Carb Spacer Question

[goodnigh]

Back in November we replaced a 351C 4V that had a cracked block.

Bought a rebuilt never fired long block (351C 4V) from Don of OMS.

The carb we had been using (four years) was never removed from

the intake manifold so we installed it as a single unit on the new

engine. Runs Great, but, when my mechanic took the car out for a

stroll he said it needs a bigger carb. The reason being the old engine

was a stock Cleveland and the new engine was rebuilt with a cam.

We measured valve lift at 0.58

I can't remember what spacer the carb has now, either square bore

or four holes. By "square bore" I mean one hole.

Since we have a new engine and the new carb is Very different from

the one currently on the car, what type of spacer to use comes into

question.

Both carbs have vacuum secondaries and the only significant

difference is the new carb has four corner idle.

Old carb is a Holley 0-80670 and new is 0-86770..

mike

 

[sm3570]

Not sure about the spacer, but square bore refers to if the four holes are equal dimensions, hence making a square shape. Spread bore is when the holes for the secondarys are bigger than the holes for the primarys.

I'm not using a spacer on my Holley square bore carb. I believe that using a spacer helps the air and fuel mix better.

 

[coilwire]

I use a 1" spacer on my 351c 4v w/ a holly 750dp. No problems and runs great.

Jim

 

[goodnigh]

Would you recommend a single hole spacer or one with four holes?

Does it make a difference?

mike

 

[Wolverine]

Would you recommend a single hole spacer or one with four holes?

Does it make a difference?

mike

In my opinion the spacer should match the manifold so there isn't any material that can wear off and find a valve seat.

 

[coilwire]

Mike the one I am using has the 4 holes.

Jim

 

[sm3570]

I've read that the single large hole ones are for racing, while the ones with 4 holes are better for the street. Total conjecture and internet rumor, but that's all I've got.

 

[goodnigh]

I've read that the single large hole ones are for racing, while the ones with 4 holes are better for the street. Total conjecture and internet rumor, but that's all I've got.

That makes sense. Why put any restrictions on the air flow.

There is a four hole spacer on the engine now, but that was for

a stock Cleveland with a base level Holley 670 cfm. The new engine

with a 0.58 lift cam and performance Holley 770 probably warrants

a single hole spacer.

On a different note, what is the purpose of a spacer?

My mechanic says to help keep the carb cooler.

mike

 

[MotoArts]

Spacer adds volume to the plenum, along with several other factors. There are spacers and deflectors that are designed for heat isolation as well.

The "best" one can only be determined on a dyno. Every combo reaction is different, and I believe cannot be calculated on paper.

Dan Jones could probably most accurately answer the question, but it will require a hardbound book worth of data.

 

[sm3570]

Again, mere internet rumor but my understanding is spacers help the carbs run cooler and allow a better mix of air and fuel.

 

[Bill73Ragtop]

"rule of thumb generally is that a 4 hole spacer will improve throttle response and low end torque while an open spacer will improve top end power."

Courtesy of VMF post

 

[TommyK]

Some spacer testing info:

http://www.network54.com/Forum/119419/message/1338393190/Re-+Is+the+stock+4V+cast+intake+good+to+6500rpm---