Edelbrock LD340 Intake Manifold Usable Max RPM?

[Newbomb Turk]

I'm attempting to stay away from a theoretical debate about whether an LD340 and 750 cfm 4150 will physically make power at 8K RPM and, instead, am trying to get real-world feedback on the RPM ranges people have practically used with an LD340 on a race 360. To this goal, I'm not following your point but am open to hearing your input as it relates to my specific build. Where do you think a practical RPM ceiling is for this specific build considering it's a vintage class.

The way you have stated your position, it sounds like you are arguing that with the LD340 and 750 cfm 4150 I must use, I should build a race 360 that spends its time at 8K RPM (with heads/compression/cam/exhaust designed for that RPM) because you say the intake manifold is less of a limiting factor. I'm having a hard time believing that the 8K version of this engine would make much more power than one designed to run at 7,200 RPM, but it would cost far more in financial and maintenance investment to build and maintain an 8K RPM engine compared to a 7,200 RPM engine. Slap a Super Victor Jr. single-plane and larger carburetor on that 8K RPM engine, and the practicality goes way up, but I'm stuck with the LD340/750 cfm.

No what you want is a bunch of guys you don’t know to tell you that what you want to do is right.

I’m man enough to tell you that you are shitting yourself if you think that manifold at 7k rpm isn’t at least 30 hp down to a good single plane.

Don’t talk about “bottom end” loss or other nonsense.

That manifold has a place but it ain’t on an engine that is CAPABLE of 7k. That thing should be on the shelf.

And I’m not talking out of my ***. I’m telling the real world straight truth.

I’d shelve it or sell it but it never was or ever will be a good manifold for that kind of rpm.

That’s the fact. And the hp it’s down on the dyno will only look worse on the track because of the nature and limits of water brake dyno testing.

 

[273]

No what you want is a bunch of guys you don’t know to tell you that what you want to do is right.

I’m man enough to tell you that you are shitting yourself shitty if you think than manifold at 7k rpm isn’t at least 30 hp down to a good single plane.

Don’t talk about “bottom end” loss or other nonsense.

That manifold has a place but it ain’t on an engine that is CAPABLE of 7k. That thing should be on the shelf.

And I’m not talking out of my ***. I’m telling the real world straight truth.

I’d shelve it or sell it but it never was or ever will be a good manifold for that kind of rpm.

That’s the fact. And the hp it’s down on the dyno will only look worse on the track because of the nature and limits of water brake dyno testing.

But he's only allowed to run that manifold for his class or stock.

 

[Newbomb Turk]

But he's only allowed to run that manifold for his class or stock.

I’d find another class. Seriously. Being jammed into a box like that isn’t my deal.

It’s ignorant to force a rule like that. It doesn’t save money. It doesn’t level the playing field. It’s just stupid.

I refuse to accept stupid as normal.

And I stand by what I posted. The rules makers have erred. And I’d bet money the LD 340 isn’t better than a an OE iron manifold.

Other than being lighter it’s not trick.

 

[273]

I’d find another class. Seriously. Being jammed into a box like that isn’t my deal.

It’s ignorant to force a rule like that. It doesn’t save money. It doesn’t level the playing field. It’s just stupid.

I refuse to accept stupid as normal.

And I stand by what I posted. The rules makers have erred. And I’d bet money the LD 340 isn’t better than a an OE iron manifold.

Other than being lighter it’s not trick.

Fair enough.

 

[273]

How much HP is required to be competitive in this class ?
Are similar cid engines spinning 7000-8000+ rpms ?

If you get the lbs-ft per cid up there you can make the power at lower rpms.

 

[Newbomb Turk]

How much HP is required to be competitive in this class ?
Are similar cid engines spinning 7000-8000+ rpms ?

If you get the lbs-ft per cid up there you can make the power at lower rpms.

That would be best if he could up the displacement but the way I read the OP is it’s also a displacement limited class.

If not I’d jack as long a stroke to it as I could to get the rpm down. I don’t think he can do that.

 

[Fish Bite]

If your choice is factory or LD340 it is what it is, obviously the LD340 is the way to go.
What mods are you allowed to do? people will cut the intake up in quarters and cut access holes everywhere to port them out it's up to you and the rules how far you take it.

The only allowed modifications to the intake are a shallow gasket match, to smooth any casting flash, and to notch or remove the plenum divider. No drilling/cutting/welding, no deep porting.

But he's only allowed to run that manifold for his class or stock.

I appreciate you focusing on the context of the thread and your constructive responses.

How much HP is required to be competitive in this class ?
Are similar cid engines spinning 7000-8000+ rpms ?

If you get the lbs-ft per cid up there you can make the power at lower rpms.

I'm not sure what power and where the really competitive cars are making, but most drivers I've talked to are running at around 7K RPM. I know there's a 360 AMC Javelin turning 8K, but he is the exception and doesn't run up front. The minimum weight for my car is 3,100 without driver, and I'll be able to hit that.

