, pistons and rods but using stock crank. Got full bolt ons, ewp, ps!, AC!, etc.
Got a set of ported stock heads and LE ported intake.
The heads flow as follows:
.550 = 214/180 -- 265/195
.600 = 214/182 -- 265/200
The heads have very low mileage CC987 springs on them
apparently the spring specs are as follows:
Installed Load: 121 lbs @ 1.800"
Open Load: 388 lbs @ 1.200"
Spring Rate: 344 lbs/in
Coil Bind Height: 1.150"
The question is in the cam selection. I'd like to just get an off the shelf cam for now. I would like to put as large a cam as I can get away with and from searching around the site for the last couple days and not being worried about smog or streetability, it would seem that I could get a way with a CC468 witch is the XFI 292. The issue that I haven't been able to find clear or consistent info on is the spring rates in relation to the ramp rates, etc. The recommended spring on comp's site is the 918 witch has the same lift but slightly different seat and open preassures. the 918's are listed as 130lbs seat and 318 open with a 313 avg, whereas the 987's are 121lbs seated and 388 open with a 344 avg.
I'm not looking to spin it up above 6500 because of the bottom end and I know that there is a lot of debate about not taking full advantage of such a large cam without shifting higher but With a mostly stock bottom end and ported stock heads I don't think I'll make a ton of power at that high rpms anyway.
What I'm wondering is, especially when taking into consideration the rate loss after break in, will the lower seat pressure and higher peak pressure help the valve open faster and not float at high rpm or are they more likely to not make a difference on the opening but possibly cause more bounce / loft upon closing due to the lower seat pressure? All the comp cams for lt1's seem to recommend the 918's but I really don't want to have to buy a whole new set of springs, etc when I just paid for these. help?
Sorry for the long winded question and I hope the actual question / point are clear, I'm just trying to include as much info so as to avoid a lot of questions and speculation. All of your informed opinions are much appreciated.
thanks for your time.
Doing the bottom end with better bearings, pistons and rods but using stock crank. Got full bolt ons, ewp, ps!, AC!, etc.
Got a set of ported stock heads and LE ported intake.
The heads flow as follows:
.550 = 214/180 -- 265/195
.600 = 214/182 -- 265/200
The heads have very low mileage CC987 springs on them
apparently the spring specs are as follows:
Installed Load: 121 lbs @ 1.800"
Open Load: 388 lbs @ 1.200"
Spring Rate: 344 lbs/in
Coil Bind Height: 1.150"
The question is in the cam selection. I'd like to just get an off the shelf cam for now. I would like to put as large a cam as I can get away with and from searching around the site for the last couple days and not being worried about smog or streetability, it would seem that I could get a way with a CC468 witch is the XFI 292. The issue that I haven't been able to find clear or consistent info on is the spring rates in relation to the ramp rates, etc. The recommended spring on comp's site is the 918 witch has the same lift but slightly different seat and open preassures. the 918's are listed as 130lbs seat and 318 open with a 313 avg, whereas the 987's are 121lbs seated and 388 open with a 344 avg.
I'm not looking to spin it up above 6500 because of the bottom end and I know that there is a lot of debate about not taking full advantage of such a large cam without shifting higher but With a mostly stock bottom end and ported stock heads I don't think I'll make a ton of power at that high rpms anyway.
What I'm wondering is, especially when taking into consideration the rate loss after break in, will the lower seat pressure and higher peak pressure help the valve open faster and not float at high rpm or are they more likely to not make a difference on the opening but possibly cause more bounce / loft upon closing due to the lower seat pressure? All the comp cams for lt1's seem to recommend the 918's but I really don't want to have to buy a whole new set of springs, etc when I just paid for these. help?
Sorry for the long winded question and I hope the actual question / point are clear, I'm just trying to include as much info so as to avoid a lot of questions and speculation. All of your informed opinions are much appreciated.
thanks for your time.
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