Box Stock

drilling the fuel /vent cap

DynoDon

DynoDon

Moderator
Ok guys, I am helping an organization with their predator rules. I have been ask a question that I don't have an answer to so I am relying on those of you who know FOR SURE to assist me. The rules state out of the box stock. governor adjusted to 5400. Stock Jetting. this is where the question comes in. There are a few trying to convince the track that there needs to be a hole drilled in the vent cap/fuel cap for the engine to run properly. Here is my take on it. I'm thinking that if the stock jets are left alone and there is a true out of the box engine on the track with only the governor turned up, there is no need to drill a hole. My thinking is the hole would be needed to feed an oversized jetting situation. Please answer me only if you know from experience on this issue. No shooting from the hip as I am doing in my question thanks Don
 
we have run a "stock" hemi predator in some of our back yard fun races.... right out of the box i have measured the brass jets and they are not the same... so that is going to be a screwed up rule that everyone knows how to cheat anyway, and on top of that the low sides are not the same and again easy to bypass...
here is the deal.. drill a hole or not the guys wanting to vent the tank will... might as well drill the tank to keep from having to inspect every fuel tank and cap and how tight they are screwed on...
the easy thing to say is "fuel tank venting permitted" or be prepared to spend hours over "his gas cap was loose" do you really want to look for an .015 hole drilled "somewhere"
 
ok, what about the size of the hole so we don't have some brain head drilling a hole that that is splashing fuel on the guy behind them. Also, how big are you seeing the low and main jets?
 
I find it hard to believe that there will be a significant difference in them as per individual part numbers. I know there is a somewhat difference between the two engines Hemi and non hemi. But I cant see a difference between the individual engines.
 
.026 to .030 on the mains I just went and checked all the ones I had pulled out of predator carbs the .030 was tight and the .026 was loose but not an .027.... had 2 @ 27 3@29 1@28 but AL would tell you one jet size is huge :)

I did not look for the low side ones... but they were all within .02 if i remember right... i had 4 stock e tubes that were all the same...

I would doubt there would ever be a need to have more than a 1/16" vent for the fuel tank...
 
DynoDon said:
Ok guys, I am helping an organization with their predator rules. I have been ask a question that I don't have an answer to so I am relying on those of you who know FOR SURE to assist me. The rules state out of the box stock. governor adjusted to 5400. Stock Jetting. this is where the question comes in. There are a few trying to convince the track that there needs to be a hole drilled in the vent cap/fuel cap for the engine to run properly. Here is my take on it. I'm thinking that if the stock jets are left alone and there is a true out of the box engine on the track with only the governor turned up, there is no need to drill a hole. My thinking is the hole would be needed to feed an oversized jetting situation. Please answer me only if you know from experience on this issue. No shooting from the hip as I am doing in my question thanks Don
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I have seen in some cases when using the stock gas tank without holes drilled has caused some vapor lock under race conditions. Drilling three 1/8 holes through the gas cap has prevented this issue. Haven't seen any fuel spillage out of the cap either.
 
DynoDon said:
W5R. Please call me
Click to expand...

Don, the hole in the gas cap is needed even with stock jetting out of the box....it allows the tank to vent somewhat to keep from vapor locking the engine. All that is needed is a couple 1/8" holes in gas cap. If I were making the rules I would make it that the fuel tank can be vented, but only with 3 or less 1/8" holes in the gas cap only, no other part of the tank, for safety reasons. We used to run the gas cap on the old blue clones so loose that they would fall off....it was common to see a couple pieces of duct tape holding the fuel cap on the tank back then lol.
 
Don the Newer predator engine had a fuel vapor capture system, much like cars have had for many years now. The cap is sealed, and it had an additional hose and valve system to vent the tank by routing any escaping fumes to be ingested through the air box. I think you will find the tube from the top of the tank allows fumes to be drawn out, the cap has a weak one way valve only allowing air into the tank when the intake is drawing. Remove the intake tube now the cap has to be vented thus drilling through holes.
 
ponytl said:
.026 to .030 on the mains I just went and checked all the ones I had pulled out of predator carbs the .030 was tight and the .026 was loose but not an .027.... had 2 @ 27 3@29 1@28 but AL would tell you one jet size is huge :)

I did not look for the low side ones... but they were all within .02 if i remember right... i had 4 stock e tubes that were all the same...

I would doubt there would ever be a need to have more than a 1/16" vent for the fuel tank...
Click to expand...

going from a .027 to .031 is a 31.763% jet area change, just a little fyi.
the .032 is 40.314%
 
I ran a out of box Pred this weekend for the first time, only the gov on the throttle plate was manipulated. nothing done internal. My brother was running in the same class and had started cutting out on the corners. a fellow racer in the pits told us to drill the hole, the next time out he didnt have that problem. so come feature time a few laps in i started to have the same issue b/c i didnt drill mine. i reached over and cracked open the fuel cap, screwed it back on and the problem was solved.
 
Scottp1987 said:
I have seen in some cases when using the stock gas tank without holes drilled has caused some vapor lock under race conditions. Drilling three 1/8 holes through the gas cap has prevented this issue. Haven't seen any fuel spillage out of the cap either.
Click to expand...
I second this. I have noticed the same exact thing.
 
Someone needs to jump on a safer vented gas cap deal for these motors. It would sell. One that has a vent hose attachment you could run away from that muffler deal that gets so insanely hot. I like the predator motor and it’s concept classes but the thought of a rollover with a home drilled cap and that muffler freaks me out.
 
I say get rid of the tank and go with a fuel pump and floor mount tank. Mount the pump on the side of the air shroud.
 
Yes and Yes, Vent the cap, or rule that says cap can be vented. fuel leaking=no. i run stock pred from the box endurance races. 250 to 350 laps 1/6 mile track, wide open.. YES you need a vent, Yes it will starve the motor of fuel. I have 3-3/16 holes drilled through the cap and all the way through the metal. Hook the chain back up to the cap and go racing..
NOTE: fuel capacity and use fullness. I run a flat mount or low mount.. if you run a 15* mount you will have 1/2 tank of fuel and will run out because the pickup is tall on the inside of the tank.

I take the tank off, remove the threaded fuel line connector to the tank, cut off the inner filter and grind down the surface, run a drill bit through it, then reinstall. i don't know if this would ever be a tech issue, but wanted to bring it up.. AGAIN the reason i pull the pickup from the tank is to ensure i get to use all the fuel from the tank.. for a 58 mile race every drop counts.
 
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