I'm about to start a build of the LS3 in my ... Miata ... even though I thought it was "done". The conversion started out with a brand new GMPP LS376/480 motor in it. During the original build, GM introduced the LS376/525, with the only difference being the camshaft. So of course I had to have that. Last winter the car got the ASA cam and a set of long tube headers, along with some other improvements.

Long story short, I wasn't satisfied with the way the car drove. It put down 462rwhp/425rwtq, but it's too unrefined and thirsty for the street usage it gets 99% of the time. I spend a lot of time running around with the throttle barely cracked, and it's not too smooth down there due to the ASA cam being rowdy enough that it exacerbates the tendency of the LS3 heads to suffer from reversion. I like to do long road trips with this car, and I want it to get at or very near 30 mpg when I do it. The original 376/480 motor got up to 26.5 mpg on road trips, the new cam dropped that to about 23. In normal mixed driving, it gets 14 mpg (the previous cam got more like 17). The car only weighs 2400#, and a car that light should do much better, IMHO.

So I talked to Tony Mamo, and it's going to get a bunch of his parts. A set of MMS220 heads, a milder cam, short travel lifters, a FAST intake manifold (need a new manifold anyway due to the switch to cathedral heads), YT 1.8 rocker arms, and other assorted stuff (3.23 gears to replace the current 3.73, for instance). Between the milder cam, the raised compression (from 10.8:1 stock CR to 11.8:1), and the better head and combustion chamber design, I expect the car will run much better. I suspect with the new heads and higher compression I'll make even more power, but that's not the primary goal of this build at all. I get wheelspin in 3rd gear at 70-80 mph with the engine that's in the car now, I'm trying to improve the street driveability under low load ... I'll still have plenty of power. :-)

 

Not knocking Tony's work at all....but you're going through a lot of expense to get to what a better spec'ed cam would accomplish. Even AFTER you sell off that LS3 top end.

Jus' sayin'.

KW

 

At some point in my life I decided that the definition of a hobby was that it didn't have to make any financial sense.

This is likely the last car I'll ever build (I'm retiring next year and will not spend money this freely again), and I want it absolutely as good as I can get it. A better cam might get me 80% of the way there, but it wouldn't be as good as a cam swap plus these heads. I want the higher compression, for instance, and not just by milling stock heads, and I think the much higher port velocity of the cathedral head will help the low speed driveability a lot.

This will be my retirement road trip car, among other things. I don't want to be second guessing my build decisions.

 

The OP wants 30 mpg or close to and ~450 rwhp with good driveability.
Those goals are not happening with OE LS3 ports and ONE Cam,...
Without VVT LOL.
The ASA Cam @ 226/236 and 11* of overlap is obviously not right for the OPs goals.
The Cam Motion high lift truck cam 206/216 117+3 .553"/.553" would drive nice and get close to 30 mpg,
lucky to reach 420 rwhp though, let alone 450.
The high lift hot cam 218/227 112+3 .600"/.600" a decent compromise is still just that a compromise, and will
not reach the mileage or driveabilty goals of the OP.

To reach the OPs specific goals the MMS 220 cylinder heads and a schmedium Single Pattern Cam
something like 221/221 or 223/223, along with ~.620"/.600" lift is definitely the way to go.
High Air Speed and Port Velociy is the key to both the fuel efficiency
(1400-1600 RPM in overdrive to approach/reach 30 mpg) & 460+ RWHP.

Is the initial investment greater ...... Obviously, But it is the only way to reach all 3 goals.
My .02

 

You could almost stuff a stock LS6 cam in it with 1.8 or 1.85 rockers with a decent bolt on package and get there as well.... Tonys heads would make that shine. I have already achieved 430RWHP with stock LS6 heads and LS6 cam before.

 

I think the late LS6 cam would work better in the LS3 than it does in the LS6. The wide duration split, etc. Not too sure the 117.5 LSA would do it any favors though.

 

The late LS6 cam is -24 degrees of overlap at .050" and only 204 degrees of intake duration. I think it's *too* tame, even for this old fart. That might have been a good choice if I'd kept the stock heads and not raised compression. But I'd also have given up a lot of power compared to the nasty, rowdy setup I have now. I *do* like the power. :-)

My initial inclination was to go with something on the order of -4 to -6 overlap, with a fairly large LSA and enough duration to put the IVC around 47-48 degrees. Say something like a 224/232 117+1 just to throw that out there as an example. Tony thought that with his heads and the high velocity they provide, there's no need to be that conservative. Since he's the expert, I will try his ideas first. Cams are easy to change, if need be.

