beneficial intake/head setup on lm7
 

Ive been doing my research trying to pick the best intake and head combo for my truck. Right now i have 862 stock heads. Everyone Ive talked to has said to go to a tbss intake. my question is will the tbss intake only work on a cathedral port head or will it work on stock 862s with rectangular ports? im considering a tbss intake with 243 heads with a valve job performed on them but do i HAVE to get them milled to keep the compression around 9.5 to 1? everyone says to mill them to keep that compression but no one has really said why u want that specific compression. another thread stated that not milling them would put compression at 10 to 1 which would make power at low and top end. any truth to this? note-i will be putting in a 220/224, 224/224, or 224/228 cam in at the same time and will be also adding spray, around 50-75 shot. lift will prolly be from .560-581ish with a 114lsa. any help or direction in the right way is appreciated. thanks!

The 243's have a 64cc chamber where the 5.3 heads have a 58cc. Taking off .006 closed the chamber by 1cc, so .030 milled off would make the chamber the same as stock and keep the compression. I would try to mill .040 off and go with a .041 thick head gasket, should bring the compression up to right at 10:1. The higher the compression, the less effect a cam has on the bottom end and it pulls better up top. Gotta keep in mind, going with any of those cams, you are going to have to put a stall in it. Then you have to balance stall speed with drivability and towing capacity if you pull anything.

862 heads are Cathedral port.

im planning on putting a 3000-3200 stall in it. i want the cam to pull better in the low-mid range, not too worried about up top.

so do you think i would be better off getting 243 heads and having them milled or just doing a port and polish job along with a valve job on the 862s im currently running and adding a tbss intake to it? think i would see any gains putting a tbss intake on it now with the stock 862 heads?

My cam is 218/224@.050 but it's on a 110LSA so it's really choppy. It doesn't really start pulling hard till around 3800 or so. If you widen the LSA out to maybe 114, it would settle the idle and probably start pulling good about 28-3000, just not make quite as much peak power and torque. It depends on what model your truck is, CC, EC or RC, the bigger the truck, the smaller the cam will need to be.

Do the 243 swap also, the design is way better than the 862's. The TBSS intake/throttle body combo works pretty good, I did it on mine and it picked up a consistent 1.5 mph in the 1/4.

my cam is a 216/220 @.050 with 114lsa and an EC Z71

First, your 862 heads have cathedral ports and have 61.15cc combustion chambers (not 58cc like someone posted). The 243 heads are 64.45cc and definitely outflow the 862 heads. If the compression ratio is kept the same they should gain you at least 20 hp. To keep the compression ratio about the same, you would need to mill the 243 heads at least .020". If you mill .030" that would give you about 59.XXcc which would raise the CR a little. Performance cams like higher CR and higher CR gives you a little more power. It will need to use premium gas with higher compression, but you will get the best performance by running about 10:1 with the cams you are considering.

243s all the way.

Mill them to 58cc and do the 220/224 cam on a 112lsa tbss intake and matching tb and it'll run real good