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RPM or stock iron intake
for a street car, cleaned up #13 heads, RAIII iron headers, roller cam, havent picked one yet but nothing too wild, 4 speed, 3.55 gears, q-jet.
which is better? |
pretty close to each other. if you want some weight savings, the rpm. otherwise a pre-smog 4bbl stock intake with a port match job will work just as well.
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What is this going on? The RPM work very well on 389+ motors and they were worth about 1.5-2 mph over a 67-72 iron intake. But keep in mind they are about 1.5" taller than stock if you have a limited hood clearance.
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The aluminum Pontiac RA4 intake is also a consideration and also has a taller port to be blended on stock heads and also have the proper height so you can use them on cars with shaker hoods you can also leave out the iron crossover to keep your intake cooler than if you just blocked off the the heat risers. like so...........
http://www.pismoderelicts.com/photog...s/p1020753.jpg D. |
I'd go w/ the iron intake, even if it's an unaltered stock one.
It seems like a RPM would be best, mostly on the largest cube engines (455+) or higher RPM engines. Cliff and Jim Hand used modified stock iron intakes, making a boat load of power. I believe Jim is currently using a RPM, he has slightly enlarged the intake ports on his 6X heads, and turning a fuzz more RPM, both possibly allowing the RPM to function as the more desireable intake, for his combination. Maybe Jim will read this, and comment... A correctly modified intake is a VERY good intake. I like the idea of a "stock" intake w/ a "stock" Q-Jet on my engine, then take one of the "know it alls" for a ride and show them how well a stock Pontiac engine performs!!! The aluminum RAIV intake is a desireable piece, but used ones are priced high??? and hard to find, and the reproductions have issues??? |
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Well yes they are expensive if original OE, but they are now being reproduced. D. |
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Several years ago we did a back to back dyno test between an HO intake, my iron intake, and an RPM intake. All were port matched exactly to a stock Felpro blue intake gasket.
No spacers of any kind were used, same carb, and same gasket. The HO intake was the reproduction unit, not an original. I opened up the HO intake and the iron intake to the same size/shape as the RPM under the carb. The runners were not ported, just the work under the carb (pics attached). The engine we used was a 428 (434cid), 74cc KRE aluminum heads (prepared here), 10.6 to 1 compression, 236/242/110HR camshaft with 1.6 ratio Crower roller rockers. The HO intake made 487HP, RPM made 491HP, iron intake made 497HP. An interesting tid-bit about the dyno numbers, even though the RPM made less power, it made it at 200 rpm's higher (TQ and HP) than the iron intake.......Cliff |
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I notice that the iron intake, in the picture, has The divider cut down. Did any, or all, manifolds have it cut down during the test? |
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Just curious Cliff, you say you used a stock Fel Pro gasket, I take not the tall Fel-Pro RA4 gasket?? I can understand the Hp , I would like to know at what RPM? Correct me if I'm wrong you didn't change the iron manifolds entire runner to match the RA4's? With the exception of the RPM manifold did you use a carb. spacer to keep the throttle blades out of the turbulence of the intake pulses? Don |
No porting to the stock iron or HO intake in the runners, just removed a few "bumps" casting flash, etc.
Stock gasket, not the RAIV. Peak power at 5800rpm's. No spacers used, other than a 1/4" thick open gasket. The dividers are NOT cut down, just added a small "notch" between the secondaries. The RPM intake is not doubt a good piece. Where it becomes any better than a stock intake is a question we don't exactly know the answer to. At least on a 440cid engine making right at 500hp, it didn't show any more power anyplace. Of course, before someone mentions it, we cheated and opened up the stock intakes to the same size/shape as the rpm under the carb. I also tested the Performer intake, once on the dyno and once on my old engine making 514hp. It was down close to 15hp on a 455 on the dyno and my engine HATED it. It didn't run well enough to continue testing with it after some brief street driving before heading to the track.......Cliff |
Cliff,
Thanks again for the real world facts!!!1 |
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Thanks Cliff, now your numbers make sense, and I'm surprised you even made that good of a number on the RA4 intake. Don |
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Completely different deal to add a small notch between the secondaries, vs removing part of, or all of the divider
It's actually a common practice. We've seen plenty of them heavily cut down and even completely removed. This is a BAD move, from what we've seen. I've had to make dividers for quite a few intakes where it was removed. Doing this can really hurt mid-range power, even if it produces a few more peak HP. It can also induce a stumble, hesitation, or bog, which is difficult, if not impossible to tune out.....Cliff |
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I could not use the stock 1968 4-barrel manifold i had because it sat too low between the heads - appears they were machined to fit some machined heads.
