Thanks for posting the card.
I've not heard a single circumstance of Jones not giving good service.

Most accounts are 500+ HP out of these combinations. That is: 383, 195's, 10.5:1 and well spec'd cam. 400 RWHP doesn't seem unreasonable to me.
It's a safe bet that the exhaust will be the most challenging.

 

I take that back.

 

i have done this in excel, use a high order polynomial curve fit. Used it to verify piston to valve clearance and how deep my piston valve relief needed to be. But it be more accurate with more points at .100, .300, .400 etc

 

True enough. But I'd imagine those points are something that Mike holds pretty close to the vest.

 

The c4 chassis makes it easy to put a good exhaust system, were you thinking of the 3rd gen f body saying the exhaust will be a challenge?

The plan is hooker super comp hkr-2149 with the emissions tubes ground off and welded shut. 1-3/4 primary 3" collectors. Keep the exhaust through the tunnel to the diff at 3" with either an h or x pipe and mandrel bends. then use vbands near the diff to be able to quickly drop the 2.5" tail pipes off. thought about even using the stock tail pipes and mufflers off of a 96 lt4 grand sport.or maybe just weld in some cut outs and not have the tail pipes removable.

Do you see anything inherently wrong with this? I was hoping by the time the exhaust got through the tunnel it will have cooled enough that shrinking down to a 2.5" stock tail pipe wouldn't hurt power too much, but if it does i could always just shoot it straight through in 3 inch and get different mufflers. ill be removing the spare tire carrier. so I will have some room in there to get creative as well. i could shoot it straight out the back with very minimal bends in the entire system without affecting ground clearance.

anything I should reconsider about this plan?

 

From what ive seen on latemodel camaros with dual 2.5 vs 3”, 3” makes more power every where and those cars are 500 hp with bolt ons

 

I would say 3" is a must at that power level but my comment was more of a general statement more than anything. Interesting test with the Camaro. I believe Toddoky from Holly/Hooker has chimed in here once or twice to say that their dual 2.5" system is good to the 450 HP level before it becomes a restriction.
Which leads to this. Airflow again is key. You have to have enough of it on the exhaust side to allow for the full output. Dual 3" in and of itself is good but it's the mufflers that tend to be the choke point. A general rule of thumb is an exhaust that'll move 2.2 CFM per HP produced at the crankshaft. Finding mufflers with at least 600 CFM each is what you're after. The average 3rd gen with it's single traversely mounted muffler made that nearly impossible. Or incredibly loud as a 1200 CFM muffler doesn't do much for noise abatement. It's a little easier now with more than one full DIY kit available for full duals.
Now that 2.2 deal isn't a make or break thing lest I get burned here. But output starts to diminish as the capacity of the system is reduced.
I like to use PipeMax to calculate header dimensions. It also provides best and worst lengths for the entire exhaust. It demonstrates how packages that have mufflers that hang off of the collectors or are placed back and dump before the rear axle could have a negative impact on the exhaust tuning and make output worse. Stuff worth paying attention to.
What interests me the most there is that collector lengths are determined. This is what I'll be taking into consideration because while I won't have the most powerful engine at the track, I'm going to be sure to wring the most of it. Cut outs placed at the appropriate distance from the primaries will be part of racing package. I'll tune to that and the cam spec will geared toward that as well in that a single pattern is likely.

 

That's the y pipe Holley sells with these headers for the c4. 3 inch at the collectors into a single 3.5 inch. but ill be able to use it and separate them and add the X / H basically right where the current Y is. they sell it with the flattened section drivers side to make room for the 700r4. hoping i can cut that out and not have it decrease in I.D. right after the collector.

Sounds like my biggest setback will be less than desirable placement of the x/h pipe. Closest I'll be able to get it to the collectors is right at 23 inches from the flange and it seems like 18" is a good general guideline for most 23° 383/406 stuff. Thought about maybe a box type terminator similar to how the 86-93 fox aftermarket systems were. Not quite a termination box. But close I bet I could make it almost 1 cubic foot inside volume. And taking off from that with dual 3" pipes is easy enough. Do Either of you guys have pipemaxx and willing to crunch some numbers for me? I'd pay you if it helps me get an optimal setup. My application is street, but I would like to be able to "uncork" the system to make a rip. If you'd call it that. Hehehe

 

Sent me your details i can run pipemax for you.

