the 4 hole will be best, that is designed for dual plenum intakes, like your's. The open plenum spacer would defeate the purpose of a dual plenum which has better idle to mid range than a open plenum.

 

The Airgap is not exactly the same as the Perf/RPM. They cut about a half inch out of the plenum. So its between a dual and single plane. The annular discharge carb prefers single plane intakes. So the open spacer would be best.

I have the same intake and I just teed off from the PCV port to the power brakes. I did the same with my Victor Jr intake as well. The brakes in both cars work fine. In both cases the spacer would have caused hood clearance problems. I would try this before spending money on an unnecessary part. The spacer may cause a HP loss as well.

 

The engine was already in my car and I had a 4 hole spacer on it with my 650 DP Holley. I had to shave a bit of the webbing back on the hood but it clears fine now, so no worries there. Seeing as how I will be helping the upper end HP with the upgrades to the motor, I thought I should see if the 4 hole should stay or if I should change it to an open spacer. The upgrades over the last engine configuration are just the heads, carb, bigger headers/exhaust and new accessories, so there should be no dimensional changes to the engine. The only thing I will notice is a better pull from 5000 to 6000 over the old configuration with the ported 305 heads and 650 Holley - even the 58cc chambers are the same. (Those 305 heads actually worked quite well... sad to see them sit now)

I never realized the annular boosters like single plane intakes, I will certainly use the open spacer for that reason. Will a spacer really cause a HP loss? I would have thought that increasing the plenum size helps increase HP. Perhaps you could enlighten me on this.

 

I said you might lose HP.

On my Lemans, I tried a 1" spacer for my power brakes on my Victor JR. My air filter was about a 1/4 in too high for my new fiberglass hood. I took the spacer off and teed the brakes into the PCV off the back of the carb. The brakes worked fine and I picked up a half second on the 1/8th mile. I don't know why.

On my Corvette, I installed a new 400 sb with an Airgap. I didn't even bother with the spacer. I just teed off the PCV. Power brakes work fine. I would imagine if Edelbrock figured you would pick up HP they would make the intake 1/2" higher.

 

Spacer

The Annular carburetor does not have a prefereance on what type of intake manifold it is used on. It's a matter of matching the carburetor size, and booster type to the application. If the only reason you're using the spacer is to gain clearance you may not need one at all. Edelbrock makes a 90 degree fitting designed to fit under the rear bowl of a modular carburetor to connect your vacuum to. With what you are doing, and looking for bottom end a 4-hole spacer would most likely be a better choice. An open spacer will most likely move your power band up a few hundred rpm, and may hurt your throttle response.

 

I don't know about the Demon carb but the 90 deg fitting does not work on a Holley with the Airgap without a 1/2" spacer.

I also had to use a 1/8 spacer on my Torker II for the 90 deg fitting.

It was Holley tech that told me the annular discharge was better suited for the single plane manifold. I use one on my Victor Jr but use the regular carb on my RPM/Airgap.

 

I have a 355 that will be getting several upgrades that will increase the horsepower to about 450 at around 6000 RPM. It is a .030 over .005 decked 350 short block with a Comp Cams XE268 cam, heavily ported L98 corvette heads with 58cc chambers (about 10.8:1 CR), an Edelbrock RPM air gap intake and a Speed Demon 750 annular vacuum secondary carb. The thing with the RPM air gap is that you need to use a 1/2" spacer in order to use the vacuum port (for brakes) on the top of the manifold. Would I be better off using a 4 hole spacer or an open spacer when I plan to run a 2300 stall and 3.73 gears and a beefed 700R4 tranny? I'm looking for the best power I can get without making the low RPM weak.

Thanks...

You forgot one thing, what N2O kit are you using? You said you were getting serveral upgrades to get 450hp at 6000rpm and with what you have listed your going to fall short about 100-150hp. I'd recommend NOS brand, always used them and never had a problem.

 

I don't know about the Demon carb but the 90 deg fitting does not work on a Holley with the Airgap without a 1/2" spacer.

