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Pool Fool Extraordinaire
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Discussion Starter · #1 ·
Admittedly, I'm not a mechanic, but I play one on TV.
Anyway, I'm hoping I can help someone else with the lesson I just learned:
"Carb spacers are not for everyone."
Here's what happened.... I am restoring an old f150 with a 400v8/c6 auto combination. It had an Edelbrock performer intake on it when I got it, so I bought a new Edelbrock carb for it and I got a universal 1" spacer with phenolic inserts and I used the open spacer.
Here's what happened: tuning the motor became difficult at best. Those of you who know what I did will already be aware of why this is not a good combo for Street driving.
The 1"spacer basically made my performer intake into a performer"rpm" manifold with the added effect of the open insert making it act more like a single plane Mani.
Ran GREAT at 2000+ rpm's but stumbled and bucked at idle.
The performer manifold is peak torque at 3500 rpm's, but by adding the spacer, peak torque hits at 4500, which is not street range.

So there's my hard learned lesson. Hope this helps someone out there to NOT add a spacer for no reason. I thought it would help my engine breathe, which it did, but up at an rpm range that I won't see often.
 

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Race it, Don't rice it!
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Pretty much.
Depending on the spacer thickness and the manifold type, and mostly valve timing, a spacer changes the way the engine pulls on the carb circuits. The extra plenum volume under the carb typically "softens" the pull but also makes the short side turn toward the intake valves easier to navigate. That will typically favor higher RPM at the expense of low speed response. Savvy carb guys can often fix that in the fuel curves.
Spacer are tricky and quite combination dependent.
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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At least you’ll know what spacer to get when it gets warmer this spring and you need to keep the fuel from boiling in the bowls.
5 or 6 years ago I had to incorporate a phenolic spacer and an aluminum heat shield under the carburetor to avoid that very problem in my daily driver. I figure the higher ethanol content in the fuel is responsible for that. The first 6 to 8 years I drove it I never had that problem. It's the only thing I could think of being any different.
 

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I seldom go over a half inch phenolic spacer simply as a heat block. I generally match the spacer configuration to that of the intake which is 4 port to four port or open to open.

My basic reasoning is if you need a thick spacer you probably choose the wrong intake for the job at hand. Additionally, trying to force a dual plane to function like a single plane with an open spacer often results in a lot of cross turbulence between the the throttle bores which disrupts the mixture flow and its homogeneity.

It takes time and a lot of messing around to get the experience to recognize what combinations work with a spacer. The TV guys make it look easy, but we need to understand that people hosting engine building shows with a dyno on their stage have built a lot of engines, have a lot of experience and probably a lot of finances behind them. So what looks so simple isn’t as simple as they make it look. It’s like I pick away at guitar, I can make it work pretty well but I’m never going to be on stage with the likes of Mark Knopfler.

Bogie
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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Negative.
Ethanol
l has a much higher vaporization/boiling point than gas. The higher the precentage the higher the LESS LIKELY it will boil.
The ethanol blend is the problem.

What you're saying about ethanol is correct with regard to the boiling point.

The ethanol blend causes the problem by impacting the vapor pressure.
 

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I can tell you in certain situations that an open spacer can help some things while making other things worse but like stated above it will vary on the build and all its specs the rpm range it runs in etc. I have used a four hole one inch spacer over the years more then any other spacer and also on a lesser extent an open spacer both in the one inch configuration and also used both styles on both an Edelbrock performer rpm or equivalent name brand intake and also an Edelbrock Victor Jr intake.

They both can have pros and cons on how they work. I have found that on a dual plane the 4 hole spacer will give the carburetor more signal and make it have more of a crisper throttle response below 2500 rpm as you found out in most situations but it does not always work like that. I have also used what is a combination combo spacer that starts off has a 4 hole spacer and then is tapered below and is a blend of both types of spacers and can give better results then one design over the other depending on the build.

I have a current 350 that is being very picky and I have been pulling out my hair trying to get my carb to tune right and its the cam being used and a few other factors I am working on and its a long story there you don't even want to know but currently I am using a one inch open spacer on my dual plane intake and with the open spacer its actually making it run better and smoother versus the 4 hole spacer and this is the first time I have encountered this response. Normally the open spacer has always taken away signal from my previous 350 builds in the past but it never caused any stumbles or for it to run horrible as I had a good carb tune.

