Head Swap Options For 5.7L 350 TBI Engine

[Majoraslayer]

I did mention earlier, but I'll bring it up again: I have actually upgraded the exhaust already. I'm running shortie headers to duals with X-pipe crossover, running back through dual Flowmaster 40's and "infinite flow" cats. If that alone actually does add about 50 hp, I may forego any more expensive upgrades. I can't vouch for whether it does from my own experience. Incidentally it was the day after I got my new exhaust installed that I was able to see the thick cloud of white smoke from the tailpipe, signifying a coolant leak as likely being responsible for my hard cold starts. I've not really had a chance to test for any power difference because I didn't want to risk any further damage by running it.

 

[NMNorsse]

I did mention earlier, but I'll bring it up again: I have actually upgraded the exhaust already.

Sorry I missed that.

I haven't upgraded my exhaust yet and am just pointing out what the performance toolbox thread says. 50 horsepower sounds like a lot to me but maybe with a chip tune it's possible.

Fingers crossed that it's your intake gasket and not the head or head gasket. It's a common failure point on these motors and has the same symptoms. Much easier to put in an intake gasket, change the oil and get back on the road. Book calls for 3 hours on an intake. Main things are to use thread sealant on the bolts (not silicone), get the right gasket that blocks the rear coolant passage, use permatex on the ends (not the rubber dam) & let it cure for 24 hours before refilling the coolant or firing it up.

 

[Majoraslayer]

I do appreciate your advice! Can an intake gasket result in coolant leaking into a cylinder? If so, what would be a good way to test which gasket would be responsible? I could do a compression leakdown test, but it seems like if the coolant is able to find it's way to the cylinder one way or another, the path of coolant flow would act as a compression leak either way.

 

[L31MaxExpress]

I do appreciate your advice! Can an intake gasket result in coolant leaking into a cylinder? If so, what would be a good way to test which gasket would be responsible? I could do a compression leakdown test, but it seems like if the coolant is able to find it's way to the cylinder one way or another, the path of coolant flow would act as a compression leak either way.

Intake gasket absolutely can dump coolant into a cylinder, especially on the L31. Had a 57K mile L31 grenade on startup due to leaking intake gaskets.

 

[NMNorsse]

You've got to pull the intake to get to the heads. You should be able to see if the gasket between the coolant passage and air passage is blown out.

I got my Felpro gasket on Amazon for $15 plus a fresh tube or RTV Black for $10, thread sealer for $10 and that Dorman steel heater quick disconnect for $12 from Autozone plus oil and a filter for $35 & coolant for $12/gallon.

If you arent sure if the IG blew you could put in the new intake gasket, fire up the engine with water and see if it's still leaking for about the same time it takes to do the leakdown test. It it doesn't leak, drain and fill with coolant. If it leaks, you haven't wasted that much time because a lot of the work is in scraping the old gasket that you wouldn't have to do the second time around and you can probably reuse the new gasket.

My valve cover gaskets were fine so I reused them.

I got a can of chevy satin black engine paint, cleaned up the valve cover rust and the intake, taped it off and sprayed them all. That'll make it easier to spot leaks later. Adds some time to the job but I'm not in any rush.

Watch a couple of YouTube videos before you get started.

Take a bunch of pictures of the engine with your phone before you start. Get a cardboard box and poke holes in it to store bolts and brackets. Don't put thread sealer on the first 1/4" of the bolts because some of them are in the coolant jacket or oil valley.

 

[Majoraslayer]

You've got to pull the intake to get to the heads. You should be able to see if the gasket between the coolant passage and air passage is blown out.

I got my Felpro gasket on Amazon for $15 plus a fresh tube or RTV Black for $10, thread sealer for $10 and that Dorman steel heater quick disconnect for $12 from Autozone plus oil and a filter for $35 & coolant for $12/gallon.

If you arent sure if the IG blew you could put in the new intake gasket, fire up the engine with water and see if it's still leaking for about the same time it takes to do the leakdown test. It it doesn't leak, drain and fill with coolant. If it leaks, you haven't wasted that much time because a lot of the work is in scraping the old gasket that you wouldn't have to do the second time around and you can probably reuse the new gasket.

My valve cover gaskets were fine so I reused them.

