Too big of a regulator seat will give you wild pressure fluctuations at an idle and at wide open throttle.
Think of it like this: You want a drink of water but you are holding a glass under a water tap opening the size of a sewer lid. The lid opens and massive amounts of fluid rushes in…ooops too much. So it slams shut, now you have no water..too little. So you size the regulator seat for the range of lbs/hr required in its operating range.
The stock Holley 803 regulator is a great regulator for up to 525 h.p. The bigger Holley 704 regulator is a great regulator for the 950 plus horsepower level. Our PG-803 is sized to fill the gap between these two applications.
On our PG-803, we install a larger seat to increase the flow capabilities..but not too much. Also, without the larger seat, typically what you will see with the stock Holley 803’s is a lot of foam beyond the 525 h.p. level. The smaller seat makes a spray head and foams it right up at about that level and above.
Many times this foam will settle down in the bowls before it gets to the main jet. BUT in some bowls and with some fuels it won’t settle down and the engine will suck up the foam and burn up or pop at the far end.
Foam reduces weight on the carburetor jets and leans the mixture. Foam is an enemy. The bigger seat and other mods cure that.
Many times if you are using a stock 803 and you switch to a modified regulator, you will need to jet down as the reduced foam will give you better fuel and a richer mixture.
Also, be aware that many dynos are equipped with an unmodified 803 (or two) as a main fuel system supply. BUT remember on most dynos lower than normal line pressure can be used (this reduces foam) as on a dyno you do not need to offset g-forces. However, if foam is being created on the dyno fuel system it will alter the fuel curve and carbs function and this can change your tuneup when the engine is ultimately installed in the vehicle as compared to the dyno required tuneup.
This is a common mistake that folks make: Be aware that a larger fuel line and even a fuel log DOES NOT help you have more fuel reserve. A fuel log was developed to slow the fuel down and get rid of foam. Logs and fuel lines do not have accumulator bladders in them. Basic physics lessons will tell you why the larger line or log with no bladder is no help in the reserve dept.
Remember, that this fuel is in a confined and fixed area. If there is no compressible bladder then the only way it can be used as a reservoir is if the far end of it is open between the pump and the inlet to the bowl AND THEN the bowl vent would need to be plugged so the carb could draw from the line. But carbs do not create vacuum on their supply fuel line or log and you can’t have an opening on the pressure side of the line.
The carb bowl is vented and the hose is a sealed area to retain the pressure so these lines and logs are not reserves.
Be aware that a carb with a float bowl full of fuel is still subject to variances in fuel pressure. Simply toggle your fuel pump on and off as you are traveling down the track…notice the vehicle surges? Why? Because as fuel stops coming in the bowl area, the booster has to start air moving into the vent tube. This momentarily leans the mixture as this air (needing to be drawn in) adds to the load of the booster and it pulls less fuel as it needs to pull air instead.
Also, as the bowl level gets lower the mixture gets leaner as the booster has to now pull from a lower level. When fuel starts flowing in again, the air begins exiting the vent tube and momentarily pressurizes the boosters as this air changes direction. The mixture gets richer as this air changes direction. Now the level moves back up, it levels off and we are back to the original calibration of the carb. So the mixture comes back to where it needs to be.
Full bowls of clean fuel at the proper level are one of the biggest keys to consistency and maximum performance.
As far as the PN-803 nitrous regulators go: We relieve the body so the seat opens quicker (very important in nitrous to avoid explosions from a momentary lean condition), we hand lap the seats so they seal up well AND flow them through their pressure ranges so they have more linear delivery. Sometimes you have to swap out and tweak the pressure springs to get rid of harmonics that will kill flow at certain rates of flow and burn up engines.
Hope this helps clear up the confusion of fuel lines, fuel regulators and fuel delivery importance.
Thanks for reading.