Darth_V8r

iTrader: (4)

To answer what I think is your original question, IVC around 43 will get you very good throttle response. Actually a smaller aftermarket cam with an ivc in that range should feel better than the stock cam, because the ramp rates on aftermarket cams are much tighter than stock. 52-55 degree range vs 80 degree range.

Something like a 224/230-114+3 will run quite well and be very responsive. Also, do not forget other details. Rotating weight is throttle response. Change to psi 1515 springs and matching keepers and retainers will take over a pound out of your valve train and really change the snappiness. Lighter clutch will also if it is a manual.

Even with that cam, bump compression into the 11.2-11.5 range, and you will be very happy with your throttle response.

Check out user lazerlemonta C6 LS3. Light clutch, 226 cam, 11.5 compression, will absolutely pin you back at 2500 rpm. And not a pain in the *** to drive either.

lazerlemonta

Do you have a z51 car? The difference in first gear is significant enough to make a difference at a 2500 rpm hit in first. 2.97 z51 to 2.66 base model. A cam motion titan 2 or 3 would be adequate for some quick revs for auto cross with 3.90 or 4.10 gears. Mill the stock heads .030 - .040 and send it. You can make 450/450 with a stock cam and proper bolt ons as well. We have done it 2 times with LS3s.

dAgent

Appreciate the advice Darth. I came up with my own cam specs a while back after I taught myself valve events and they're not too far off what you suggested actually; 226/231 112+2.5 3.5 IVO 42.5 IVC 50 EVO 1 EVC I figured a little overlap (4.5*) should be ok to pick up some top end while stil keeping that IVC early but after your suggestion maybe I should keep the overlap closer to 0* so I don't loose too much low end response. Something like 225/230 113+3 so 2.5 IVO 42.5 IVC 51 EVO -1 EVC What do you think of a little more overlap than you suggested?

Maybe I should be clear about what it is I'm going for, as I mentioned before I do some autocross which is all 2nd gear and sometimes you're coming out of the slow corners around 2-2.5k so I don't want to loose torque or throttle response at 2k, wouldn't mind if I started gaining a little starting around 2.5k. I beat the **** out of my car doing other stuff like drifting hence why throttle response is so important, also riding of the rev limiter happens so I'm not raising it more than 100-200 rpm; I want to peak near 6000-6100rpm and don't mind the power reversing by 6300-6400rpm if I'm shifting by 6600-6700rpm as long as I can pick up some low end in return. 500rwhp would be nice but throttle response and valvetrain stability/reliability is my main concern which is why I was planning to use gentle lobes, .625 beehives (like PSI 1511ML) and lifts below .600. Still debating weather I should use rectangle or church aftermarket heads. If I go rectangle I'm not going over the stock port size so porting stockers is not happening, I was considering something like the TSP 255 heads or maybe spring for Mamo 260's, I do have a cathedral Fast 102 with the NW 102 TB on top of my Rick Crawford ported stocker so I could go either way as far as heads are concerned. I do like the TFS 225's, AFR 230's or MMS 220-235 cathedrals as their port velocity, lower lifts & spring pressures needed go along well with my goals. I want to bulletproof everything as much as possible so want to do the Johnson lifters (maybe the tie bar,axle oiling, slow leak down kind), C5R timing chain, LS7 style chain tensioner, an ATI dampener(not sure if I should go the underdrive route), the comp BSR or the new BTR shaft rocker system to tie all the stock rockers together and anything else I need to make this thing live a long but abused life. Greatly welcome any suggestions Guys, Thanks again.

dAgent

Both cars are C6 GS so both have the Z51 gearing, same tires even, his car has the 230/234 cam w/ 47* IVC and full Kooks exhaust, my car is stock except for TSP headers & X-pipe, ported/rodded stock intake and TB; that's all. The difference in snappiness at 2.5-3k was night and day. His car makes 497rwhp to my 417 and the same torque at 2.5-3k but my car feels way faster due to the crisp throttle response. We both drove our cars back to back and both noticed right away the huge difference in what we tough was low end torque when it really wasn't; I realized it was throttle response when I looked at the dyno graphs. My car was always all over the place in 1st to his car with no drama at all; that power just came in progressively, so much so that it was boring for me actually. I guess if I ain't all over the place I'm not having fun.

I just read a couple of your threads per Darths suggestion so I'm up to date on your build and than build again from a stock cam to a 236 cam than back down to a 226 cam, you lost some horsepower from the big cam but I bet the car doesn't feel like it with the throttle response you picked up and from what I read the big cam wasn't faster at the track either although I don't know what the 226 cam did? Very interesting stuff though. From what I read you had a titanium spring retainer failure on the stock cam with the 1.8 rockers and PSI 1511's after 50k, do you think I should use the metal retainers? Valvetrain weight is very important to me so that I can stay with the lighter spring pressures.

Darth_V8r

iTrader: (4)

The main reason I went a bit lower on overlap was that increasing overlap can make the transitions a bit sloppier - coming off a corner, then hitting the go pedal hard. Less overlap tends to make that a bit more instantaneous. you are correct, increasing the overlap will help it carry power up top without a later IVC. To be honest, if the AFR230 or mamo 235 is possibly in the cards for you, I think that would run even better. High port velocity heads can really help tame a cam. So those two options would allow you to run a bit more overlap, still have the instant hit down low, and carry the power up top. If you stay with the LS3 heads, i would definitely lean toward less overlap. FWIW, Lazer's cam pulls to 7K very cleanly. I drove his car with both the larger cam and the current cam. I honestly think the current cam is faster, regardless of what the dyno says.

lazerlemonta

If you replace them at a service interval, titanium all the way. Tool steel is not much heavier though. I currently have titanium retainers on my .660 springs.

NAVYBLUE210

Given your specific goals and moderate rpm & cam lift requirements and that you already have the FAST 102.
Your best cylinder head decision IMO would be the MMS 235s along with porting the FAST.
My .02

dAgent

Yeah, going the church route is where I'm leaning. I like 225 ports for a 6.2 though, kind of think 235 ports might be too big for the throttle response I'm going for, I don't know what you guys think? Been reading some older threads where 6.0 LS2's did over 517/483 with the TFS 225 heads & G6X3 cam, albeit that cam is huge with 17.5* of overlap. The question is: can I get to 500rwhp with a much smaller cam, at only 1-2* of overlap, on a 6.2L? I have doubts.

grubinski

I built my 6.2 SBE with MMS220 heads, a FAST102 (ported by Tony Mamo), and a cam spec'd by him at 1.5 degrees of overlap. Compression is 11.8:1.

Before the engine mods it was just a stock crate motor with an ASA cam in it, and it made 462 rwhp. It feels *much* stronger now, but I haven't been to the dyno yet, and won't until spring. I expect it to do 500 rwhp +/-.

I have no complaints about the throttle response.

dAgent

I know, I have been following your thread and begging you for a dyno. A church headed 6.2 throttle response monster in a freaking 2400lbs Miata; that's like the "Holy of Holies" to me. That thing must be a riot.

NAVYBLUE210

A 6.2 with MMS 223s (as cast TFS 220s with Tony's hand finishing) 220s fully CNCd or 235s will Easily Exceed 500+ RWHP with
Titan 4 227/232, 11.0:1-11.5:1 Comp (depending on 91 VS 93 Octane, E85?), a good exhaust system and the attention to details, quench
1 7/8" Lts etc. in a manual trans.

With a 4.060 bore I would use the MMS 235s and cam according to RPM range & Throttle response desired.
Always easier to switch cams VS Heads should you ever decide to stroke or go larger.
Just my .02

grubinski

You have to be *very* careful.