We settled on a 227LSL/232LXL 114+1. That gives +1.5 degrees overlap, and an IVC point of 46.5 degrees. Compression ratio will be 11.8:1 ... I will likely run meth injection to keep out of knock retard under load, it may not "need" it, but it will be cheap insurance.

I bit the bullet and decided springs are going to be a maintenance item, so I'm running 1.8 rockers and both intake and exhaust will be near .650" lift at the valve.

 

Looks like you decided on a cam, but I'll throw this out anyway.

Cam Motion LS3 Stage 3, 220/230, .595/.595, 117+4, which would give you about .630 lift on 1.8 rockers.

 

Hashing over cam specs is the most fun that it's possible to have without spending any money. :-)

What you are suggesting is -9 degrees of overlap. In that vicinity is what I commonly see online for cams said to work well with a stock torque converter, which is really just code for "doesn't buck and jerk at low load, smooth idle". Pat G spec'd me a cam with -8 degrees of overlap when I talked to him. A guy on the Corvette forum that goes by the nom de forum of 'SpinMonster' used to recommend a cam with -6 degrees of overlap for LS2s with autos that didn't want bad driving manners. That's why I was thinking along the lines of negative overlap to start. If I was sticking with the rectangle port heads, I would be going that way.

Mr. Mamo says that his heads don't need that much negative overlap because the port velocity is higher. And I picked his smaller head, the MMS220 rather than the MMS235, in order to have higher port velocity ... it still flows better than my stock LS3 head. So I'm willing to try out his idea on the cam.

 

I agree on your first statement! Cost is ZIP!
It slipped my mind about you going to cathedrals (wise move, BTW!) The extra flow velocity they will give will allow a little less LSA, giving you a bit more low end torque. Looks like you have a solid plan moving forward!

 

I've got it up in the air ready to pull the engine. The engine and trans come out the bottom as a unit, attached to the front subframe. I have a wooden gantry crane that I built to lower it onto the wheeled steel cart I built to roll it out from under the car. I support it on these cribs because it'll be up in the air a while, and I don't like to put it that high on jackstands. These are much more stable. They are not just individual sticks stacked up, they are blocks 3" high consisting of 3 pieces in each direction, glued and screwed together.

 

Those look STRONG! AND low cost!

 

grubinski,
What size are your rear tires?
That 227/232 will drive real smooth, and with 3.23s instead of 3.73s you will still spin the tires in 3rd gear,
... only now at 90-100 mph LOL!
That is a schmedium sized cam in a 5.7 with another 30" all bore the throttle response and mid-range will be insane to 6500+.
I think the cam is a little big to hit 30 mpg at cruise, more likely 490+ RWHP IMO, I could be wrong about the mileage, but like you
said easy enough to change and fun bench-racing in the meantime.

Tony's cathedral heads not only have extreme velocity, they have outstanding E/I Flow Relationship (75%+)
which is why the do not need large exhaust splits or overlap (NA speaking).
Looking forward to your progress and results.

 

The tires are 225/45-15 ... I am going to do a little work rolling and pulling the fenders to get 245/40-15 under there.

I am a EE by training and profession, and one of the items on this winter's list is to get my homebrew traction control working.

Corvettes get 30 mpg highway (I've heard that, anyway), and this car is over 1000# lighter and has a smaller frontal area. I'm hoping the added compression will get also help with the mileage. A HotCam with the stock 10.8:1 compression did 26.5 mpg in this car with 3.73 gears. I'm hoping that the 11.8:1 CR and 3.23 gears will give me some gains in mpg since the cam is pretty much a wash, overlap-wise, compared to the HotCam. Also, freeway driving is at very low throttle openings. The new heads should be smoother (less reversion) under those conditions, and so hopefully more efficient. We'll see. :-)

Thanks for your interest.

 

You do have less frontal area, but I suspect the Vette has a lower drag number via better aerodynamics. It's more slippery.

 

You need to put an NT01 or Toyo R888R out back.... traction will greatly improve. You can't put down much power on anything with a 180-200 tread wear rating like you have. It'll be fun.... but I would keep the 3.73's!

 

Today I reassembled the gantry crane that I use to drop the engine out of the car. I think I'll pull the engine next weekend.

 

I like your crane! Looks plenty strong!

 

That's cool!

Typical EE...…..ha! I worked for Tektronix for 38 years.

I'm doing an LS3 for my C5 vette. It will be a cathedral port setup with AFR 205 heads worked by Tony.
Currently reside on my LS1.

Ron

 

When my vette was stock I was able to get 32 MPG after i tuned it lol added 4.10 and a few other goodies and that instantly went to 27-28....... What is your transmission gear ratios?