Rattle under Boost

Author
Discussion

oakdale

1,786 posts

201 months

Tuesday 25th November 2014
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I'm assuming this car is a jap import?

If so, it will be running on lower ron fuel that it was designed for and is therefore liable to detonate without there being a problem with the engine if the knock sensor is faulty.

I'm just saying let's not condem this engine yet until the obvious thing have been checked first.

Vixpy1

42,620 posts

263 months

Tuesday 25th November 2014
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BG or BH, If its a BH the MAf sensor will have failed.

Viperz888

Original Poster:

558 posts

157 months

Tuesday 25th November 2014
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BG5 EJ20H.
I'll try some octane booster, that might at least tell us something. I thought Tesco stuff was the best you could get here other than race fuel.

Surely the likelihood that the knock sensor has failed in such a way that the car doesn't notice though the diagnostics is incredibly small, otherwise I'd start there. Unfortunately it's a right pig of a job on a TT.

stevieturbo

17,229 posts

246 months

Tuesday 25th November 2014
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Is it definitely only under boost ?

Who rebuilt it and how long ago ? and why ?

Go onto the UK Legacy forum, there is a guy there, or at least used to be called Craig ( McD ? ) or something, I think he is fairly local to that area and might be able to help.

Someone on the form would be able to point you in his direction.

But it could be detonation for various reasons.

Or I've seen older engines where people have used thinner modern MLS gaskets which have resulted in pistons hitting the cylinder head causing strange rattles.
Although this was at any load and higher rpm's. Not usually apparent below 2000rpm rpm so though

PeterBurgess

775 posts

145 months

Tuesday 25th November 2014
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The best fuel we have tested this year is Shell V-Power Nitro+ Unleaded. Till we did several back to backs we used to tell everyone to use the Tesco Momentum as we had very good results from that. I attach a race B graph (running 1 1/2" sus and restricted on engine and valve sizes) with upper lines Shell and lower lines our previously favoured Tesco fuel. If I have already put this on ph in the past I apologise. The fuel must have been good as we got first and second place in the championship smile



Peter

Viperz888

Original Poster:

558 posts

157 months

Wednesday 26th November 2014
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stevieturbo said:
Is it definitely only under boost ?

Who rebuilt it and how long ago ? and why ?
I'm very confident it is only under full boost (approx 9-10 psi). It would be harder to attribute if it wasn't twin, as it would only be under high rpm, but it happens twice in one gear, due to the turbo changeover.

It was rebuilt in September due to a spun bearing - we determined this was most likely due to a previous owner running it low on oil and it just deteriorated in the time I had it. The rest of the bearings/surfaces were as new, so not in line with the car being thrashed constantly or from cold, and that I was very careful with oil level & grade, and it never overheated.

I’m actually on UKL and have asked there already, but had no real luck.

I have put some Octane Booster in it, just going to give it a few days to come through fully (using it as little as possible at the moment, for obvious reasons) and see if there is a difference. Have been in touch with the builder, and he is going to have a look at it – I think it’s only fair he is first, if the problem still exists I’ll go elsewhere for an opinion.

Boosted LS1

21,165 posts

259 months

Wednesday 26th November 2014
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I'd drop the boost and see if the noise goes away. You'll know it's detonation if that happens and can plan a fix.

stevieturbo

17,229 posts

246 months

Wednesday 26th November 2014
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IF it is detonation, you can still drive the car off boost with total safety.

But for this to happen all of a sudden, and no actual changes have taken place would be rather strange.

Or has this problem appeared immediately after rebuild ?

Boosted LS1

21,165 posts

259 months

Thursday 27th November 2014
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^ probably after the turbo's were added.

Viperz888

Original Poster:

558 posts

157 months

Thursday 27th November 2014
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Problem started about a week or two after the rebuild. It definitely wasn't there immediately afterward.

Boosted LS1, its a standard engine. The only thing that is modified is that it has an exhaust and the aforementioned mls head gaskets. When it was rebuilt, that was the first time the engine had been split.

stevieturbo

17,229 posts

246 months

Thursday 27th November 2014
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Viperz888 said:
Problem started about a week or two after the rebuild. It definitely wasn't there immediately afterward.

Boosted LS1, its a standard engine. The only thing that is modified is that it has an exhaust and the aforementioned mls head gaskets. When it was rebuilt, that was the first time the engine had been split.
What year is the car, and what thickness head gaskets were used ?