[rohrt]

I have been reading several threads on intake modifications to the stock cast iron intakes. Studying Cliff and Jim's comments mostly. Some great discussions and information in here.

http://forums.maxperformanceinc.com/...ghlight=intake

http://forums.maxperformanceinc.com/...ghlight=intake

http://www.sdperformance.com/newsStory.php?newsID=44

http://psp.aquacomp.net/topic.asp?TOPIC_ID=429

http://www.hotrod.com/how-to/engine/...take-manifold/

Couple questions that I had.

A few times it was mentioned that on Cliff intake he modified the plenum. That this is the modification that SD Performance does when an intake is sent in. What is this modification to the plenum? Is it just the opening up of the primary and secondary holes and smoothing the contours or was there more to it?


The second question is bit more controversial concerning the use of spacers. It sounds like for all practical purposes that a spacer will add performance in almost all cases. The unknown is with the height and whether to use an open divider between the secondaries. There was some discussion that an open divider in many cases will kill power but not sure if that was from the perspective of intake or the spacer.

Jim listed these reasons on another board of why use a spacer.
"One significant method of adding performance to almost any combination of engine and intake is the use of a carb spacer. Here is a brief rundown on spacers and effects:

1. They increase the volume of the intake manifold plenum. This provides better fuel/air delivery at higher RPM.
2. They change the intake tract length, and this can improve intake tuning by peaking the manifold at a more favorable RPM.
3. They can provide some crossover air between the left side and right side of the carb., thus making the carb appear larger.
4. On a stock manifold, lifting the Q_Jet up via a spacer removes the serious blockage of # 8 Port caused by the Q-Jet secondary throttle plate. My flow bench indicates a significant increase in flow through #8 port with a one inch spacer.
Jim Hand"

So the question is without a dyno or track testing what would be the safest most guarantee way to go about this to increase performance?

My thinking was to open up the Primary and Secondary as Jim H shows in his book. Keeping the divider in place, make a 1" spacer out of wood also with a divider. My thinking on this is the 1" should address Jim's comment on #4 and hopefully not mess with hood clearance. It also may make bending the gas line and connecting the choke a bit easier staying more conservative.

I'm looking at this for both my stump puller 455 motor and a very conservative 068 400 motor in the works.

[Skip Fix]

No way to tell other than track/dyno.

An example for you fairly similar components on 2 motors. My RAIV 400, 72 HO intake, 73 SD SR Qjet, UD 288/296 HFT cam 2" hooker headers. Picked up 5 HP with a 1/2" spacer(all that woudl fit with a Shaker).

Friends 72 455 HO ported heads, 72 HO intake , same model 73 SD SR Qjet, 2.5" RA manifolds, flat tappet colid cam. LOST power with the same spacer.

[Will]

I envy anyone with enough hood clearance to run a spacer.

The nice thing about home made wood spacers is you can make as many as you want. Try it with the secondaries separated AND with them connected. Only way to know what your specific combination will like.

ETA: Nice hole shot Skip.

[1969GTO]

WILSON MANIFOLDS makes a nice tapered spacer for the Q-JET.
I picked up 2mph and 2 tenths in the 1/4 mile

[rohrt]

Originally Posted by Skip Fix

No way to tell other than track/dyno.

An example for you fairly similar components on 2 motors. My RAIV 400, 72 HO intake, 73 SD SR Qjet, UD 288/296 HFT cam 2" hooker headers. Picked up 5 HP with a 1/2" spacer(all that woudl fit with a Shaker).

Friends 72 455 HO ported heads, 72 HO intake , same model 73 SD SR Qjet, 2.5" RA manifolds, flat tappet colid cam. LOST power with the same spacer.

skip was this a 4 hole spacer, open or like Jim's with only being open on the secondaries?

[Skip Fix]

4 hole.

My 470/409 liked a 1" 4 hole better than a 1" open on the dyno.

The 500" IA liked a 1" Wilson taper on top of a 1" open.

[Formulajones]

I've played around with spacers on the stock iron intake. However I only have room for 1/2-5/8". I have ZERO intake mods and the stock intake in my case seemed to like the open 1/2" spacer at the track right on top of a stock 4-hole intake, with marginal gains.

With a modified iron intake, having the divider removed between the front and rear barrels and leaving the center intact from front to back, I'd be inclined to try both styles of spacers. One with a complete divider and one with the divider removed at the back barrels only. Very easy to make both and swap them at the track.
However I don't have the hood clearance for a 1" spacer and will have to settle for experimenting with 1/2". Might try to squeeze 3/4" in there though

[78w72]

question#1: the plenum mod is mainly just removing the 4 holes & opening up/smoothing the plenum area, but its also cutting a small notch at the rear of the divider to allow the secondaries to feed both sides instead of keeping them divided.

but the bigger performance gains are SD's stage 2 & 3 options. #2 is where they gasket match the port openings to the ram air gasket which matches the rpm intake & #3 is actually cnc machining the runners to open them up. i had mine done to stage 3 to go along with e-heads & get the most out of the stock intake. i have NO room for spacers or taller intakes under a firebird formula hood.

