Stock intakes
 

How much horsepower can a stock Pontiac intake support? I'm aware that Cliff and a few others have modified the 67-74 non-egr intakes to support upwards of 425 hp, but those are exceptions. So what about non-tampered units?

My port matched cleaned up HO intake made 420 easily on my old 455. It was the cork on my roller cammed E head 4 though.

With only a gasket match my 455 wirh 70 iron intake/Qjet made 490hp,,570 trq.

Skip ,I apologize for the confusion. Guess I should have made it a lot clearer. The HO as well as the RA 4/5 intakes flows better than the "run of the mill " Pontiac cast iron units. There's information being circulating that non RA , HO or any Pontiac " special " intakes are making 500hp. Not to say it can't be done, just never heard of the combination of parts. Many years ago I contacted Jim Taylor/ Erney of Scientex about one of their TFX solid ft cam
We installed a 244/244@0.050 cam with .520 lift in a 455 74 GTO , using the 74 GTO #98cc heads, Marty Warden ported intake to 240 cfm, installing 2.11/1.77 valves. Degreeing the cam per Jim's instructions. The car had 8.5 rear and a 4 speed Muncie, shifting @54-5600
I initially tried a stock 69 GTO intake adapter to use the 800 spread bore Holley . The best 1/8 mile time was 7.9_8.0. Changing nothing but the intake to an RPM, the car went 7.4s. All runs were done with an MSD ignition system with 3400 total @ 3k rpm. Used 3 tube headers We could never get the stock intake to perform better
I didn't dyno or weigh the car.

I did 507hp/571tq on a 455 I built not too long ago with a stock 72 HO intake.

Not sure on HP numbers but we ran 11's at 124mph with an unported late EGR intake fitted with a 1" spacer.
Car weight was 1850kg.
At over 4000lb Wallace calculator shows nearly 600 hp but I think that seems a little optimistic?.
Manual trans does mph a little higher, so I am guessing arounf 550hp?
Definitely over 425hp though ��

Yes, the '67 - '72 intakes are all basically the same from a flow perspective.

From what I've seen the factory aluminum D-port intakes do NOT flow any better than the iron intakes. I don't think the round port intakes do, either. They have a slightly shallower plenum floor due to the divorced crossover. Other than that, they're basicially the same as the iron intakes from a performance perspective.

I don't know what they'll support in stock form, but when ported they'll easily support 500+ horses.

I thought I read that the HO intakes flowed less when comparing the regular intakes because of the separate crossover? Also I believe all 67-72 intakes are the same and by 455+4+1 description not much difference in the later intakes with the egr either.

I reposted because of spelling will

The iron intakes love even a 4 hole 1” spacer since it greatly helps flow to make the turn into the shallow side Plenum that feeds cylinders 2,3, 5 and 8.
On iron intakes when you gasket match the runners on the lower Plenum ( 1,4,6 and 7) on back into the runners from the flange where they pinch down pretty good you should try and raise the roof by 1/16” if you have a good fine cut 6” long Burr.

Matching these iron intakes to RA IV size ports is just a flat out waste of time, and yes it can be done size wise at the flange and for a short distance down each runner, but the outcome of such work is just a narrowing up of your motors power band!

How do I know? Because I Tried such out in the mid 80s at the strip with 2 different manifolds in the same 1.5 hour time span.

Dave at S.D. Performance, says his fully CNC ported iron intakes will support 600 HP.....FWIW...

Are you taking 600 hp from a CNC D port iron intake , or iron SD 455 intake ?

600 hp is a tall order as that would mean each runner would need to flow 280 to a ideal 290 cfm @ 28” which is something a out of the box TQII and performer rpm can’t do!

I've raced my car back and forth between the two and have found no difference at all.

Whether they flow less or not I can't say for sure. You might see a measureable difference on a dyno but I'm guessing very negligible, not enough to see a difference at the track. Would probably need a large higher HP build to make any real difference. Nothing that anybody does or is worried about here in the street section.

