HP limit of 1973 A body V8 340 manifolds?

[StreetSleeper]

A blown alcohol 526 wedge on nitro that gets 31mpg with a 2800rpm converter and a 3/4 race cam. Why?

How the hell is that possible?!

 

[StreetSleeper]

in my experience every application has been unique. my 65 dart had manifolds with tti and jones mufflers dumped at the axle and it wasn't ear-splittingly loud. contrast that to my 69 barracuda with manifolds, flow masters and pipes to the bumper that is damn near painful.

more muffler will mellow it out, and depending on the performance level not be detrimental to performance-- at least not in any meaningful way.

but glass packs are always gonna sound glasspack-y

Were the two different car’s engines significantly different? Displacement? Compression? Camshaft?

And thanks!

 

[StreetSleeper]

.

Starting to wonder if it's one of the DTM 318 Specials.

I represent that remark.
Although it is nigh impossible to defend DTM.
I imagine people like body work guys, perfectionists, wanting every fraction of a good idea not wanting to leave anything on the table.
Although you might never buy/build a car, or it becomes a undriven garage trophy if completed.

I am looking forward to seeing a monster big block 9000 get 30 mpg’s!!

 

[318willrun]

I just picked up a 1971 340 from a friend who had it for years. Bottom end is rebuilt with 40 over pistons. It has X heads, unported as of yet. Not sure yet if I will build it or just sell it.

But with the purchase came a set of 1973 340 exhaust manifolds, casting dates of May 1973, casting numbers 3418623 (right) and 3614368 (left).

Assuming a moderately built 340, what HP level will these manifolds allow before becoming a restriction? And what HP can the '68-'70 high flow 340 manifolds handle?

Apologies if this has been written 50 times before, I've only been in the Slant 6 engine section here for the most part.

My input would be "they become restriction right from the factory". I put headers on a 318 2bbl in a van, that already had dual exhaust and dropped 2 tenths and gained 2 mph in the 1/8. I pulled stock manifolds off the 360 in my Duster and went to Dougs, dropped the 1/4 mile times but can't remember the exact amount. I've never added headers and not drop the ET, and I've done it a bunch over the years. Now, can you run with stock manifolds? You bet, but it's just whatever route one would like to go.

 

[junkyardhero]

Were the two different car’s engines significantly different? Displacement? Compression? Camshaft?

And thanks!

not particularly. the barracuda has a little more compression and cam. same size motor.

 

[MopaR&D]

Nope. In an all out performance situation one only needs to look at what top fuel does. A single pipe per cylinder aka zoomies. Thats the best an exhaust system can get for all out performance.

I might've missed something but are you saying even N/A engines don't benefit from having the header tubes merged into a collector? Top Fuel and other supercharged drag-race engines use zoomies because the blower negates any need for exhaust scavenging...

Also exhaust after the header does affect scavenging quite a bit although it's only below peak torque, Engine Masters tested it and saw big gains when they added collector extensions vs. headers open at the collectors.

 

[TT5.9mag]

Here is the current passenger side manifold on my car. It has been 10.11@133. The outlet is just under 2". If you look at it and don't think it's a restriction even in its current form on a stock motor...

View attachment 1716543525

On my 68 manifolds I have done practically nothing. Took the lumps down a bit on inlet side and opened the exit up to the gasket size. Car weighs 3245 going down the track at 121. My passenger side is much better than the later ones. Oh, removed the flapper valve.

All the money, all the time, all the effort, to go that fast with manifolds is definitely respectable. But I have one question for both of you, if long tube headers were allowed in F.A.S.T how quickly would you have a set on your car?

P.S. you don’t have to answer, I know already.

 

[TT5.9mag]

How the hell is that possible?!

It’s not.

I might've missed something but are you saying even N/A engines don't benefit from having the header tubes merged into a collector? Top Fuel and other supercharged drag-race engines use zoomies because the blower negates any need for exhaust scavenging...

