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Response

Some of this week's Letters to the Editor!

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Hmmm...

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I just read your article titled 'Blown Dynamite'. One thing that caught me as strange was the (relatively) slow 0-100 km/h and 1/4 mile times. For a car with so much power on tap - I would have thought that they could do better - there actually isn't all that much difference between the modified car and the quoted times for a stock car. Me thinks this guy must be a bit over optimistic on his power figures, either that or the guy laying down the performance times couldn't drive....

Jeffrey Morton
Australia

And Another...

Re the article 'Blown Dynamite'.

Pardon me for being sceptical, but the 360kW quoted for the South African Coupe is way off the mark if you know anything about power to weight versus 400m terminal speeds. AutoSpeed (and its readers) should easily pick up on this, as I will use one of your own articles ["The Best Performance Determinant"] results (the 400m speed versus power/weight graph) to query the power figures of the M-coupe.

OK - a standard M-coupe weighs 1390kg. With 228kW, this gives a power to weight of 164 kW/tonne. Using the aforementioned graph, the 400m speed should be about 166 km/h. The results for the standard car give 164 km/h, a very good match given all the variables that occur in reality.

Now modified - let's be generous and add 50kg to the car for all the supercharger, intercooler etc. So now we have a 1440kg car with '360' kW. Well the graph predicts about 194 km/h, which sounds reasonable given the huge increase in power claimed. However the test result is only 175 km/h! Even allowing for different test conditions, that's far too different to ignore. Inputing 175 km/h into the graph you get a power to weight of 187 kW/tonne, or 270kW for a 1440kg car.

Now I'd be pretty unhappy to spend all that money and get 1/2 second off the quarter and pick up only about 11 k's! 42kW or so is a fairly small increase to be had from such a dramatic change to an engine - remembering that you've basically doubled the air pressure that the intake ports see.

I understand that AutoSpeed did not write the article in question, but putting '480hp BMW' on the cover and expecting your readers to swallow it is really a bit much. There are plenty of other magazines that are guilty of accepting owners/tuners stories without questioning, but I thought that you may have been a little more discerning than that! Anyway, good work usually - keep it coming.

Julian O'Hara
Australia

Missing Power

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I can't believe the "at wheels" lack of power of the 225kW CV8 Monaro ["Real Time Re-Mapping the Monaro CV8"]. Chad got 152kW at the wheels but pays Holden for 225kW! Chad, wouldn't you want to write to Alan Fels about getting 2/3rds of the power claimed? And 157kW is the power Ford claims for my Falcon 4 litre 6.

I think a story on dyno power at the wheels for a handful of our most common makes would be very interesting reading after seeing the Chip-Torque results from their state of the art dyno equipment. Please start with renting a 4.0 and a 5.6 Falcon and dyno them.

Shane Quinn
Australia

On a Dyno Dynamics machine all cars typically lose 20-30 per cent of the claimed flywheel power when it's measured at the wheels. Holden claim 225kW at the flywheel, not at the tyres. However, Chad's car did have a surprisingly low rear wheel power figure - but it was never going to be 225kW.

Turbo Boost

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Regarding the recent article titled SX Speed ["SX Speed"], can you please explain how replacing the restrictive 200SX exhaust system with a more free flowing system results in increased boost pressure? I understood the boost pressure on the 200SX to be ECU regulated via the wastegate control solenoid. If that's the case, I would have thought the boost pressure map would have primarily been a function of the ECU control rather than associated engine mods. What am I missing?

Congratulations on a great magazine. Well done!

Gary Saddington
Australia

The actual boost developed will depend on the behaviour of the intake, exhaust, and of course turbo wastegate control. Nissan would have programmed the boost control system with the exhaust and intake in place to take into account their affects; making the exhaust much more free-flowing than the factory system alters this relationship. A closed-loop boost control system with the ability to sufficiently learn would not alter in boost levels.

Grading the GT-R

I know that the article 'Grading the GT-R' ["Grading the GT-R"] is probably old but I just found your site and WOW. You need to change the name of your site to STiLovers.com because that is what you sound like. How can you even compare a STi to a GT-R, yes the GT-R is heavy but it has the balls to overcome that with ease. You say in the article "To give you a typical real-world comparison, a WRX shopping-trolley with simple exhaust and boost mods can easily bully this "performance benchmark"." What kind of drugs are you on. OK maybe a stock GT-R with my grandmother driving it will get beat by a WRX but give me a break. And as far as doing a second-gear 45-50km/h I have had a Lancer GSR and the ass end would get loose in that too.

