skinny z

Which 4" muffler are you speaking of that will meet your CFM requirements and not be deafening?
Remember, without splitting hairs (as the 2.2 CFM/HP is at the extreme end), you're still looking for a minimum 1200+/- CFM. (I forget exactly what your crankshaft HP is but I'm reasonable certain you're on the north side of 700 no?)

Fast355

iTrader: (2)

Most of you would be suprised how well a 1-5/8" primary and 2.5" collector into a 2.5" dual to single 3.5" exhaust will work. I have dual 3" to my muffler because my factory built 350 already had that size tubing from the manifolds to the muffler. I swapped the cats out for new spun Thunderbolt metallic core cats and put a dual 3" in/single 4" out muffler into a single 4" tailpipe to replace the restrictive GM muffler and factory 2.75" tailpipe.

570hp with 1-5/8 primaries and dual 2.5" collectors and exhaust. Given the heat and pressure of a nitrous exhaust port, I doubt it would lose much on juice.

https://www.google.com/amp/s/www.mot...-pump-gas/amp/

Orr89RocZ

iTrader: (20)

i thought the same thing based on sizes pipemax always recommended but sometimes chassis design restraints will compromise bend radius and hurt power some.

it was clearly evident on late model ls engines, anything in that 350-400+ whp range almost always made more power and never lost anything when going to larger 1 7/8 headers vs standard 1 3/4 options. Nobody ran anything smaller and those large sizes seemed way to big compared to what is run on small block chevys. But dyno and track results dont lie. Id be curious what is left on the table with a larger collector at least and then a 1 3/4 tube
same with duals. Late model 5-6 gen camaros with dual 3” always seem to pick up over dual 2.5” in that 400-500 hp range. Consensus is it’s probably too big but it worked. A good single 3.5 can go a long way, a 4” even better except for weight

Fast355

iTrader: (2)

The 1-7/8" guys for the most part did seem to comment alot as to how much low-midrange they lost especially at part throttle. No free lunch there. Larger pipe = less veloctiy and that shows up most at lower rpm and part throttle. Faster on the track but sluggish in normal driving.

QwkTrip

iTrader: (22)

Eh, low end torque is over rated for a performance car. You only need so much to drive around and gears will make torque at the rear tire if you want more. Swell that torque curve at high rpm and the car will be smokin' fast. Add cubes and gears to improve drivability.

Power is a function of Torque and RPM. Everybody talks about torque but RPM is often lost in the discussion and waaaaay under utilized by most people.

IROCZman15

iTrader: (25)

i was swapping out the Lakewood 90/10 front drag struts for my Koni yellow struts today and while under the car I checked over the exhaust. So far, teh exhaust is workign great and the ground clearance is also great. Not one sign of any exhaust toughing the roadways or speedbumps. I know the v-band clamp bolts are in a precarious position, but its actually the only way I can position them. Heat wrap is holing up great, and even the over-the-axle pipe has zero signs of contacting the axle or body. The only thing that does bother me, is the stains that are on the stainless headers.

QwkTrip

iTrader: (22)

Stains or just changing color? They will discolor with heat cycles, that's normal.
(And remember, I did warn you that cheap stainless will rust.)

IROCZman15

iTrader: (25)

ah, the change in color was expected. many many years ago I had those edelbrock TES stainless headers and they did the straw yellow/blue color change. And yes, I remember ya mentioning the cheap stainless pitfalls; but fortunately (so far) there is no sign of rust on these! however, this "staining" is almost like a "hard water" looking stain that has appeared on the lower parts. Up top, the headers are doing ok, and I even wiped them down once with a metal polish. but down low, it looks like hard-water stains, and I can't think of what it might be caused by except...I think i was spraying some purple degreaser under there one day when the headers were hot, and this might have done it.

- all these below photos were taken today, June 12, 2022

here is a photo of the headers up top:





and one from underneath at the collector area:
...see how it looks like liquid drip marks?

Fast355

iTrader: (2)

To run more RPM than I currently do would be $$$$ and sacrifice durability. Torque is what is fun especially on the street. My 383 just put down 399 rwtq uncorrected on a Mustang dyno and carried more than 370 ft lbs from 2,500-5,200 rpm. HP peaked at 382 at 5,600 rpm and it held in to 6,200 rpm where it was still making 370 hp. It was a 102F, 38% humidity and 29.70 barometric pressure in the shop, giving a 1.079 std correction factor for those that want the inflated number. Keep in mind I also have a 4L85E and a 10.5" full float 14-bolt and kept it in 2nd gear to keep the driveshaft in it. The torque makes 6,500 lbs of van feel light on its feet so to speak. I would still pick this engine in a car over a 7,000+ rpm screamer with less low-speed torque.