Also exhaust after the header does affect scavenging quite a bit although it's only below peak torque, Engine Masters tested it and saw big gains when they added collector extensions vs. headers open at the collectors.

No I didn’t say that. What I basically said was scavenging comes from the header, more detail would say that scavenging comes from long tube headers and a merge collector and usually is best with 12-18 inches of tube past that. But we didn’t go in to too much detail. I could have been more clear. I did however say that with manifolds, and a tti exhaust (like George Jets has) there is NO scavenging effect and I meant it. Top fuel uses zoomies because it’s the best. Period. If something was better they’d use it. Supercharged street engines with street/street race cams can absolutely benefit from a long tube header and scavenging. I think you’re confusing what I said about TURBO stuff.

 

[StreetSleeper]

It’s not.

No I didn’t say that. What I basically said was scavenging comes from the header, more detail would say that scavenging comes from long tube headers and a merge collector and usually is best with 12-18 inches of tube past that. But we didn’t go in to too much detail. I could have been more clear. I did however say that with manifolds, and a tti exhaust (like George Jets has) there is NO scavenging effect and I meant it. Top fuel uses zoomies because it’s the best. Period. If something was better they’d use it. Supercharged street engines with street/street race cams can absolutely benefit from a long tube header and scavenging. I think you’re confusing what I said about TURBO stuff.

Yeah from other threads on this topic someone said Mazda (skyactive?)ran 14 to compression (not on topic, but same engine) and their exhaust manifolds were much longer than all other makes /the number 14 inches pops in my head no reference though:

Google: “Mazda utilized an extensive suite of engineering modifications—such as a unique 4-2-1 exhaust system and special piston cavities—to achieve these high ratios without causing engine-damaging pre-ignition…”

Piston cavities boggles my mind

 

[StreetSleeper]

My input would be "they become restriction right from the factory". I put headers on a 318 2bbl in a van, that already had dual exhaust and dropped 2 tenths and gained 2 mph in the 1/8. I pulled stock manifolds off the 360 in my Duster and went to Dougs, dropped the 1/4 mile times but can't remember the exact amount. I've never added headers and not drop the ET, and I've done it a bunch over the years. Now, can you run with stock manifolds? You bet, but it's just whatever route one would like to go.

I drove 150mph on exhaust manifolds with 1973 340, less power yes, restrictive, no.

 

[StreetSleeper]

If I remember correctly, some of the most efficient exhaust was ‘turbo compounding’-1950’s tech from piston engines on planes using turbos


“
Instead of simply venting exhaust out or using it exclusively to drive a turbocharger (which compresses intake air), a turbo-compound engine routes exhaust to dedicated turbines. [1, 2, 3]

• Power Recovery Turbines (PRTs): The high-speed exhaust spins these turbines.
• Mechanical Linkage: The spinning turbines are connected directly to the engine's main crankshaft using a combination of fluid couplings, gears, and shafts.
• The Result: This action directly provides extra rotational force to the propeller, significantly increasing horsepower without burning any additional fuel

”

 

[junkyardhero]

I drove 150mph on exhaust manifolds with 1973 340, less power yes, restrictive, no.

i call into question the veracity of this statement.

 

[TT5.9mag]

i call into question the veracity of this statement.

Here we go

 

[TT5.9mag]

Google: “Mazda utilized an extensive suite of engineering modifications—such as a unique 4-2-1 exhaust system and special piston cavities—to achieve these high ratios without causing engine-damaging pre-ignition

I will not be doing that. I have a good friend that is an engineer for a major auto manufacturer. He was designing a variable compression engine (similar to what Mazda was doing there) and his drawings just made my head hurt.

 

[StreetSleeper]

i call into question the veracity of this statement.

1973 Plymouth road runner, a833, unknown axle ratio
I tried passing 1955 Chevy with a 454 & 700r4 on the way to ?Waycross? Georgia to a car show there. I was taking the backroads. Previous deployment RRR tuned up my 4160 carb & fixed a broken transmission mount. I buried my foot to the floor & buried the needle past the 150mph speedo.
I still claim that it is true.

