A couple questions from a newbe.....

Hey all, been lurking a while and new to blown alcohol. We run a drag boat that races against either a 7.70 or 8.0 index. We run 565" BBC with an 8-71, 2% over, about 8 lbs boost using a 110 pump. We easily made enough HP to run the number. However, we ended up with 45's in the hat, 32's in the ports, 100 in the pump trimmer, 70 in the high speed and still need around a 160 main in good air. The tune up is still very safe.
After lurking here and talking to other racers, I've learned it's likely my pump is way to big and I might be taking a risk running such small port nozzles. I talked to Enderle who suggested I get rid of the port nozzles, go to running everything through the hat and possibley switch to a 600 or 80A-1 pump.
My questions are
1.Should I get rid of the port nozzles and run everything through the hat?
2.Rather than change pumps, can I continue to increase the trimmer jet to decrease the main size? If so does a 10 increase on the trimmer equal a 10 decrease on the main?
3. Can I calculate the areas of the port/hat nozzles to come up with a new size to run everything through the hat?
I hate to start over with a complete new fuel system but also concerned about plugging a nozzle and nipping a piston. We do have a good fuel filter before the pump. Appreciate any feedback.
Thanks!!

 

No idea on fuel pressure. Planning on adding a data acquistion system this season to help answer some of these questions. Also, we never hit 8k RPM, peak is only about 7500....

 

Tell us about your blower.
Is the bottom outlet a big rectangle or a pie shape?

My questions are
1.Should I get rid of the port nozzles and run everything through the hat? You probably can if the blower outlet is not a pie shape, personally I would keep the port nozzles at about the size you have.
2.Rather than change pumps, can I continue to increase the trimmer jet to decrease the main size? If so does a 10 increase on the trimmer equal a 10 decrease on the main? Not at all RPM's
3. Can I calculate the areas of the port/hat nozzles to come up with a new size to run everything through the hat? Yes

 

The outlet of the blower is rectangular.... So what is a considered a good fuel pressure? And thanks for the input, appreciate it...

 

David,

As Enderle, Mike and SoDak are trying to explain, your pump is way too big. A fuel pump has a "flow curve" that needs to be matched to the engine size with respect to fuel used. A .010 size chane in main bypass is not a 10% change in fuel flow. In fact, when you get too a .150 range in a bypass jet, you have pretty well reached the peak flow of a poppet. Instead of trying to "crutch" the overfueling in some manner as I have seen by using a dual poppet arrangement is some injection main bypass setups. It will be much more efficient to use a proper sized pump and you will probably gain performance on top of that. I have used the Enderle 600 pump in a similar application with good results. In relation to hat versus down nozzles on a rectangular opening blower, be careful to keep your cylinder to cylinder temperatures consistent.

I hope this helps.
Gear

P.S. The 600 pump is a 110 housing manufactured with a thinner gear set.

 

Digging up bones here. I have been searching this very question.
I run a 600 David. I ran an 80a-1 on the 468. This engine just wants some more fuel for some reason. 492 vs 468 I guess.
Fuel pressure... WOW 150 ish? Really? I am a bracket boat guy too. I just got a RPM system to monitor stuff and fuel pressure. What will I gain from stepping up on my pressure from x (I don't know what it is now) to the 150 range?
Thanks
Wags