[bluesmobile]

Hi there racers,
My 1971 400 in my Grand Prix suffers from blown head gaskets every ~20 hours of race time and intake valve recession (#62 heads) on only the center 2 cylinders of each bank. Exhaust valves have hardened seats. I've attached a picture of the intake valve seat after 18 hours of racing on a new valve job.

Races are 8-24 hours long so these failures are getting annoying. I'd also like to be able to do races in hotter weather and be confident in good engine durability.

T-stat is at 180* and gauge runs 180 until the head gasket start seeping coolant into the oil. The head gasket failure has always occurred on the center cylinders head/block coolant passage nearest the intake manifold flange.

Engine makes about 350hp and is at 10:1CR using some #62 heads with filled crossovers. Stock-ish camshaft. Cliff's Q-jet on a stock intake, long branch exhaust manifolds. I think the road racing duty cycle just allows too much heat to build up in the center 2 cylinders of each bank, as evidenced by the valve recession. Ultimately this high heat in that area also allows the head gaskets to breach right there. I've used standard and performance gaskets from Felpro, and Butler's head gaskets. They all fail. Heads and block are flat.

I know racing ain't cheap, and I really enjoy the endurance road racing with multiple team members (friends), I just want better durability so I can spend more time racing and less time wrenching. And I don't want to have to put an LS in!

I have coolant ports in the back of each head (the outlet that used to go to the heater core - I put one in each head), going to a merge, and then back to the crossover by the t-stat. I think I also need to ADD coolant flow in the center of the head near the intake manifold flange to allow more coolant to flow across the center 2 cylinders in the head and keep the valve seats cooler.

Anybody else experience this issue? Does my root cause seem reasonable?

Have the factory heads been modified before to add coolant flow across the center 2 cylinders?

thank you for your help,
Jeremy

[steve25]

If you look at the head gasket in between the center cylinders when sitting on a block you will see a hole in the gasket that is not in the block or heads.

Drill this hole in them to aid in Cooling those center cylinders.

Also your Intake valve seat is likley too narrow for the spring pressure your running!

.045" is the minimum for drag race usage and for endurance I like no less the .055" even if it gives up 4 cfm of air flow!

Also what can be done to aid in head gasket life is to finish the head deck and block deck surface near mirror smooth so that as the head and block expand and cool at different rates it does not chew the fire ring up and promote blown gaskets.

[694.1]

The car sounds like a blast, got any Youtube links?

[455-4+1]

On tbe Jetsprint engine wid did tbe following. Only 60 seconds at WOT at 6500 rpm, 15 times a race day but still a load on gasket seal at 14:1.
We drilled the extra hole in the head and deck as mentioned.
Then added a direct _6 feed to each head between the 2 centre ex valves. On an iron head there is plenty of room to tap in an NPT to AN nipple (3/8 NPT from memory)
I will post a photo when back at workshop.
This evened up gasket colour (temp) in this region and we never had a failure after this.

[mgarblik]

First, I think it's cool you are endurance racing your Pontiac engine. There are a number of things you can do to improve the situation. I would do the water mods outlined above. If you use the existing seats and make the intake mating area wider, say .055"-.060", you may need more valve spring pressure to transfer the heat effectively. You may need more spring pressure anyway. When you see receded seats, we often think the spring pressure was excessive. Usually, the opposite is true. The effective seat pressure is less on the intake valve anyway because of it's larger diameter and weight, they tend to bounce. This is especially true at higher RPM's with a 30 degree seat. Not sure if you are running a 30 degree intake or not. Higher spring pressure will help with the bounce tendency and when the valve is closed, the heat will transfer more effectively with more seat pressure. The ability to cool is in the seat and the heat is in the valve, so transfer must happen between the valve face and seat and stem to guide. The way to eliminate the recession completely is to install hard seats, intake and exhaust side. But that is pretty expensive. I believe GTOFREEK can supply SBI or similar part numbers for intake seats that will sneak in the head without requiring an interlock with the exhaust seat. Ideally, if using interlocking seats, you would install the intake seat first, then cut for the exhaust seat, leaving a full diameter exhaust seat. Since your exhaust seats have already been replaced, you can't do that without replacing all 16 seats. You could do an interlock by cutting the intake pocket with the exhaust in place, it's just not ideal. Would save a bunch of effort and $$ though. Good luck with the repair and anything we can do to keep a damn LS out of the car, I would be happy to advise. Dare to be different!!

[azbirds]

Good luck with the repair and anything we can do to keep a damn LS out of the car.
I love this!! Running around in Phoenix, Az all year long I can tell you that the cooling hole mod works. Definitely let us know how this goes because we are ALL pulling for you.

[bluesmobile]

thank you for all the responses! Sounds like I have some hope!

I am running a 30 degree seat that's 0.060" wide on the intake. I don't think its the seat that's the problem because 5 or 6 of the 8 intake seats look perfect (like new!), its only the center-cylinder 1 or 2 seats that has recession, usually near the head gasket breach location. But of course I always have more to learn!

Video's are not uploaded to youtube, here's a picture instead. Car performs pretty well for being so minimally prepared, we were leading overall (70) cars at Road America last October before we blew the gaskets after 40 laps. It was the heaviest (by 1000lbs), oldest, and coolest (my opinion) car in the race.

