vac 91 stinger size

[jamie anderson]

could i get some help,i have a chd rigger with a vac 91 motor and I'm running a small volume pipe(67 pico pipe)

but it is running too hot.

head shim is 14 thou on 50% nitro, 1667 prop,is there a better pipe for this combo or should i try something else?

regards jamie

 

[shoboat]

Jamie,

Not quite sure why a lot of people are running such a small pipe

on a big block motor. Change to a 15 cc pipe and let it flow some

fuel. Maybe you can get a new pipe for your birthday. A lot

of ways to go fast in this hobby.

Good Luck Testing,

Mark Sholund

 

[Don Ferrette]

Not quite sure why a lot of people are running such a small pipe on a big block motor.

Well maybe because when the stinger size is right they actually work. Just because the motor is bigger doesn't mean the pipe has to be. I did extensive testing a few years back with pipes on a modded CMB purple head 90 and the 13cc Macs pipe consistently outperformed all the 15cc pipes across the board. Jamie if there is enough wall thickness on the stinger drill it out to .470". As for other pipe choices I have seen the VAC91 motors run extremely well on the CMB version of the original AB67 black pipe (pic attached). Not a big volume pipe but it has been used successfully on everything from .67's to gas motors. I'm fairly sure Hobby Supplies down under where you are has them in stock if you can't drill out your Picco pipe.

 

[Joe Warren]

The 91 Vac works Very well on a MAC`s 13cc pipe @ 11 3/4. the STK head volume is BORDER line too big. Be sure your not running the boat too tight if it is getting too hot??. A pipe too short will also cause it to run hot? If You like the pipe you are running & just want a bigger stinger size? Drive a small chrome socket thru it the size you want.(something that has a little bigger OD than the singer ID) I will swedge the stinger open especially if the tubing is too thin to drill? I personally would put a 80 (13cc) pipe on it. Or a Small diameter 90 size pipe like a ops 90 pipe....Sometimes it is not that the stinger is too small but that the header pipe is too small on the front of the pipe?? if you are running 60 pipe it would be around 5/8 ID you would need a 7/8 ID Header Pipe...... jw

 

[shoboat]

Don,

Did you ever test a Muck 15 cc pipe on the 90 motor? or a 101 motor?

If you did not, then you don't know why I would make that statement.

Use whatever works for you, but I think quite a few people are not

getting the most out of their set ups with them small pipes. I know

a little about pipes, I have quite a collection to put it mildly.

But use whatever is working for ya. Just remember if you don't try

different combinations you will never find the best one.

Keep Testing Them,

Mark Sholund

 

[BigChuck]

B)

 

[ALLAN YUEN]

B)

Hardly find this Steve Muck 80/90 nitro pipe Where did you get this pipe? h34r:

 

[Don Ferrette]

Don,

Did you ever test a Muck 15 cc pipe on the 90 motor? or a 101 motor?

If you did not, then you don't know why I would make that statement.

Use whatever works for you, but I think quite a few people are not

getting the most out of their set ups with them small pipes. I know

a little about pipes, I have quite a collection to put it mildly.

But use whatever is working for ya. Just remember if you don't try

different combinations you will never find the best one.

Keep Testing Them,

Mark Sholund

Yup, sure did and the 13cc Macs was still the best pipe on the rigger during that rather extensive test session. I will say the .90 Muck was a strong mono pipe but we're talking about rigger applications. I have quite a collection myself Mark especially for big blocks and happen to know a little about pipes too.
And BTW - I'm also recommending a pipe that is READILY AVAILABLE.

 

[Tim_Duggan]

The Muck pipe was a stand-out for me on a K90 in an Eagle SG, and the HR91 could well be a similar deal.

I think I still have one @ home somewhere Jamie, I can loan it to you if you want to test it.

Another trick for expanding stinger diameters in Aluminium pipes is to us a Dynabolt to stretch it.

 

[jamie anderson]

thanks very much for the replies and some great tips.

i might just take you up on that offer Tim would be good to test it.

 

[brett english]

guys were finding that with the VAC 91"s, it looks like the longer you run these pipes(cmb 80muffled) the more speed were getting...proven this past weekend by tom foley and larry beils..they are somewhere close to 12 inches or longer..couple others were at 10 1/2 to 11 inches and had less speed..can someone please explain that one??? but

its true..Stu? Marty? Andy?

 

[shoboat]

Brett,

Pipe length is going to be directly related to engine load.

I think I know what Tom was running, and I doubt if a short

pipe would pull all that pitch he was running. This is why we

have to try a lot of different combinations in testing. I have

quite a few customers using a lot of different pipes on the VAC-91

and most are running them longer.

Thanks,

Mark Sholund

 

[dwilfong]

guys were finding that with the VAC 91"s, it looks like the longer you run these pipes(cmb 80muffled) the more speed were getting...proven this past weekend by tom foley and larry beils..they are somewhere close to 12 inches or longer..couple others were at 10 1/2 to 11 inches and had less speed..can someone please explain that one??? but

its true..Stu? Marty? Andy?

Brett

The VAC91 has along stroke this puts the power band at a lower RPM hence a longer pipe. This is why a VAC will pull a bigger prop in a heavy boat. Shorter stroke RS has a higher power band.

The VAC is a great eng for a heavy boat.

David

 

[Joe Warren]

.. :blink:

 

[BigChuck]

:blink: :blink:

 

[Tim_Duggan]

Jamie,

Yes, I do have the Muck 90 pipe at home. Can you send me your details, and I'll send it to you to test with. I'd forgotten just how big these pipes are in the belly and stinger

Tim

 

[DickJones]

guys were finding that with the VAC 91"s, it looks like the longer you run these pipes(cmb 80muffled) the more speed were getting...proven this past weekend by tom foley and larry beils..they are somewhere close to 12 inches or longer..couple others were at 10 1/2 to 11 inches and had less speed..can someone please explain that one??? but

its true..Stu? Marty? Andy?

Brett, not sure where U came up with (longer pipes = more speed) staement, I radared all the twin races except for one, fastest speed for the twins on the rough water was 77 MPH.

JM2C

dick

 

[dwilfong]

guys were finding that with the VAC 91"s, it looks like the longer you run these pipes(cmb 80muffled) the more speed were getting...proven this past weekend by tom foley and larry beils..they are somewhere close to 12 inches or longer..couple others were at 10 1/2 to 11 inches and had less speed..can someone please explain that one??? but

its true..Stu? Marty? Andy?

Brett, not sure where U came up with (longer pipes = more speed) staement, I radared all the twin races except for one, fastest speed for the twins on the rough water was 77 MPH.

JM2C

dick

The truthometer speaks not with a forked tung. :huh:

 

[Andy Brown]

I love the "truthometer"

 

[Tim_Duggan]

My radar gun is affectionately known as the BS detector