How much boost with a standard head gasket?

**bussone** · 19-03-12, 13:59

Dear friends, I will be having a custom chip tuning (MaxiChip) by MaxiBoost Hakan Caliskan here to reach descent 240 hp levels. The head gasket is stock for the time being and I do not plan to replace it with a steel reinforced one (Cometic or Spesso) before doing a complete engine overhaul in the next stage (in depth examination of cylinders and valves, new forged pistons, maybe new forged con rods etc.), which will be at least a year ahead.

The question is, what is the healty (not overconservatively safe but reliable enough to keep the engine away from disaster) boost can an OEM head gasket handle? The Squadra chip limits the boost to 1.2 bars as also done by MaxiChip. However, as the chip is tailor made for my Q4, I may have the opportunity to raise this limit a bit more (such as continuous 1.1 bar boost with 1.3-1.35 bars of overboost) based on your valuable inputs. Your comments and feedback are really appreciated. Thanks.

**mpampis_** · 19-03-12, 15:15

I was running 1.35 bar boost with stock turbo and stock headgasket bur be sure that your chip can run in this boost. I mean be sure about afr, egt and preignition problems. If you have a good chip for working well in this boost you won't have any problem. It depends of course on what health is your engine

**Steve Webb** · 19-03-12, 15:52

One the whole, 1.35bar is considered the maximum you can safely run with the standard head gasket. Of course this is assuming that everything is in good condition and the chip is written correctly.

You also need to bear in mind that the standard Q4 Map sensor will only measure up-to 2.5bar (1.5bar boost).

**bussone** · 19-03-12, 19:48

Thanks for the feedback, I have the Maxidata system for monitoring and logging afr, egt, tps, map, coolant temperature and some other data. Thus, the chip will not be an over the shelf type and be custom written based on the wideband afr, egt and tps logs. Considering that the engine seems to be sound, I guess I may ask for 1.35bar boost levels, of course on my risk.

**mpampis_** · 19-03-12, 20:36

As we all say with a good chip you won't have any problem even with a bit more boost. 1.35 is the limit of the stock turbo. Above 1.35 some time the turbine will break. Just be careful. If you you are planing to pick even 1.35 it would be good to make a good and bigger exhaust system with at least 100cpi cat (better decat) and a free flow filter. Also a bigger fuel pump (ex walbro255lt) and if you want about 1.35 boost increase fuel pressure to 3.2 bar

**bussone** · 19-03-12, 21:06

Thanks a lot mpampis_. I think I readied enough foundation for my Q4 for the "a bit more boost" thing, here they are,

HKS air filter (mushroom)
Walbro GSS342 fuel pump
Brand new stock cams in/ex.
Hybrid and overhauled turbo
Tubular exhaust manifold
70mm dia. straight through exhaust pipe with single rear silencer box
EGR system removed
Balancer shafts are inactivated
NGK 8EGV race spark plugs will be used right after chip tuning
97 RON fuel all the time
AFR-EGT-TPS-MAP monitoring system

I hope these with a proper chip will provide me in the order of 240 hp power (maybe 250

)

**mpampis_** · 20-03-12, 06:29

I had 266 hp with stock pistons and head gasket. I was using 100ron fuel and I had a front mount Intercooler with a T3/T4 turbo at 1.35 bar boost. If your engine is in good health you won't have any problem. The head gasket will have problem if you push the boost for a long time

**bussone** · 20-03-12, 07:40

Thanks mpampis_, now I'm clear to implement the 1.35bar limit rather than 1.2bars. I will have a dyno and share the results with you when chip tuning is done and hopefully goes well with one piece.

**Brul(tm)** · 20-03-12, 09:47

If you still use the original IC, you risk blowing it to pieces (the plastic ends).
I believe this is also one of the reasons why Squadra sets the save limit to max ~1.3 bar.

**bussone** · 20-03-12, 11:31

I was not aware that the IC is susceptible to failure at such modest boost levels. Did you experience an IC failure due to such reason?

**Brul(tm)** · 20-03-12, 13:01

I never experienced any problems with the OEM IC and I do have a Squadra solution, but no more than 1.35 bar boost.

