The throttle blades were cracked as I always have them the throttle was bumped a few times getting the carbs off but not opened up all the way or "pumped" also the car sat with no carbs and a fender cover over the intake for over an hour while I got my sons car going that should have been plenty of time for the fuel to evaperate I thought but we all know what happens to thought I am a little concerned about the intake valves hard to beleive there was an explosion big enough to blow the intake off and it didn't pop the intake valves open and hit pistons has anyone had bent valves after the big boom

fuel needs heat to atomize or it will fall out of suspension puddling more fuel. when the fuel falls out then the engine goes lean and you get a backfire. this is the reason OEM put a heat crossover in intake manifolds

I know this is an old thread but does anyone have any part numbers or suppliers for these blow off valves for a 426 Max wedge cross ram.. I looked and could find nothing.. Thanks in advance.

Here ya go. This should help

Something we do on those, in addition to the sneeze valves is plastic screws. They act like a sacrificial part. If and when it pops you just roll back to the pits, replace the screws and go again. No damage to the intakes and off you go.....Todd

Sasquatch, Thats a good idea that I hadn't thought of, are you using any sealant where the top and base bolt together? Mine leaks unless its sealed with silicone or the Right Stuff, thanks for the great idea

You can use the Right stuff or have the manifold o-ringed if you are feeling spry.
Todd

I run the same Wilson sneeze valve, but what I also have done is to separate the cranking and ign circuits.

Now I give it some pump shot, give it 20-30 secs, crank it over then add fire....lights off nice everytime.

Works like a charm

Lot of truth in this.

Lean is the cause. If any one cylinder is lean, you will have your ignition source. Any fuel that puddles adds to the boom. You can stay with carbs, and create a vent for the path for the inevitable boom, or inject it and solve the issue. You will not likely be able to evenly distribute the fuel with carbs. Having choked carbs would help. Less air for the lean condition. Open throttle plates on start up seem like a double edge sword. Creates the lean condition, but does help vent the backfire if not to excessive.
Take any engine and start taking fuel away... even your lawnmower. It will start popping through the intake. Doesn’t matter if the engine is in perfect condition, timing is correct, engine speed, it will pop when lean. Now you take that phenomenon and add an intake with huge surface area for that pop to work against....

If you have a factory style cross ram, it doesn't need a blow off. In fact if started correctly the Indy 440-25 doesn't need one either. Mine popped the lid once. Wasn't even a big bang. Just a poof. Once I learned how to start it, never ever another issue. It does have a pop off but has never banged it. Cold start; fill bowls with electric pump, shut pump off. Pump throttle 3 times. then let it set 30 seconds. 1 more pump, ignition on, throttle cracked slightly. It should fire up on one revolution. Warm start does not require the 3 pumps. Very cold (less than 45-50 degrees) through a cloth fender cover over the carbs then use the standard cold start procedure. My car has 700+ passes with this intake. This procedure works.
Doug

This be true
I've saw this same issue years ago with the Eddy STR type (Street Tunnel Ram) intakes

Thanks for all the responses..

I walked into a shop one time, about half an hour after a guy "popped" a Rat Roaster on a Hemi. He said "What?" a lot for another hour. Then there's the story Allyn Lee has told me, a few times, about how he wrecked an intake AND the hood on their 68 car at the Winters. He said it was a toss up if that scared him worse than the time they cut down the bump stops on the control arms only to find it makes the car really spooky when you drop the nose at a buck-forty.

Probably have around 1000 on mine since 2011. I do the exact same procedure except I get the engine spinning with the starter before I hit the ignition. Only time I ever had a problem was on a 40° day when I thought the motor had heat in it and it was dead cold.

Not everyone understands the proper starting method or the tuning methods as well as temperture conditions and can have an intake explosion unexpectedly.With that being said I can recall many -25 manifold
mishaps and some racers more than once.We installed pop-off valves on many and on more than a dozen we welded the intake floors to prevent gas puddling or buildup in the manifold.I recommend anyone running that manifold to excercize care when starting usually a couple of pumps and hold the throttle slightly open before cranking.The installatiom of pop-off valves will insure you don't blow the top of the intake off and the welding of the floor eliminates the problem.Years back I shared the information with Indy but I never seen any change in the manifold'instead they offered an epoxy insert to install in the manifold it did little to correct the problem and killed the idea of a large volume intake which helped the larger displacement engine making the 440-25 manifold not much if any better than a Mod-Man.
Just my thoughts and observations
Respectfully Bob