Hello All.

I have a '94 rx7 I built with a t56 magnum and a stroked LS2 with a stock LS3 top end and stock style exhaust manifolds thru dual 2.5". Rear end is an 8.8 cobra with 3.73 gears.

At one point in its life it put down 468/451 rwhp/tq. I've been a best ET of 11.20 and a best trap speed of 129.80.

Current cam is a hydraulic roller 226/242 on 117+3.5 on LSG lobes @ .600/.600 lift. Idles and drives very stealth which was fun for a while but I got upgradeitis big time.

I purchased a set of the new SPS Haymaker 11* LS3 heads with 2.125" intake and 1.600" exhaust valves. I think they're based off the Mast LS3 casting and I think should be a good match for my 402. These have the same 5.450" long valves with super tall installed height compared to stock. They're being built right now and I will flow them on my bench when they arrive.

I want to cam it up a good bit without making it impossible to drive on the street. I think the light 2850 curb weight and 3.73 gears will aid in driveability even with some overlap. Freeway RPM typically 1800+ rpm so I imagine the thing will be able to cruise in 6th even with a pretty aggressive cam. The smaller intake valve should help prevent reversion as well.

Build -

11.5:1 compression Stroked LS2
4.005" x 4.000"
Callies crank and rods
Diamond ceramic coated pistons with 5.8 cc valve reliefs
SPS haymaker heads 2.125/1.600" hollow/solid stainless valves and 264cc/106cc runners @ 63.5 cc chambers. .685" BTR dual springs and Ti retainers.
.060" thick cometic gasket w/ pistons .016-.018 out of the hole for a low .040" quench
GPI "rod mod" LS3 intake
1 7/8" long tube headers into 3" Kooks green cats and dual 2.5" to the bumper
LS3 rockers w/ trunion upgrade & shims under the stands for setting lash
3/8" manton taper pushrods

Cam specs I am liking right now are 242/246 on 115 + 5 which is 14* total overlap at .050", but I'm looking for input.



Later IVC close and early EVO open to promote high RPM tuning/efficiency. Late intake close will also help keep the long intake runners working at high rpm. Dynamic compression will be right around 8.40 which will keep it 91 octane friendly (hopefully).

I want to go with a LLSR which means final cam specs would likely be 247/251 on 115+5. As for lift I'd like to have around .650" on the intake to take advantage of the heads but want to check valvetrain geometry first.

Power levels of 550whp+ would be nice, but maybe not achievable with an ls3 style intake.

My real goal is to make the engine run from 4k to 7k like a bat out of hell. With stock heads and exhaust manifolds I have always struggled to make the engine want to run beyond 6k, and it has been sluggish below 4k without any scavenging. I know most people want to focus on building a broad powerband with a lump of torque down low - but I'm looking for more of a sports car experience with a high winding engine that runs hard to redline and encourages you to run the gears out. I don't mind a cam that really only comes alive above 4k because aside from initial take-off it should always be wound up.

Any input on cam specs or similar builds?

 

 

My .02 With long tubes I would say 242/250 (8* split),
Minimum, with a LSA 115+3, you are choking off the Exhaust.
Also the FAST 102 w/mid length runners will help
Your top end significantly. Check out my results and build
With LLSR 243/249 W Cam Motion & FAST 102 w/ mid length
Runners. I peak 7100-7300 RPM and carry to
7600+. Contact Kip @ Cam Motion.

 

Gah..yep that's what I want lol. Maybe a little less radical with a slightly smaller cam.

I just don't have room to easily fit a fast 102 in the Mazda engine bay. People have done it but it requires cutting and bashing.

Your other posts say 249/257 for duration though right? Not 243/249?

 

One question why does anyone Guess anymore when you can have a Cam Tailor made for any application with the right Cam Designer. Every build and car is different. Same price of getting a cam made from guessing. One is hear say and guessing and the other is Professional. Call it in and be done!