**bussone** · 20-03-12, 14:54

If I happen to replace the head gasket for fear and reliability, would you recommend Cometic MLS Head Gaskets? As far as I remember the OEM head gasket thickness is 1.9mm, so I guess it will be best to keep the same gasket thickness (for CR) which correspond to 0.075 inches in Cometic specs. Also can these metal gaskets be used multiple times, or should they be thrown away everytime the head is removed?

**mpampis_** · 20-03-12, 15:15

the standard intnercooler can hold 1.5 bar boost. the reason of squadra, i think is that the oem chip has limit brake point to the injection and advance table to 1.1 bar of boost. because they don't change this they limit the boost to 1.35 for being advanced enough up to this boost level (if it will not if you push more boost it will detonate).
i would prefer a spesso gasket with steel fire rings but there are advantages and disadvantages. advantages are that you can boost more than 2.5 bar boost with no problem in head gasket and disadvantage is that if you are not very careful in placement you will have a big problem. a steel multilayer like cometic is good enough but no so strong as the spesso one, it is easyer in placement but you have to be sure that both surfaces (block and head) are well planed for a good contact between them

**Steve Webb** · 20-03-12, 17:16

Going back to the intercooler and its plastic end caps, its not just the overall pressure that causes problems, its the fact that you need to clamp the hoses onto these plastic ends.

Years ago I cracked the inlet endcap by over tightening the clamp. Real pain in the ass for the sake of using cheap plastic endcaps instead of metal ones.

**bussone** · 20-03-12, 20:15

mpampis_ do you mean Gr.N or Gr.A Spesso gasket?

As for the intercoolers, I plan to adapt an all aluminum Chrysler AS950 truck intercooler in the next stage. This IC is very common and relatively cheap here in Turkey. It is also very convenient to fit behind Q4's bumper as its dimensions are very suitable (core W630mm x H225mm x T40mm) as well as providing sufficient volume. The downside of this IC is that the inlet and outlet are oriented perpendicular to the core face, protruding about 50-60mm from the core surface. Sorry for my English if described the IC in a complicated way.

**Steve Webb** · 21-03-12, 07:51

Have a search back through some of the discussions about IC size and orientation. Sometimes large intercoolers like that don't actually give you any real benefit and introduce other problems into the system.

**mpampis_** · 21-03-12, 08:54

http://www.walkers-garage.co.uk/shop.../en-uk/p2.html
I mean this. I agree with Steve about ic. Power doesn't means only more boost. There are many other parameters. For a tuned car cold intake air is a very important parameter. You could have colder air with a smaller and better ic. I rebuild my engine recently and I saw that if you search you will find quality products in a good price. Try to find quality spares

**bussone** · 21-03-12, 11:52

I concur with our ideas that boost is not single source of boost and I'm not final on the IC size and application. However there are very successful applications of the AS950 IC here. I think it will be appropriate for me to post and join to the intercooler thread instead of creating a seperate discussion here.

**bussone** · 21-03-12, 12:45

I think I will go for the Cometic head gasket at this stage. I will be happy if you can share your experience about the multiple usage of metal layered gaskets. Are they replaced with the new one each time the head is removed or can they be reused is they are still intact?

**mpampis_** · 21-03-12, 15:32

I really don't know mate if you can use it again after refitting. Keep in your mind that any head gasket have a clearance so when you fit the head it will pressed. I hope you understood what I want to say because my English are not so well

**bussone** · 21-03-12, 20:44

mpampis_ you explained it very well and clearly. English is not my native language either, we do our best to express ourselves.

Anyway the Cometic gasket will go to its new home either for long time or up until the next session of head removal. Thanks a lot for the feedback.

**Evodelta** · 25-03-12, 21:32

I found that Cometics are stronger and more reliable than Spesso*

* What we call Grp N type, not Grp A with separate fire rings.

**mpampis_** · 26-03-12, 08:01

I meant this with fire rings and it is for sure stronger

**jimnielsen** · 29-03-12, 09:29

I have used the same cometic gasket several times - never had any problems..I have also used them at 1.5 bar without problem - and they only cost about $120.00