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post #1 of 16 (permalink) Old 03-31-2014, 05:15 AM Thread Starter
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Stroker intake manifold RPM change-PSIG???

I am looking for the formula that calculates the expected new RPM max of an intake manifold once its installed on a much larger motor.

Pertinent examples--If max on an intake is rated at 8500rpm on a 351w, what would the expected max rated RPM be on a similarly equipped 428W?

Same calculation of a 7500rpm max on a 351w to the 428w?

Would the same formula apply to the lower range of the power band (lets say 351w @ 4500 vs 428w?)

Thanks.

Dennis

65' Stang Street/Strip. Dart 434W NA, Victor heads, G101A 4 Spd, 4:56 rear gear, on 93 octane pushing 3550lbs. [email protected]
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post #2 of 16 (permalink) Old 03-31-2014, 02:59 PM
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Re: Stroker intake manifold RPM change-PSIG???

Hey Dennis - We can split hairs all day on this issue. My initial answer is a generic one that should fit the needs of most hobbyists. If you have more specific requirements, then we would need to factor those needs. Based on that, we have two primary things to consider. One is the harmonics of the manifold that are "tuned" to a general RPM range with runner area, length, plenum volume, etc. The other is the flow capability of the manifold. If you know it has the ability to flow enough to cover your needs at a reasonable port velocity, then the RPM range it's tuned for is going to be very similar. If it needs porting to get the required flow, then that will alter the tuning range somewhat.

This is different than how a cam's performance would be altered by engine displacement, which is where I assume you were coming-from. Does that help?

David

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post #3 of 16 (permalink) Old 03-31-2014, 03:16 PM Thread Starter
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Re: Stroker intake manifold RPM change-PSIG???

Thanks David, that makes perfect sense.

Specifically, what I am trying to decide is if I swapped from Victor Jr. to a Super Vic for racing on my 428w, would it gain with a Super Vic? What motivates me is the advertised RPM range given by Edelbrock is for a 351w (of unknown build.)

I have a 4" stroke, 4.125 bore block. I shift at 6600 while running it out the back at 6900. Estimating 575hp at the motor to move my 3550lb behemoth (including me) down the track. Have been as fast as 129.xx mph in the 1/4.

Dennis

65' Stang Street/Strip. Dart 434W NA, Victor heads, G101A 4 Spd, 4:56 rear gear, on 93 octane pushing 3550lbs. [email protected]

Last edited by dennis111; 03-31-2014 at 03:52 PM.
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post #4 of 16 (permalink) Old 03-31-2014, 04:38 PM
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Re: Stroker intake manifold RPM change-PSIG???

I would say your flow requirements will dictate which. Up-front, understand both the VJ and the SV are cast to be ported to the application, as they both have tapered runners for this purpose. Normally, a Vic Jr. would bet he choice to keep as much average TQ and HP through the useful range as possible. Best averages win. So, going to a SV for that last 300 RPM in the traps would normally be an unsound move.

The two factors for you to juggle are available flow and stroker flow. Obviously, if you port to your heads and there is not enough flow to feed them, you have to go SV. Strokers also have need for larger airflow in gulps due to the R/S ratio. While this means bigger is better to a point, you can't use much more than your heads will flow without losing velocity, fuel suspension, and softened torque peak.

So, although we could throw flow numbers around all day, that does not give the dynamic answer we need. Which to choose? I would take a simple view on this, as the port area at about 50% of the tapered runner should equal or exceed your head port area. You would port-match and blend to just beyond the point the areas matched.

Just to add some drama, I would also match flow transition in each runner, as well as port-to-port. This can be done without a flow bench by using a shop vac and an electronic manometer. You can get set-up with one for around $20. OK, kick it back at me.

David

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post #5 of 16 (permalink) Old 03-31-2014, 04:54 PM Thread Starter
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Re: Stroker intake manifold RPM change-PSIG???

David, you are the voice of reason. Still chewing on some of this but in the end it sounds like I should stay with the Vic Jr. until I can install a better head (and exhaust.)

Still the temptation is there to give the Super Vic a whirl just to see what happens (I've got one stashed.)

Thank You!

Dennis

65' Stang Street/Strip. Dart 434W NA, Victor heads, G101A 4 Spd, 4:56 rear gear, on 93 octane pushing 3550lbs. [email protected]
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post #6 of 16 (permalink) Old 03-31-2014, 06:30 PM
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Re: Stroker intake manifold RPM change-PSIG???

Hey - have fun. Just remember, the SV should be port-matched (not gasket-matched) and blended to get a fair test out of it. That's a lot of work to just try it. Is your VJ as-cast? If by some chance it is, I'd do the work to that first (or while the SV is on) just to see what it gets you. The effects are greater the harder you are pushing it, but those in the 600hp range claim 20-30hp peak. I've seen a fat tenth to two and a nudge of MPH in that neighborhood on the asphalt - many variables considered. Post some results if you play.

David

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post #7 of 16 (permalink) Old 04-01-2014, 05:24 AM Thread Starter
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Re: Stroker intake manifold RPM change-PSIG???

David, I have 3 manifolds to mess with.