I also had to use a 1/8 spacer on my Torker II for the 90 deg fitting.

It was Holley tech that told me the annular discharge was better suited for the single plane manifold. I use one on my Victor Jr but use the regular carb on my RPM/Airgap.

Sorry about that, thought it was a Performer Air Gap, not the RPM. On an RPM Air Gap you've gotta have a spacer.

As far as Annular vs. Downleg boosters it's a matter of how the carburetor is built, and the rest of the combination. Take a cup engine some run Annular boosters, while others run downleg. Same type of intakes.

 

You forgot one thing, what N2O kit are you using? You said you were getting serveral upgrades to get 450hp at 6000rpm and with what you have listed your going to fall short about 100-150hp. I'd recommend NOS brand, always used them and never had a problem.

thats what i was thinking. :nono:

 

I don't think I will have a problem getting 450HP with these parts. The motor that is being upgraded already had 400HP, and I am going to much better flowing heads (comparable to AFR 180 with the porting, I have the flow numbers), bigger headers and a bigger carb, plus I am eliminating my flex fan and going to electric and adding an underdrive pulley. Not to mention switching to Royal Purple oil to reduce friction. I may also upgrade to 1.6 rockers as well.

Considering I am using a vacuum secondary carb with decent gears and stall, would I still notice a reduced throttle response with the open spacer?

 

The converter isn't too loose, and with only a 3.73 gear you'll get better throttle response and acceleration using a 4-hole spacer.

 

I used a 90º fitting in the AirGap, just cut the threads a little deeper and I used an Edelbrock divided heat insulator #9266.
I now use a four hole spacer as I needed to raise the carb to add a heat shield and correct throttle cable problems, works just fine.

 

Interesting thread...I can see years of job security for Tech @ BG

450 HP out of a SBC with a 214 at 50 cam, I guess I'm doing something wrong?

We make an Aramid fiber 3/16 spacer gasket in both 4 hole and open, this usually moves the carb up just enough to get the vacuum line on....$10.00

Available from all FBO Dealers worldwide: http://www.4secondsflat.com

 

basic question - which is better?

So far as I know, the 4 hole is great for increasing bottom end and getting you out of the hole faster, while the open is good for mo' top end.

It all depends on what you want. You set up your engine with the intake of your choice, get it running and then play with your phenolic depending on how you want it to affect your torque curve given your setup.

I personally wouldn't put on the spacer before I had other things dialed in, but of course I've done the opposite and it complicated my life some.

Arn

 

450 HP out of a SBC with a 214 at 50 cam, I guess I'm doing something wrong?

Nope, this cam is 224/230 @ .050, with .477/.480 lift and 110 LSA.

Not much when you look at it, but consider these flow numbers. Up to .300 lift the intake flows better than the hefty AFR 215 raised runner heads. This really helps with the overlap phase of the cam. A little secret called progressive valve blending is what helped here.

Tested on a Superflow 600 bench at 28" H2O

lift............................intake......................exhaust
0.100........................93.5........................70.7
0.200........................161.2......................117.3
0.300........................216.8......................148.7
0.400........................233.7......................170.3
0.500........................249.5......................189.3
0.600........................249.5......................187.9


Tech @ BG, I'm more inclined to use the open spacer for better high RPM performance, based on a hunch that the annular boosters will help a bit down low. Seeing as how you have a lot of experience with the Demon carbs, how much difference in response do the annular boosters give over the down leg boosters? Is it significant enough to consider in this application? Or would I still be better off with the 4 hole?

 

The Annular carburetor does not have a prefereance on what type of intake manifold it is used on.

That is what I have been preaching. Some people just don't want to see the light I guess.

 

Maggot,

With the tight converter, and low gear ratio you're still going to need more bottom end, unless you simply have not tires what so ever. I'd bet you'll see better performance using a 4-hole spacer on your combination.

