Edelbrock intake differences

[TJ]

Anyone tell me the physical differences between the Performer 390 and the Performer RPM ?  They look like they have the same basic shape but the 390 has smaller tunnels and ports?

Everywhere I read and everyone I talk with says the RPM gives better performance at higher rpm and gives up nothing at lower rpm.  But I'm guessing few have really analyzed the differences in performance in the 2000 to 3000 rpm ranges.  And very few would have a reason to analyze the differences in the 2000 to 3000 range unless you're working the motor hard in that rpm range (like when towing).  Would the smaller tunnels of the 390 give better turbulence and thus better mpg and better power in the 2000 to 3000 rpm range?

In my F250, I have a relatively tame 482 in front of a NP435 tranny and gear vendor.  Rear end is 410.  Adding the gear vendor got me no noticeable improvement in mpg.  My guess is my particular build is more efficient around 2900 rpm (where I used to cruise on the freeway) than it is at 2200 rpm (where I freeway cruise with the gear vendor).   Perhaps the lower rpm results in less turbulence and a "lazier" air:fuel mix with my current RPM intake.  In theory, the smaller tubes in the 390 intake would make for a better air:fuel mix at low rpm?   BTW, my engine hits peak torque at 3700 rpm.

[e philpott]

you have enough cubes to justify the RPM . Difference looks like the difference between a 2x4 medium riser to a low riser 2x4

[frnkeore]

In theory, the smaller tubes in the 390 intake would make for a better air:fuel mix at low rpm?

That may be but, on a engine your size, it will choke it of, big time, above 4K.

I'd stick with the RPM, raise the CR, if possible and get a O2 sensor hooked up, to try and get a better, overall A/F, playing with carb adjustments. May be a water injection set up, too. Hook up a vacuum gauge, too, to see how you load the engine, with your driving.

[Joe-JDC]

The Performer 390 out of the box only flows about 230 cfm average, and the RPM out of the box flows 315-320 cfm average.  I have flowed several of them, ported both, and the best you can get out of the Performer 390 is ~280-290 cfm.  The RPM can be ported to 390 cfm average.  For anything over 352 or 390 stock, you should definitely go with the RPM.  Joe-JDC

[Stangman]

Maybe I’m not reading it right but he just wants to know which is better between 2 and 3000. I don’t think he cares about above 4 or 5 thousand rpm.

[frnkeore]

First, I think he is confusing "turbulence" with velocity. You try to avoid turbulence, in the intake track but, velocity can help a lot, with both power and mileage.

Your right, he was asking about  2 - 3k rpm. With as large as his engine is, I think he has plenty of velocity even at 2-3k with the RPM. The engine seems to have the most efficiency at the peak torque, of 3700.

We need to know the carb type and size, as well as the Adv & .050 duration of the cam and the LSA & ICL. The bad mileage, could be as simple as to much overlap.

I forgot to add in my first post, that along with the CR increase (if possible) a decrease in quench clearance (if possible), would also help mileage.

[blykins]

The RPM is the best choice of the two manifolds, for sure. 

This engine made right at 540 hp @ 5200, had 570 lb-ft of torque available at 2500 rpm, and peaked at 620 lb-ft at 3700.  Any less intake would be a considerable bottleneck.  Having to add throttle to compensate for a lack of power would also hurt the fuel economy.  Keep in mind that this engine will idle the OP's 10-12k travel trailer around the yard while he gets out and walks beside it. 

I built this engine 7 years and ~30k miles ago.  It's one of the engines that was first featured on BBM's webpage.  Instead of jumping right into compression ratios (9.7), quench distances (.040) and everything else, I feel like the obvious question that everyone should have asked first was......what's the current fuel economy?   Hard to deem something "bad" when we don't know what it is yet.   Pushing a large displacement, high horsepower, brick through the air isn't going to command big numbers.  To be honest, I'd be very surprised and ecstatic if it were close to hitting double digits, especially without VCT, EFI, etc.

The carburetor tune can always be in question and a timing sweep could also be beneficial.  If I remember right, total timing to make the best peak horsepower was somewhere around 30-32°, but fuel efficiency can sometimes take advantage of a different setting. 

[TJ]

Appreciate all the input.  I'll try to gather all the comments so far.

I'm a bit of an oddball not caring what happens above 4000...might have passed that once...rarely pass 3500.  MPG isn't too bad... 11.5 - 12 if I keep it on the freeway and stay out of town.  What made me wonder is the mpg did not change going with the gear vendor. 

O2 sensor (when it worked) seemed good at around 13.  Plugs looked okay (too me). 

If air velocity is what I want then I'd think smaller tunnels would help.  The engine draws a given volume.  Smaller tunnels should force that to travel faster.

Might look at carb adjustments.  I set up my timing curve with my "chassis dyno"...stop watch and freeway on ramp near my house.  Put it in 4th and floor it from 40mph to 60mph.  Adjusted timing rate of advance to get shortest stopwatch time without pinging.

