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Post by ryan0348 on Oct 22, 2014 8:10:10 GMT -6
I have been messing with the power valve jetting on rochester 2 barrels lately the create motors it helps a little but it really helps with the open motors above 6000 by rejetting the power valve leaner u can uo the main jets to produce more torque in the lower end and the top end wont b to rich cause of smaller jetting of the power valve. I have measured a lot of big bore 2 barrels and they can range from 70 power valve jets to 40 so u can image if they all had 74 jets why each one will a richer or leaner fule curve. If u want to know the details hit me up.
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Post by flipflopoo1oo on Oct 23, 2014 19:34:35 GMT -6
Most have been ruled out by the testing gauges of the 4412 Holley! I as a rule of thumb I start by blocking any power valve and working more on timing and fire-power to burn all I can! If your class can run one, try popping the centers, drilling out and use shorter (lower setting) flow-bars with a drop of the roll point to draw harder with more CFMs to match 83-86 Holley jets!
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Post by ryan0348 on Oct 24, 2014 10:31:27 GMT -6
Imca only allows the use of rochester 2 barrels there isnt any classes around iowa where i live that allow holleys only rochester. I dont race but i do build 15 to 20 carbs a year for guys around iowa and missouri. I actually shorten the boster height and put 2 gaskets umder the booster cluster to pull the booster up farther out of the venturi for more air flow but when doing so u have to close up the main well air bleeds so it has more booster signal cause of the booster not being in the center of the point of greatest flow. By rejetting the power valve smaller u can run 78 79 jets for more torque. On nights that it is really dry slick and hardly on the gas it works out better then blocking the power valve cause if your not wide open but the carb is jetted higher cause of the lack of power valve t will run to rich. The air flow has to match the fuel flow if the carb iys only flowing 450 cfm from not being on the gas but is dumping the fuel requirements of 550 cfm then power goes out the window. The power valve allows the extra fuel for the extra cfm espically if it starts to pull a vacum at high rpms provided your power valve is set higher than max vacume pull.
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Post by flipflopoo1oo on Oct 25, 2014 10:38:59 GMT -6
We are never not full throttle off the corner and the extra fuel down low helps to keep us hooked as the timing falls back also in the corner for a bit! The excessive timing and fire-power does the rest to restore max power! It would be hard to race with our guys not hammer down or letting the track have control traction! It takes more fuel but the plugs are snow white, we read the oil residue left on the threads for jetting! Weather and to run the BRA or not is like two jet sizes! The amount of vacuum I create and the refrigeration process of freezing the intake, along with less reversion to slow things down uses the fuel for a longer power burn stroke rather than compression and octane having control of my timing or jetting! As long as it wins, we all do what it takes to make and use horses. The Rochester was all ways my favorite carb! I don't care how much is lost as long as it moves when you mash on it instead of not being able to! Most still have a power-valve but have locked their timing, I prefer the other way to have more horses and control of traction with timing loss for a second or two that controls itself on the floor! Most have to run 32-34 to be able to start their engines with compression and octane dictating, I only crank there and run from 38-57 depending on what runs best with my combination! (DON"T TRY THIS AT HOME) A total change of 28-38 with fuel and timing changing to match with compression is about as far as you can go safely! Rip the tops out of those flow-bars and drill them thin! Regrind the top of the roll point and drop with lower flow bars to draw easier from the bowl, 83-87 jets with timing and fire power added should wake it up a bit without the use of a power-valve! Too clean with a power-valve always leaves too many horses and torque to deal with until moving!
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Post by flipflopoo1oo on Oct 25, 2014 10:56:49 GMT -6
How much modification do they allow on these carbs? Do the pull them and test only the bottoms? Do you have to run the bolt tower? If not, you can gain by using all-threads across with a center T in the choke shaft hole to hold the filter on! The bending of the air and the slicing of it with the treads stirs it up a bit to aide in vaporizing with the fuel!
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Post by ryan0348 on Oct 26, 2014 10:03:00 GMT -6
No u cant put the air cleaner down low. It has to b stock appearing. The bottom of the booster at the venturi parting line is about the most signal u can get. I have played with the rochester on the flow bench a lot the most u can.get out of it is 610 cfm at standard pressure in stock appearing form. Im going back to the dyno a few times this winter i will setup a carb without the powervalve and rejet it with using heavier springs and really light weights to bring in max timing later on in the power band instead of locked out like we usally run it.
