RASP on a 3rd Gen, Well worth it!

[Gypsyman]

I've ridden in a few trucks with the FASS and and the AirDog and I knew that the noise in the cab would drive me crazy. So, while I was having the twins installed at PDR I ran down the road a bit and stopped at DTT to pick-up the RASP system for my truck. What a nicely engineered mod this is. We trimmed the fan blades while I was at PDR but ran out of time so the install was done at home.



The 3rd gen kit comes with a sweet little adapter plate to keep the factory LP in the stock location. The total install took me a few hours but the end result was well worth it. I added a few fittings that allowed me to hard mount the Hobbs switch and all of the hose connections to the adapter plate. I then modified the Cummins extension harness that we use to trigger pusher pumps by cutting the hot wire to the factory pump and running it thru the Hobbs switch. Worked out perfectly, all plug and play, and never has thrown a LP code from the Hobbs turning off the factory LP when the RASP takes over.



The small rotary pump is so under driven for the pressure it supplies that at an idle you can put your finger on the lower pulley and follow it around. At these speeds the pump should last forever. I've got 18k flawless miles on it so far. Performance is excellent with 15-1/2 lbs at idle, 16 to 17-1/2 lbs at cruise. I've never been able to pull it below 14-1/4 lbs no matter how high the boxes are turned up or how long I have it on the mat. I haven't even messed with the bypass spring setting since I'm perfectly happy with the pressures that I'm seeing.



Overall one of the best mods that I've made to date and best of all it's 100% silent! If you've got the bucks go for it and forget about watching your fuel pressure gauge. Between the twins and the RASP I hardly have to look at my gauges at all anymore. :-laf Pictures are up in my gallery if your interested.



Richard

 

[LightmanE300]

Gypsyman, sounds sweet. I think the fact that this option doesn't make noise is a big selling point, as well as the apparent durability/reliability factor. Finding someone who can/will install it is the problem on my end.

 

[paulb]

I've got about 33K on mine, and no problems at all. I used to keep an eye on the fuel pressure gauge while drag racing, now I have time to watch the EGT gauge hit the peg...



Paul

 

[Matt400]

Hey Richard,

I was just looking at one of those and wondered about its operation.

The 3rd gen kit comes with a sweet little adapter plate to keep the factory LP in the stock location.

But why? seems like a better idea would be to remove it. Is the Rasp having to suck through the LP?

never has thrown a LP code from the Hobbs turning off the factory LP when the RASP takes over.

Do you mean to say the OE LP functions normally then at a certain point (pressure I suppose) the RASP takes over? if so what about when you said:

Performance is excellent with 15-1/2 lbs at idle, 16 to 17-1/2 lbs at cruise.

Sounds like the RASP has taken over right after start up. Doesn't seem like a good idea to pull fuel through a less capable pump much less one that had been shut down. Educate me on this RASP set up.



One more thing. . trimming the fan blades? How much? I would be worried about causing an imbalance.

 

[Gypsyman]

The factory fuel supply line now has a "T" in it. The main line feeds the RASP and the other leg of the "T" goes to the factory LP. I have the Hobbs switch set at 10 psi so that when the key is turned on the LP runs normally and as soon as the RASP makes ten lbs the Hobbs kills the power to the factory LP. The adapter plate allows the RASP to supply pressure ahead of the LP and directly to the filter. Since the factory LP is a zero leak design no check valve is needed to stop back flow thru the LP like the 2nd gens.



This way in the unlikely event that you break a belt the Hobbs will see the pressure drop and supply power to the LP so you can continue on until you can get around to changing the belt. Since I already knew that the max pressure from my stock pump was 9 psi I set the Hobbs at 10. 1 lb above the stocker and 4 lbs below the RASP. Set up like this the LP can still be used to prime the system after a filter change also. Just turn on the key as you normally would.



If you don't watch your gauges closely you could also add a small light (powered by the Hobbs) that will come on when the LP runs just to let you know if there is ever a problem. I think that some of the pictures in my gallery have descriptions of which line goes where on my installation.



Considering the threads regarding the doubling of the price on the AirDog I think the RASP is about to become very popular. :-laf



Richard

 

[Matt400]

Thanks Richard, after doing a little more searching I found a pic OPoole posted here that showed the lines, it all makes good sense now. Better pump with an automatic back up.