 

hey Orr, what exactly do you need from me to get accurate results bro?

 

Here's a screenshot of a Pipemax file.
The data points are across the top in bold text.
Post those and Orr should be good to go.
I'll be interested to see how it plays out against some of the files I've accumulated (although my program is on an older PC and not accessible at this time).
Hope that helps.

 

I probably have most of your information but bore stroke rod length, compression, valve size, and cam specs lift duration and rocker ratio. I should beable to get everything else

 

385 cubic inch-3.750 stroke -5.7 i-beam rods - 4.040 bore 12cc circular dish with 7/8" quench full circle speedpro #H859cp40. I softened the sharp edges of the valve reliefs, nothing intense, just a machinist deburing tool10.43 scr , pistons are @ zero deck.
.041" compressed thickness 1003 felpro 4.166 fire ring 195 street eliminators 2.05 intake, 1.60 exhaust 8017 springs angle plug afr# 1040, heads cc @ 62.8cc. had them skimmed when the plan was stock l98 short block. Cam card is in above post but, 276/280 228/232 @ 50 .576/.576 valve lift 110 lsa w/107 icl
1.6/1.6 shaft rockers. Believe pushrods came in @ 7.100" perfect contact patch.
i had to do quite a bit of grinding to the headers inside the flange to get a decent gasket match, think hooker designed these headers for stockish heads. But there is absolutely none of the pipe blocking the exhaust port now 1-3/4" primary 3" collectors. Hooker lists collector length as 8 inches, primary length as 26". #hkr-2149
Intake is a miniram, not quite a perfect gasket match to the heads, it does however match the 1205 gasket almost perfect, slightly larger than the head port entrance, maybe a .040-.060" lip.the intakes runner corner radius are sharper than the gentle radius of the heads. I used a bore scope to line it up as best I could. i showed the mismatch to several on speedtalk and the consensus was SEND IT. so I didnt pull it and have the intake welded and matched more precisely.
Has an old accel 58/58 mm 1000 cfm throttle body, I opened up the intake to make sure there was no lip at the mating surface. I think it's accel #74191??
36pph injectors
With a stock 89-92 c4 starter I've got 198-204 psi. That was @ 50° cold, never started engine.

 

Race header long tube 1.69-1.818 primary OD pipe size
30.8-33.6” long. Low to mid range power

1.893-2.018” mid to high rpm power
same lengths. But this to me seems large for a mildish 385, even tho i have seen ls motors make better power with 1.875 tubes than smaller ones

collectors 3.12-3.376” dia about 18.3 long or 36.6 long
max collector size for top hp high rpm is 3.376 to 3.876”

h pipe 18.3 from end of primary tubes. X pipe 73.1”

total exhaust tuned lengths 18.3, 36.6, 73.1, 146.3“ primary to tailpipe
lengths to avoid 27.4, 54.9, 109.7, 219.4

street header primary 1.63 to 1.755” od and 30.8-33.6 long
3-3.5” collectors
same h or x pipe info

shorty headers primary 1.63-1.755 low to mid range
1.693-1.818 higher rpm hp. 15.4-16.8” long
3-3.5” collectors
h pipe 36.6” from end of primary or x pipe 73.1”


all assuming 5900 rpm hp peak with that cam which should be about right

 

this would fit nice it's 3" But the length from collector flange would be around 27" guess I could get a parallel x and place it further back to work with the numbers you came up with.

 

Note how the x and h pipes are placed at points which coincide with the 1st and 3rd best tuned lengths. A pulse generated at this transition would arrive at the exhaust valve at the correct time for a net benefit.

At 27", any pulse generated from this distance would have a detrimental impact at the valve reducing VE.

Not that this is stuff that any of you didn't know but having had experience with PipeMax only on a header design scale, (I never considered tailpipes, h's or x's) I thought it was worth noting.
Thanks for posting gentlemen. Very informative.

 

I never dyno’d pipe max recommendations, only tried to build around their header recommendations. However i have seen the difference collector lengths make on dynos and at the track for others so there is something to it, and would bet it works for full exhaust setups. How much i do not know. Wish i did

 

looks like the best compromise ill be able to get is the X located at the 73.1 from the primarys that is doable in the driveshaft tunnel.