Carb spacer question

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GRTfast
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Carb spacer question

Post by GRTfast » Tue Mar 13, 2018 8:13 pm

I have a 1 inch 4 hole phenolic spacer on my street big block. Carb is a mark whitener annular booster 850 dp, intake is rpm air gap. Motor is in the 500hp range with a hydraulic roller. Street driven, 1500-6000 rpm.

I was thinking of porting the carb spacer to blend it into the intake interface. The idea is to have the 4 circular holes gradually open up and become square as they approach the intake side of the spacer.

Do any of you have experience with this? I know from my two stroke days that what seems like a good idea isn’t necessarily always a good idea. Any advice is appreciated.

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Re: Carb spacer question

Post by cjperformance » Tue Mar 13, 2018 8:56 pm

There are spacers with this design available. As with any spacer they are combo and use specific and the best way to find what works for you is to try a few different ones and see what reaction you and the engine like best.
Get an off the shelf taper spacer or a cheap 4 hole and do the mod, then you can back to back it against what you have now. Even compare them to a 1" open or a .5" 4 hole on top of a .5" open etc. The engine and your driving style will soon tell you whats best.
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Re: Carb spacer question

Post by GRTfast » Tue Mar 13, 2018 9:06 pm

cjperformance wrote:
Tue Mar 13, 2018 8:56 pm
There are spacers with this design available. As with any spacer they are combo and use specific and the best way to find what works for you is to try a few different ones and see what reaction you and the engine like best.
Get an off the shelf taper spacer or a cheap 4 hole and do the mod, then you can back to back it against what you have now. Even compare them to a 1" open or a .5" 4 hole on top of a .5" open etc. The engine and your driving style will soon tell you whats best.
Thanks for the reply. I figured I could get various different operating characteristics with different spacer heights and styles. I’m wonderinf if there are any general truths that apply to the different styles, especially when applied to a split plenum intake like my air gap. I shall commence experimentation.

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Re: Carb spacer question

Post by cjperformance » Tue Mar 13, 2018 9:27 pm

With higher output dual plane application increasing plenum volume via spacers generally will increase upper rpm hp and can also help tame hard to fix mixture variations at low/mid rpm. Sometimes dividing a dual plane intake is of advantage over keeping it divided but in many cases simply staying divided and increasing volume is better for true street applications BUT not always!
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Re: Carb spacer question

Post by BOOT » Wed Mar 14, 2018 1:49 am

If you grind/sand on that phenolic spacer and it's really phenolic n not plastic use a dust mask.

Lots of diff spacers, I got a few $$$ ones and mod cheap ones now n then for fun, mix n match to try stuff n figure out what fits that cars needs. Someone on here post about turning the shallow side of a four hole into an oval for dual planes, finally gonna try that one in spring myself. Also seen it mentioned several times in these spacer threads bout using a 4 hole tapered spacer upside down, pretty much a shear plate like that but not as good in my opinion. I think it says for one of my alum HVH spacers to not blend the machining marks on the taper, prob so it can shear the fuel easier and why I don't think a wood/phenolic/plastic tapered would be a good idea.
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Re: Carb spacer question

Post by cjperformance » Wed Mar 14, 2018 7:15 am

BOOT wrote:
Wed Mar 14, 2018 1:49 am
If you grind/sand on that phenolic spacer and it's really phenolic n not plastic use a dust mask.

Lots of diff spacers, I got a few $$$ ones and mod cheap ones now n then for fun, mix n match to try stuff n figure out what fits that cars needs. Someone on here post about turning the shallow side of a four hole into an oval for dual planes, finally gonna try that one in spring myself. Also seen it mentioned several times in these spacer threads bout using a 4 hole tapered spacer upside down, pretty much a shear plate like that but not as good in my opinion. I think it says for one of my alum HVH spacers to not blend the machining marks on the taper, prob so it can shear the fuel easier and why I don't think a wood/phenolic/plastic tapered would be a good idea.
Yes i think it was Dave Mclain (apologies if spelt wrong!), that had good results with the 'hybrid' spacer, oval on shallow side and 2 holes on deep side.
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Re: Carb spacer question

Post by GRTfast » Wed Mar 14, 2018 7:39 pm

I milled the shallow side into an oval, and did some light blending on all the holes as the approach the manifold. Seems to run smoother at low rpm cruising. Haven’t had a chance to give it the beans yet. I’ll report back when I do.