 

I don't think I will have a problem getting 450HP with these parts. The motor that is being upgraded already had 400HP, and I am going to much better flowing heads (comparable to AFR 180 with the porting, I have the flow numbers), bigger headers and a bigger carb, plus I am eliminating my flex fan and going to electric and adding an underdrive pulley. Not to mention switching to Royal Purple oil to reduce friction. I may also upgrade to 1.6 rockers as well.

Considering I am using a vacuum secondary carb with decent gears and stall, would I still notice a reduced throttle response with the open spacer?

So you think all this is going to make more HP. Just bolting on bigger parts doesn't make more power. So what dyno did you get these figures from? DeskTop dyno doesn't count! 400hp already with lesser heads? What vehical do you have this in? Have your had it to the track? What kinda times are you getting?

I know the answer. Its not a drag car or a hot rod its your daily driver and you dont race it. As far as a dyno, you talked to a few guys about what you had and they said it should be 450hp. Yadda Yadda Yadda

A good web site HP calculators has ET and MPH to HP calculators and if you know (not a guess) the weight of your vehical and have your time slip from an actual drag strip with all the ET's and MPH's you will be able to calculate rear wheel HP. The only bad thing about calculators is that it takes into account that you have a matching combination geared towards performance. There is about 10-15% loss of HP through most street transmissions to the rear wheels so if you take rear wheel HP and add 10-15% to it that would be a close estimate on flywheel HP. Try that out and see where you stand.

 

So you think all this is going to make more HP. Just bolting on bigger parts doesn't make more power. So what dyno did you get these figures from? DeskTop dyno doesn't count! 400hp already with lesser heads? What vehical do you have this in? Have your had it to the track? What kinda times are you getting?

I know the answer. Its not a drag car or a hot rod its your daily driver and you dont race it. As far as a dyno, you talked to a few guys about what you had and they said it should be 450hp. Yadda Yadda Yadda

A good web site HP calculators has ET and MPH to HP calculators and if you know (not a guess) the weight of your vehical and have your time slip from an actual drag strip with all the ET's and MPH's you will be able to calculate rear wheel HP. The only bad thing about calculators is that it takes into account that you have a matching combination geared towards performance. There is about 10-15% loss of HP through most street transmissions to the rear wheels so if you take rear wheel HP and add 10-15% to it that would be a close estimate on flywheel HP. Try that out and see where you stand.

You just don't get it, do you? :boxing:

I don't post fairy tale numbers from a wannabe bench racing program - when I say 400 HP it is because my as-measured 3464 lb 85 Trans Am with a maxed out suspension (every part upgraded) and subframe connectors, and only 3.27 gears with 26.2" diameter 265/50R16 tires runs consistently high 12's with a G-Tech sensor (which is proven accurate), and has put out 343 HP on a chassis dyno - using your magic formula that equates to approximately 400 HP. All this at an altitude of about 3500 feet. I also know some guys at a reputable machine shop who will let me use their dyno and once the engine is complete I will personally email you a photo of the results they give me so you can see for yourself that my claims are not bogus. Have you stopped to consider all the factors of my engine before you automatically dismiss the numbers as not plausible? Probably not. Hopefully for your sake the little number "22" beside my name did not attribute to your attitude toward this. I know that bigger isn't always better and that all parts must match each other to work properly, and that is in fact what has been meticulously researched in this engine build. If you want every single specific part I put into this engine so you can make an "informed assumption" I will be happy to provide it.

Anyhow, if you feel you must get into a pissing match about this, use the handy PM feature of this website, otherwise this thread will likely get dumped.


Now, for the back on topic stuff...

Tech @ BG, I will use the 4-hole spacer I currently have in light of your advice, however the holes in the spacer are just a shade bigger than the bottom of the throttle bores. They match up to the bigger 1-3/4" bores on an 850 Demon, but the 750 I believe only has 1-11/16". Should I get one that matches to the 750 throttle bore size to eliminate the small step here and reduce turbulence, or will this be insignificant? I already plan to radius the bottom half of the spacer where it meets the intake plenum to further reduce turbulence, because the 1/2" cut-out of the plenum divider in this manifold would have more cross flow from the other side in the high RPM if it has a radius to move over rather than the square edge.

