12 replies to this topic

[nobbycameron]

Hi,

So i got my supercharged 1275 running and driving down my drive last weekend. Sounded great with the straight cut drops. The engine has not been set up (mixture and timing) but was good enough to run. I put my foot down a bit and it blew the head gasket. It blew out of the side by the factory fitted steady bar. So much so it was popping out the side. I took the head off to inspect the gasket and the metal ring has mis shaped slightly next to the hole where an 11th stud would be. The gasket is a bk450 and i have reused the existing head studs. I havn't checked the block and head for flatness yet.

I was just wondering whether people generally replace head studs and if so which ones would you go for, there seems to be a big difference in price for standard and uprated stud kits on mini spares.

Also are bk450 head gaskets up to the job?

Thanks in advance

[Bullet]

I did not think that head gasket was designed for superchargers.

What is the rest of the engine / head spec? How have you lowered the compression ratio?
I'm presuming you've not just bolted a supercharger onto a standard 1275. If you have and it is still ok, although not ideal at least use something like http://www.minispeed...c-120thou-thick to lower the copression.

Edited by Bullet, 19 April 2011 - 12:01 PM.

[Wil_h]

The BK450 is the best gasket to use, well proven in some engines running lots of boost.

Do you have a photo of the failure? it might help diagnose the failure.

However, failures out of the side are generally caused by two things:
1) Under torqued head (check your torque wrench is reading right)
2) Warped head.

Too much boost, too much ignition advance or too high a CR will almost certinally end in detonation and a different type of gasket failure to the one you have experienced.

I would advise that you don't go blasting around without setting the advance and fuelling, you might get away with it on a no forced induction car, but it's asking for trouble with a super or turbo charger.

[TopCatCustom]

As Will said, blasting it without setting up timing and fuel is asking for trouble on a FI car, guarenteed. I blew both head gaskets on my blown V8 on my 3rd run up the strip with perfect mixture and timing, so with timing and fuel both out there's no chance of reliability.

Fit ARP studs, 11 bolt the engine and you should be ok, how much boost are you running? I fitted copper head gaskets with copper head gasket spray and they are solid.

[mini.cooper998]

are you running a decompression plate or have you had the pistons and head modified for a compressor

[nobbycameron]

thanks for your replies,

I have had the chambers in the head enlarged so no de-compression plate.

I have made my own kit so i'm not 100% sure what boost it's going to be running at the moment, but i have a selection of pulleys i can use if it is too high.

What i am trying to decide is whether it is nescesary to have 11 studs and arp bolts? presently i am using the old used studs (only 9). Have any of you ran FI engines with 9 standard studs? would it be better if i got 9 uprated studs or do you think i need 11, i know theres probably no right or wrong answer here but i would just like to get a feel for what other people have done,

cheers

[TopCatCustom]

I'd think 11 studs were definitely better than 9 ARP's, knowing what boost is crucial! A pressure gauge is cheap and you only need a tiny outlet tapped into the manifold for it.

[nobbycameron]

yeah ive got a boost gauge tapped into the manifold, it reads a vacuum at idol, then when you open the throttle it jumps to about 10 psi boost then if you hold the revs it will return to a vacumm. Thats when the car is stationary. I didnt look at the boost when i was driving becasue its not mounted on the dash yet so couldn't see the gauge.

[TopCatCustom]

You will only get proper boost readings when the engine is under load- i.e. accelerating fully but pulling hard up a hill is best to get a full reading as thats when the engine is working its hardest.

[shellspeed]

Don't think you can lower the compression enough with just the head being modified and standard thickness gasket. There was a simlar post on here a few weeks ago discussing this very subject.

[nobbycameron]

yeah that was what i thought about the boost gauge reading but i am glad you have clarified that.

i have worked out the compression ratio to be 8.5:1 by filling the relevent spaces with parafin and measuring the volume with a seringe, so unless my calcs were wrong i reckon it should be ok. The head has been worked a lot and the pistons are dished as standard. but i would be interested in rerading that thread, if you know the link could you post it??

any other thoughts on head studs??? what have other people used on their forced induction engines???

cheers

[Wil_h]

You CAN get the CR low enough with just head mods on a 1275, it's ona 1380 that it's a bit harder.

[new_zealand _minis]

i blue the decompression plate and the 2 head gaskets on my 1275 vmax supercharger kit . it did about 500-600 kms befor it did . now im using forged 16cc dished pistons with the bk 450. with the chambers cleaned . get a air fuel gauge easy way to see if it is running lean or rich . go for the 11 stud arp kit thats what i have done now