Does the RASP come with the hobbs sw or was that your idea and what about trimming the fan blades?

 

[Gypsyman]

One more thing. . trimming the fan blades? How much? I would be worried about causing an imbalance.

Missed this the first time. Just use a straight edge and a jig saw and trim about 1/2" off of the back of the blades. I've had zero cooling issues even when towing heavy up grades and still have no vibrations at all. I think the fan was the easiest part of the whole installation. Just pull it out and do the trimming on a bench.



If I had a shop of my own I'd install these all day long for people with nary a worry. The hardest part for me was getting the hose pushed all the way onto the fittings. Them little buggers REALLY grab. As slowly as the pump turns to achieve the given pressure it's probably going to last longer than the truck will.

 

[Gypsyman]

Thanks Richard, after doing a little more searching I found a pic OPoole posted that showed the lines, it all makes good sense now. Better pump with an automatic back up.

Does the RASP come with the hobbs sw or was that your idea and what about trimming the fan blades?

That picture is of a 2nd gen but the application is the same. The RASP comes with everything you need including the hose. All I added was two additional 90s so that I could hard mount everything but the bypass valve up on the filter adapter.



In the picture below the front line is pressure in from the RASP and the rear is for the bypass overflow back to the tank. The little bypass valve is adjustable by installing different tension springs and is mounted down on the frame in the return line.



#ad




As far as the pricing goes it should be listed on the DTT website under new items or new releases. If you can't find it give Stefan a call at DTT and he can set you up.



Richard

 

[Matt400]

Ouch. . $629. 00 with no plumbing kit is what they show here



Makes one wonder what would be so bad about an electric plumbed in the same way.

 

[Gypsyman]

Nothing at all wrong with an electric plumbed the same way. After my second gen I was sick of killing electric LPs and the falling pressure at high demand times. This kit isn't for everyone but I for one have had enough of electric pumps.



As far as the plumbing goes DTT supplied all of my aeroquip fittings, hose, and needed parts for around $725 if I remember correctly. I've been down the "do it once" or "do it a few times" road and I decided not to cut corners this time. After riding in three FASS equipped trucks and listening to the ridiculous amount of noise and then looking at the price of the Air Dog it was a simple decision for me.



Gotta go crash. I'm heading to Portland in the morning to have the Don M injectors installed.





Richard

 

[Matt400]

Nothing at all wrong with an electric plumbed the same way. After my second gen I was sick of killing electric LPs and the falling pressure at high demand times.

What electrics were you running? this one looks good but no idea of the noise level.

I am off to bed too, let us know how you like the injectors.

 

[Gypsyman]

What electrics were you running? this one looks good but no idea of the noise level.

I am off to bed too, let us know how you like the injectors.

I've run both the Holley and the Carter. Just never had much luck in the longevity area. At least with the RASP my spare is the factory LP and it's always ready to go.



Rip Rook was kind enough to put a brand new set of spare injectors back in my truck so I wouldn't be down while Don M works mine over. The new sticks should be going in on Thursday.



Richard

 

[Matt400]

with the RASP my spare is the factory LP and it's always ready to go. The new sticks should be going in on Thursday.

Good point on the RASP, it is a nice system for sure.

Why the new injectors? can you not turn your TST up enough?

 

[Gypsyman]

That and I'm hoping for a little better mileage.

 

[Matt400]

What about fuel pressure adjustments on the RASP? Personally I would like to see lower pressures that the CP3 is accustom to while not forcing allot of fuel back to the tank that could promote foaming. A regulator or change in pulley size possibly?

 

[Gypsyman]

I'm 99% sure that you could under drive it further to lower volume and it has an inline "bypass" valve that you can change springs in for more or less pressure. The only problem I see is that you need to keep pressure above what your normal LP puts out so that the Hobbs switch stays open and the factory LP isn't running all the time.

 

[Jeff Clark]

Gypsyman, is the Hobbs switch and the additional plumbing necessary for the RASP installation or did you do that for yourself? I would rather just bypass the stock LP and maybe carry an extra belt should the original one break.

 

[Gypsyman]

I don't know if the RASP would give enough volume at cranking speed to prime the system. Keeping the factory LP only involves 1 extra "T" in the feed line and a "T" for the hobbs switch. Stefan would be able to give you a better idea on this but the factory LP doesn't complicate the system at all and still gives you priming ability and a back-up fuel supply.



Richard