455-4+1, I would love to see your plumbing setup.

thanks,
Jeremy

[johnta1]

What kind of gas/octane are you running?
Would think the center exhaust valves would be having problems before the intakes.


Good luck racing!

[ponjohn]

Very cool.

[mgarblik]

Car looks pretty serious and very cool. I want you to keep Pontiac power under the hood. How long of a down period do you have? PM me if you want hard seats put in all locations. Lets get that beast in the winners circle!

[pontiac6269]

Nice car, hope you get figured out. What transmission do you use?

[bluesmobile]

Transmission is a wide ratio Muncie with a rollerized first gear and a sealed inlet bearing to keep the trans fluid from soaking the clutch. I ran a TH400 for the first 2 years and it was surprisingly fast for being an auto. The switch to the Muncie has only had a very minor effect on bringing down lap times, and comes with a lot more maintenance requirements (shifter and clutch adjustments, fluid changes, etc)

I use pump premium fuel, we can usually find 93 octane near the tracks. I think once in New York we used 92 octane at Watkins Glen. base timing is 14* with 20 degrees of mechanical advance. It pings if 36* total, so I keep it at 34* total and its quiet. It uses so much fuel over the course of the races that its cost prohibitive to use anything except pump gas.

Regarding adding the holes between the center cylinders, should I still keep the rear coolant outlets connected back to the water crossover? I added those rear coolant outlets a couple years ago and have not had any noticeable difference in head gasket failure rate.

[Mike Davis]

Originally Posted by bluesmobile

Transmission is a wide ratio Muncie with a rollerized first gear and a sealed inlet bearing to keep the trans fluid from soaking the clutch. I ran a TH400 for the first 2 years and it was surprisingly fast for being an auto. The switch to the Muncie has only had a very minor effect on bringing down lap times, and comes with a lot more maintenance requirements (shifter and clutch adjustments, fluid changes, etc)

I use pump premium fuel, we can usually find 93 octane near the tracks. I think once in New York we used 92 octane at Watkins Glen. base timing is 14* with 20 degrees of mechanical advance. It pings if 36* total, so I keep it at 34* total and its quiet. It uses so much fuel over the course of the races that its cost prohibitive to use anything except pump gas.

Regarding adding the holes between the center cylinders, should I still keep the rear coolant outlets connected back to the water crossover? I added those rear coolant outlets a couple years ago and have not had any noticeable difference in head gasket failure rate.

Have you thought about 100LL?

Besides the "421" coolant mod in the deck I would keep the coolant hoses.

[455firebird1969]

I don’t know if the rules allow E-85, but you might want to consider it. It will support up to 14/1 compression, runs cooler than gasoline, and cost less than gasoline. Cool car, good luck racing it!

[bluesmobile]

Originally Posted by Mike Davis

Have you thought about 100LL?

Besides the "421" coolant mod in the deck I would keep the coolant hoses.

Yes I have considered other fuel, I do expect there would be some benefit to the higher octane gas. We use about 350 gallons of fuel during the weekend, we also travel anywhere from Wisconsin to Texas to the races, and there is just so much effort required to go endurance racing, that trying to find a local source or transport that amount of fuel is not prudent.

Also, E85 is banned, but even if we could run it, I wouldn't. It would mean more fuel stops which take a long time (min 5 minutes fuel stop per rules, driver has to exit vehicle), and we are already at maximum fuel cell capacity, E85 uses fuel at faster rate.

[Mike Davis]

350 Gallons a Weekend??????

[bluesmobile]

Originally Posted by Mike Davis

350 Gallons a Weekend??????

Yup, 350 gallons. We get about 3.5mpg on track.

Races are 16-24 hours long, often split into 2 days, sometimes run through the night as a continuous 24 hour race. Lots of seat time!

[Mike Davis]

That's allot of fuel. I would be interested to see how it ran with a slight mix of the 93 with some 100LL and a splash of MMT.

[455-4+1]

Originally Posted by bluesmobile

thank you for all the responses! Sounds like I have some hope!

455-4+1, I would love to see your plumbing setup.

thanks,
Jeremy

Hi there

Ours was a different system, with raw water cooling, but there are some things that could definitely help.

Our cooling want into the block at the front (via motor plate, but Water pump would be the same), through the block and up into the heads as per stock.
We staid away from reverse cooling as we wanted to preheat the water before it got to the heads.

It then came forward through the heads and out a restriction (to keep pressure in the block) at the T- stat housing

From the front feed we ran -6 lines to directly upstream of the centre 2 Exh ports. This can be seen as a "T" at the top in one of the pics. This could be tapped in from the water pump feed somewhere in your case.

A few more things to look at for longevity are pictured as well

We ran large drain backs from the rear of each head to the sump and blocked off the oil drain passages at the front. Oil draining back past the cam / rods etc gets a hammering, and even though you may have pressure, the condition of the oil may not be good causing issues (foamed etc)

We also ran an accumulator plumbed directly into the gallery hole near the dizzy (enlarged hole to match feed size).

Pics to come

[455-4+1]

Pics