P.S. 1000HP, I've never seen that in a STi.

Michael Piper
Japan

Moving the Airflow Meter

Today I read with interest the latest instalment on intake mods. I am planning some major mods to my intake system (88 Mazda 323GTX) this summer and have a question that might fit with Part 4 of your series. What are the pros/cons of moving the AFM from before the turbo to between the IC and the TB? Can it take the heat? Should the intake air temp sensor still be before the turbo? And finally, are the answers the same for either vane and hot-film AFMs? I'll be switching from the vane style to a hot-film (it's OK, I've already built the electronics to convert the signals) and was planning on mounting it just before the TB, but wasn't sure if it would be able to effectively heat the sensing film above "ambient" the turbo generates.

Thanks for considering my questions,

George Barrett
USA

Hmm, short answer to your questions is that we don't know. And the reason that we don't know is that we simply don't see a lot of point in doing as you suggest. The single advantage in positioning the airflow meter after the turbo is that you can crank up boost a little to take into account the flow losses through the airflow meter. But if you are already switching to a hot wire airflow meter with adequate flow, there will be very little pressure drop through it anyway. Given the potential bag of worms that might be revealed in making the airflow meter work with pressure, temperature and airflow characteristics (eg degree of turbulence) not envisaged by the manufacturer, we wouldn't bother making the location change.

Bending Plastic Pipe

Regarding your excellent well documented article 'Heavy Breather' ["Heavy Breather"].You might also want to include the addition of a concept that I have thought about.

Now this is fairly low tech but when considering the use of the heat gun you place an equivalent to the 60's/70's toy called the slinky (which is no more than a fairly loose steel spring coil) of the same inner diameter and insert it into the inner diameter of PVC that is to be heated and then slowly bent, the portion of the PVC furthest away from the bended joint is then packed with a rag to provide resistance for the spring/slinky to keep a taught rounded pipe/profile which will in turn help to retain the PVC diameter under heating/bending, then another rag is inserted at the other end to do the same.

Once the exact heating and bending are complete to required duct alignment allow to cool, then remove rags(or equiv material) used to provide spring resistance and your done and your tubing has retained its diameter while being bent with heat.

Not a big deal but just something that I thought about.

David Tobey
USA

Car Joy

Mr Edgar has said it all in this last week's 'From the Editor' ["From the Editor"]. Outright straight line is seen as very important, especially to my particular under 25 male age group. It seems that the most important things are how good it looks and how crazy it can be made to look and how quick it is down the quarter. My imported Gemini is no slug for a 20 year old car but it is one of the most fun cars I have ever driven. Its nothing on friends' late model RX7's and WRX's but taking through a bendy road or puttering around with the music going is one of the most rewarding things. Again Julian thankyou for saying what is constantly running through my head as I see thousands upon thousands of dollars spent on that killer engine rebuild thats gonna make a car do 10's.

Martin
Australia

Masterpiece

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Another masterpiece!! I just read your Polaroid Camera article ["Land and the SX-70"], what a treat to read stuff like that from someone else that obviously shares my enthusiasm for neat engineering. And yes, can we please have the article on the film transport mechanism.

Graham Allen
Australia

Glad you enjoyed that article... and we're sure that you'll be pleased with the major new sister title to AutoSpeed that we're now getting ready for launch.





Measuring Fuel Flow

You've got a great website with lots of auto-tech stuff, just what I like!

And now to my query- I'm doing research project on petrol fuel flow sensors on EFI engines. But haven't seen any cars where they not only measure the air flow or MAP, but also the fuel flow. Looked up a bunch of SAE tech papers but it just confirms what I know from looking at a lot of car engines - no one measures fuel flow (except the Oztrip Trip Computer, but that's another story!). Anyway, could you tell me why nobody checks the fuel flow to ensure the right ratio of fuel to get stoichiometric air/fuel mixtures?

Also, know any websites or other organisations which deal in this fuel flow control matter?

Andrew Chiak
Singapore

Direct fuel flow measurement in order that Brake Specific Fuel Consumption and (sometimes) air/fuel ratios can be ascertained is often done on engine dynos, but as you has indicated, never on production cars. Fuel flow sensors are available - RS Components, for example, sell one. However, in an EFI car with a return line, two sensors need to be used, with the flow reading of one subtracted from the other. We assume that taking this approach is simply too expensive on production cars.

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