 

[Fish Bite]

It’s hard to judge really because that combo wants 260-270 @ .050 and a big single plane. And I’d want more lift, like .630-.650, but then throw the LD340 on there and I’d want to see 230 @ .050 and .500 lift and 9:1 comp. So I’m gonna tell you to not be set in stone on any of them. Have a cam ground and if it doesn’t do what you want tell the grinder and get a different one ground. And if you’re not rules limited to a SFT, I’d run a hard roller in that thing without thinking twice about it.

I'm completely open to the cam profile and building the other components around that, so I appreciate the input. Unfortunately, we're restricted to flat tappets.

 

[Fish Bite]

I’d say the practical limit for the LD340 on OP’s combo would be 7000-7200.

Thanks. Do you have a recommendation on solid flat-tappet cam profile?

 

[273]

I imagine if the rest is built to turn 7000 + rpm the manifold will go there maybe kicking and screaming a little, obviously won't make as much hp as the proper manifold but the whole class is basically held back the same as you (as long their not cheating). I'd check into the Darin's idea of tuning the headers higher than the manifold among other things.

 

[TT5.9mag]

I'm completely open to the cam profile and building the other components around that, so I appreciate the input. Unfortunately, we're restricted to flat tappets.

At least you’re blessed with .903 lifters. You should definitely take advantage of that.

 

[NCmtnDWELLER]

Unfortunately no longer Sir,...
John Cadamore AKA PittsburgRacer Has Passed Away

He just did one for me about 8 months ago , I will get numbers before and after give me two days not in home state currently
Thanks Chris

 

[RegularJay]

I ran a non-cut LD 340 on my 10-1/2 to 1 340 years ago. Had an MP 557 solid cam, 3:91 gears and a Holley 3310 on a 1" spacer. Stock X heads and generic headers. This was in a 4-speed 73 Duster. It was still pulling strong at 72-7300 but I ran out of testicular fortitude.

 

[RustyRatRod]

He doesn’t, but if he did it would easily be capable of running well over the OP’s 7 k question.
You’re the one that says they stop making power at 6800. My point is there is no set “ limit” of where they stop at. Other factors come into play.
Compression isn’t a big factor in rpm. Vic’s motor is around 10 to 1, if not a hair less.

Look at what some of them stock eliminator boys spin them small blocks to with stock intakes. Course they ain't stock on the inside. lol

 

[RustyRatRod]

He just did one for me about 8 months ago , I will get numbers before and after give me two days not in home state currently
Thanks Chris

Glad to see you on. How did you fair through the storm?

 

[Bewy]

If the class is limited to that type of intake, then all of the participants are going to be affected/limited by the intake's capabilities. What I see is a level playing field....& the smart fellas will find ways to use the short comings of particular parts...to their advantage.

 

[TT5.9mag]

Look at what some of them stock eliminator boys spin them small blocks to with stock intakes. Course they ain't stock on the inside. lol

Ask em what the .050 intake duration is. I’m betting you won’t get an answer. Maybe @GTX JOHN can chime in.

 

[Fast340cuda]

I recently took my car to a local chassis dyno and ran it with the LD340 intake. Combo is 4.06” bore, 3.58” stroke, 11.1-1 compression ratio, solid flat tappet cam (252/257 @ .050, .550 ish lift, 108 LSA). Intake was gasket matched and the plenum divider was cut down 1” and 2.5” length wise. This was topped off with a 750 double pumper. Here is the dyno graph for reference.

 

[273]

I recently took my car to a local chassis dyno and ran it with the LD340 intake. Combo is 4.06” bore, 3.58” stroke, 11.1-1 compression ratio, solid flat tappet cam (252/257 @ .050, .550 ish lift, 108 LSA). Intake was gasket matched and the plenum divider was cut down 1” and 2.5” length wise. This was topped off with a 750 double pumper. Here is the dyno graph for reference.

View attachment 1716316318

What heads are you running ?
Impressive numbers.

 

[Fast340cuda]

What heads are you running ?
Impressive numbers.

Edelbrock RPM’s that were touched up by Ray Barton.

I use the numbers as a reference. Was more interested in the power curve. I have tried the performer RPM, Weiand action plus, Victor 340 as well as the M1 single plane. I have been the happiest with the LD340 so far on my combo.

 

[a-bodyguy]

I’d find another class. Seriously. Being jammed into a box like that isn’t my deal.

It’s ignorant to force a rule like that. It doesn’t save money. It doesn’t level the playing field. It’s just stupid.

I refuse to accept stupid as normal.

And I stand by what I posted. The rules makers have erred. And I’d bet money the LD 340 isn’t better than a an OE iron manifold.

Other than being lighter it’s not trick.

Its not your deal
Post your big red x for yourself
That big red X is for 18 yr olds and little mans complex comes to mind

 

[a-bodyguy]

I recently took my car to a local chassis dyno and ran it with the LD340 intake. Combo is 4.06” bore, 3.58” stroke, 11.1-1 compression ratio, solid flat tappet cam (252/257 @ .050, .550 ish lift, 108 LSA). Intake was gasket matched and the plenum divider was cut down 1” and 2.5” length wise. This was topped off with a 750 double pumper. Here is the dyno graph for reference.

View attachment 1716316318

very nice numbers