I got a can of chevy satin black engine paint, cleaned up the valve cover rust and the intake, taped it off and sprayed them all. That'll make it easier to spot leaks later. Adds some time to the job but I'm not in any rush.

Watch a couple of YouTube videos before you get started.

Take a bunch of pictures of the engine with your phone before you start. Get a cardboard box and poke holes in it to store bolts and brackets. Don't put thread sealed on the first 1/4" of the bolts because some of them are in the collant jacket or oil valley.

It's been a few years, but I do have some experience changing the intake gasket, as I had to install the current intake during my last engine swap. However, though I've seen what's under there, I'm not really sure which passages are supposed to do what. This is probably a dumb question, but how do I identify the air passages vs. the coolant passages?

 

[Das Hatt]

The upgraded TBI heads that used to be found on summit were made by Trick Flow.

Cylinder Heads - Trick Flow Makes Serious Horsepower

Find Cylinder Heads and get Trick Flow Makes Serious Horsepower!

www.trickflow.com

 

[Schurkey]

how do I identify the air passages vs. the coolant passages?

The air passages are paired, and you can see the valve stems at the end of the ports in the cylinder head. They're the biggest openings.

The coolant passages are at the front, and rear of the head, or manifold. On TBI, the rear passages are essentially blocked in the gasket, but not in the castings.

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TBI and earlier heads have an exhaust-crossover passage dead-center. There's multiple openings in the manifold on the right side, the two smaller ones on the right side for EGR are blocked by the gasket.

This gasket set is not intended for TBI, but typical of SBC pre-Vortec.

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Intake with two smaller openings for EGR just visible on right side of photo.

You must be registered for see images attach

 

[NMNorsse]

If you haven't found it yet, here is a pic heavy thread on GMT400 about changing the intake where the gasket blew and was letting water into the cylinders.

TBI small block intake gasket replacement (PIC HEAVY)

1994 TBI 5.7 intake gaskets Written 02-10-2011 At 158K miles or so the intake gaskets on my 1994 C2500LD with the 5.7 TBI engine failed. Not an outright failure but obvious signs of seepage at the front of the driver's side head. Not wanting to let it go until the problem got worse, I tore into...

www.gmt400.com

The only thing I'd add is that an angle die grinder and 2" 3m Roloc suface conditioning disks to buff off the gasket make quick work of it. It'll wear down the aluminum on the intake if you stay on the same spot too long so be careful there, but you cant hurt the heads with those. I used 2 on my intake and heads after I got of what I could with a scraper.

You could probably use them on a cordless drill or impact if you don't have a compressor and angle die grinder

 

[Schurkey]

an angle die grinder and 2" 3m Roloc suface conditioning disks to buff off the gasket make quick work of it. It'll wear down the aluminum on the intake if you stay on the same spot too long so be careful there, but you cant hurt the heads with those. I used 2 on my intake and heads after I got of what I could with a scraper.

You could probably use them on a cordless drill or impact if you don't have a compressor and angle die grinder

NO!

GM and the Automotive Engine Rebuilders Association (AERA) have both issued bulletins forbidding use of those surface-conditioning discs.

Examples:

https://static.nhtsa.gov/odi/tsbs/2017/MC-10137601-9999.pdf

and

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They WILL wear-down iron, they will wear down aluminum more quickly. One bulletin suggests that fifteen seconds can remove .008 of metal. The abrasive dust contaminates the oiling system and it's so fine that the oil filter won't remove it. It's been known to contaminate the vehicles in the stalls adjacent to where the surface conditioning discs are used. And aside from getting the dust in the oil...it's getting in your lungs and the lungs of everyone in the area.

The '97 C/K service manual page 6A-252, for example, warns against their use.

Notice: The following is recommended gasket cleaning procedure for General Motors engine components. Carefully remove all gasket material from the part using a plastic or wood scraper. Use Loctite brand "Chisel Gasket Remover" (P/N 4MA) or the equivalent. Do not use any other method or technique to remove the gasket material from a part. Do not use abrasive pads, sand paper, or power tools to clean the gasket surfaces. These methods of cleaning can damage the part. Abrasive pads also produce a fine grit that the oil filter can not remove from the oil. This grit is abrasive and has been known to cause internal engine damage.