 

My build is 396" with a 3.600" Stroke with highly efficient
MMS TFS LS3 Heads, most efficient ported or aftermarket
LS3 Heads need at least +8-12* exhaust splits NA,
LLSR 249/257 115+3 would drive pretty well in a 416",
Might go just a touch smaller w/402".
You are right I misread. (4-6*Split for MMS 235 Cathedral
Heads)
With a 4" stroke You need the shorter runners to
Peak ~6500 and carry to 7000.
Again I would talk with Kip.

 

Agree with paying professional for cam specs which I suggested
Twice. Just sharing my personal experience and observations.
Not the same as hearsay.

 

I guess I should have said first - I wrote to Cammotion before I did anything and didn't hear back from Kip. I got someone else who didn't have much to offer. I'll call them before ordering of course.

I also sent BTR $20 and all my info to see what they suggest. I'm curious because I shaped my 242/246 idea around some valve events Brian Tooley was talking about in a thread on Yellow Bullet some years back where he was sharing a lot of info not just about what he targets, but also why.

I made the thread to get some feedback exactly like you posted - badass stuff I haven't seen before despite hours of searching.

Also - I kinda like talking about this stuff and sharing ideas.

I agree the intake is going to be the limiting factor in high rpm performance and will likely hamper things by a good 30+ horse upstairs. If it flatlines and carries to 7 I'd be okay too...just don't want power to fall off a cliff like so many strokers do.

 

While I agree you mostly see long duration splits intake vs exhaust - if I'm holding myself to a max overlap of ~14 degrees the 242/246 on 115+5 was kind of the compromise I was looking at. I figure these heads have pretty radical exhaust flow and a smaller than stock intake valve - so it likely doesn't need as big of a split.

Also I feel that with the long runner intake the additional intake duration will help more with high rpm potential rather than more exhaust duration. It allows me to open the valve sooner to get the air moving as well as get to max lift sooner. Coupled with a wide separation angle I can keep the closing point late to allow enough time for that long runner of air to reach the chamber at higher engine speeds.

239/249 115+4 or something would be doable as well, but I would not want to open the exhaust valve any earlier than 63*, and I feel that a later closing point of the exhaust will offer much less benefit than an earlier opening intake valve.

That's my thought process at least behind a smaller split compared to most LS3 cams. I might get completely different feedback from the pros.

 

Found the flow numbers on a FaceBook link. Nice.

 

Hi Spanks, I have modeled your camshaft @ 682HP (7000RPM)

MY concern is WHY you would ADVANCE the camshaft by four degrees past Split Overlap ?

Your car is low weight and the small torque gain with the advanced camshaft timing may not be able to be put to the ground.

The HP difference @ 7000 RPM is 22 HP

My choice with your stated cam specs would be to change the C/L to a 116* also at Split Overlap.
That result would be a greater torque below 3200 RPM.

The best EAP model, a power guess, could be improved when port flow numbers are provided ?
The Intake/Exhaust specification are also needed ?

Lance

 

Hi Pantera.

Sounds like through your simulator that I'm in the correct ballpark duration wise.

Intake is factory LS3 intake with radius rods from GPI
Exhaust 1" 7/8 headers into dual 3" kooks green cats and 2.5" to the bumper

LS3 style 11* heads with 2.125" intake and 1.600" exhaust valve. Runner CC 264/106 int/exh. Flow numbers from 4.150" bore - no pipe on the exhaust. When I receive the heads I'll flow them on my bench on a 4" bore and compare them to LPE CNC'ed LS3 and stock LS3 castings.

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You're recommending no advance with a 116* separation angle? I may be misunderstanding.

I agree low range torque is not my goal. With a 6 speed, 3.73's, and 2850 pounds it gets up and moves just fine.

 

Don't wanna take up space on your post.


NAVYBLUE210: that wasn't intended towards you just in General.

 

FWIW, @ your target power level, that dual 2.5" exhaust will probably cost you some power vs a full dual 3" setup...not familiar with RX-7s as to how much room there is, but try to incorporate an x-pipe in there to improve scavenging

 

I'll share the combo from my car. Its a 402 with heavily worked LS3 heads that have flow numbers similar to yours. Our compression is about the same too. My cam is a custom HR ground by comp 238/255 0.652 lift with a 1.8 rocker. 114 lobe sep with intake lobe centered at 108 degrees. This engine saw 5 similar cams. My exhaust was 1 3/4 long tubes with a single 3.5 exhaust. I later went with a true dual 3 system that made virtually no more power on motor but shined really well on some nitrous. I also am using a stock LS3 manifold with a 92mm tb. Its my opinion after working with several of these motors with LS3 heads no matter who ports them that at least a 15 degree split in duration is needed NA and 20 or more split when on nitrous.

