[Steve C.]

My previous pump gas 4.210 stroke 462cid street engine dyno tested with a modified Holley Street Dominator intake.

HSD / no carb spacer:
577.9 hp at 5700 rpm, 581.0 ft.lbs. at 4400 rpm.

HSD / 1/2" open spacer:
589.4 hp at 5600/5700 rpm, 589.0 ft.lbs. at 4600 rpm.

HSD/ 1" open spacer:
589.8 hp at 5700 rpm, 590.8 ft.lbs. at 4400 rpm

Here a 11.9 HP increase by adding a 1-inch spacer may not seem like much.
But what about performance on the track, noting Steve25 good info in post 36 above.

.

[RocktimusPryme]

Originally Posted by Steve C.

Here a 11.9 HP increase by adding a 1-inch spacer may not seem like much.

12 HP for the cost and ease of installing a simple open spacer is a heck of a deal. Its not even a fancy expensive tapered spacer.

Side note: In a world where 3d printing is now a thing, IDK how to heck WIlson and HVH still manage to charge the absurd prices they do for their combo spacers.

[Steve C.]

Opps, sorry. I meant to say Steve25 good info in post 38


.

[slowbird]

Originally Posted by steve25

Spacers add Plenum volume .

They also change the tuning length of the runners .

More volume also helps to dampen reversion pluses so air flow back into the runners restarts sooner.

More plenum height above the roof of the runners helps the air fuel mixture turn into the runners so the runner area becomes more efficient.

All of these pluses as in

Ram effect
Shock wave tuning
Better velocity gradient
Better mixture and reduced reversion

These details at times can make a 50 hp difference with 10 to 15 being a low end average.
Over square motors like the 455 with racing cam’s need a lot of plenum dampening to come on the cam sooner, no less for added high rpm hp.

Spacers change the tuning length of the runners? How is this done?

[Dragncar]

Originally Posted by RocktimusPryme

12 HP for the cost and ease of installing a simple open spacer is a heck of a deal. Its not even a fancy expensive tapered spacer.

Side note: In a world where 3d printing is now a thing, IDK how to heck WIlson and HVH still manage to charge the absurd prices they do for their combo spacers.

Because the guys who 3D print them charge the same kind of prices. I have 3 of them. One was 260 $

[steve25]

Sorry Slowbird I should have detailed that one more.

If a single plane intake has minimal height between the runner roofs and the carb pad and then a spacer is added and then blended in to get a more air flow friendly turn into the roof of the runners, then you have in effect changed the tuned length of the runner.

The same effect takes place with the port dividers if an intake has them in the plenum area.

Some stick out evenly from top to bottom out into the plenum, some are angled, some have there tops rounded over, and these differences all make for different tuned lengths.

[Half-Inch Stud]

If a Spacer is helping to rid effects from reversion pulses, then change the Collector design (length, dia, termination config)

[steve25]

No, reversion pulse’s start during the compression stroke and only once the cylinder pressure rise exceeds the ambient pressure coming thru the intake tract,
Exh scavenging like your referring to only happens on the exh side of the overlap triangle.

[Half-Inch Stud]

Originally Posted by steve25

No, reversion pulse’s start during the compression stroke and only once the cylinder pressure rise exceeds the ambient pressure coming thru the intake tract,
Exh scavenging like your referring to only happens on the exh side of the overlap triangle.

Oh thaat reversion. Hmmm i've always considered that sort minor even with my oversized street cams.

I concern for the reversion that leaves carbon tracks and even coats the intake valve; thatsa the exciting result to mitigate.