The open spacer only mad the bottom end below 2500 rpm to 2800 rpm a lot softer and less responsive versus using the 4 hole spacer which only made it a lot stronger and more peppy and responsive versus running no spacer at all. This was with camshafts that was not over radical. On my current builds its been a weird one to where the open spacer has given the best results but this has been a trial and error and my plan is to get it figured out when it gets warmer so I can go back to using my 4 hole or 4 hole tapered spacer and see what one give me the best results.

On my old build that was a victor jr intake being used I installed a 4 hole one inch spacer to get me some more throttle response on the bottom end and some nice snappy throttle and stronger signal back but like I said this was with not radical big cams. Most of them were [email protected] or less on 95 percent of my builds over the years.

Sometimes they can take away or give more regardless of style as all things its a tuning aide that can make some things better or worse as it all depends on the build and what it flows and the cam and heads etc. In all instances your carb has to be tuned and re calibrated for said spacer your using and tweaked to work for said combination. As the saying goes results will vary.
 

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Race it, Don't rice it!
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The ethanol blend is the problem.

What you're saying about ethanol is correct with regard to the boiling point.

The ethanol blend causes the problem by impacting the vapor pressure.
How so.....I have not found evidence of this.
Ive been studying E85 for a few years now and it's well understood the E needs a higher temps to vapor, 173' actaully, below that, it's lost power on the dyno. 200 is better.

Are you suggesting the E10 acts different than E50 - E95?
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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How so.....I have not found evidence of this.
Ive been studying E85 for a few years now and it's well understood the E needs a higher temps to vapor, 173' actaully, below that, it's lost power on the dyno. 200 is better.

Are you suggesting the E10 acts different than E50 - E95?
I'm not merely suggesting E10 acts differently than E50 - E95....it's a fact.

It's a nonlinear relationship when ethanol is blended to gasoline.

Rectangle Slope Font Plot Parallel



The Reid Vapor Pressure (RVP) is a measurement of the pressure of the vapors diffused in the fuel (a fancy way to demonstrate volatility). The dotted line represents ethanol free gasoline. The higher the vapor pressure, the easier it is to vaporize (i.e. boil).

You can see by the chart the 85% ethanol (E85) you studied has a far lower vapor pressure. Your data and the information from your research is 100% correct. Higher vapor temp, higher boiling temp and very unlikely to vapor lock.

As you can see 50% ethanol (E50) also has a lower vapor pressure, albeit only slightly less than ethanol free. The crossover happens somewhere in 40's.

The theory on the 5% and 10% ethanol blend is that the smaller amount of ethanol mixed in the gasoline actually makes the ethanol (or the gasoline in the presence of a low percentage of ethanol) MORE likely to vaporize. It raises the vapor pressure and lowers the vapor and boiling point. The blends with the vapor pressure above the dotted line are more prone to vapor lock and the percolating we see in the fuel bowls of our carburetors.

The benefits of adding ethanol to gasoline (emissions, cost, less foreign dependence) and the modern fuel injection being far less affected by it supports continuing to do it.
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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1979Malibu

Thanks.....You started a fight between my carb guy and I. That 30 pack of round ethanol cans samples had nothing to do with it all at all.
Drinking a certain amount of ethanol contributing to a boil over while debating the subject of a certain amount of ethanol contributing to a boil over....that's bench racing at it's finest!!! Good times! Hahaha!
 

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Pool Fool Extraordinaire
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Discussion Starter · #13 ·
Update:
I removed the universal spacer and the Edelbrock 1405. I put a new Edelbrock 1906 electric choke model and after seeing the low idle screw correctly, she idles great now. Around 600 rpm in gear with my foot on the brake. 850 or so in Park. No issues at all now though.

My dad always said "you gotta be smarter than what your messing with".
He was a wise, wise man.
I'm definitely not smarter than Ford engineers so I was way outta my league. Luckily I got it right.
I guess that Even a blind squirrel gets an acorn now and then.
 

