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Individual Cylinder Tuning

I would like to invite your attention to the following:

SAE paper 890044 Saab Direct Ignition system and its cold start performance.

SAE paper 950004 Ion-Gap Sense in Misfire Detection Knock and Engine Control

Ion-gap sensing for engine control SAE magazine Automotive Engineering /Sept 1995

SAE paper 982476 Knock Suppression in a Turbocharged SI Engine by Using Cooled EGR SAE paper 2001-01-0992 Employing an ionization sensor for combustion diagnostics in a lean burn natural gas engine

Investigating GM's Compression Sense Ignition "Motor" magazine november 2004 - Bosch ME engine management system

Bentley Saab 900 "Official Service Manual" ISBN 0-8376-0313-7 6/1993 PAGE 340-2

EZK Knock Sensor Operation and Ignition Timing: ".....The timing can vary from 5deg to 22deg BTDC in response to engine speed, engine load, or detonation. If engine knocking occurs, the ECU determines which cylinder(s) are knocking and retards just eh affected cylinder by 3deg....."

Spark-Advance Control by Ion-Sensing and Interpretation

David Calabrese ME

United States

Fiat Nomenclature

Guys, I have just noticed an error in Michael Knowling's June 2000 article on Rigoli's modified Fiat 124 Coupe. The article states:"And the later AC model - like the one photographed here – is arguably the cleanest shape of all 124s, thanks to its totally revised nose cone..." In fact the AC version of the 124 Coupe is the first incarnation of this model (1967-69), followed by the later BC (1970-72) and CC versions (1973-75), each one arguably less attractive than its predecessor, although engine size and power also increased with each successive version.

Mark Northage

Thanks – fixed.

In-Line BOV

Thought you guys might find this interesting Company is I also make CNC billet turbo manifolds which you might get a kick out of. There are videos of those on youtube too. Love your site! Lots of good grassroots stuff.

Leen Steed

Trans Coolers 1

In regards to the article Cooling the Trans

I have had a similar situation and think that I have something to add. My modified 2002 forester had trans cooler fitted. When we fitted the modified valve body we also braised a temp sensor into the pan of the trans. I found that running just a trans cooler and not running through the radiator saw the hottest temps of all. In fact I even saw the trans temp go over 110 degrees on a hot day while stationary at traffic lights after a long highway run.

With quite a bit of fiddling I found that running the trans cooler (from a V8 VP commodore) in conjunction with the radiator gave the gest results. On most trips and around town the trans temps would never go over about 96 degrees, even sitting at traffic lights after a long hard run.

Having the trans cooler gave on average about a 10 degree drop in trans temps (cruising) compared to just using the radiator but there was very little difference between having the cooler before and after the radiator.

Hope this is of interest to you.

Brent Muldoon

Trans Coolers 2

RE: Cooling the trans - teamed with an appropriate oil filter adapter, would those air con heat exchangers be suitable for use as engine oil coolers as well?

Andrew Rodrigues


Not sure – pressure shouldn’t be a problem but flow might be.

Small Turbo Engines for Economy 1

Comments:"Turbo'd for Fuel Economy". You will not be surprised to hear that VW indeed make a smaller version of the TSI turbo engines. There are 1.4L versions in various states of tune that easily slot into the Golf range in Europe. One version gives a quite adequate 90kW and 200Nm (1500-3500rpm). Apparently there is a 6% improvement in economy over the naturally aspirated 1.6L it replaces not to mention a 30% increase in maximum torque.


Small Turbo Engines for Economy 2

If you were talking about Golf's I would have thought the obvious car to include in the comparison would be the Golf GT. But would the fact that it required not just a turbo to get the power up to 2 litre NA levels but also a supercharger to get the low end torque have destroyed the premise of the story, that you can make a small engine with a turbo feel like a big engine? The problem with that premise is the low end of the rev range where a small engine with a big turbo on it isn't going to be responsive. If you're adding the mass and cost and complexity of a turbo, and you can't go to a lot smaller engine, like the 1.4 in the Golf GT, it suggests the whole idea isn't very viable. Of course its different on a diesel because it doesn't have to spool the turbo up when you press the accelerator.

Gordon Drennan

The 1.8 litre turbo engine has far more torque (and so power) at the bottom end than the 2 litre naturally aspirated engine. As the above letter writer points out, even the 1.4 litre FSI turbo develops far more torque (and so power) at the bottom end than the 2 litre naturally aspirated engine. Who said anything about small engines with big turbos? Not us! In fact, clearly these are small engines with small turbos. On the 2-litre turbo there is simply no detectable on-road turbo lag. Also, the idea that it’s different on a diesel "because the turbo doesn’t have to spool up" is completely wrong. A diesel turbo has to spool up just like a petrol engine turbo – the off-boost exhaust flow is not sufficient to develop full intake manifold boost. In fact, many current passenger car turbo diesels have more turbo lag than petrol turbos.

