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so we took off the heads to see whats up
here are somepics
no signs of detonation
headgasket failure (cosworth)
the engine builder blames me (tuner) saying we ran it on the dyno on 4th and it was a long run (time)
i think they need to use better bolts and gasket. they are using stock size head studs apr 625 torqued to 16 kg
I have always, and unless there's some reason I cannot fathom, will always use whatever gear is 1 to 1. Usually 4th in the vehicles I work on but in the case of aftermarket transmissions/some 6 speeds 5th.
6-7 seconds for a 4th gear dyno pull doesn't sound too long to me. I checked datalogs from a ~700hp 4-cylinder engine and it was about 9-10 seconds to accelerate from 2000-8000 RPM during the dyno pull. This is using a Mustang chassis dyno with large heavy rollers and electric load control.
For some real-world data, one of my coworkers has a ~900hp Bonneville (land speed) racing car with a 2JZ engine and one of his datalogs shows about 10 seconds to accelerate from 115 MPH (5700 RPM) to 170 MPH (8400 RPM) in third gear. The car takes even longer to accelerate in 4th gear, the chassis has plenty of aerodynamic drag. I don't know all his gear ratios or final drive but hopefully that helps.
I'm not experienced at engine building, so I don't have much to say about those pictures. Hopefully others can chime in. How was oil and coolant temperature during the dyno runs? I wouldn't be surprised to hear about engines getting too hot on the dyno, especially a fresh build that may still have air pockets in the cooling system. It's also pretty rare to find a dyno fan setup with enough pressure and flow to simulate an actual car moving at high speeds.
I have a 15 kw dyno fan so everything was cool
Ect was low 90c after each run, maximum I saw was 94c after a run with 2.45 bar boost
I think the heads are just lifting can't think of anything else
From the look of the pictures it looks like head lift, what studs were used?
FWIW I've seen a few Cosworth head gasket failures in the last 12-14 months, all have been clamped with ARP head studs.
It's definitively not too long! I've done alot of Time attack Evos. A few run with 600whp+ all day long. The usually see full load during 20-30min stints (training). On the dyno i do 15sec runs, and to verify the tune and check that ther is no knock under very high load, I do 2x 25second run just after the other. If you build 4G63 properly and spend alot of time into mapping, you get a very reliable engine, even at high power levels.
If I remember right, the final ARP 625+ bolts torque is arround 120Nm. Means your head gasket has been overtorqued by a big amount. Its likely that the bolts are in the elastic range at this amount of torque.
My advise is to replace the bolts with new ones. ARP 625+ or other with simillary tensil strenght are fine. Use a good head gasket. If possible noth thicker than 1,3mm. Resurface the head and if needed the block, too. The surface finish must be as smooth as possible. Now the most importend thing, you must use exactly the grase and the torque the bold manufacturer recommends. You must retorque the head 3 times:
- after initial tightening wait a night and retorque on the next day
- retorque after run in of the engine, before big boost
- retorque after the first track day.
You are going to be surprised how much you can retorque each time!
If the temperatures are under control you should be able to run for much longer than that. Think about all those endurance racing engines. They are basically continuous in that range.
What fuel are you using and what timing advance? You may have to retard spark to bring the cylinder pressure down if you can't come up with a more reliable head solution.