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Race it, Don't rice it!
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I don't know a lot of the AVS series but I'll say the smaller primaries and no spacer gives a much better signal to the idle circuits AND the carb itself likely more better calibrated for the application needs. Good to know its working for ya. I understand the AVS carbs are really good out of the box.
 

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On most instances that I have heard the Edelbrock AVS 2 has out performed the Edelbrock performer AFB carburetors since they installed annular boosters and also a better design since you can adjust the secondary opening rate on them. How much of a difference between the two on the primary side I don't know as I have never used one but the AVS2 definitely gets recommended 99 percent of the time over the AFB version.

Good to hear you got your carb situation figured out and I am going to try the same next and try to get it running right without the open spacer and get it to run with either my 4 hole or 4 hole tapered spacer and just like you the bottom end will always be soggy with an open spacer on a mild application with a dual plane. I won't post my hair pulling story here but I have some thing I need to iron out with mine but needed the weather and I have four days next week.
 

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Old(s) Fart
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So there's my hard learned lesson. Hope this helps someone out there to NOT add a spacer for no reason.
I've frequently wondered why people think they are smarter than the engineers who designed and tested the intake manifold. Common sense should tell you that if the intake performed better with a larger plenum or longer runners, it would have been trivially easy for E-brock to just make it that way from the start. And yeah, every part of your engine is a compromise. An F150 isn't a drag car. If you plan to use it as a truck, build the motor for torque, not max HP at high RPMs.
 

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Race it, Don't rice it!
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Engineers are bound up between the bean counters in finance and the fools in marketing.
They can design something, but it may not be profitable or sell enough of em.
it better to sell something that works good enough to most people.
There’s usually room for improvement for specifics.
 

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Most ALL PRODUCTS are a compromise between quality, cost, and what the public will tolerate as being acceptable balance between the quality and cost.

Understand well all weighed out $$$$$$$$ is king and function secondary in the product producers eyes.
 

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Admittedly, I'm not a mechanic, but I play one on TV.
Anyway, I'm hoping I can help someone else with the lesson I just learned:
"Carb spacers are not for everyone."
Here's what happened.... I am restoring an old f150 with a 400v8/c6 auto combination. It had an Edelbrock performer intake on it when I got it, so I bought a new Edelbrock carb for it and I got a universal 1" spacer with phenolic inserts and I used the open spacer.
Here's what happened: tuning the motor became difficult at best. Those of you who know what I did will already be aware of why this is not a good combo for Street driving.
The 1"spacer basically made my performer intake into a performer"rpm" manifold with the added effect of the open insert making it act more like a single plane Mani.
Ran GREAT at 2000+ rpm's but stumbled and bucked at idle.
The performer manifold is peak torque at 3500 rpm's, but by adding the spacer, peak torque hits at 4500, which is not street range.

So there's my hard learned lesson. Hope this helps someone out there to NOT add a spacer for no reason. I thought it would help my engine breathe, which it did, but up at an rpm range that I won't see often.
A carb spacer will lean the fuel mixture due to lower signal from the engine. My cousins S10 slow down a tenth in the quarter from using a 2 inch spacer.
 

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Pool Fool Extraordinaire
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Discussion Starter · #20 ·
I seldom go over a half inch phenolic spacer simply as a heat block. I generally match the spacer configuration to that of the intake which is 4 port to four port or open to open.

My basic reasoning is if you need a thick spacer you probably choose the wrong intake for the job at hand. Additionally, trying to force a dual plane to function like a single plane with an open spacer often results in a lot of cross turbulence between the the throttle bores which disrupts the mixture flow and its homogeneity.

It takes time and a lot of messing around to get the experience to recognize what combinations work with a spacer. The TV guys make it look easy, but we need to understand that people hosting engine building shows with a dyno on their stage have built a lot of engines, have a lot of experience and probably a lot of finances behind them. So what looks so simple isn’t as simple as they make it look. It’s like I pick away at guitar, I can make it work pretty well but I’m never going to be on stage with the likes of Mark Knopfler.

Bogie
You nailed it. Watching TV guys with dynos ..... Great. Upper rpm power, but at what costs? Fwiw- I build my own guitars and I don't get to play with the greats either. Keep on pickin though! It's all about having fun.
 
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