Orr89RocZ

iTrader: (20)

that i am not sure about, i have only seen the wot dyno pulls at my friends dyno shop. Part throttle feel would be hard to measure and is a driver preference i guess. Ofcourse when you have a good header the cam needs to keep that in mind, you certainly can over scavenge exhaust.

skinny z

With excessive overlap?

skinny z

Which 4" muffler are you speaking of that will meet your CFM requirements and not be deafening?
Remember, without splitting hairs (as the 2.2 CFM/HP is at the extreme end), you're still looking for a minimum 1200+/- CFM. (I forget exactly what your crankshaft HP is but I'm reasonably certain you're on the north side of 700 no?)

Orr89RocZ

iTrader: (20)

exhaust valve open and close points, overlap, total duration…yeah all of that

skinny z

EVO, EVC and duration all combine for the overlap value which is why I stated it the way I did.

That said, as you mentioned, it takes a good exhaust to get to that point of over scavenging. I can't say it would ever be a reality given my current engine package.
Perhaps cutouts will make a difference there as, if all goes to plan, I'd build around more of a track orientated car with open headers than one with a full street exhaust. I'm safe to say my street racing days are long gone and I'll do my testing at the track.

That is if I can afford a $200 tank of fuel for any given race weekend. Man, that sure got expensive in a hurry.

Orr89RocZ

iTrader: (20)

yeah but you can have same overlap with totally different evo evc points. Would they behave the same? The combination of parts can have influence

surprisingly these two cams seem to perform the same for me, only 3 deg diff in overlap. Similar power, similar powerband, similar idle and drivability, smaller one spool faster. Different events

254/259 109 lsa
267/272 114 lsa

skinny z

That's 3 degrees at .050". But .050" isn't a good measure of overlap in my opinion. But I know comparing advertised values is a mixed bag so we can leave it there.

To bring the question back around regarding over scavenging, with the same overlap but relocated exhaust and intake events (which keeps duration the same), would the effect of the exhaust induced induction cycle be equally the same? Let's not go outside of what a reasonable cam specification would be.

QwkTrip

iTrader: (22)

I haven't pursued it any further.

Orr89RocZ

iTrader: (20)

true. 303/309 267-272. Vs 285/292 254/259. 78 vs 69. Which overlap window matters most? Entire shape and position relative to crank degrees? Even tho intake opens 5 deg later and closes 9 deg sooner on the smaller cam, exhaust closes about same point. 1 deg difference. But surprised they behave similarly.

if you keep same lobes and change the opening closing points while keeping same lsa and overlap, you are changing valve events with relation to piston position so everything changes with regards to scavenging effects imo

skinny z

I believe the real value is inch degrees of overlap.
Even with two cams with identical seat values and valve events they will (should) behave differently if the .050" numbers are significantly dissimilar.
I've got a choice between a 284/236 and a 284/224. Look at that spread. How much differently I can't say other than one appears to produce more power than the other.
I'm in agreement on valve events vs scavenging but if you keep everything the same (duration, LSA and lobe profile) what you're really doing there is just changing how the cam is timed into the engine aren't you? Those results of ICL are well documented.
Keep in mind this is smaller CID NA engines I'm talking about. The behemoth twin turbo of yours speaks another language altogether.

Orr89RocZ

iTrader: (20)

To a point, the faster lobes will make more power if timed right. Darin morgan has said the key to engine masters challenge where making power from like 2000-6500 rpm was valve motion out the ying yang lol. Meaning fast. These are not street endurance lobes.

so the 236 at .050 should have much more area under the lift curve and pass much more air in a cycle than the 224. Power band should be higher rpm. Ofcourse you have your drawbacks…more aggressive valve motion, more overlap at .050 for lower speed drivability, etc. good tuning can help with all that however

skinny z

And this is my current dilemma regarding a cam spec. I haven't fully decided what purpose the car will be now. This is especially true now that fuel prices have gone stratospheric. (FTR: We're over $7.00 USD for a gallon of 94 octane fuel).
I'd go with an aggressive lobe like .360" from Jones Cams (or COMPs XFI) if I stuck to the drag strip. That would the 284/236 profile. Maybe 288/242 which is still within the capacity of my heads and RPM limits. Overlap in the seat to seat 70's with a 108 LSA.
If I decide on more of cruiser, then I'd dial it back a bit. Or a lot.
The rest of the engine spec is in place for now save for the final measurements for compression ratio (and actually getting my shortblock back from the machine shop). Perhaps a change in carb or intake manifold down the road depending on which way I go but the car needs a thorough going over and that'll take more time. Most certainly a better exhaust (which is why I'm posting here...)

And a garage!! That part is just killing me.