Carb spacers, what about a 2 hole?

[drdano]

In Jays book there is good data on 4-hole spacers and open spacers on a performer RPM intake.  What would a 2-hole adapter do most likely, i.e., a 4-hole that had the centers cut out on each side of the plenum divider? 

[jayb]

If I had to guess, I'd say it would be compromise between a four hole and an open spacer.  The four hole spacers are good for providing a strong vacuum signal the carb, and boosting low end torque.  The open spacers increase plenum volume, allowing both planes of a dual plane manifold to draw from a common volume, improving the top end at the cost of the low end.  So a spacer with two large oval holes would limit the vacuum signal to the carb, but not as much as an open spacer, and it would allow the engine to draw from a larger plenum area for better top end, but not as much as an open spacer.

It's all a guess though unless you can measure the improvement somehow, either on the dyno or at the track.

[Joe-jdc]

I recently had a chance to spend a day on the dyno with Ted Eaton, and we tested 7 different combinations of spacers on different heads and manifolds.  I took several spacers of mine to test, and I had a 1" morroso 4 hole that I cut the centers out of front to back, and left the center divider in, and tapered all the holes.  It made great torque below 4800 rpm, but lost out to the 2" 4 hole tapered with all the bottom cut away in the centers, by about 8 ftlb torque, and 2 hp.  A 2 inch open was worst, and a 1 " 4 hole phenolic spacer was very good all the way around.  The peaks were similiar, but the graphs, when overlaid showed a trend.  The best in every instance was a 2" 4hole with tapered holes like a "Super-sucker" by Wilson manifolds.  This was on a 352CI Y-block engine that made 504 hp/452 lbft. Joe-JDC.

[machoneman]

Good to know Joe and Jay.

Funny thing is, a engine/car combo can be mighty fussy, meaning that a spacer change may be detectable on the dyno but may make virtually no difference in e.t., even with a ride that is pretty much optimized.  Results may vary (ha!) but 2 HP on a 500 hp engine is .004%, less than 1/2 of 1 percent and at that small a change, a second dyno test the next day, with different air/humidity/ barometric pressure conditions, could easily overwhelm (or add to) that gain.

I'd go for it but we experimented with various spacers long ago on Holley single carb-equipped drag cars but they hardly changed the e.t. and the variance could have been chalked up entirely (A-B-A back-to-back runs) to changing atmospheric conditions. Given though these were pretty good pretty good manifolds to start with but, unless it's a dedicated drag car, I'd slap on what one has and take a ride!

On edit: we never had anything like the SuperSucker designs so popular today. Those would have been cool to try if they were available.

[jayb]

Joe sent me the following pictures of the spacers they ran at Royce's dyno session.  I'll let him comment:

[drdano]

Holy pile of spacers, Batman!  That red spacer is interesting.  I can't run a 2", I've got hood clearance problems as it is and I'm not about to put a hood scoop on my wagon.  I think I may modify my 1" spacer to look similar to the red one with an open/blended bottom.  The wrench in the blender with all of this is that the spacer is also going to be a squarebore to spreadbore flipped upside down so I can run my beloved *cough* GM *cough* carb. 

[drdano]

Got bored last night and decided to make a 2-hole adapter.  These run about $20 each, so not out much if it doesn't work well.  Got it roughed in with the cutter, just need to finish it with the sanding rolls and blend it all nicely.  Still a restriction from the massive secondaries, but better I think than squeezing the big secondaries down to the smaller rear holes in the 4-hole version.

[jayb]

Nice job on the spacer, I think that looks pretty good!

[machoneman]

Looks pretty good! Yeah, it would be nice to have a smoother transition but that would take a 4" to 5" tall spacer that would not fit under a car's hood w/o a cut-out or tall scoop.  Maybe a truck but no Ford passenger car flat hood for sure.