 

[StreetSleeper]

Here we go

No big deal. I have much more important irons in the fire than ego and pride, at least right now. I know I did it, in the next life maybe they can watch me do it. The 55 Chevy wouldn’t slow down for me to pass & traffic was on coming enough to back off to avoid scaring the other drivers-it was a two lane black top, so to speak.

 

[junkyardhero]

1973 Plymouth road runner, a833, unknown axle ratio
I tried passing 1955 Chevy with a 454 & 700r4 on the way to ?Waycross? Georgia to a car show there. I was taking the backroads. Previous deployment RRR tuned up my 4160 carb & fixed a broken transmission mount. I buried my foot to the floor & buried the needle past the 150mph speedo.
I still claim that it is true.

really selling it here.

 

[318willrun]

I drove 150mph on exhaust manifolds with 1973 340, less power yes, restrictive, no.

Less power equals more restrictive. You’ve basically said what I said without meaning to say what I said, lol

 

[TT5.9mag]

1973 Plymouth road runner, a833, unknown axle ratio
I tried passing 1955 Chevy with a 454 & 700r4 on the way to ?Waycross? Georgia to a car show there. I was taking the backroads. Previous deployment RRR tuned up my 4160 carb & fixed a broken transmission mount. I buried my foot to the floor & buried the needle past the 150mph speedo.
I still claim that it is true.

It would take almost 300 (real) wheel horsepower to make a coefficient of drag of .51 and a frontal area of 24 square feet (those are rough numbers for a 73 roadrunner) to hit 150mph in absolutely perfect conditions. In 1973 the 340 was rated at 240 net.

 

[StreetSleeper]

It would take almost 300 (real) wheel horsepower to make a coefficient of drag of .51 and a frontal area of 24 square feet (those are rough numbers for a 73 roadrunner) to hit 150mph in absolutely perfect conditions. In 1973 the 340 was rated at 240 net.

For the sake of fun/not caring to argue, it was bored 30 over (the 340), had the ‘428’? Labeled, (lower than 10 to 1) four valve relief pistons, and a larger than stock camshaft (no idea, seemed mild to me-Rusty’s observation was that it was larger than stock,

I never fully bought into co-efficient auto wind ‘science’ after getting ticket in a 1980 impala 4 door sedan, 3 speed auto, 267ci sbc powered car going 120mph. Everyone says that’s impossible as well. Can’t convince everyone, though if any doubters see me in the after life, I want an apology.

In both vehicles, it took quite some time to get to those speeds, much much much longer in the Chevy, which was dangerous enough to pull out into traffic (highway gears). The Chevy was a daily driver that made a few trips back home to Texas from being stationed on the east coast.

 

[junkyardhero]

I never fully bought into co-efficient auto wind ‘science’ ....

well, if you don't believe in science then the conversation is over.

tell yourself whatever you want, amigo. if it makes you feel good then that's all that matters.

 

[junkyardhero]

It would take almost 300 (real) wheel horsepower to make a coefficient of drag of .51 and a frontal area of 24 square feet (those are rough numbers for a 73 roadrunner) to hit 150mph in absolutely perfect conditions. In 1973 the 340 was rated at 240 net.

ahem. that's a theoretical 150mph, sir.

 

[MopaR&D]

Speedo error increases with speed so even if it's only a few off at 65 or 70 it'll be off double that amount at 130. Makes me wonder back before GPS how people checked if the drive gear they put in after swapping rear end gears was actually accurate or just stuck with the one the FSM table said to use and assumed it was right. Cop cars had to have a "certified" speedo for a reason...

 

[furrystump]

I could definitely go quicker with a header. A better question might be, can you get to your performance goals with a manifolds. You can quite easily get to needing to run a bar with manifolds.

 

[340six]

I drove 150mph on exhaust manifolds with 1973 340, less power yes, restrictive, no.

So a 1973 340 150mph? What was that like driving off a cliff? Bet ya could also jump beer cans, and put hundo's on da dash board too.