[Formulajones]

Originally Posted by 78w72

question#1: the plenum mod is mainly just removing the 4 holes & opening up/smoothing the plenum area, but its also cutting a small notch at the rear of the divider to allow the secondaries to feed both sides instead of keeping them divided.

but the bigger performance gains are SD's stage 2 & 3 options. #2 is where they gasket match the port openings to the ram air gasket which matches the rpm intake & #3 is actually cnc machining the runners to open them up. i had mine done to stage 3 to go along with e-heads & get the most out of the stock intake. i have NO room for spacers or taller intakes under a firebird formula hood.

The plenum mod still maintains the center divider in most of the successful mods I've seen. Some try to remove a small portion between the back barrels with mixed results. Most of the success I see and read leaves the center divider intact throughout on the intake itself, and the notch at the rear barrels is made with a spacer.

You should have wiggle room with a formula hood. I have a fair amount with my 70 formula running the original ram air setup. I currently run a 1/2" spacer, and using the aluminum foil trick on top of the air cleaner, with the hood shut I still have roughly 5/8" to play with.
I could techically run a 1" spacer under the carb and have a very small amount of hood clearance.

[78w72]

most the plenum mods i have seen or read about use the notch in the rear, including cliffs results & what SD does based on cliffs info. in fact SD says that the plenum mod alone added 12hp over a stock intake, hard to say how much of that was due to the notch. so im not saying it does or doesnt work as i dont have the means of testing it, just pointing out what i have read & what cliff says is a definate advantage. maybe cliff will chime in with his results.

there is a little wiggle room on my car, i did the aluminum foil test & came up with about 3/8 with my non stock air cleaner set up. my hood is uncut & im using a 78 t/a base & lid with plans of adding a 2nd snorkel for dual cold air intake. not sure if the drop of the t/a air cleaner is less than a factory ram air set up but i have less than 1/2" to work with so no spacer for me at this point. would have liked to use a RPM intake but it sits too high, so i opted for the SD modified cast iron 1970 cast iron intake.

[Formulajones]

I do believe Cliff had success with cutting a notch at the rear of the divider on the intake itself, but if you read alot of Jim Hands experiments, he found it worked best with some of his last attempts if the notch was done in the spacer itself, and also using the spacer to make the transition at the notch between the back barrels as smooth as possible. However if you don't have room for a large enough spacer to do this then you have to resort to putting it in the intake.
If that is the case then I'd prefer some back to back testing at the track or dyno with a temporary filler placed in the intake since that trick seems to affect each engine a bit differently as Jim pointed out, it wasn't always affective with different combos.

[Will]

Originally Posted by 78w72

there is a little wiggle room on my car, i did the aluminum foil test & came up with about 3/8 with my non stock air cleaner set up. my hood is uncut & im using a 78 t/a base & lid with plans of adding a 2nd snorkel for dual cold air intake. not sure if the drop of the t/a air cleaner is less than a factory ram air set up but i have less than 1/2" to work with so no spacer for me at this point. would have liked to use a RPM intake but it sits too high, so i opted for the SD modified cast iron 1970 cast iron intake.

I'm envious of formulajones. With my factory RA aircleaner I have just a bit over 1/2" clearance. I wouldn't want to run much less than that for fear of making contact when the engine torques over on launch.

This is why I also have a beater with a TA hood to make into a race car.

[Formulajones]

Poly mount on the driver side cures that.

[Cliff R]

I recently switched from an RPM intake and custom Shaker assembly with a filter in the inlet back to a CNC ported HO intake with my plenum modifications. I re-installed all the factory Shaker parts, and stock paper filter/lid, etc.

I also installed a choke flap in the carb, electric choke on the carb, and smaller 2.5" mandrel bent tail pipes to replace the 3" "turn downs". The 1977 q-jet was also set up with primary metering rods/jets instead of running straight off the jets.

Since I was running well under the roll bar rule anyhow, and doing more street driving, figured I might as well make things a bit more user friendly and more efficient for "normal" driving.

I went to or local track recently and low and behold the car ran just as quick in the 1/8th miles with the "stock" components as it did with the RPM and modded stuff!

I didn't use a spacer with either intake for fitment reasons, do use a 1/4" thick Chevy style q-jet gasket between the carb and intake. Being a fully open gasket, it allows both sides to see each other and eliminates the need for a "notch" between the secondaries.