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Post by flipflopoo1oo on Oct 26, 2014 11:06:50 GMT -6
I never had the use of a DYNO or flow tools but the process of thought to improve flow by all means starting with lower engine temps to reduce the expansion of the fuel mixture instead of the condensing of it to expand only at the point of ignition in my head! Larger runners or loss of vacuum on the way to the cylinders by timing the valves and dropping compression heat factors and by less reversion just kept asking for more fuel and timing to get the correct burn stroke! It seemed that retuning (adjustments and not new plugs) was rampant with each change down to the header wrap, air filter design or amount of fire power to get it burning! Most was against all useful means at that time but it put us out front! I seem to question more all the aspects of parts to be addressed by simple logic! Nothing was ever not improved by more thought! Testing a carb on the same engine without the rest to handle the fuel would be fruitless! I have no idea of the horses made or the need of drop for traction on other engines but it helped ours to win more than not! A bit rich off the turn to handle the load but cleaned up quickly and a bit lean up top with more fuel sucked in to cool back down the piston when lifting, this left it loaded again! A wicked lean boost up top with a good top oil for insurance by reading the oily plug threads now, tomorrow, or next week seemed the best control of jetting instead of use of a uncontrolled power-valve mix showing clean! You never knew the power-valve was missing and blocked in the response! Not referring to dropping the cleaner but the change of the hold down to increase flow! I use light springs as for cranking and a block of 10 degrees on each, vacuum and weights! Low compression and more pump gas has proven to be a winner for us!
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Post by flipflopoo1oo on Oct 26, 2014 11:33:12 GMT -6
Blocking the power-valve also helped with gear changes not effecting vacuum or our fuel ratio by load or top-end! Air and engine temps had more to do with tune and are easier to adjust with the breather net! Re-gaping the hotter cylinder plugs to fire later to even out the burn timing from heat helped to balance the flow of power to the point of having to re-jet up again! More horses anywhere you look for them!!! This gets all the oily threads the same safe number of three!
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Post by ryan0348 on Oct 27, 2014 5:55:19 GMT -6
Oil in the combustion chamber causes preignation and weakens and annels the tops of pistons ask any big time engine builder how they feel about oil in the combustion chamber. On the level we all race we cant control it like we want to without spending a buch of money but if theres oil on your spark plugs u better figure out y during the next rebuild. Porcelan color and electrode burn back and exhust color is the best method for jetting and timing.
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Post by flipflopoo1oo on Oct 28, 2014 1:22:51 GMT -6
Oil in the combustion chamber causes preignation and weakens and annels the tops of pistons ask any big time engine builder how they feel about oil in the combustion chamber. On the level we all race we cant control it like we want to without spending a buch of money but if theres oil on your spark plugs u better figure out y during the next rebuild. Porcelan color and electrode burn back and exhust color is the best method for jetting and timing. Did you miss the part about THREADS! All fuels have lube! All cylinder walls have lube! A intake valve gets a bit running no positive seals as I do to protect the steel guides from wear with so much fuel being used! The plugs always look new when burning all the fuel so I read the number of wet, oily threads as a means of balancing each cylinders burn! I even recommend adding more top lube in the fuels! No color to read but the oil is there and protects from being lean! It will stay there and can be checked anytime! I check #3 cylinder to be correct and adjust the rest to it by valves and plug gap! It may be a bit over the top but how many horses are lost other wise by not having your builder on hand to tune to the conditions of load or weather! I do build winning engines and always have a edge over most by tune alone! I have a Hydrogen cell on my personal car and the entire plug is coated with a snow white film that looks like enamel! Two years running the same plugs! We might change plugs in the race cars twice a year for good measure but with indexing and the chance of defects I prefer not to as long as its still winning with my 57 degrees of timing! You may not want to ask builders what they think of that! All the ones I know hate to see me coming with my off the wall questions! But still, I question everything and every-one to try and get a better understanding of it all! Most things are subject to change when pushed to their limits! I have been pushing a long time on the edge of gaining another horsepower! |
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