audacity

there is more gains to be had below the water live vs. above it....look at doing bottom work and changing the set-up to accommodate current propeller technology.

p4-33

Peak hp was 610 @5400, peak tq was 625 @4700. We also had 550 tq @3000, and that was our primary goal, lots of tq down low, and fairly flat up through WOT of 5400.

Whiteknuckle

Another thing you may want to consider is how the spacer effects low and mid range performace. Everything is not WOT all the time. We noticed on the dyno playing with spacers that there is no free lunch. You may gain some power at high RPM but you are likely to sacrifice some on the low end. What price do you want ot pay to get every bit of top end power?
Brians Konrad boat is a race boat, not a recreational boat for the family, am I right?

p4-33

A race boat, yes... but I do a fair amount of pleasure cruising and poker running. You're right, there's no free lunch. Everything I've done to my motors has revolved around mid-to-high end torque. 320cc (fairly small) runners on aluminum heads... small runner rect port Dart single plane intakes port matched to the bigger rect intake ports on the heads... port work on the heads... custom ground cams... custom metered carbs... all to help me get out of the corners of the race course quicker.

But the side benefit is she cruises pretty well at 3000-3500 rpm, and pulls real nice when a Baja comes along and wants to play.

All comes down to what your goals are; set them and work from there. A Supersucker spacer has helped, but there's been a lot more done to tune the whole "system".

Brian

ROTAX454

Brian, At what RPM was the 55HP gain over the best w/o the spacer? And, what was the "before" best RPM. Just trying to compare the RPM differences. Thanks.

RumRunner

Spacers are a great tuning aid, to help move the power band, or make up for a mismatch of parts.

The only way to know for certain how a spacer is going to affect your combination is to try it.

baja36ft

I ALL SO USE THE TWO INCH WORKS VERY WELL.

cstraub

Correct. The intake along with exhaust both run on "pulses". To take advantage and optimize the power from either the tuning length has to be the proper length. Spacers are part of this measurement. One engine may want a 1" and another may need a 4". It is a variable and can only be verified as to what your combination needs on a dyno.

Now as for HVH's spacer and does it work, yes. One of the first ones that Joe did back in the 80's was on Petty's car when he won either Daytona or Taledega. Nascar outlawed the spacer. The spacer cleans the signal up as it enters the plenum by routing air to the highest vacuum area in the intake.

RumRunner

Spacers are not going to be an end all be all. As stated it's a matter of what the combination needs. In a perfect world if the engine was designed and engineered properly you shouldn't need one. But not too many people can afford to manufacture their own intakes, cylinder heads, etc. for each and every engine. Spacers can work great, I've seen as much as 30HP from one on a Dyno, but I've also seen that exact same spacer do nothing on a different engine. It's all a matter of giving her what makes her happy.

Just because your buddy's boat picked up using a set of 4 blade props does that mean that's what you need?

This why it's called fine tuning.

p4-33

Sorry for the delay... had to dig up the dyno sheets.

"Best" pulls for each scenario:

No Spacer, 88 jetting 4-corners
rpm. tq...... hp...
3000 552.9 315.8
3250 540.4 334.4
3500 535.0 356.5
3750 550.3 392.9
4000 565.9 431.0
4250 570.2 461.4 *Best tq (oops, edited)
4500 558.6 478.6
4750 561.2 507.6
5000 558.4 531.6
5250 544.7 544.5
5500 522.3 547.0 *Best hp

1" Supersucker, 90 jetting 4-corners
rpm. tq...... hp...
3000 544.0 310.7 (lost some low-end tq)
3250 550.9 340.7
3500 542.3 361.4
3750 556.9 397.6
4000 567.7 432.1
4250 555.8 449.8
4500 556.7 477.0
4750 565.4 511.4 *Best tq, 5 ft/lbs loss (edited again)
5000 564.6 537.5
5250 561.5 561.3
5500 544.8 570.5 *Best hp, 23hp gain

2" Supersucker, 94 jetting 4-corners
rpm. tq...... hp...
3000 571.8 326.6 (she's back! 19 ft/lbs gain @3000)
3250 567.1 350.9
3500 549.5 366.2
3750 559.5 399.5
4000 589.9 449.3
4250 599.9 485.4
4500 605.5 579.3
4750 611.7 553.2 *Best tq, 41 ft/lbs gain!
5000 608.5 579.3
5250 599.9 599.7
5500 582.1 609.6 *Best hp, 62hp gain!
5750 553.2 605.7

Some observations... my original post stated 55hp gain, was actually 62hp. Also stated 95 jetting, was actually 94 with 2" Supersucker. Peak tq moved up from 4250rpm with no spacer to 4750 with 1" or 2" spacers, but max hp stayed at 5500rpm in all 3 cases. Also have 571tq @3000, not 550tq, and "only" 609hp, not 625hp. The original numbers were coming from dusty brain cells; dyno sessions were done last winter.

I have a "bobble" in tq coming in at 3500rpm in all 3 cases, and Supersucker didn't change it. Assume it's related to intake, and head port work/sizes, runner length and type, etc. Ideas anyone? I can live with it, but just wondering if there's anything to look at.

So, these things work... for me. Will they work for your application? Only way to tell is to try them on the dyno and see what happens.

Man... winter sucks. Thanks for getting my pulse up again.

Cheers,
Brian

(post edited after having some math errors pointed out)