Small Turbo Engines for Economy 3

Your "Turbo'd for Fuel Economy" was an interesting article, but I feel there should be some clarification on some facts. The energy required to drive a turbine wheel shouldn’t be referred to as "free energy". Exhaust gas speed required to spin a turbine wheel to speeds high enough so the compressor wheel can actually pump more air than the engine can use (generate boost pressure), is substantially (3-4 times) higher than most normally aspirated engines exhaust gas speed through the exhaust manifold. This can only be achieved by restricting the flow though the turbine housing. This flow restriction then causes higher pumping losses on the exhaust stroke. Perhaps referring to it as better utilization of unused energy would be more appropriate?

Secondly, all the examples given were of engines with long stroke/small bores. The same application on a bigger bore/shorter stroke engine probably wouldn’t give the same low RPM torque results. I just feel that this should have been mentioned as a contributory factor.

Nice article.

Howard Hartman


We take the point that pumping losses increase when the engine is turbocharged. However, the relationship between bore/stroke and developed torque is more problematic. An engine with a long stoke and small bore also has less developed force on the piston...

Small Turbo Engines for Economy 4

Click for larger image

I think you need to put the two power/torque graphs on the same axes to get a real appreciation of the difference.


LED Lighting 1

I was very interested in your first article on LED front lighting systems for bikes. A friend of mine has modified a couple of standard front bike lights by inserting 5W LEDs in place of filament bulbs. I have powered these using a bottle dynamo, but another friend of mine uses a front hub dynamo on his bike. The LEDs seem to draw less power somehow than filament bulbs, such that a standard 6V/3W generator can satisfactorily power 5-6W of LEDs.

I'm surprised such lights are not more widely available from cycle lighting manufacturers. The battery-powered variety are common enough, but pricy, while there are hardly any dynamo-powered LED front lights available. Coupled with a hub dynamo this gives a robust, battery-free system which creates little drag, is always ready for use and is bright enough for riding unlit roads at night.

Ben Garside
United Kingdom

You need to be very careful with dynamo-run LED lights that the current rating of the LED is not exceeded – current limiting is needed or high road speeds will result in a damaged LED! But we agree that dynamo-powered LED lighting should be more widely available.

LED Lighting 2

Having access to many excellent Mtn biking venues in the ACT i have become an avid night rider. I was just wondering why you didn't use the more efficient cree style LEDs for your light and if you did, do you think you could get the thing down to a helmet wear practical size with the same light output?

There are already commercial options out there using the cree and they are pretty good, but also pretty pricey. A good follow up project perhaps?


The headlight project has evolved over a number of years; when the project began we don’t think Cree LEDs were available. That said, the major performance outcome of the headlight is governed not so much by the brightness of the LED but by the collimator and external focusing optics. For this reason we can’t see such a headlight becoming helmet wearable in the near future.

Tuning Diesels

My brother and I are about to start a small hobby tuning business (weekends only as we both work) for 306 Td's and Hdi's.
We recently went for a dyno again, my car with my own remap file from scratch, made 195lbft and 119bhp.
There is more to come, but not much, my AFR's were up around 16 and then 17 ish past 3000rpm, but the non-intercooled 306Hdi means I can't go too far as intake air temps rise with more EGT, and the associated small increase in boosting.
An intercooler is the next job, and then I'll be trying to find a cheap EGT measuring solution, then I can push up the fuelling. 140bhp and 240lbft seem easily and reliably achievable.
My brothers Td, quite amazingly, made 131bhp and 200lbft.

More interestingly, the peak torque is at 2500rpm, the peak power at about 4000rpm, but it has over 125bhp from 3500rpm to 4800rpm, a really wide range of power.
His AFR's were less impressive low-down, hovering around 14.5 through 1000-2000rpm, but that helped the turbo spin up, no boost spike (a manual boost controller may see peak torque rise and come down the rpm range further!), and then a solid 15:1 right through with a wiff of smoke. The Bosch boost compensator does it's job perfectly!
He has made some modifications to the Bosch pump that we were toying with doing back five years ago on our 405 Td's, which appears to have worked well, along with opening up the max rev potential.
He has several spare engines, turbo's and pumps, and can swap an engine in about half a day, so I think the current idea is to see how long it lasts.
The current general spec is.

Stock intake but with K&N panel filter.
GT15 turbo (late 306 Td), boosting to around 1.3-1.4 bar by 2000rpm, and holding that boost to around 4000rpm where it falls a little (don't have the reference with me, sorry)
Decat pipe, and Powerflow stainless steel exhaust from a 306 2.0 16v S16/GTi6.
Bosch pump fitted (was Lucas)
The usual mods to fuelling screws, along with a few specials inside.
I'm not sure on his economy, he doesn't check, he has a temp sensor on the intercooler > intake manifold union (post intercooler), and they stay down under 40degC at this time of year even under very hard use. They only rise significantly when you stop the car running totally. I believe as noted in a past article here, the intercooler is an interwarmer at idle, so if you sit still but with the engine running it's better for the top-mounted intercooler than switching off it seems.
All good fun, I will keep you updated in the future if you wish, or maybe just send a link to our website, where we will keep all our little tests and latest ideas and experiment write ups!

David Crabtree
United Kingdom


simple, clear english for non rev head people, explaining what i need to know, think about and consider before i add something to my car. just excellent. i wanted to know about cold air intakes and, lo and behold, it's all here. excellent site. concise and informative. well done


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