Ok so I got the new motor in the truck, I have over 2000 miles on it now and it is fast as hell. I got my 11 second time slips and all and I have a question.

Why is it that when the truck looses traction and hits the rev limiter it automatically lifts the cylinder heads and I looses coolant ?

Since I have had the truck running I have lost 2 or 3 cups of coolant and could not tell why. A couple of weeks ago I was poking around with a bright light and noticed wet spots under the intake manifold coming form the head gaske area. I have not noticed any wetness on the outside of the cylinder heads near the exhaust headers but then again I didn't really look that close either.

When I was coming home from the race track last sunday I got on it hard on the street and lost traction and then I finally smelled it. Hot coolant.

Any ideas......How does the rev limiter work on these damn things? What exactly does it limit? Is it shuting off fuel or ignition?
Thanks for your input
Dale

 

What kind of motor was replaced? Did they reuse the stock heads, and the torq to yeild bolts? Some of the 5.4 heads have casting flaws and do not seal well, and you prolly got a set. Usuaully its oil that finds it way out, but it could just as easily be coolant. So get back to us on what you got.

Rev limiter cuts fuel, and will also drop boost if your boost bypass is still there and hooked up.

Brandon

 

How much boost are you running?

 

I guess I shoulda been more specific.....enigine is 00' L 5.4 with new forged rods and pistons. Cylinder heads and most of the intake intake including blower have been ported. Stock cams....roughly 15lbs of boost. I haven't had a guage on it in a while.

When it looses traction the motor revs extremely fast and then goes BAP-BAP-BAP before you can get your foot off the pedal.

At that point the cylinder heads lift and it looses coolant. There is no detonation....this only happens on an over rev....Well it is detonation but I'm thinking it is caused by something the computer is doing.

I just want to know what is happening at that point. If it is the rev limiter then it damn well aint no "Soft Touch".

And further more is there anything that can be done in a computer chip to help the situation?
Again Thanks
Dale

 

What does your oil look like? What color is it? I'm thinkin Crazyone might be on to something....I've never heard of heads lifting...

 

heads lifting with a lot of boost.....is a very common problem
Use the search, and there is a world of info out there

 

You didn't mention if your engine builder used the ARP head studs. These will increase your clamp load considerably over the stock bolts. The stock head gaskets are also a weak link at 15+ PSI; unfortunately that's all that is available right now unless you want to have custom copper gaskets made and o-ring the block...

Did your engine builder check the flatness of the block and heads prior to installation? We've seen them out by quite a bit on some engines.

 

Most likely your making alot more boost when you spin it up as far as it does to hit the rev. limiter. therefor at that point your lifting the head. Do you have *stock* head bolts or Head studs? You also could be lifting the intake. check all the bolts on the intake for proper trq!(also check the intake gasket for any damage!) we have run upwards of 25# of boost with the *stock* head gaskets and head studs! and have Never lifted a head. or lost Any coolant. So we know the *stock* gaskets with Head studs and properly trqd! should be just fine for upwards of 25# of boost....JLP

 

I am using the ARP studs with stock head gaskets. The block was lightly milled for flatness and so was the heads. Surface finish was near perfect. I assembled the engine myself.

Specifically what I would like to know is what is happening when the engine over revs? How does the computer control that?

If the computer is shutting off the fuel and then turning it back on again....then that could potentialy be more damaging than not having any rev limiter at all.
Thanks for the input
Dale

 

Basically it shuts off the fuel pump momentarily. there are two steps to it, 1/2 fuel then total fuel shut off. the 1/2 fuel is there to help slow the creep up in rpm, and the all fuel kills the motor. During an overrev it will also back down timing and bypass boost (assuming you had a boost bypass still installed)

Brandon

 

Brandon
Thank you.....the answer you gave me is what I was dreading.

The computer control to the boost bypass has been bypassed so to speak. So the truck is making 15+ lbs of boost during an over rev.

I guess I will change the way I drive the truck. When I was at the drag strip last sunday I over revved it in the water box and then the engine struggled a little bit....had to slip it into neutral and clean it out and for a second and it didn't sound to good. But then it went right back to business as usual, and made a descent pass.
Dale