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Re: Carb spacer question

Post by cjperformance » Wed Mar 14, 2018 8:04 pm

Good stuff..
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Re: Carb spacer question

Post by MadBill » Wed Mar 14, 2018 10:56 pm

Since open spacers have come up and I believe the divider is only slightly cut away on this manifold, it's worth mentioning that any open spacer would significantly change its characteristics, basically converting it into a poor cousin single plane... #-o
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Re: Carb spacer question

Post by groberts101 » Wed Mar 14, 2018 11:52 pm

MadBill wrote:
Wed Mar 14, 2018 10:56 pm
Since open spacers have come up and I believe the divider is only slightly cut away on this manifold, it's worth mentioning that any open spacer would significantly change its characteristics, basically converting it into a poor cousin single plane... #-o
That seems to be the popular consensus, Bill. I have not seen that to be completely true in practice though. What we need to remember here is that even with a heavily chopped divider or full open spacer the snakelike runners of a dual plane buffers away some of the returning waves much better than a line of sight single plane manifold. Port to port cross talk happens over much longer pathways. Ideally it's just another fine tuning method or possible crutch for other less than perfect parts match ups.

But I do agree that some of the main benefit to using a dual plane in the first place gets traded for increased rev range potential.

What I ljke to do to these types of manifolds to improve midrange and top end power is weld a 1.5- 2" merge spacer directly onto the manifold and then heavily radius the shorter plenums transitions into each end. Get the right solid 4 hole spacer to work from and you can make a VERY large radius which further increases the shorter plenums volume even further.

You'll lose a bit of throttle response right off idle and slightly above but the gain in rev range is well worth it for some combo's. Idle chops a slight bit more with the extra cross talk but manifold vacuum is nearly unchanged.

PS. I will hopefully be chopping up a 351W eddy air-gap manifold in the next few weeks to fit onto a welded high port 302 conversion. Since I've seen such good results from this aforementioned spacer mod.. it's near the top of the list of things to do to that manifold.

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Re: Carb spacer question

Post by englertracing » Thu Mar 15, 2018 12:56 am

Image

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Re: Carb spacer question

Post by GRTfast » Thu Mar 15, 2018 6:42 am

The issue that led to phenolic spacers was boiling fuel in stop and go traffic. I’ve since converted to a return line fuel system, but I’m reluctant to get rid of the thermal isolation a phenolic spacer affords for the carb. It gets hot in central Florida, and it seems the pump gas these days boils easily.

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Re: Carb spacer question

Post by cjperformance » Thu Mar 15, 2018 6:49 am

GRTfast wrote:
Thu Mar 15, 2018 6:42 am
The issue that led to phenolic spacers was boiling fuel in stop and go traffic. I’ve since converted to a return line fuel system, but I’m reluctant to get rid of the thermal isolation a phenolic spacer affords for the carb. It gets hot in central Florida, and it seems the pump gas these days boils easily.
Gets hot here too, Adelaide, South Australia.
I use phenolic, plastic, wood spacers with fiber washers under the carb retaining nuts to isolate the studs from the carb.
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Re: Carb spacer question

Post by GRTfast » Thu Mar 15, 2018 7:44 am

cjperformance wrote:
Thu Mar 15, 2018 6:49 am
GRTfast wrote:
Thu Mar 15, 2018 6:42 am
The issue that led to phenolic spacers was boiling fuel in stop and go traffic. I’ve since converted to a return line fuel system, but I’m reluctant to get rid of the thermal isolation a phenolic spacer affords for the carb. It gets hot in central Florida, and it seems the pump gas these days boils easily.
Gets hot here too, Adelaide, South Australia.
I use phenolic, plastic, wood spacers with fiber washers under the carb retaining nuts to isolate the studs from the carb.
Exactly what I did... and I thought I was being clever. Looks like I'm not the only one. :D

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Re: Carb spacer question

Post by rp930 » Thu Mar 15, 2018 11:12 am

cjperformance wrote:
Wed Mar 14, 2018 7:15 am
BOOT wrote:
Wed Mar 14, 2018 1:49 am
If you grind/sand on that phenolic spacer and it's really phenolic n not plastic use a dust mask.

Lots of diff spacers, I got a few $$$ ones and mod cheap ones now n then for fun, mix n match to try stuff n figure out what fits that cars needs. Someone on here post about turning the shallow side of a four hole into an oval for dual planes, finally gonna try that one in spring myself. Also seen it mentioned several times in these spacer threads bout using a 4 hole tapered spacer upside down, pretty much a shear plate like that but not as good in my opinion. I think it says for one of my alum HVH spacers to not blend the machining marks on the taper, prob so it can shear the fuel easier and why I don't think a wood/phenolic/plastic tapered would be a good idea.
Yes i think it was Dave Mclain (apologies if spelt wrong!), that had good results with the 'hybrid' spacer, oval on shallow side and 2 holes on deep side.
I made one of these after reading about it here. It made a nice improvement in throttle response over an open spacer. Wish I could have dyno’d it. I swear it feels much better. Using a stock “163” intake.

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