Option #1: The first is an old Vic Jr. that was had the carb pad angle milled to fit under a stock flat hood. Basically dropped the front of the air cleaner. It now uses a standard unmodified drop base air cleaner. It has been hack ported in the plenum and the manifold ports have been cut .080" per side to best fit the heads horizonally. Still about .015" (or less) verticle head overhang that can't be corrected by moving the intake for and aft since it moves the problem to the other side. Would require a little head grinding or maybe offset head dowels. This is the intake that I have always raced with and is currently on the car and the street driveability is very good.

Option #2: The second intake is also a Vic Jr. that was used for a break-in on an engine dyno. The car the motor went into was FI. It fits the AFR205 head ports horizonally and vertically extremely well as-is with no head overhang whatsoever (perhaps a difference in production tolerance or a change at Edelbrock?) This manifold is stock and hasn't been modified in any way. It will fit under the current hood nicely if I cut down the neck of a drop base air cleaner maybe 1/2". Normally these necks are 1" tall so it should still be able to direct the flow, or there maybe other air cleaner options. It uses a standard 14x3" air filter. This is the intake I would have properly ported if I continue on with the Vic Jr. course.

Since I mention hood clearance it should be noted that my motor is set down as low in the engine compartment as possible with the stock suspension. I've even clearanced the oil pan somewhat for the steering center link. I also use a chokeless carb that offers a little more clearance than a choked version.

Option #3: The Super Vic is an old one but it hasn't been modified. It needs .090" taken of the sides to better match the heads horizonally. Like the first intake, there is some verticle head overhang in to the ports also-probably a good .020", so again the heads would need some work too. To use the Super Vic under the current hood would require some additional work. The carb pad would probably be flat milled (about 3/8") and the same 1/2" or so cuttoff of the air filter base as in manifold #2. Of course the plenum would require a little blending work, but it would be less than I did for the Vic Jr in option #1 since the Super already has a nice lead-in.

Conclusion (?): The cost of option #3 Super Vic swap would probably nearly equal the cost of simply having option #2's Vic Jr. professionally ported. The current out of pocket cost would be even less if I sold the Super Vic and applied those funds. Perhaps #1's Vic Jr. could be sold also as there are always people wanting to mount one under an early stock hood.

It should be so obvious since I have just spelled it out plain and simple. Kind of like checking out that hot chick at the end of the bar when you are happily married . . . . .

Decisions, decisions, decisions . . . . .

Dennis

65' Stang Street/Strip. Dart 434W NA, Victor heads, G101A 4 Spd, 4:56 rear gear, on 93 octane pushing 3550lbs. [email protected]
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post #8 of 16 (permalink) Old 04-01-2014, 05:40 AM
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Re: Stroker intake manifold RPM change-PSIG???

Quote:
Originally Posted by dennis111 View Post
Thanks David, that makes perfect sense.

Specifically, what I am trying to decide is if I swapped from Victor Jr. to a Super Vic for racing on my 428w, would it gain with a Super Vic? What motivates me is the advertised RPM range given by Edelbrock is for a 351w (of unknown build.)

I have a 4" stroke, 4.125 bore block. I shift at 6600 while running it out the back at 6900. Estimating 575hp at the motor to move my 3550lb behemoth (including me) down the track. Have been as fast as 129.xx mph in the 1/4.
As a precursor to this post I enjoy reading your conversations as a learning tool. Just wondering if anyone saw the Car Craft issue from about a year ago where they dynoed the edelbrock performer, rpm, victor, super victor and their dual quad intakes on an 8.2 based 363? This was the same issue that they compared budget ford heads. I know this is apples to oranges but it is an interesting comparison nonetheless and may illustrate the differences between the supervictor and the victor.
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post #9 of 16 (permalink) Old 04-01-2014, 06:58 AM Thread Starter
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Re: Stroker intake manifold RPM change-PSIG???

Quote:
Originally Posted by zandifam View Post
As a precursor to this post I enjoy reading your conversations as a learning tool. Just wondering if anyone saw the Car Craft issue from about a year ago where they dynoed the edelbrock performer, rpm, victor, super victor and their dual quad intakes on an 8.2 based 363? This was the same issue that they compared budget ford heads. I know this is apples to oranges but it is an interesting comparison nonetheless and may illustrate the differences between the supervictor and the victor.
I found the article online:

Ron Burgundy IV - Manifold Test - Car Craft Magazine All Pages

Yes, certainly apples to oranges comparison to my situation, but now you've muddied the waters even more. I am surprised how well the Super Vic did across the range. Darn you!!!

Also surprised at how well the dual quad manifold worked.

Thank you Z for uncovering the article.

Dennis

65' Stang Street/Strip. Dart 434W NA, Victor heads, G101A 4 Spd, 4:56 rear gear, on 93 octane pushing 3550lbs. [email protected]
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post #10 of 16 (permalink) Old 04-01-2014, 09:39 AM
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Re: Stroker intake manifold RPM change-PSIG???

