Less compression and bigger cam vs more compression and smaller cam
Thread Starter
TECH Fanatic
iTrader: (10)
Joined: Mar 2003
Posts: 1,106
Likes: 2
From: St Simons Isl, GA
Less compression and bigger cam vs more compression and smaller cam Alright here's my situation...I've got a LQ4 short block that I'm going to build to go in my WS6. The only components that are set in stone right now are the short block and the LS6 intake with a Shaner S3 throttle body. I've been searching, reading, and debating until my head hurts about a head and cam combo for this motor.
I know when it comes to a cam selection, most of you would say to decide on heads, pick out (or have spec'd) a cam, measure PTV, and roll...flycut if you need to. Problem is, I live in Alaska, and apparently none of the machine shops here can flycut my pistons. I'm not making this up...I called the two most reputable ones in town today.
So I'm in a dilema. I'm having PatrickG spec me a cam out, and if I go with a set of 59cc ported PRC 5.3 heads, I can only go up to about .230 on the intake duration on a 110 ICL. 59cc heads with a stock gasket on a LQ4 makes just under 11:1 compression, which is what I was shooting for when I was hoping to run a larger cam. If I drop down to a 62cc or 64cc head, I'll have more room for a larger cam, but I'll be closer to 10.5:1 comp with the 62cc and 10.25:1 with the 64cc head.
So long story a little bit shorter, should I shoot for a larger cam with heads that yield .5-.75 less compression, or should I go for the smaller cam with closer to 11:1 compression. My goals were for 425+hp, but the hp number really isn't that big of a deal...really wanted to focus on building as much torque as possible.
Opinions, please.
I know when it comes to a cam selection, most of you would say to decide on heads, pick out (or have spec'd) a cam, measure PTV, and roll...flycut if you need to. Problem is, I live in Alaska, and apparently none of the machine shops here can flycut my pistons. I'm not making this up...I called the two most reputable ones in town today.
So I'm in a dilema. I'm having PatrickG spec me a cam out, and if I go with a set of 59cc ported PRC 5.3 heads, I can only go up to about .230 on the intake duration on a 110 ICL. 59cc heads with a stock gasket on a LQ4 makes just under 11:1 compression, which is what I was shooting for when I was hoping to run a larger cam. If I drop down to a 62cc or 64cc head, I'll have more room for a larger cam, but I'll be closer to 10.5:1 comp with the 62cc and 10.25:1 with the 64cc head.
So long story a little bit shorter, should I shoot for a larger cam with heads that yield .5-.75 less compression, or should I go for the smaller cam with closer to 11:1 compression. My goals were for 425+hp, but the hp number really isn't that big of a deal...really wanted to focus on building as much torque as possible.
Opinions, please.
you probably need more horsepower with a 6spd and 4.10s tho ?.. not torque , what does the combustion chamber have to do with cam size , just wondering?
Last edited by blackmagicturbo; Jul 6, 2010 at 03:50 PM.
Thread Starter
TECH Fanatic
iTrader: (10)
Joined: Mar 2003
Posts: 1,106
Likes: 2
From: St Simons Isl, GA
Not a daily driver, but I do want sane driveability. I wasn't shooting for a Trex or anything like that to begin with, but something along the lines of a MS3, G5x4, etc. Car will be tracked occasionally, but will be driven more in a blend of city/highway driving.
Thread Starter
TECH Fanatic
iTrader: (10)
Joined: Mar 2003
Posts: 1,106
Likes: 2
From: St Simons Isl, GA
It won't clear unless you get the heads set up with recessed valves from TSP. I called them today, and they're about 3 weeks out from shipping. In another month, my summer will be almost over up here, and I'd rather not wait that long if I can avoid it.
Thread Starter
TECH Fanatic
iTrader: (10)
Joined: Mar 2003
Posts: 1,106
Likes: 2
From: St Simons Isl, GA
The farther down you mill the heads (which makes the combustion chamber smaller), the closer your valves get to the pistons. A large duration camshaft can cause piston-to-valve issues with a small chamber.
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Topdon ONE vs. Artidiag 800 BT2: Which is the Diagnostic Tablet For You?
Pouria Savadkouei
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Thread Starter
TECH Fanatic
iTrader: (10)
Joined: Mar 2003
Posts: 1,106
Likes: 2
From: St Simons Isl, GA
Whats up with the rolleyes? If you don't believe me, thats fine. I called Alaska Drag Bike and also Midtown Machine today...ADB told me they couldn't possibly flycut a piston with it still in the block, and MM told me they didn't have the tools to do such a thing. Those are the only two machine shops I know of in town, and certainly the only ones that would come recommended by anyone up here...
I don't know if you're rolling eyes at me, or rolling eyes at the fact that Alaska sucks.
I don't know if you're rolling eyes at me, or rolling eyes at the fact that Alaska sucks.
Last edited by -Q-; Jul 6, 2010 at 06:47 PM.
That is the best answer but honestly I didn.t do it either because it is a PIA. I guess it boils down to how much do you want it..
I would go with a smaller cam that will have a good DCR and make broader power losing only a bit up top.... You prolly will be faster but I gaurantee it will be a more fun streetcar....
I would go with a smaller cam that will have a good DCR and make broader power losing only a bit up top.... You prolly will be faster but I gaurantee it will be a more fun streetcar....
actually i read that no local machine shops would do it which is why i suggested he do it himself. it not exactly rocket science, if you can use feeler guages it's not that bad. if the op wants a big cam and compression it's smart to do it right the first time. either that or buy an off the shelf combo and flip a coin on your clearances.
I went the high comp mid size cam route.... I have milled PRC 5/3 heads and a Torquer V2. I had to fly cut big time and I wish I would have went with a bigger cam! I can fit a cam that is any bigger so I need new heads if i want more lope
5.3s have a narrower deck hieght than a 241 ,243? i thought the combustions were just smaller in shape ?...