 

I was thinking the smaller intake valve and high flowing exhaust would require less of a split than a traditional LS3 head.

How much power did you end up making? From your signature it looks like it likes the juice

Here's a pic of our SBE LS3 powered wagon. 10.4:1, 239/251 on 110+2 with a victor jr and LPE CNC ported heads. It's run 10.13@131.

 

[QUOTE=spanks13;19578116]I was thinking the smaller intake valve and high flowing exhaust would require less of a split than a traditional LS3 head.

How much power did you end up making? From your signature it looks like it likes the juice

Here's a pic of our SBE LS3 powered wagon. 10.4:1, 239/251 on 110+2 with a victor jr and LPE CNC ported heads. It's run 10.13@131.

Actually the car in my sig is my big block car. The 402 is in a 4th gen Camaro. I don't dyno my cars anymore. There isn't a dyno close enough to me with out driving 2-3 hrs one way. A 1/4 mile track is my favorite dyno. I would like to try a carbed style manifold on it but I refuse to cut anything on the car. I think it would wake up some more. I forgot to mention I only rev this thing to 6800. Gonna try to increase that next time out. I cant post on here what kind of times it runs but it does OK.

 

I think you did a very good job picking cam specs for your combo. I also think you are wise to be mindful of drivability. Many people pick "dyno hero" cams and then end up hating driving their car.

At 14 degrees of overlap, the car will have a very defined lope, and will buck some. I am thinking it should be all cleaned up by about 1400 RPM in an 11.5:1 402"-416" engine.

If I were specing it for you with your 14 degrees of overlap parameter, I would probably do 242/248 on 115.5+4.5. But, the differences from what you chose are pretty small.

When you are ready to order just let me know. I would be glad to help you. My extension is 7004.

~Steven

 

Spanks13
The above mentioned cam recommended by Steve (AKA SpeedTigger
i believe), would run awesome with your heads/engine combo.
Very close to the 243/249 115+3 that Kip & I put together
for my 396".

I believe as long as the valves are unshrouded the E/I relationship
is more critical then bore/stroke relationship for cam design
in a desired RPM operating range.
but that is only my personal opinion, I would love to hear the
Pros weigh in on this.

The SPS Heads have excellent E/I flow relationship and should
only be held back a little from 6500-7000 RPM due to the
2.5" exhaust section, and less still by a well ported LS3 intake
VS a FAST w/ Mid-Length Runners, again with a ~6500RPM
Peak carrying flat to ~7000 RPM.
Check out Big Hammers 388" thread also with LLSR.
On another note I love the last generation RX7 LS transplants
you have a beautiful car which will be wicked fast with this
combo.

My .02 based on flow #s & exhaust, "if it was my car"
240/248 115+3
as Pantera mentioned with such a light car and
3.73:1 gears you don't need the advance for low end.

 

Thanks to both of you - especially the compliments on the car! It really is a blast to drive.

Steven I'll be sure to give you a call when I order. I'm probably 2 weeks away from having the heads in hand. I want to run them across my flowbench with a 4" bore before making a final selection. Also want to check the valve train geometry and see how much lift is realistic.

The cam specs we're talking are 5* short on intake and duration if converting to a solid roller, right? Or are we talking final numbers for a LLSR?

It's funny - my goal with the advance was to get the exhaust to open sooner, not so much to get more torque down low.

One thing I'm curious about as E/I ratio seems to be the latest metric everyone is looking at for spec'ing cams (at least on this site I mean nothing is really new) - these values are super easily skewed by using a pipe on the exhaust port or not. An exhaust pipe can increase exhaust flow values by a huge margin on a flow bench. Which are appropriate to use?