Good example: Blown head gasket

[z-ya]

O-ringing is fine and there is lots of info about that here. I street tuned it myself without the aid of a dyno or knock sensor. I really expected to find the limit. This motor is going to be totally worked next year anyhow. The factory head gasket was quickly replaced with another factory head gasket. It does it's job fine when the tune is proper. O-ringing the head without building the rest of the motor is like repairing a rock climbing rope with a single strand shoe lace.

 

As far as I am concerned, the L28ET motor is one tough muttha...the head gasket is a "fuse" for those that want to find the limit of the stock long block, like me.

 

I have added fuel to get a fatter mixture and pulled some timing at boost. It feels faster now at 10psi than it did with the previous tunes at 15psi.

 

What are you running for timing at 10psi? I'd say 24-25deg is a good start. I've run that for years on my stock L28ET at 12psi without any detonation. AFR should be in the 11.5-12.5 range. 15psi is the most you should ask of the stock head gasket. Any more than that, and you should be running a metal gasket. Then things get really tricky because if you mess up your tuning at 18-20 psi with a metal gasket, something has to give. As Tony said, usually it is pistons.

[cygnusx1]

This is less aggressive than the map that popped the gasket. I guess it can go even more conservative.

 

AFR hangs around 12.5 - 13.5. I suppose I should tune a bit richer in the high boost areas. I used to run 15psi but I have now cut back to about 10psi because it pulls almost as hard, and is safer. After I build up the motor, I will have it tuned correctly on your dyno.

[Tony D]

Then things get really tricky because if you mess up your tuning at 18-20 psi with a metal gasket, something has to give. As Tony said, usually it is pistons.

 

With a metal head gasket, no o-rings, and 8.39psi of boost on the dyno, without ANY detonation being heard, JeffP sunk five sets of ring lands on his expensive forged-piston 3.0L.

 

With a Metal Head Gasket, or an O-Ring, you can make pistons go away, and never even hear it!

 

Hence my suggestion to everyone when they get a Standalone "just learn to tune it on a stock engine" before they start putting money into parts. A blown stock L28ET makes a great donor core for your big-dollar buildup. With another $450 and a junkyard motor you're back on the road learning!

 

Coincidentally, I did see a guy blow his megabuck motor on a dyno, go out and buy a 160K mile ZXT engine from the JY...reinstall it with all the other engine's externals, and then 'just because' ran some dyno pulls on it just to see what it would do. 450HP at the rear wheels, everybody looked at each other, then they turned the boost down and said "Let's just be conservative till the other engine is finished"...He's the guy that told ME to build up the externals first, learn to tune, and once you have the formula down, build your big$$$ engine last, as everything external will still bolt right on! It's not my original thought, and it just made enough sense to me that I parrot it as well!

[z-ya]

This is less aggressive than the map that popped the gasket. I guess it can go even more conservative.

 

From you map, it looks like you are running 31deg at 180Kpa (80 kpa absolute pressure, or 11.6psi). You should be in the 25deg range to be safe. This is also the torque peak RPM range of a L28ET. Also, 40deg advance below 100KPA is also aggressive for a 7.4:1 engine with a stock cam. Max advance across the entire table should be 35deg.

 

I would set you table from 1000RPM up like this:

 

KPA Advance

220 20

200 23

180 25

160 27

140 29

120 31

100 33

 

 

Did you verify that your actual timing matches your advance map with a timing light?

[cygnusx1]

Pete, yes, my timing numbers are verified with a light. I will triple check again anyhow. No wonder she feels so fast. I have the timing so far advanced. BTW the idle spec on my '83 motor from the factory is more advanced than any other year L28ET. I think it's 23 or 25btdc in the manual.

 

TONYD, you have spoken my philosophy. Fiddle with the stock motor while learning to tune. Then build it, and tune it with knowledge and experience.

 

I don't care if I damage this motor a little while I learn to tune. The rest of the car will be there sorted and ready, debugged, waiting for the monster motor.

[Careless]

O-Ringing in this case would have resulted in blown pistons, ring lands, or skirts, instead of a $60 Gasket! Get your tuning down on as stock a setup as possible so you only break things like a cheap head gasket. After you get it tuned, then put your money into the block.

 

good point! I remember you (i think) saying in a previous thread that having the gasket go is something you hope for in an engine catastrophe for that very reason.

 

If it's the weakest link it might be the first and only thing to go, but if it holds in all that pressure... connect the dots

[datman]

Here's a shot of my advance table

[cygnusx1]

I multiplied my advance table by 0.9 and then multiplied my VE table by 1.05. And adjusted my AFR targets to be richer. I went for a drive and datalogged it. It seems to pull just as hard if not harder. So I must have been "overtuned", or past the point of diminishing returns on the timing. The timing map is close to what Pete listed up above and it seems to work. Thanks Pete. I may try Datmans map if I decide to exceed 15psi boost later on.

 

The car is driving just great. I retorqued the ARP studs (moly lube) backing them off and setting them back to 55 ft-lb's one at a time. I may do this one more time in a week or so.

 

One of my hydraulic posts is a little loud again...It's always the same one that bleeds down, so I am trying to track down a single good hydraulic post.

[z-ya]

I multiplied my advance table by 0.9 and then multiplied my VE table by 1.05. And adjusted my AFR targets to be richer. I went for a drive and datalogged it. It seems to pull just as hard if not harder. So I must have been "overtuned", or past the point of diminishing returns on the timing. The timing map is close to what Pete listed up above and it seems to work. Thanks Pete. I may try Datmans map if I decide to exceed 15psi boost later on.

 

The car is driving just great. I retorqued the ARP studs (moly lube) backing them off and setting them back to 55 ft-lb's one at a time. I may do this one more time in a week or so.

 

One of my hydraulic posts is a little loud again...It's always the same one that bleeds down, so I am trying to track down a single good hydraulic post.

 

You should not need to re-torque a stock head gasket.

 

I've got a parts P90A head with hydraulic lifters. I don't know if they are good, but I can send you a couple to try.

[cygnusx1]

I re-torqued for peace of mind. It's just me. A little bit obsessive

 

Pete, I will PM you about the hydraulic posts. Thanks again.

[Z728]

Had the same prob last season blew out three different times, raised the octane redused the advance replaced the head bolts with arp stud kit no more prob....

[george.bryant]

30psi later, OOPS! LOL

[Tony D]

If you are blowing them, do more than simply clamp it better---figure out what is causing the detonation and you will be better off!

You can pull a lot of fuel past torque peak and make great power. We were really suprised by how much fuel we could pull out of JeffP´s engine after torque peak. We were in the high 12´s, and in some cases low 13´s with EGTs running cooler than we had previously. Then we satarted playing with timing and the EGTs wer coming down some more as we added advance. When the HP stopped coming, we backed off three degrees and called it good.

 

Then, he removed the ECU/EFI system, and we are now going to start all over with something else...

[ktm]

Back from the dead. I just blew out #5 on my car on Sunday. I was on an empty highway, driving uphill and did a 5th gear load pull. POP! psssssht pssssht pssssht pssssht. This is my second head gasket. After my first one went, I had the head rebuilt, pulled quite a bit of timing and added fuel. My AFRs were 10.5 ish to 12, timing at 15 psi is right around 21 degrees.

 

Just like others before me, I thought it was the exhaust gasket. I changed that last night only to be confounded by the same problem. I'll be pulling the head over the course of this week.