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Those cams are all so tiny to my brain. I run a 212/218 112 .600/.600 in a 5.3 truck!
The 408 gets by with a 247/255 113.5+2 625/.615
I know you can over-cam an engine badly, but I fear you are under camming the bajeezus out of your engine. If you must pick one of those cams and nothing else, I'd pick the 3rd option because of the DCR
Well. Like I don't need 600rw. I've got 305s on the main wheels. So if I'm not going whole hog for power then I don't need to run a big cam and experience a big cam profile. It's still bigger than the oem LS7 cam. Ball park GM hot cam, which I know is consumed by the big cubes.
That third cam is essentially an LPE GT11 but with 4 advance.
It's hard to get everything I want out of low compression. And esoihard to be mature and continually tell myself I don't need a goofy giant cam to enjoy the car when the size of the engine is going to make plenty on its own.
9cr and a 205 intake runner.... Harder for me to conceptualize a working combo, especially when the intake is essential opposite of what I'd want for it now. But maybe the intake and runner velocity will match better now?
Goals:
6500 redline (or at least 6300)
Negative overlap purely for fumes
No chop (goes hand in hand with overlap)
Lowish IVC because of low compression
And last being that, attaining this (ish) I then want the smoothest cam, idle, and mpg
It's all semantics on this end since I am basically somewhere between a GM Hot Cam and Arun's Jam Cam for very loose specs. Nothing wild for sure in a 427.
What I'm finding with the now presumed 9.0 compression is that I am pigeon holed to a great degree because I need keep dcr between 8 and 8.4. That means keeping intake duration in the low 220s or high 210s and dropping LSA while keeping advance.
This shoves me against a wall when trying to keep that overlap at -9 or lower and I am pushing the IVC down close to 40 or at least not higher than 46 while also not seeking a 115 or 116 LSA. That's just me. So I'm looking at 118+4. If I knew the actual piston to valve clearance I could consider more advance but I'm not opening the engine up any more than I need to - keeping that project snowball effect to a minimum.
At best, I do now know the heads appear to have began life as AFR 205 Mongooses which were then subjected to the madness of Brian Tooley twenty years ago who opened them up to a 72cc bowl and bore larger than 3.90 and I believe went to 228cc intake runners (possibly 238cc though). They are allegedly some very high velocity heads for the time and flow about 346cfm. From my driving experience which could be a combination of Tune/Blower/Cam/Heads the car felt like it had an on/off switch at 2000 rpm where it went from loud but sedate cruiser to ON KILL like a dog about to bite that slow fat kid down the street. Running maths.... (not really).... I'd guess at least a -20cc dish or maybe a lot more to be near 9.0:1. But I've got high velocity runners from the intake, high velocity runners in the heads, and a bunch of BIG cylinders trying to suck juice through a straw. I can conceptualize it but I do not have the experience to say anything about how it might affect the final product other than to say I'm trying to target the highest DCR within my constraints without ending up with a lame duck unresponsive engine. I didn't really think the car would be 9 when I started out. I really thought 9.5 was a fair base. This new knowledge doesn't make it harder to set up, it just narrows my options vs my preferences.
And honestly I can really do no better than taking that GT11 and corrupting it to have lower lift (my heads gain nothing significant above 615 intake or 595 exhaust) and a +4 advance. It's magic is *because the intake duration is lower at 215 that it beats the IVC down to 41.5 when paired with the 118+4. That gives me an 8.4 DCR on a 9cr engine which is the snappiest way to build pressure I have found in this LSA area. It does soften the top end more than I wanted and hits peak around 6000 or so. It can hold out to 6500, but it would no longer be pulling all that way to redline.
This is the snappiest fix I've found so far for that 9.0:1 noose and a strong contender. I have a few others which are 8.3 DCR and IVC up to a 44 max I'm still musing. But the decision will be made today.
I just caught up to where you are in this build (been staked to garage projects for the last 4 months) and, holy smokes, what a conundrum! Dealing with the challenges you face, especially under limiting restrictions, including the ever restless gray matter procession of cumulative information…goodness, sir! In what ever state you arrive in, just from the world I live in, parts and pieces of everything that make up that engine would even be in the new room (please excuse, li’l Tusc!) to be mic’d, cc’d and so on to hone calculations while sticking with what is on hand. I know, right?, just my world. I keep looking over your shoulder and think about solid engineering and physics working in dynamic environments and the changes to tune that occur until reaching optimal equilibrium.
Anyone would be influenced by the tribal nature of testosterone but the sciences so very often run far from the male squeeze. I totally admire the direction you are taking with exotics still in play and truly honoring the processes of pristine efficacy. All said while ingesting the morning round of deep, dark and concentrated liquid boost. Great processing!
