2014 G23 and G25 with Fresh Air Exhaust designed exhaust

[ers906]

It usually takes longer than ten minutes for me to realize that I have said something stupid, wrong, or just plain screwed up

[niap101]

I have always wondered how much HP is robbed from an FAE while the boat is underway. There has to be more backpressure from an FAE vs a transom exit exhaust when the boat is underway.

We have back pressure information on our website. For the typical inboard ski boat the back pressure will stay under 2 psi except at higher engine speeds where it may reach 3 psi; some boats may be higher and some lower. I've measured a Nautique without FAE and it reached 3-1/2 psi. We had a customer measure his turbo-charged Master Craft with FAE and he said it never went over 2 psi. The following was sent to us recently from a customer and are typical measurements we expect:

"Here are the Back Pressure numbers taken on my boat with Ballast Tanks full with the system installed:

Engine: Indmar 8.1 Liter 450HP
FAE – 3-1/2” diameter

1000RPM: Back Pressure .6 - .7 - Speed 4 Knots – 5 mph
1500RPM: Back Pressure .4 - .5 - Speed 7.5 Knots – 9 mph
2000RPM: Back Pressure .2 - .3 - Speed 8.5 Knots – 10 mph
2500RPM: Back Pressure .5 - .7 - Speed 10.9 Knots – 12.5 mph
3000RPM: Back Pressure 1.7 - 1.8 - Speed 27 Knots – 27 mph
3500RPM: Back Pressure 2.2 - 2.7 - Speed 34 Knots – 39 mph

The rationale for a low back pressure is that a high back pressure may impede engine performance. As our customers attest, FAE does not impede engine performance. The figure of 2 psi is kinda the industry standard though its application in the boating industry is not consistent. I had one boat manufacturer tell me that they measured the back pressure on the exhaust hose near the transom. Measuring at that location is mostly worthless; you could have a collapsed muffler causing high back pressure at the exhaust manifold yet read very low back pressure down stream of the muffler. All of our testing is conducted at the rubber hose that exits the exhaust manifold.

Any of our customers can borrow a back pressure gauge from us to test their own boat and FAE installation. To measure, drill a 1/2" hole in the rubber hose and insert the gauge; take the boat out on the water and note readings every 500 rpm. The probe is held on with hose clamps and we provide hose and hose clamps to patch the hole when completed.

FAE Sucks. Check out the video. FAE sucks the exhaust out of the engine. We can fabricate FAE to increase the suction and lower the back pressure; but the trade off is increased drag. With a decade of experience and over 1400 FAE installed we have the "sweet spot" dialed in for maximum performance yet still vastly reduced Carbon Monoxide (and other exhaust gas) levels.

Larry Mann
Fresh Air Exhaust

[nyryan2001]

^^ Need these redone for surf speeds and data will likely get worse. need to see what 3500rpms at 11.6mph backpressure is when the water isnt sucking as hard as it is at 39mph.

[bsurfin]

do you have a picture of the gauge installed?

[jbach]

^^ Need these redone for surf speeds and data will likely get worse. need to see what 3500rpms at 11.6mph backpressure is when the water isnt sucking as hard as it is at 39mph.

Your boat runs 3500rpm at 11.6mph? What's your top speed 14.6?

[Nordicron]

Your boat runs 3500rpm at 11.6mph? What's your top speed 14.6?

Remember he is prob pushing 10k lbs when sac'd out for surfing so yes I could see it running 3500rpm at surf speed. Jeez

[ers906]

When I am running full ballast, full tank of gas, another 2800# of ballast, with the ncrs and nss deployed, I am happy that the rpms are only at 3200-3500. I was fully expecting to be in the 4000 range with that set up. Plus with the 550 only using 6-7 gal per hr is a bonus.

[fatchance720]

My stock ballast is 3200 rpm, I get 3500 rpm with about 4 or 5 people and 750 in back left. I tried 1100 bow, 1100 rear left and 600 rear right and it was over 3700 rpm. I have the 450

[niap101]

Back Pressure Guage

do you have a picture of the gauge installed?

Here are the requested pictures. The gauge is calibrated and tested for low pressure readings. The port on my boat is permanently mounted; just aft of the header. When we loan the gauge we send it with the fitting that hose clamps over a hole in the exhaust hose. Once done, a piece of rubber hose (we provide) is glued and hose clamped over the hole.

It is important for me to test the back pressure with Fresh Air Exhaust and understand its ramifications; but from a real world understanding, I'd venture to guess that no one reading this post knows what the exhaust back pressure is on their boat. The highest exhaust back pressure I've measured on a boat was a Nautique with stock exhaust (3-1/2 psi) and the FAE only increased that by 1/4 psi.

To understand engine performance it is far more important to measure acceleration and fuel consumption. If the boat's acceleration and fuel consumption remain unchanged, then engine performance remains unchanged. Our's and our customers studies indicate no change in performance. If you wish to check back pressure on your boat we are pleased to loan you this testing setup and once complete please forward us your results.

To check acceleration you need two fixed points or buoys about 1/4 mile apart and a stopwatch. When we've tested there was no change in acceleration with FAE. The reduction in exhasut noise from FAE is so much that some people have perceived a loss in power. No FAE customer has demonstrated a reduction in acceleration.

I installed an electronic fuel consumption meter on our boat and tested with and without FAE and found no difference. No FAE customer has demonstrated a loss in fuel efficiency.

We have a very liberal return policy and yet have less than 1% returned; our over 1400 customers are happy with the performance of their FAE.

Larry Mann
Fresh Air Exhaust

[niap101]

Obviously Correct Craft and Pleasure Craft Marine think so too.

[wakeslasher69]

Just a heads up guys, my dealer said there is a $750 dollar option (surf exhaust) from the factory for retro fit. I haven't seen it yet for real but thats what I was told.

[ers906]

Ordered one the other day, around 750$. Should be here in the next week or so. WIll take pics of both sides of the hull etc when it gets installed. Nothing against the FAE, but figured the difference of a couple of hundred bucks and going through the dealer increases their responsibility if there are any problems.

[wakeslasher69]

Ordered one the other day, around 750$. Should be here in the next week or so. WIll take pics of both sides of the hull etc when it gets installed. Nothing against the FAE, but figured the difference of a couple of hundred bucks and going through the dealer increases their responsibility if there are any problems.

Agreed. Can't wait to hear more and see it installed!

[lion90]

Ordered one the other day, around 750$. Should be here in the next week or so. WIll take pics of both sides of the hull etc when it gets installed. Nothing against the FAE, but figured the difference of a couple of hundred bucks and going through the dealer increases their responsibility if there are any problems.

Is that ~$750 for parts and the labor?

[wakeslasher69]

Is that ~$750 for parts and the labor?

Its what my dealer said....