I've done a LOT of intake and spacer testing over the years, and could write many pages on it here. I'll say as a general statement that using a very well made spacer is REQUIRED on all single plane intakes, or you are going to be down on power some.

For dual plane intakes, fully open and 4 hole spacers ALWAYS slowed my car down everyplace. Fully divided with a notch ran close to the same as no spacer at all. For all runs I've picked up MPH using a "semi-open" spacer as close to what Jim Hand shows in his book and prefers on his intakes.

I've also played around with divided spacers and removing the divider or lowering it in dual plane intakes. This is NOT a good idea, and all testing I've done to date lowering/removing the divider has hurt vehicle performance. As Jay Delaigle about that deal sometime, as he has dyno and track numbers to show how bad we can hurt power removing the divider from a factory intake.

Anyhow, when it comes to this topic, one should consider several things. In most cases we are only chasing a few hundreths of a second here, comparing no spacer at all to a 1" spacer of any configuration used on a dual plane factory or aftermarket intake. Installing spacers reduce hood clearance, and may require "custom" fabrication, drop base air cleaners, and often moving the air cleaner lid closer to the carburetor. Doing that alone can have a TREMENDOUS negative impact on vehicle performance, so something to consider when it comes to this topic.

I would also say that my car runs nearly into the 10's in full street trim with a "ported" factory intake and no spacer at all, using all factory Shaker components on top of it. Put up some 7.20's this summer in hot/humid weather just under 96mph. Most folks don't run nearly that quick, yet I see them "hacking" up some pretty nice stuff and going to extremes to put an RPM or single plane intake and 1" spacers to improve vehicle performance. Not saying they aren't making improvements, but one has to ask if it's all really worth a couple hundreths in the big scheme of things, and I'll bet, more times than not, they actually slow down just a bit instead of picking up some.......Cliff

[Formulajones]

An interesting subject that Jim brings up is how the rear throttle blades (being as large as they are on a quadrajet) block the #8 port when fully open, and how a spacer brings the carb up enough to eliminate that issue. If it is indeed an issue.

With this in mind, notch or no notch, it seems the spacer could be beneficial in that respect, plus the fact that you are lengthening the runners and making the transition easier for the air/fuel. I've always found a gain with some form of a spacer on both dual plains and single plain intakes. Just what type of spacer takes some experimenting though.

My current spacer (which is actually a pair of 1/4" gaskets) are completely open gaskets just as you describe Cliff, where both sides of the carb can "see" each other. So no need for notches was the same theory I had. My car ran a tick quicker in this configuration, Almost a tenth and about 1/2 MPH on average. My intake however is unmodified and never touched with any tools.

What's more interesting is Jim Hands spacer, with the short 3/8-1/2" spacer on the intake that follows the divider completely (no notch) and then another 1" spacer on top of that with a notch in the rear, picked up nearly 20 HP and 20 ft lbs. on a bone stock iron intake with no mods on the intake at all. That should equate to nearly 2 tenths and 2 mph in the quarter, which is a huge improvement for no money and just a little time spent. So there is power to be found with the spacers on these iron intakes.
The problem with that though is that like most everyone else, I don't have room for 1-1/2" worth of spacer under the carb. So experimentation is in order to find what works with limited room. I'm not going to be so quick to notch a factory intake though since that's much more involved to replace if it doesn't work on my particular combo.

[steve25]

On any Pontiac making over 400 hp and running a duel plane manifold of any type you need more Plenum volume and not by means of cutting out and or notching dividers, so this means unfortunately getting it by means of going up with the Carb!
On 455 cid motors and greater with a factory intake the addition of a 1 inch spacer is worth 8 hp even with stock heads, no less ported or aftermarket heads!

[1969GTO]

Not to step on toes here gents,but Cliff mentioned the air cleaner filter top/cover make sure not to be close to the carb inlet.
I run a 69 GTO Judge Ram Air set up on my 69 GTO, and am wondering if there is a taller air filter for this set up than the stock height one being sold?

[Formulajones]

Originally Posted by 1969GTO

Not to step on toes here gents,but Cliff mentioned the air cleaner filter top/cover make sure not to be close to the carb inlet.
I run a 69 GTO Judge Ram Air set up on my 69 GTO, and am wondering if there is a taller air filter for this set up than the stock height one being sold?

My father ran the stock ram air setup on his 69 goat for years with a stout 455 combo that got him down in the mid 11's in street trim.
Yes the lid is very close to the top of the carb. The saving grace with his setup was the 950HP holley he ran with no choke housing, which clears the way quite a bit. He also ran a slightly taller K&N filter to raise the lid slightly (not much room to play with here though). Later on he added a K&N filter lid on top of that. That configuration is when the car ran it's best times.