All that and then recall that optimal may neve be able to be achieved because I made the financial decision based on what was on the market and marketplace as the time to choose an intentionally partly mismatched intake. And now to see that 9.0cr takes it further away from me where the 9.5 would have allowed my preferred version of the cam to pull straight to 6500 at least. This current pressure-grab design is great in many aspects but it dives off at 6000 softly.
Dyno tuning session. Funny guy! This one is getting only a street tune. Likely an in depth one though! Mark and I are probably going to spend a weekend or ten getting it dialed in.
HP tuner in the hands of two mildly experienced users (I won't call either of us tuners yet) but chasing logs with a paid access AI and a ton of Google reference gets the job done.
Would it even be possible to squeeze the head for a half point CR? Clay the CC to verify clearance pre razor. Spacer the intake, if necessary. IDK, just passin’ air…
If this were my only, or my primary project and my spine worked without tagging me out if I do more than even basic work.... Absolutely. I'd actually change out the pistons to get a proper 11:1 compression out of it and have whatever cam combo I wanted. My emotional and financial investment is in the Z06. This coupe is badass, but I need to keep the project scope low. I already snowballed it today by buying a body panel targa roof for it. My buddy is working in Akron this week and is going to stop in PA on the way home to grab it for me.
So the coupe? I'm trying to keep it to just the cam and be done.
And yet the LPE TT kit has not sold yet..... And the thought of selling the Kooks pipes to install the turbos is even more enticing now that I know cr is lower and it need a a little air to breathe properly.
Twinz, of course. I gotta say when I first read about your purchase, I had to spend some time in confession afterward. Also, I’m very sympathetic toward back support circumstances. Recently spent 6 months rebuilding core strength to regain horizontal hover ability.
In the world I occupy, I was just fortunate to land the FRC without attracting to much attention from the sponsors. A second coupe would be the verboten.
The audio on the GT11… Dang the influence of vicarious social media!
Right? For all the science and maths applied I still end up significantly motivated by the salacious sensory audio input of a random YouTube vide from twelve years ago.
It helps that the maths happen to be optimal in that combo save for the extended rpm range.
I ranged the intake duration and LSA up and down a bit. I was considering one at 219 which looked great.
Where I ended up was 216 and if the model is at all tangible (or at least relative in comparison) then the truth is that the Intake duration drove the IVC / ICL lower which also drove DCR up a point and pulls a consistent 10-15 tq gap and maybe 5ish hp over the curve while slightly extending peak power out by maybe 100 rpm. That was vs the 219 variant.
All this amounts to is absolutely just splitting hairs. Inconsequential minor data points which will never be realized by SOTP and may simply be wrong from the get-go. In a month or so I'll find out if this thing is boring, slow and weak or if it retains some of that throttle snap I'm after despite the low compression ratio.
Under uncommonly perfect conditions it may yield a 9 / 17 split for mpg in town and highway (3.73s out back, remember). Power tends to flatten off around 5900 with a peak at 6200 and holds through 6500 without dropping off severely. Not at all the hard puller I had initially plotted to keep pulling straight the 6500 and yet I am not married to reaching that RPM too often. Power under the curve, part throttle pulls, responsive throttle, and making a low compression dog jump and act like it wants to bite... I think it will excel at these while still not stinking of gas at a stoplight. I know it is barely bigger than a GM Hot Cam in the end for pure duration specs and very small for a 427 but that is where this is taking me. If the model is horribly wrong and it only makes 490rw.... heck... that is still awesome in my book! One of my favorite C5 setups was a stock LS1 with 10psi which may have made that power but still never made the torque this 427 ought to put down.
I am really curious to see what the final outcome is. I'm thinking it will rip vs a 346cid LS1 with a Track Weapon cam while still being far more street civil. Not nearly as wild while delivering more power.
Pretty darn close to the LPE GT11, so I am sure all will be fine and you should be happy with the results in your cathedral port 7.0L and yes way more torque than a 5.7L. Would have 10.5:1 to 11.0;1 been better, again yes of course, but then it would not have been that engine in that car.
Ten point five would have been awesome. Nine point five would have been acceptable. Nine flat is less than I want and I'm adapting to make it work. I will still say a fond farewell to whatever tires get mounted.
This looks much much better as a new offering for the market. It also is a nice nod to the C5-R and therefore a soft reference to the engine here. I think it looks amazing and am eager to see more installed pictures.
Does it actually evacuate heat from the engine or fenders if you mod them? Eh maybe. Does it help with downforce? Probably not. Does it help withe radiator airflow? Who fricken knows, so long as it does not hinder it. That is definitely one of those hoods you do just for the look. I'd be after it without the fender vents too. That would be a clean look.
That is one of the better looking vented hood options out there. Not sure if they still make it in the lower raise style or not. Too bad there isn't one out there like it without the fender vents.
