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Some of this week's Letters to AutoSpeed!

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Boost Bungle?

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Your article Brilliant Boost describes plumbing a bleed valve into a Nissan Skyline GT-R and is incorrect. When a bleed valve is placed inline to the factory boost control solenoid (or even after it) the following happens...

- Valve fully open - boost is exactly what it was before
- Valve fully closed - boost is regulated by wastegate spring
- Valve somewhere between the two - boost is between the two

I have no explanation for the results obtained by Julian Edgar. Perhaps in his installation process he bypassed the inline factory restrictor, which regulates boost to a maximum of around 8 psi? The reason I mention this is that the article is still readily available and people may still be getting confused.

Saliya Wimalaratne

The valve installed in that article is not a bleed valve. It functions as a flow control valve - it is fitted upstream of the boost solenoid and can be adjusted to increase the amount of air bled by the factory boost solenoid. Have a read of Bumped Up Boost  - this story outlines the same approach with similar results.

More Bang for BA

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I’ve bought a new Ford BA XR6 non-turbo (though now I wish I did buy the turbo...). In the next six months I’m looking at spending up to AUD$5000 to get more performance out of the BA. I have been told to go turbocharged or supercharged. What would you advise and what type of performance would I get at the end? And, yes, if I have to spend more than planned I will.

Gary Blazejewski

First weigh up how much you'd need to spend to achieve X power and consider resale value and reliability compared to a factory XR6T.We'd be reluctant to spend heaps on the car for the above reasons - but that doesn't mean you can't have fun! As always, start off with a high-flow exhaust, modify the air intake and maybe revise the management system with an interceptor. We imagine this could give around 10 - 20 percent more power. If you want something big, a CAPA BA Falcon supercharger kit would probably be the go at a bit over $5000. This is said to give 305kW (together with an upgrade exhaust). Compare that to a XR6T with 240kW and similar torque and you've gotta be talking 12s over the quarter mile - traction permitting.

Another Blown Beemer

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Just a short addition to 2004 Engine Epic - BMW Engines ... After the M102 turbo engine came M106, which was a 3.5-litre six with 8.0:1 compression, lower boost (0.4 Bar), Motronic management, electronic boost and timing control with knock sensing. It made the same power as M102 but more torque at lower revs. It was employed from ‘83 to ‘85 I believe.

Janis Velbergs

Big Banger GTi

I have a question about an engine conversion. I'm owner of Suzuki Swift GTi 1.3-litre DOHC 16-valve but the bottom-end is damaged. I have two bottom-ends that I can replace it with – one is from G16A 8-valve and the other one is G15A 16-valve. Both are a perfect match to the GTi transmission after making some alterations but the G16A bottom-end has the oil pan on the other side compared to the G13B and G15A. Which would be the better one to put with the GTi head? Would the G16A have more power and torque with the G13B head?

Oscar Lafebre

Have a read of Head Start. We suggest the G16A engine as the platform because, yes, it will give more torque than the G15 and we’ve seen these combos work well. You might want to check out the resulting compression ratio when dropping the GTi head onto the 8-valve G16A block. Perhaps the G13B or G15A oil pan could be fitted to the G16A bottom-end - or maybe one could be made to fit without too many mods.

Filter Findings

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I read one of your older articles (A Shot in the Integra's 'R's)and your comments on pod/cone air filters producing no power gains. I’m unsure about the matter. I've always thought that on the dyno, the car is stationary so the air in the engine bay should be fairly static. But, once on the move, air enters from the front so the engine bay temperatures should be cooler. Maybe some in-gear acceleration tests are in order to compare performance of factory air boxes and exposed pod/cone air filters?


The amount of airflow through the engine bay on a chassis dyno depends largely on the size of the dyno fan. Generally, though, there is less airflow than typically experienced driving down the street. This causes heat soak, which kills performance if there’s an exposed under-bonnet filter. The same will happen on the street in stop-start conditions.

Identified Fan

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The fan you show in Fan-Forcing Your Intercooler, Part 1 is a 1974 to 1979 VW Combi cabin blower from vehicles fitted with the Type 4 1700, 1800 or 2000cc engine. It’s the same as in a 914 Porsche. This fan comes controlled by a dash switch with, I think, three speed settings. It can be found in the engine bay above the motor.

John Howard

Thanks for letting us know! We’ve added a note to the end of the story identifying the fan.

Clever Valve

I read with interest The Delta Throttle Timer Breakthrough and have thought up a possible project. I was wondering if there is a low current motor that can turn a shaft 90-degress when voltage is applied and then, when the voltage shuts off, will snap back to the previous position.

The reason for the question is that I want to try to build a butterfly for the exhaust that is linked to the TPS so that if the voltage on the TPS rises above 4 volts the butterfly will snap open. In part throttle driving it will be closed for quiet operation. I basically want the unit to operate as close to WOT as possible and, when you lift off, to close the butterfly within about 10 seconds.


In this application, you could use a simple timer circuit and throttle position switch. However, the Delta Throttle Timer (which looks at rate of accelerator movement) could also be used. Use an electric solenoid and a spring to open/close the valve .

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