I picked up a used RPM. 35 pounds lighter. I like that alot. |
From post #11:
"No porting to the stock iron or HO intake in the runners, just removed a few "bumps" casting flash, etc. Stock gasket, not the RAIV. Peak power at 5800rpm's. No spacers used, other than a 1/4" thick open gasket. The dividers are NOT cut down, just added a small "notch" between the secondaries." One last time....ALL intakes were tested in the same manner, same modifications. No dividers were removed, or cut down, just a small notch added between the secondaries. This really isn't required if you use a 1/4" thick open gasket. The open gasket allows both sides to see each other in actual use. We've tested intakes where the entire divider was cut down front to back, and even completely removed. This move can really KILL some mid-range power, and induce a stumble/hesitation/bog going quickly to full throttle. I've had to notch quite a few intakes at both ends and make inserts for them to put the divider back in place over the years, sent here from folks who got carried away when putting a small "notch" between the secondaries I'm assuming. If you want it done right, send your stock intake to Dave at SD Performance. He has a CNC scan of our finished product, and will do the work for. On an iron intake, it' takes hours to grind the drivers side down to the size/shape of the intake in the pic above. Those things are some TOUGH material!. I've done spacer testing as well, but that's another topic. Best advice I can provide in that area....not worth the time or trouble if raising the carb up another 1" or more requires any "cobbling" to fuel lines, throttle linkage, etc, to make one fit....at least for most of the "street" engines folks are doing this to......Cliff |
Cliff did the RPM peak at 6000 compared to 5800 for the other 2 manifolds?
Cheers Steve |
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Steve, the entire power curve, HP and torque was a near mirror image of the iron intake, with a "shift" in power about 200rpm's at every point. It just made a tad less power everyplace. Also keep in mind the testing was done on a 500hp engine, not some 350hp 9 to 1 compression 400 in a 4000lb car pushing a stock converter and 3.08 gears! I see folks take later T/A's and cobble up EVERYTHING to install an intake or spacer that more often than not, makes LESS power at every rpm.
"Sorry. I guess I'm a little dense. It wasn't clear to me, if all the intakes got the "notch", etc." Not a problem, I wasn't overly specific with the original information right to start with. We add the notch to all of them when modded. I'm not sure exactly what it does, aside from allowing both sides to "see" each other. I know when I've tested these things, fully divided intakes and fully divided/4 hole spacers produced the least power everyplace. Even with that said, most track testing is pretty close, seldom over a tenth and 1mph, and more often than not only a few hundreths and less than .5 mph. Knowing this I often wonder why folks chase carbs, intake and spacer modifications with a vengeance, cutting, hacking, and modifying parts like their going to find a second or two improvement and another 10mph on their next track outing. Anyhow, there is a LOT going on in an intake and exhaust system with the engines valves opening and closing many times per second. I'll never claim the results I've obtained with intake and spacer testing is anything more than what we did with a particular application. Even so, it's quite interesting how my testing mimics similiar testing Jim Hand has done over the years......Cliff |
Cliff no not a stock convertor and I do have 3.9 diff gears, will go drag that iron intake out from the lawn locker!
Cheers Steve |
"seldom over a tenth and 1mph, and more often than not only a few hundreths and less than .5 mph. " Cliff if the intake makes 5-10 Hp more or less wouldn't that show up on track times by 0.05-.10 sec?
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Listen to Mr.Ruggles, he tryed to talk me into a stock intake and i went ahead and spent 180.00$ for a new rpm, so far id been better with the stock unit, i see no real gains with the rpm unless heads are ported ect. and seeing high rpm. I could of bought a set of Roller Rockers for a little more cash plus the 180.00$
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"Cliff if the intake makes 5-10 Hp more or less wouldn't that show up on track times by 0.05-.10 sec?"
