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Some of this week's Letters to AutoSpeed!

7 September 2003

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This weeks email favourite in the office was this little gem of an ad from the UK. Click here (MPG 1mb in size)

Lag Time

I recently read your article on the TurboZet ("The Twin Turbo Zet") and it got me thinking as to the huge increase in lag that a front mount intercooler brings - or so some of my mates believe...

The increase in lag would just be the time it takes to suck through the bigger volume of air that the front-mount intercooler and piping adds wouldn't it? Let's assume you add 3 metres of 75mm piping for your 600 x 300 x 70mm 'cooler core that has an internal volume 33% of its external dimensions plus two end-tanks that are 300 x 70 x 70mm in size. That will add around 20-litres of volume to your intake path. Quoting from your TurboZet article, a 3-litre motor will inhale 120-litres of air per second at 6000 rpm, meaning it'll take 0.15-seconds to inhale all this extra air - the extra lag will be 0.15-seconds.

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I realise that lag is almost always felt lower down in the rev range, but I don't totally understand the formula for getting the number of intake strokes per rpm. Even so, if the figure was five times that predicted above it would still be under 1-second - which isn't much at all in real world street use.

All this also ignores the performance benefits that a front-mounted intercooler brings. The only other performance disadvantage I can think of is extra weight. I'll be very interested in your reply.

Dan Boman

As you suggest, the amount of air sucked by an engine is huge, and so it doesn't take very long for the volume of an intercooler and its plumbing to be overcome. Note that the amount of airflow restriction through an intercooling system also influences lag time.

In any case, we doubt whether any intercooler fitment would cause a lag time of around a second; on the road that would seem an eternity and is much more likely to be caused by a really badly matched turbo than any size of intercooler and its associated plumbing.

You'd be surprised, though, how even only small amounts of lag can detract from a car's overall performance; this is particularly the case in genuine streetcars, where 'point and squirt' is so very important. It's interesting that many people today are willing to accept lag when the early turbo cars were so heavily criticised for it...

Wounded Warrior

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I was very interested in your story about battery relocation, but I reckon the coolest part was the last picture showing all the bandages on your fingers. Julian must be an Aries like me, 'cos most of my fingers end up bandaged too - apparently us Aries are prone to cuts and bruises! Keep up the good work and keep the bandaids handy!

Mark Naish

He's a Virgo...

Cool to Paint?

Way, way back in Issue 1 ("Cool Change") you said this regarding radiators:

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"You want as much heat from the core to be transmitted to the air as possible. Black surfaces dissipate heat much better (and absorb it too - it's a two-way process) than bare aluminium or copper surfaces. In fact, a perfectly black surface will get rid off 14 times as much heat as an unpolished aluminium surface, and 1.5 times as much heat as an oxidised copper surface. With radiators made from these two materials, it makes sense to make sure that the radiator stays as black as possible. A can of matt black spray paint will work wonders."

I've never seen it mentioned in relation to intercoolers, is there some major difference I'm not aware of, or is a can of matte black likely to 'work wonders' for my intercooler?

Charlie Driver

The data quoted above in the article is, we have since found out, for energy wavelengths closer to visible light than to the sort of heat exchange experienced with radiators and intercoolers. But as ever, the sure-fire way to know is to take some measurements - a temp probe in the post-intercooler induction air will tell you everything.

Shot Overboost

Many thanks to Michael Knowling for his excellent article ("Shooting the Overboost"). This particular issue has been a common problem for those of us with Audi/VW cars fitted with the infamous N75 valve, which is prone to spiking when used in conjunction with simple valves to give moderate increases in boost. I have just carried out the modifications discussed in Michael's article to an Audi S3 with superb results - the initial overboost spike has disappeared completely.

I have actually used a couple of products off an American website "". The boost valve, which is a simple pressure controller, fits before the factory electronic boost controller and from the same site you can obtain a superb needle control valve. Both products retail for around US$25-35 and they ship worldwide.

In the article Michael pointed out that easier calibration would be possible from a finer controlled needle valve - this particular valve has 35 click positions for each full turn and has a locking collar, thereby giving very fine adjustment.

Congratulations on another excellent article - you provided the solution for what has been a constant source of irritation. Regards.

David Wilson

Farewell Friend

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I recently came across the following page on your site: "Readers' Cars"

Dave Benson, who the article refers to, was tragically killed in a motorcycle accident earlier in the year. The members of S.C.O.R.E. were shocked at the news - Dave was a wonderful person who was always willing to help out. We'll all miss him.

Allan Williams
New Zealand


Some thoughts on sound deadening re Ryan Parker's email in "Response"...

If it is an older car you're looking at, make sure that the door and window seals are in good condition. As for extra sound deadening, why not double the amount of factory treatment? Go to a wrecker and try to get the sound deadening from the same model as the one that needs to be treated. This stuff can be recut to go into doors, the rear parcel shelf and even the roof. Just bear in mind that the inside of the doors will get wet, so only put the rubber or plastic parts of the sound deadening in there. I would suggest using a good contact adhesive too - you don't want the bits coming off. That's my $0.02...

Damian Sander

Thanks for that. Since Ryan Parker's email we have decided to do a story on fitting sound-proofing - stay watching...

We've Got 'Em Too!

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In the article about the Galant VR-4 ("Australia's Best Value Performance Car"), just a couple of things for your information... They were sold in New Zealand as well as Japan, Australia and the US, and they were sold with an automatic trans though I have not seen these as imports from Japan. Other than that, keep up the great work!

Peter Cadwallader
New Zealand

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