I know some times companies make extra options hoping everyone will buy something but I'm guessing Edelbrock made the 390 intake for a reason.  My RPM intake is installed so I can't see the ports so I was guessing they're bigger than with the 390.  I have a used but uncut 390 that I ran on a 390FE I used to have.  Checking differences on my "chassis dyno" would cost me some gaskets and some time.  If I swap it I won't do it until winter and then test next summer.

Like I said, appreciate the input.  Hope this is an interesting change of engine strategy than talking about boring hot rods 

[JamesonRacing]

I have a 445 in my F250, with mildly ported D2 heads and a very mild roller cam.  I have an iron CJ intake on it and seems to work like a champ.  Plus it looks like a proper truck engine should

[blykins]

You don't want to make that swap. 

That Performer intake is not even sufficient for a 390, much less something with 100 more cubic inches.   Just because it's smaller doesn't make it more efficient.  Velocity without sufficient volume is going backwards.   Instead of 540 hp/620 lb-ft, you would have a huge bottleneck/hp loss, which would require you to input more throttle to achieve the same results in cruising, towing, etc.  Not a good scenario.

12 MPG would make me giggle.  My uncle's 1993 Chevy 454 dually with 230 hp got 8.

Try some total timing adjustments over a period of time, hook up a distributor with vacuum advance.

[My427stang]

Throwing my 2 cents in, you will lose power everywhere and gain nowhere.  The RPM is a well designed manifold, the Performer 390 was built at least a decade earlier and a cork.  Your theory is potentially correct, but the Performer 390 won't do what you want

If you really think you want to shift the RPM range even lower (in what was a really cool build already if I remember it correctly), it likely means a cam change to change the peaks and likely a compression change to support the cam, but even then, you likely won't get paid back in mileage for the cost

I think you have what you have without big investment and it's pretty darn good, if you want to turn it into a tractor or make it run at diesel levels, you will likely lose a significant amount of power.  IMHO this is a 482, they use more gas...14:1 mixture..., the displacement is 90 cid higher, that means the 14 and the 1 has to be increased filling a bigger cylinder.  It'll cost you money and power without any real payback

[TJ]

Okee doke.  I'm almost convinced...still curious what would happen in 2200-2900 rpm range...

BTW, the 11.5 - 12mpg is empty.  Roughly 7.5mpg pulling the fifth wheel but haven't pulled enough to be confident in that number. 

I feel my timing is optimal at this point.  Might talk with my guy on carb adjustments for lower rpms. 

To be clear, the engine is doing just what I want.  I'm wondering why dropping 24% rpms (2900 down to 2200) didn't give me at least a smidge better mpg. 

[My427stang]

Okee doke.  I'm almost convinced...still curious what would happen in 2200-2900 rpm range...

BTW, the 11.5 - 12mpg is empty.  Roughly 7.5mpg pulling the fifth wheel but haven't pulled enough to be confident in that number. 

I feel my timing is optimal at this point.  Might talk with my guy on carb adjustments for lower rpms. 

To be clear, the engine is doing just what I want.  I'm wondering why dropping 24% rpms (2900 down to 2200) didn't give me at least a smidge better mpg.

Brent mentioned vacuum advance, are you running one?  May not be drastic improvement, but that's what it's there for.

[blykins]

I'm wondering why dropping 24% rpms (2900 down to 2200) didn't give me at least a smidge better mpg.

Because the engine is in the same efficiency band across that entire rpm range. 

You honestly need to stick it on a real chassis dyno in order to get the most out of the carburetor and timing adjustments.  I can't remember what you're running now for a distributor, but it seems to me that we dyno'd the engine with a Mallory or something.  Adding a vac advance distributor would most likely help. 

Changing your driving habits can do a lot as well. 

Above that, something like a MPFI system would help, where the computer is mapping and adjusting the A/F ratio and the timing curve on the fly. 

[jayb]

Sheesh, doesn't anyone on this thread have my book?  The data from 2500-3000 is all in there, Performer vs Performer RPM.  On my 410 HP 428CJ, the Performer makes torque of 389 to 438 lb-ft from 2500 to 3000 RPM, and the Performer RPM makes torque of 340 to 406 lb-ft.  On this engine the Performer is better in this range, and is actually better than the RPM up to 3500 before the RPM takes over and makes a lot more power.  Both intakes peak at nearly the same torque, 485 lb-ft around 3500 RPM. 

On my 500 HP 390 stroker engine, I only tested from 3000 RPM up, but basically the two manifolds behaved the same as the other engine from 3000-3500.  But on that engine the RPM made more peak torque, and caught up with the Performer a little sooner.

I have heard a lot of anecdotal evidence that the Performer RPM is better than the Performer 390 at all engine speeds, but it is all based on the "seat of the pants" dyno, not actual data.  I'll stand by the back-to-back test data in my book, and say that the Performer 390 is better than the Performer RPM up to around 3500 RPM.