Maybe, maybe not. It's the average power produced in the rpm range the engine is ran in that determine ET. More often than not, showing more HP, is accompanied by a shift in power as well. The engine really doesn't spend all that much time at peak power on a run anyhow. When I tested intakes a few years ago, installing a single plane intake right after testing a dual plane intake would show some more MPH, with losses in 60' and short times. In all cases, the intake running quicker in 60' also ran quicker in ET, even if it gave up some MPH. The only intake I've tested to date, that made up most of the lost ground after running slower in 60' times was the Tomahawk intake with a 1" spacer. It ran a solid 2 mph faster than my iron intake with no spacer, but ran almost a tenth slower in 60', and a few hundreths slower in ET on the run.....Cliff |
Did we ever determine what car this is going on? Given the OP's user name, I assume it is an F-body car. OP says its a street car. Cliffs testing has been very valueable to us all, but consider all the info and the intended purpose of your car before just running what he runs. Cliff's car is primarily used at the track, so obviously he runs what test best for that situation. Unless your car can dead hook on the street with 1.5x 60fts using similar gear ratio etc, his intake choice may not be best for you. I have found that If I can drop my 60ft times by only .10, I can pick up close to .30 in quarter mile. So this is the best place to work on your ET. If you look at all of what Cliff post on intake swaps, you should see that for a limited traction street car that will be run most of the time from a roll or passing gear etc, the Tomahawk stands out by far....look at the MPH...and this without a spacer. Couple that with the fact that the Tomahawk will fit under any hood and works great with a q-jet and the choice is clear.
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Just a bit of info from a friend who dyno'd his 535 engine......just a tad below 700hp @ 5600rpm with a ported IRON intake.
He cut two holes underneath the intake to gain access to the inner walls to blend the ports. He used some old style type flanged freeze plugs to cover the holes after doing the port work. Runs with a Q-jet modified per Cliffs book. |
Larry, can we presume the work was done for class racing reasons where he had to retian a factory intake ? Or just wanted the 'stealth' effect ?
Related- Probably could be done easier in conjunction with the aluminium material using a Edelbrock Performer intake. I've taken aluminium intakes and acid etched the inside to increase runner and plenium volume before. . |
LOL....just the stealth look Steve.
The engine is an IA2 iron block, crower crank, ported E-heads, "street car" solid roller. Oh I forgot to mention that the dyno figures were also obtained using RARE long branch exhaust manifolds. |
That is impressive!! Very stealth to say the least. Larry...have you tried the q-jet?
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the car this would be going in is a 65 lemans.
mostly street, prob all street but we live 5 miles from atco so ya never know. |
Cam specs? That's what will make the decision
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I have a question for the Basic Budjet Builder who may do a search in the future on Intakes and stumble across this , Which has been very informative
My question is what can be expected as far as Hp increase, for a 400 and a 455 stock no other mods any change from the performer or the rpm vs stock intake and what changes to the power band, losses in low end tourque vs top end increases |
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"My question is what can be expected as far as Hp increase, for a 400 and a 455"
Two completely different applications. A 400 isn't going to be pulling nearly as hard on the intake as a 455. The Performer intake has small runners. It's probably fine for a 400 engine to at least 1hp per cid, and a 455 to nearly that rating. For higher power levels, it starts to become restrictive. When I tested a Performer intake on my old engine at 514hp it wouldn't even work. HUGE hesitation, stumble, bog followed by some "surging" in the mid-range. The engine absolutely hated it. The factory and RPM worked fine on the same engine. Since that testing, I've avoided the Performer intake, but it would probably be fine on mild set-ups. When we dyno'd the 3 intakes mentioned earlier, ported HO, iron and RPM, all of them were tested pretty extensively on the street, and I've ran all of them at the track as well. Here's a clip of my current engine a few weeks ago at Norwalk, launching at 1100rpm's and shifting at 5000rpms, to stay roll bar legal. http://www.youtube.com/user/69tiger?...are_video_user Keep in mind that the intake being used is a 1971 HO, fully ported and modified under the flange as well. No spacer is used, and it's topped with a 1977 Pontiac q-jet, and 1974 GTO air cleaner, filter and Shaker assembly (stock).....Cliff |
What a cool ride thanks Cliff.
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Nice video Cliff!! Motor sounds....Happy!