 

Now, for the back on topic stuff...

Tech @ BG, I will use the 4-hole spacer I currently have in light of your advice, however the holes in the spacer are just a shade bigger than the bottom of the throttle bores. They match up to the bigger 1-3/4" bores on an 850 Demon, but the 750 I believe only has 1-11/16". Should I get one that matches to the 750 throttle bore size to eliminate the small step here and reduce turbulence, or will this be insignificant? I already plan to radius the bottom half of the spacer where it meets the intake plenum to further reduce turbulence, because the 1/2" cut-out of the plenum divider in this manifold would have more cross flow from the other side in the high RPM if it has a radius to move over rather than the square edge.

I wouldn't worry about it, just try it the way it is. The .0625" difference shouldn't cause a problem.

 

okalie dokalie :thumbup:

 

You just don't get it, do you? :boxing:

I don't post fairy tale numbers from a wannabe bench racing program - when I say 400 HP it is because my as-measured 3464 lb 85 Trans Am with a maxed out suspension (every part upgraded) and subframe connectors, and only 3.27 gears with 26.2" diameter 265/50R16 tires runs consistently high 12's with a G-Tech sensor (which is proven accurate), and has put out 343 HP on a chassis dyno - using your magic formula that equates to approximately 400 HP. All this at an altitude of about 3500 feet. I also know some guys at a reputable machine shop who will let me use their dyno and once the engine is complete I will personally email you a photo of the results they give me so you can see for yourself that my claims are not bogus. Have you stopped to consider all the factors of my engine before you automatically dismiss the numbers as not plausible? Probably not. Hopefully for your sake the little number "22" beside my name did not attribute to your attitude toward this. I know that bigger isn't always better and that all parts must match each other to work properly, and that is in fact what has been meticulously researched in this engine build. If you want every single specific part I put into this engine so you can make an "informed assumption" I will be happy to provide it.

Anyhow, if you feel you must get into a pissing match about this, use the handy PM feature of this website, otherwise this thread will likely get dumped.


Now, for the back on topic stuff...

Tech @ BG, I will use the 4-hole spacer I currently have in light of your advice, however the holes in the spacer are just a shade bigger than the bottom of the throttle bores. They match up to the bigger 1-3/4" bores on an 850 Demon, but the 750 I believe only has 1-11/16". Should I get one that matches to the 750 throttle bore size to eliminate the small step here and reduce turbulence, or will this be insignificant? I already plan to radius the bottom half of the spacer where it meets the intake plenum to further reduce turbulence, because the 1/2" cut-out of the plenum divider in this manifold would have more cross flow from the other side in the high RPM if it has a radius to move over rather than the square edge.

You know I never noticed that age was displayed on there? But now that you pointed this out and did realize why I'm having a hard time believing your HP claims, it because you probably using a METRIC dyno and haven't converted your numbers over to the English measuring system. Damn Canadians

 

Ok Madmaggot check out the reply's I got from this forum

Someone please help. I need to get 400hp out of a Chevy .030 over 350 with ported 305 58cc heads and flat top pistons with static ratio of 10.8:1 and Comp Cams hydraulic XE268, RPM air gap intake with Demon 650 vac secondary and no nitrous. Running in a class all my own, well I think there is one other car on this forum that has this combo. Can it be done???

Thanks

Flow is power, unless you can get the head ports in decent enough shape to flow well enough to provide that kind of power, then I`d say your gonna come up a bit short. Also to reach that goal your cams a bit short also.
Stock 305 castings don`t flow very well.

*********
Sounds like a circle track hobby stock engine/ which would make a pretty snappy street engine.

I don't know much about those 305 heads or your particular set's valves, porting/ actual airflow.

You are requesting 1.14 horsepower per cubic inch.

Based on the numbers from other combos: You will need a 180 cc intake port volume and 230 cfm intake flow, a 750 cfm carb, and 6200 rpm, and maybe the 274 cam.

You are going to have to shoot for more than 400 calculated horsepower if you actually expect to see 400 REAL hp on the engine dyno. Theory is only theory. The proof is on the dyno.

