uraloser2me2

As the title states what are the advantages or disadvantages of running a carb square jetted with no power valves?

Greg.H

The main disadvantage is that your part-throttle cruise will be as rich as (or close to) your WOT.

If you trailer the car to the track and don't do any street driving at all, then you'll probably be fine.

The double pumper series carbs generally trade off the power valve circuit for the main jets in order to enhance performance, but I'm not sure that you would see a linear improvement if you jetted front and rear for performance and did away with the power valve circuit altogether.

And for a car that sees any street driving, you'll be drinking gas for no reason (most likely running too rich

uraloser2me2

Thanks for the reply. The car runs on e85 so it pretty much drinks fuel anyway. So far I am having trouble getting it rich enough at WOT. With the timing at 28 it is still a little lean with an 86 in the front and a 96 in the back. I am mainly trying to hit my target afr without going past a 99 jet.

Greg.H

If 99 is your limit then I would try that and see where you are. If you're still lean then you could raise the pvrc some, and as a last resort jet it square.

Pop N Wood

iTrader: (1)

Sure you have enough fuel pump?

uraloser2me2

The fuel pump is good for 3 times the power I make. I am sure that is not the issue. My air fuel is at 12.3 to 12.5 and I would like to get it into the high 11's. I would like to get there with out having to buy another jet kit. My current one only goes up to 99, but if it is the only way I will buy a 100 to 110 kit. I was told by a well known e85 carb builder that he square jets all his carbs. Since this is the first carb I have tuned I just wanted to get some more info.

pancherj

Drill out your PVCR (power valve channel restrictor). That is orifice that leaves fuel in when the power valve actuates. It looks like a small jet. If it is an E85 specific carb, it should have the passages modified to flow more fuel.

As mentioned above, the "racer trick" is to block the OV circuit and up the jets. This is a poor practice for street driven cars.

uraloser2me2

The carb is a holley e85 xp 750. I do drive the car from time to time, but it is trailered to the track.

dogsballs

I was lean with my e85 carb and jetted up square, but eric niefert said to drill out pvcr, did it and dropped primaries a heap. Much better on transition. I ran 96/105 on my holley e85 850. Just buy the jumbo 100-110 kit, not that expensive.

I also upgraded to 150thou methanol needle and seat

speedtigger

iTrader: (16)

Running with no powervalve murders the plugs and dirties the oil. I just don't see any point in doing it.

uraloser2me2

Thanks for the info, What air fuel did yours like the best and what plugs were you using?

Thanks for the reply, my carb guy says I am leaving a lot on the table not doing it. It runs so good on the street the way it is I am not sure I want to even try it.

speedtigger

iTrader: (16)

I have never seen any evidence of this.

1 FMF

iTrader: (1)

my understanding is no power valve is most beneficial on a circle track type of application where the motor basically sits within a narrow rpm range and a narrow manifold vacuum range... manifold vacuum would be high, throttle 3/4 to wide open all the time. if manifold vacuum does not change then there is no need for a power valve since it would basically do nothing it would either be fully closed or fully open all the time. and running off just 4 main jets simplifies fueling and you can control a/f ratio tighter under that specific condition.... and make the most power and most fuel economy under that narrow operating condition.

you would not want to remove the power valve on a carb that uses them if it's a street car and the motor has to provide performance between 1000-3000 rpm, where manifold vacuum will vary greatly as the load on the engine varies greatly. The transition circuit and accelerator pump in the carb do not have the capacity/capability to do what the power valve does under those conditions.

Mr.Nitrous

iTrader: (51)

Circle track engines see a lot of vac load changes on most applications unless you are on a superspeedway. Short tracks go from wide open in the straight aways, then completely off the throttle going into turns 1 and 3 and the throttle is usually picked up between turn 1-2 and 3-4 to drive the car off the corner. We run power valves in our circle track carbs.

uraloser2me2

I will have to agree. Since it was easy to do I gave it a shot. It ran fine as long as you were on the idle circuit, or wot. Cruise was complete garbage. Needless to say the power valve will stay in from now on.

Pop N Wood

iTrader: (1)

That's not a bad way to drive...