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Author Topic:   intake manifold
chris n
Dirt Newbie

Total posts: 2
posted February 10, 2002 02:42 PM
i'm running a 355 chevy in a street stock class and i would like to know the best way to plug off the heat crossover in the intake. I tried using gaskets from a propane engine, and they eventually burned a hole through the centre.Does anyone know the best way to plug it off? Thanks.

6pack
Dirt Maniac

Total posts: 128
posted February 10, 2002 07:06 PM
Mr. Gasket #101b gaskets come with a metal block off.

Machinah
Dirt Forum Racer

Total posts: 79
posted February 11, 2002 04:58 AM
The way I understand it, and I've known this for years, is that this crossover is not for heat transfer. It has a more important reason. It does the same thing, not quite as well, as running a pressure balacing tube between your valve covers. The heat that your motor generates, unless there is something weird going on, should be fairly equal and not necessarily in need of any correction.
With all of the internal rotating mass of the engine and the motion of the pistons, the internal pressures of your motor become unbalanced. This leads to improper seating of your piston rings. With the two sides connected, it allows the unequal pressures to transfer from one side of the motor to the other.
I have a 351M factory HP motor that I'm building for a Willy's SW. This HP motor came with a Weiland aluminum intake with a nice, big crossover passage. I don't plan to block it off. If the HP version of a motor comes with this feature and the non-HP doesn't, just that should tell you that there is a good reason for it.
There are many myths that we have come to beleive, some of which are from the earlier days of performance. This one fits into that category, along with polishing your ports (a real no-no). These statements should cause some to religeously argue with me, but such is the way of age-old myths. I'm sure that I have my own myths that are dead-wrong, but you have to aproach all that you know with an open mind and try something different once in a while if you are going to win some races.

jdukes74
Dirt Full Roller

Total posts: 37
posted February 11, 2002 07:46 AM
My two cents is that the race intakes don't have them so I don't want them. in order to be able to use regular gaskets, I cut pieces of steel to fit the holes and then welded them in with a nickel rod.( remember weld short strips and then forget it a while and let it coool real slow before you weld more. cast will crack if you get it real hot in one spot. (for a cooler intake---better charge)

6pack
Dirt Maniac

Total posts: 128
posted February 11, 2002 10:04 AM
The heat crossover passage comes directly from the exhaust ports. It has nothing to do with crankcase pressures. It is there for cold engine operation on a street driven vehicle.

devil wrench
Dirt Forum Racer

Total posts: 100
posted February 11, 2002 10:30 AM
6pack is exactly right. The crossovers are there purely for driveability on a street car. When it's cold out, a warm intake makes a world of difference in mileage and driveability.
If it connected the left and right heads to equalize pressure, it would have oil in it...but it doesn't (think about where the EGR valve is and what would happen if oil was being sucked into the carb from the EGR instead of exhaust gases). It just fills up with carbon and eventually plugs itself off. Besides that, why would you put a 3/4" hole to equalize pressures when the entire crankcase is open and free to equalize pressures.

Homer62
Dirt Roller

Total posts: 10
posted February 11, 2002 08:44 PM
Chris, go a scrapyard and get piece of thin,.030 or .040, stainless steel sheet. Cut two pieces 1.25" by 1.25". Stick one to each head, with a bit of RTV, so that they cover the crossover ports. Then install the intake gaskets and manifold. Cheap, reusable and just plain neat. Good luck racin'. Homer.

Machinah
Dirt Forum Racer

Total posts: 79
posted February 16, 2002 05:15 AM
Sorry for my confusion... I am only going on my knowledge. My modified -did- come from the factory this way. The port is -not- connected to the exhaust. I have closely inspected it and it is ported to both sides of the motor, not the exhaust, and balances the internal pressures.

These other guys right... I have checked into the GMs and find that these are for heat from the exhaust on cold start. Follow their advice and ingnore me... my head was somewhere else when I made my first post... DUH!!!

By the way... racing intake and heads -would- be made without the passages that I have, because the proper way to do this is to run rigid tubing between the valve covers with dual filter vents in the center of this tubing. The vents relieve the pressure while connecting both sides to provide balance just like installing an exhaust crossover on your exhaust. My motor came out of a Bronco and it seems that there were not many made. Heck the VIN said it was a Winsor and they had stopped making this Cleveland block two years before! Such is a Ford.

I'll try to think with my head instead of my rear from now on. I would rather someone set me straight than provide wrong info.

Thanks IMG]http://www.thedirtforum.com/ubb/smilies/cwm4.gif[/IMG]

chris n
Dirt Newbie

Total posts: 2
posted February 24, 2002 05:51 PM
thanks for all the info. i'm in the process of rebuliding my engine, so i'll try a couple of idea's in the process, hopefully i can get it to stay blocked off.

dirtracer50
Dirt Full Roller

Total posts: 42
posted February 24, 2002 10:07 PM
I've melted down old pistons and poured it into the heat crossover on the heads and the intake before. If you decide to try this on the heads block off the cross over on the intake side of the heads and pour from the chamber side leaving extra material in the bowls to grind away. Be your own judge on this but I've never had a problem with it.

powercar821111
Dirt Maniac

Total posts: 118
posted February 24, 2002 11:16 PM
I didn't start the feature one night because of the stupid crossover. It went up through the intake and melted out some of the gasket, so I had a big vacuum leak, couldn't even get it started!

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