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Some of this week's Letters to AutoSpeed!

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Cooler Tech

I have read Julian Edgar's excellent theories on intercoolers and am hopeful that he can offer a bit of his expertise about my double-pass intercooler...

In basic terms the first (hotter) pass is through 7 cores and, after the U-turn at the other end, the second (cooler) return pass is only through 6 cores.  I have a difference of opinion between two engineering friends that I hope that Julian can help decide. My first friend says that the construction is wrong and both cores should be either 6 or 7 cores.

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My second friend's theory is more interesting. Apparently this construction is deliberate as after passing through the first (hotter) core with 7 tubes, the air volume is decreased after cooling by about 15% and the construction of only 6 tubes in the second (cooler) core is deliberate to compensate for this reduction in air volume.

I hope that the second friend’s theory is correct - the intercooler was constructed by Radtec, a reputable UK intercooler manufacturer.

If you should need to know, the car is an MG Maestro with a 2-litre 16-valve turbo engine from a Rover 620ti. It is boosted to 13 psi. Intercooler core size in total is 600mm x 295mm x 40mm. Thanks in advance for help with this head-scratcher.

Victor Kish

The only way to find out for certain is to do some testing of pressure and charge-air temperature drops across the core. No theory beats real-world testing.

3S-GTE Wrong Way ‘Round?

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I'm surprised that a rear-wheel-drive Toyota 3S-GTE engine was put into the front-wheel-drive Celica (at Low Altitude Strike). The injectors in the RWD engine are not in the same place and the orientation of the block is the opposite. I would really like to have an explanation about this because I plan to do the same thing. Keep doing good work on the site.

3SGTE Pimp

Hmm, interesting point! We've long since lost contact with the owner of the CEPER Celica but it would seem likely the engine was from a GT4 - not an MR2, as we were told.

Overlooked Subie Engine

I’m a reader and customer of AutoSpeed and enjoy all of the articles and technical bits of information you publish.

In your 2004 Engine Epic on Subaru (2004 Engine Epic - Subaru Engines ) you wrote that you will talk about the most desirable engines from Subaru. Pretty good and informative article, but you forgot to talk about the USDM (US Domestic Market) 2.2-litre full close deck (EJ22G) engine, as found in the ‘91-94 Legacy Sport sedan. I may understand your omission because you don't have this engine in Australia, but I think you should have mentioned it since it's becoming a very popular (and strong) base to build 300+hp reliable engines.

Nicolas Vallee

More on the XJ-SC

You just knew you were going to hear from me as soon as you did a Jaguar article didn't you ( Jaguar Speed )?!

Some additional info...

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The reason there was no soft-top initially for the XJS was that thanks to Ralph Nader and his campaigning, Jaguar was told that convertibles were going to be made illegal in the US by 1977 (a couple of years phase-in period). So they didn't design or tool up for one. [This law] never happened but then by that time, the company was in the process of divorcing itself from British Leyland, which slowed down deployment until the mid-80's. The Cabriolet was the shortcut that allowed suitable "chassis" stiffness (it's a monocoque so that's not really the right word) until they could get the real convertible on the deck and certified by DOT in the US (ADR equivalent)

Auto trans in the 5.3 XJS is indeed GM400 3 speed (both HE and Pre-HE). 6L has a 4sp GM equivalent (4L80)

12.5:1 compression happily runs on 95ron but prefers 98, Oz PULP was 91 only initially at introduction hence they stopped making the high comp engine available after unleaded was introduced.

6-cylinder first hit the XJS in 1984 not the early 90's but was never a big seller-  it was, however, the only manual gearbox available in the entire Jaguar range in Australia until the introduction of the S-type (the UK got the manual box in the 4-door XJ6 for its entire production).

The Supra conversion for the V12 releases a new world of performance from the V12 - it's amazing the difference to the slush box. There are full details on the Jag-Lovers website on the how to do a conversion using Dellow components.

John Littler

Dump Duel?

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I was wondering if it was possible to see a comparison between different dump pipes? Say between a twin pipe system incorporating a separate wastegate pipe plumbed back into the system and a large single opening to the back of the turbo? As I am about to change my exhaust on my R33 GTST, I would love to see the comparo using this car!!? Keep up the good work.

Gene Halden

No, we don’t have any immediate plans for a dump pipe comparo.

There are simply too many variables to give any concrete answers – the post-dump pipe exhaust flow, boost pressure, the amount of exhaust gas exiting the wastegate and other factors make it very difficult. Testing would also be difficult – a dyno could be used to show torque and power differences but driveability (ie throttle response) is hard to quantify.

It’s a case of ‘suck it and see’, but – in any case – a big-mouth or twin-pipe dump should be a lot better than the factory arrangement.

Intercooling Q

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I have read most if not all of your articles about intercoolers. They are very informative and have taught me a lot about cooling the charge-air, but there is one thing that has bothered me about intercoolers. A big pressure drop across the ‘cooler is bad yet, in the act of cooling the air, it becomes denser; therefore more air occupying less space, therefore a pressure drop will result. So how can it cool the air without dropping the pressure?

Daniel Strachan

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