Proof is in the dyno! Words to live by! Well sort of.

Dyno's are only as good as the dyno operator because there are figures that they have to put into the dyno program for it to calculate HP correctly like baro pres, air temp, humidity, fuel consumption and all you have to do is put the wrong number in and you'll get all kinds of grand HP readings. The drag strip has been a time honored tradition of measuring HP and using ET and MPH figures for the standing start 1/4 mile you can get altitude corrected HP that will be mostly correct.

I'm not meaning you didn't dyno 343 rear wheel HP @ 3500 feet above sea level, you say its corrected HP, but I am saying not with 305 heads and XE268 cam. You may think that what you have or maybe mislead to what you have but 305 heads no mater who ports them theres not enough room in them to get the HP figures you say plus that cam is on the small side.
Your new heads will work very well because they are more performance oriented and flow well but I still say that the cam is still to small to get you to the 450HP flywheel mark.
Its allot easier to say its a 450HP 350cid than it is the actually make it?
Your age has nothing to do with it. Fact is, small block chevys have been around over 50 years and every combo has been tried at least once by somebody somewhere and its not to say that maybe you have the only 305 heads in the world that flow enough to make 400HP but I call BS on it and I'm not alone on this.

 

Mad Maggot...Check out this post I got about 305 heads

It is going to be really hard, but it might be possible with the right porting and enough cam. Here is a company that seems to know what they are doing porting 305 heads. http://www.castheads.com/factory_chevy_305.php they are expensive, but trying to get this kind of hp out of parts that arent made to get you big hp will not be cheap. I would look in to a solid roller cam. I think the XR274R (230 236 @.050 .552 .564 ) cam from comp might work well. It has a little more lift that I think you need, but it is the smallest dual pattern solid roller that they offer, you could also look into a custom grind somewhere closer to .500-.525 lift. Depending on how well your heads are ported, the cam swap amy get you close, but I would not bet on it.

Adam

But still they only get a 35cfm improvement over stock briging it up to 200cfm intake flow @ .400. This is a machine shop with flow bench and who knows how many years R & D before they got it. But if there willing to do it and they have a market and maybe you got some, na I still dont see it!

 

For the record, I got 213 intake and 168 exhaust cfm at .500 out of my porting job (Superflow 600 bench), and that was after going over the heads 3 times to get the most flow I could get (winter project, up here winter is long...). I removed a ton of material from these heads, it turned out to be quite a big pile of shavings on the floor when I was done, and considering the heads I have are 165cc to start (14014416), I figure I probably came close to the 180cc mark. The heads have 1.94/1.60 valves and the chambers have been unshrouded big time seeing as how they are now on a 350. After getting them decked the chambers still measured 58cc.

But in any case it appears it still isn't enough. I don't know how to explain the results I got with the G-Tech or the chassis dyno, perhaps one or both were not calibrated correctly and I was misled in my information. Story of my life... do not depend on others. Now thanks to them I'm eating my foot big time because my motor apparently does not produce what I have been led to believe. The only way I can verify these results is with an actual dyno test but seeing as how the motor is being torn apart I don't think this will help much. Plus, for $800 or more to get this done it does not seem compatible with a carpenter's salary here in Canada. (You guys need any carpenters in the US?) When I get the motor dynoed after rebuilding it again I'll post results, but it sure seems like I will be disappointed now. What a waste of money if it doesn't produce 400HP, I could have bought a used LS6 for half the price and have fuel injection to boot.


Fultron, I must say one thing in addition. For someone who is new to this forum (only 20 posts), you sure put a lot of effort into discrediting people rather than helping them with their questions. Was it really necessary to do this to answer a question about a carburetor spacer? Or worse yet get the entire forum to prove your point and act like a gang to beat me down, on top of that insulting me because of my nationality? Please explain this, because you will not make many friends on this site if this is the way you act toward people. :evil:

Jon I would suggest sending this thread to the dump, as it appears the original topic is no longer being discussed.