I know about those hot chicks, and the lure they have. The CC article is interesting, and I love that they included average HP numbers, but be sure to consider a few things:
  • The manifolds were not port-matched to the heads - a cripple-factor for some of them. The runners are are conical and designed to give material to port for best flow, and are relatively restricted without it. The point is that manifolds designed to be ported for racing cannot be fairly compared as-is.
  • None of them were flow-balanced. As-cast differential can run 40cfm or more from port-to-port. That's a lot of lost power, and highlights that race manifolds are not meant to be a "bolt-on" solution.
  • The awkward dual-plane still provides amazing power for it's convoluted runners, and slightly better average power than the "race-only" manifolds. Higher peak HP or TQ only means it was weaker somewhere else. Peaks are meaningless except for dyno racing and diagnostics. Averages are more useful, but must be in your useful range.
  • Another dual-plane, the dual-quad has better runner layout than the RPM, so pulls ahead in average power. Double carb cost, double setup, double failure points, but double fun. Not a fair comparison to a ported manifold, though. Gotta love the un-ported bolt-on numbers.
  • Yep, they had to throw a spacer in there, and only on one. We know why they did that, and should have done it to all if to one. Spacers always add dyno power.
So, it apples-to-oranges, but we can still see trends and factors that would apply to any engine combo. Another example - the header/exhaust combo was not specified for it's breathing/harmonic traits, so it may have helped certain combinations and hurt others. With attention to the exhaust, any one of them could have been a clearer winner.

As far as porting your own, note that head port/runner mismatch is usually solved with both grinding and filler, and this way the runner can be moved wherever you need it to match the head. One filler that works with high heat and fuels including ethyl alcohols is A-788 (aka Splash Zone) around $40/quart kit. Methanol needs a sealing coat for extended durability. Split it with a buddy or 3, as it will still be too much and shelf life is a year. Perhaps you might play with your old mis-aligned VJ while you're having fun with the SV? Nothing like some cheap real-world practice to see where things really happen on your combo.

David

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post #11 of 16 (permalink) Old 04-02-2014, 06:24 PM
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Re: Stroker intake manifold RPM change-PSIG???

You need to check port opening location in Edelbrock intakes from the VRJr on up as the port location in the vertical plane might not match up. The Jr sits about .05 inch higher top to bottom comapaired to factory location. Supper migh be raised more.
What yor heads flow and what lift cam you have determines intake needed as well a cubes. Your intended usage is important also.
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post #12 of 16 (permalink) Old 04-05-2014, 11:37 PM
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Re: Stroker intake manifold RPM change-PSIG???

Come on, run the Super Vic!

Of course, if you want to sell it, I may know someone who would like to buy it. (Insert whistling emoticon here. LOL).
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post #13 of 16 (permalink) Old 04-06-2014, 04:06 AM Thread Starter
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Re: Stroker intake manifold RPM change-PSIG???

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Originally Posted by Jeff351w View Post
Come on, run the Super Vic!

Of course, if you want to sell it, I may know someone who would like to buy it. (Insert whistling emoticon here. LOL).
LOL.

A very good idea was presented to me. Cut an appropriate hole in an old scrap hood and then give the Super Vic a try, as-is. (I just so happen have a candidate hood.) If I see potential, then I can have the milling/light porting done. If it falls on its face, then I can slap the old Jr. back on and have the newer one properly ported. All I'd be out are some intake gaskets, a can of flat black paint, and a little time. Would be interesting to do the intake swap at the track on the same day to get more of a real world comparison.

Not a proper laboratory controlled test but at least it might satisfy my (our) curiosity . . . .

Not going to jump on this at this time, but it does sound very enticing. We'll see.

BTW Jeff, way to up the 5 year old post count! LOL

Dennis

65' Stang Street/Strip. Dart 434W NA, Victor heads, G101A 4 Spd, 4:56 rear gear, on 93 octane pushing 3550lbs. [email protected]

Last edited by dennis111; 04-06-2014 at 04:12 AM.
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post #14 of 16 (permalink) Old 04-06-2014, 06:29 AM
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Re: Stroker intake manifold RPM change-PSIG???

There is a formula to figure it out but you need to know the air flow of your heads, Air flow of the intake bolted to the heads, the Cu In of the engine and cam lift.
To pick a cam exhaust flow is needed

As for the test are those heads stock port location or raised port on the intake?
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post #15 of 16 (permalink) Old 04-06-2014, 06:58 AM Thread Starter
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Re: Stroker intake manifold RPM change-PSIG???

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Originally Posted by turbo2256b View Post
There is a formula to figure it out but you need to know the air flow of your heads, Air flow of the intake bolted to the heads, the Cu In of the engine and cam lift.
To pick a cam exhaust flow is needed

As for the test are those heads stock port location or raised port on the intake?
Don't know the air flow of the 2 intakes to the heads. Super and NIB Jr are untouched. Not easily going to figure them out when bolted together. Heads are stock port 58cc AFR 205's, 427.68ci, .619int/.600 exhaust lift. I know what an untouched super vic flows on a calibrated bench for each cylinder.

Dennis

65' Stang Street/Strip. Dart 434W NA, Victor heads, G101A 4 Spd, 4:56 rear gear, on 93 octane pushing 3550lbs. [email protected]
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