Well I know for a fact they'll at least support 507 HP in stock form.

I just did this on a 455 not long ago. 9.98:1 compression pump gas, ported iron 7F6 HO round port heads, a 239 @ .050 hydraulic roller, stock aluminum HO intake with heat cross over intact, and a stock Q-jet that I modified with Cliff's kit. And I did that with the factory iron exhaust manifolds in place with it's stock points distributor.

Well your 507 hp was right nicely there at the edge of the 491 hp that heads flowing let’s even just 240 cfm@28” will support .

That works out to a 4% dyno correction factor which is something I could surly live with in terms of a street motor!

Some folks do not think they flow any better.
Figure some of the NHRA stocker guys like John Schloe are into the 10s in their first gens firebirds with one ,so maybe close. Teh 600 number I have a hard time believing

My E head 259@ 0.050 roller cam 455 picked up a bunch over the HO did. I had used it to keep the Shaker until I found and extra base to modify for a Holley/Demon.

A lot of good informative responses. Kinda what's said in Pete McCarthy and John Angeles book, " Dollar for dollar, the cast iron 4 BBL manifolds off 1968-72 engines are hard to beat".

Not sure what the peak hp is for a stock intake if any, but I tried running a stock intake modded in every way possible using a qjet and 1” spacer. At the end of the day there was no point whatsoever, the rpm was simply better. At around 500+ hp at the time. . Will they work at higher hp levels ? Sure, just not worth the effort in my book, unless you have good reason.

"...Figure some of the NHRA stocker guys like John Schloe are into the 10s in their first gens firebirds with one ,so maybe close..."

Yeah, there have been several Stockers run real low 10's with iron intakes, including some '68 Birds & Randi Lyn Shipp's '67 Bird. It's been posted here that Scott Burton dipped into the 9's, with his RAIV '70 Bird. I think Brad Burton's 455HO Bird is also capable of low 10's.

So, some of you guys who know how can probably figure the aprox hp.

Most know that the quick Stockers are NOT running completely "STOCK" components. BUT, head & intake porting to the max would probably not pass even a visual inspection. So, I figure these quick Stockers are about as "stock" as you'll find making 500+ hp with a factory Pontiac intake.

I realize that most of the "programs" that some use here will say that much power can not be made with the components the Stocker guys are using. But, they're obviously doing it, regardless of what the programs say. The Stocker performances speak for themselves. :)

Modified (by Dave at SD) HO Intake made 589 HP on street 505.
http://forums.maxperformanceinc.com/...d.php?t=797155

I tested 3 intakes back to back a few years ago on a 428 (440CID), 10 to 1 compression, 260cfm KRE heads and 236/242 custom ground HR cam. I tested a 1970 iron intake, HO (reproduction) and an RPM.

The iron intake and HO were opened up under the carb to the same size/shape as the RPM, all were port matched to a stock intake gasket, no ported of any kind in the runners.

The iron intake made 497hp. The RPM made 491hp and the HO made 487hp, all with no other changes.

IF you are going to use spacers I tested 4 spacers at the track on iron intakes and found that the fully divided and semi-open (open between the secondaries) work best. The 4 hole was horrible and so was the fully open spacer.

I'd also recommend to leave the divider intact on any dual plane intake and at most just remove a small half circle amount between the secondaries or use a 1/4" thick open gasket on it.

Removing the divider or using open spacers can cause distribution and turbulence issues even if they make more power on the dyno. I've tried all of that stuff and experience noticeable hesitation/stumble/bog going quickly to full throttle that will not tune out.

I know that the intakes above were not completely stock but they were all the same under the carb and none of the runners were ported in any of them.

For BIG power levels I would NOT use an RPM intake. I've had several customers experience issues with leaning out one cylinder and spinning rod bearings with them. I'm taking over 700hp and running well into the 9's. For those set-ups you'd be better off with a well made single plane intake and at least a 1" spacer on it......FWIW......Cliff