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Thanks. It's got a few degrees timing taken out, and running pretty heavy at 3740lbs race weight. Between that and shifting at 5000rpm's we kept the Officials happy again this year!.....LOL....Cliff
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durability
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i'm no expert; but swapping carbs a few times has fatigued the holes in my aluminum intake despite being very careful of the soft metal, and i'm sure my carb isnt as tight as i want it to be.
my iron intake doesnt sweat that. i've read cliffs book and i realize that you needn't over tighten the carb but still... this is for my brothers 65 lemans 4 speed 3.55 posi. i just want his first pontiac engine to be strong and reliable. he's from that "other" brand school where you need to replace everything w/ aftermarket parts. so far we've convinced him to use a q jet; and factory RA headers(whew!). i guess it wont be a big deal to get an RPM, but i just think the money could be used elsewhere more sensibly. we'll have tons more questions and debates as this progresses. we're open to roller cam suggestions too. thanks for all of your replys. |
"i'm no expert; but swapping carbs a few times has fatigued the holes in my aluminum intake despite being very careful of the soft metal, and i'm sure my carb isnt as tight as i want it to be."-Helicoils!
A 400 will respond alot different to intake choices than a 455, a single plane wil kill alot more bottome end and be harder to pick it back up even if it makes more on the top end. I think a good dual plane for a 400 in an average weight vehicle will get you much better down the road. ""Cliff if the intake makes 5-10 Hp more or less wouldn't that show up on track times by 0.05-.10 sec?" Maybe, maybe not. It's the average power produced in the rpm range the engine is ran in that determine ET. More often than not, showing more HP, is accompanied by a shift in power as well. The engine really doesn't spend all that much time at peak power on a run anyhow. " "The HO intake made 487HP, RPM made 491HP, iron intake made 497HP." Just to give you a hard time Cliff :) then why even dyno them or compare dyno results as your comparisons(or mine). They can act totally different in the car so actual in car tests are the best way. A cleaned up HO intake on some moderately ported E heads on a 455 with a loose race convertor was losing almost 0.5 seconds and idled worse than a Torker II we swapped on with the same carb.The intake a fresh tranny and real loose comvertor dropped the car from high 11s to high 10s. My 400 RAIV lost so much bottom end with a Torker 1 over the same HO intake in 60 ft I could never make it up even though it had 2 more mph. So its all in the individual combination in that individual car. |
any opinions on the aluminum warrior intake and how it may compare?
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helicoils, sure.
but if the intake isnt better than the iron one, than its something else to eventually fix. ( i mean no disrespect tho!) i bought an iron for my car and will soon be recycling my performer. (its not an RPM). does the RPM have any advantage on the low end torque, compared to the iron? or does the engine lose any torque by useing the RPM instead of the factory iron? this car will mainly be a cruiser/ tire smoker, we dont wanna lose torque heh heh... i'm just trying to save him a few bucks as we need TONS of stuff to get this thing going. there's a tight budget, and we still need a dist, cluch, pressure plate, flywheel, ect ect ect.... |
My bet would be the bigger runners of the RPM would loose a little to the iron or HO intake. Both can perform good up to a fair amount of HP so save the money for another part.
I think if money is tight, like most of us are now, I'd go with the iron, or an HO if you had it. FWIW I've have lots of aluminum intakes on lots of different motors, if you are careful you can keep the threads OK with alot of use. Now early 60s GM alumium intakes used a really soft aluminum that was even more prone to that, but even my aluminum 409 intakes have all good threads. |
If the 455 is different. What would be better intake to use on a 455. One from 1969 or one from 1975?
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The earlier one. The 75 is heavier, uglier and has the EGR tumor growing out the side of it's neck.
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i wonder how it compares to the earlier intake? i see those egr intakes for 20 bucks on craigslist often. |
Close yes, but just because Rosanne Barr can cook almost as good as Cameron Diaz...well you know.
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Got the 69 on now, curious how everyone thought of the 75. Looking fot a HO one for the car
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i had a very similar combo to yours...13 heads but i had 3.90s, headers, and TH400.
I tried the '71 stock iron intake and it lost something like over 3 tenths at the track compared to the rpm. nothing else was changed not even the jets in the carb. i have some more posts on this topic but it needs to be searched. |
"My bet would be the bigger runners of the RPM would loose a little to the iron or HO intake."
X2 I just went from an unmodified T2(+1" spacer) to head gasket matched RPM (no spacer-clearance issues)and lost approx. 5mph. No other changes were performed and the idle, cruise and wot afr was identical on both intakes. |
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