I'm at a bigger disadvantage with my 70 ram air formula. That lid is a very tight 5/8" above the choke housing on the factory quadrajet. What's worse is that it's only that high right in the very center of the factory lid where it "raises up" but it quickly contours downward within a 2" circumference as it heads out towards the base.
This measurement is with a slightly taller K&N filter placed inside, with the stock paper filter the clearance is barely 1/2". Nothing I can do about this setup unfortunately, but I've found with track testing that without it the car slows down 2 tenths and almost 2 mph, and simply removing the filter but keeping the ram air housing functional also slows the car down substantially.
I realized that these ram air setups on the formulas are extremely effective, with the scoops front and center. There is so much air turbulance inside that air cleaner that it would blow out the PCV filter after every pass, and I'd remove the lid to find it resting in the very back of the air cleaner. Above 80-85 mph seemed to be the magic number. I had to wire tie it to the PCV housing inside the air cleaner.
It's this turbulance that I believe caused the car to slow down so much without the air filter in place. The filter installed slowed and straightened the air flow and the car picked up MPH and ET.

[Blackened]

A side note to this discussion, does anyone know which level of modified intake that SD used in their testing? They mention a 12 hp gain but don't specifically mention which of the three choices they offer was used during this test. Was it the first with only the plenum modified?


"Patterned after Q-jet guru Cliff Ruggles personal modified OEM iron intake, a back to back dyno test showed a 12 hp gain over a stock plenum OEM intake. Call for core availability and price or you can send us your OEM iron or aluminum intake. Below prices do not include an intake core. Water Crossover can be seperated at an additional charge, call for more info.

$175.00 CNC plenum + hand finish
$275.00 CNC plenum + hand finish + port matched runners.
$375.00 CNC plenum + CNC port runners + hand finished (we've made over 600hp with these modifications!!!) "

[rohrt]

Originally Posted by Blackened

A side note to this discussion, does anyone know which level of modified intake that SD used in their testing? They mention a 12 hp gain but don't specifically mention which of the three choices they offer was used during this test. Was it the first with only the plenum modified?


"Patterned after Q-jet guru Cliff Ruggles personal modified OEM iron intake, a back to back dyno test showed a 12 hp gain over a stock plenum OEM intake. Call for core availability and price or you can send us your OEM iron or aluminum intake. Below prices do not include an intake core. Water Crossover can be seperated at an additional charge, call for more info.

$175.00 CNC plenum + hand finish
$275.00 CNC plenum + hand finish + port matched runners.
$375.00 CNC plenum + CNC port runners + hand finished (we've made over 600hp with these modifications!!!) "

Originally Posted by 78w72

question#1: the plenum mod is mainly just removing the 4 holes & opening up/smoothing the plenum area, but its also cutting a small notch at the rear of the divider to allow the secondaries to feed both sides instead of keeping them divided.

but the bigger performance gains are SD's stage 2 & 3 options. #2 is where they gasket match the port openings to the ram air gasket which matches the rpm intake & #3 is actually cnc machining the runners to open them up. i had mine done to stage 3 to go along with e-heads & get the most out of the stock intake. i have NO room for spacers or taller intakes under a firebird formula hood.

I didn't see the three stages of optionss on the SD website. Thanks for that info.

So I was trying to figure out if SD was really doing anything that I couldn't do with hand grinders. I already have mine port matched to the RAIV gasket and I don't see any special skills needed to open the plenum.

The CNC port runners option is interesting. I assume here that the RAIV opening is made all the way through each runner. I could see that being very time consuming work and that is where having SD doing the CNC work would be a time saver.

Originally Posted by Cliff R

For dual plane intakes, fully open and 4 hole spacers ALWAYS slowed my car down everyplace. Fully divided with a notch ran close to the same as no spacer at all. For all runs I've picked up MPH using a "semi-open" spacer as close to what Jim Hand shows in his book and prefers on his intakes.

I've also played around with divided spacers and removing the divider or lowering it in dual plane intakes. This is NOT a good idea, and all testing I've done to date lowering/removing the divider has hurt vehicle performance. As Jay Delaigle about that deal sometime, as he has dyno and track numbers to show how bad we can hurt power removing the divider from a factory intake.

Anyhow, when it comes to this topic, one should consider several things. In most cases we are only chasing a few hundreths of a second here, comparing no spacer at all to a 1" spacer of any configuration used on a dual plane factory or aftermarket intake. Installing spacers reduce hood clearance, and may require "custom" fabrication, drop base air cleaners, and often moving the air cleaner lid closer to the carburetor. Doing that alone can have a TREMENDOUS negative impact on vehicle performance, so something to consider when it comes to this topic.

Great confirmation there that the Jim Hand spacer works. At this point chasing 10 to 12 hp for very little money sounds like a good deal to me. Maybe if I find a few more tricks like that I can beat my brother's TA