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Frequently Asked Questions - Block/Pistons, Rods & Crankshaft
Effect of upgraded rod bolts and big-end bearings
Will increasing compression obtain extra performance?
Installing Steel Rods, torque or stretch?
Engine Running Rough after a track day
Effect of upgraded rod bolts and big-end bearings

Question: What revs is the engine good for with standard big-end bolts and bearings and with the upgraded ones?

Answer: As far as big end bearings and rod bolts are concerned, there are effectively two slightly different issues that you are overcoming by upgrading the rod bolts and the bearings.  Replacing the rod bolts adds strength to the rod construction by fitting a stronger bolt and we normally suggest a rev limit of 7750rpm when the stronger rod bolts are fitted (in combination with the bearing). 

The standard bearings are of a tin/aluminium construction and are very strong and hardwearing, designed to do potentially over 100,000 miles.  The issue with these bearings is that when used in a high stress application, there is potentially a chance of oil film breakdown and the bearing of the con rod touching the crankshaft.  When this happens with a tin/aluminium bearing, it is most likely that the high friction will cause the bearing to spin, this can occur in a split second causing catastrophic engine failure.  The uprated bearing has a softer surface and if this issue occurs, the friction will not be as great and potentially only remove a small amount of bearing material, thereby saving the engine.  

Important Note: The fact that you have achieved bearing to crankshaft contact would also be an indication that your engine is having an oil supply issue.  The fact that the high specification bearing gives you additional protect does not mean that it is safe to continue on with this problem as failure with occur much later due to the additional protect of the bearing quality.  In order to know that you having been having oil pressure issues, it is recommended that you have a minimum of an oil pressure gauge, which will give an indication that there is fluctuations in oil pressure. 

So therefore you need to have a combination of the two for increased strength and increased reliability.

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Will increasing compression obtain extra performance?

Question: If I increased the compression to from standard to 12:1, how much more power would you expect to be produced at sea level and at altitude with no other changes to cams etc, but just re-tuning the ECU?

Answer: I understand what you are asking about the compression. There are many things that control the maximum power of each specific engine and the compression ratio chosen by the manufacturer is based on a range of important factors, the efficiency of the engine, cam duration and the expected fuel type to be used. All of these as you can imagine vary throughout the world, but the Duratec engine being of a reasonably modern design is quite efficient and runs high compression than a similar design of engine of say 10 years previous. In order to determine what would be the best result possible by changing compression could only be done by testing on the dyno and involve expensive complex tests. But from experience from what we have done from manufacturers in the past, in most cases the gains were very small if any, are seen particularly from the extra work you are having to do and go through to achieve it.

For example as the cam duration increases, the valves shut later in the cycle e.g. the piston is further up the bore before the valves begin to shut, so the effective compression ratio is actually reducing because of this. So the static compression needs to be increased to optimize the squeezed fuel/air mix.

If the compression were too low, the engine would quite often begin to produce its power later in the rpm range and become less efficient at low to mid range torque and only lose top end performance in our experience if the compression is way too low. If the compression is too high, ignition needs to be reduced.

If the compression gets excessively high you may find the ignition has to be reduced by so much that performance begins to get lost because of this. There is quite a large amount of initial mass required to work out what may be the optimum and then the final result can only be tested on the dyno.

But I would suggest that changes to the internals of the engine at the level you are currently looking at, it is not worth increasing the compression. It is only once the cam profiles have changed, that increasing the compression should be considered at that time. Each of the kits we have developed have been extensively tested before release, at which point we can recommend the compression to suit each package.

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Installing Steel Rods, torque or stretch?

Question: I cannot source the correct ARP Assembly lubricant required to tighten the rod bolts. I have been in touch with ARP who tell me that they have not used the specified 100-9902 Assembly lubricant for 5 years and don't know where I can get it in the UK. They now use the same one that you sell but say that the torque figures will be different for this lubricant.

Will using a stretch gauge negate the requirement to use the specified assembly fluid?

Answer: ARP changed their lubricant to suit many of the cheaper Chinese rods, where the thread quality is particularly poor. It has meant that the torque settings have had to increase with this new lubricant. Because ARP only supply the lubricant in the blue sachets (new spec), our instruction sheets state the torque settings for this lubricant and there is a picture so they cannot be mixed up. The earlier lubricant is certainly better in our opinion and we can normally source this lubricant. It is always better to use the correct type of lubricant rather than just oil.

You are correct in stating that stretch is the best way to get the bolt to the correct length. When doing a torque setting for a bolt, the way this is worked out is to take a bolt, lubricate it with the type of lubricant you are intending on using, slowly tightening the bolt until the desired stretch is reached. Then recording the torque setting used to reach this stretch. This is a fairly accurate way to achieve the correct stretch. But obviously the best way to get the bolt to the correct length is by measuring it, so a stretch gauge is always the correct way to do it and use the best lubricant. We always use stretch gauges here, but we understand why customers may not wish to spend out on a stretch gauge.

If you would like to purchase a stretch gauge we will supply it with the most suitable lubricant, that way you will know everything is correctly tightened. I have attached a quote to give you a cost for the gauge.

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Engine Running Rough
Question: I went to a track day, the car was running a bit rough, but naively I put that down to the mapping being a bit out. I could not fix the noise issue so ended up bringing the car home - it was good to get the car running though, shame I could not run longer as the track was just starting to dry out.

Anyway - on inspection yesterday, the rough running was down to the injector wires for cylinders 3 and 4 being on the wrong injectors - not sure how this happened but the upshot is that, having run the car for a few laps like this, I think I may have knackered the pistons on these 2 cylinders - I will confirm for sure this coming weekend. Symptoms are very poor idle, removing ignition to these 2 cylinders does not make the idle any worse, swapping coils and plugs with cylinders 1 and 2 makes no difference (removing coils from 1 and 2 stalls the car), wet plugs, and colder exhaust manifold on cylinders 3 & 4, difficulty revving, would also explain why everyone was faster than me!

I know that if I am taking the engine apart to put in new pistons in I should probably upgrade everything, but at this stage I am keen to get the car running without spending a load more cash.

Replied on the phone: We received this email from one of our customers, you can see that he was obviously worried that he had a major problem. Since I hadn't see the vehicle that long ago, I knew that it was unlikely to be anything serious but it is quite often that a very small problem can lead the owner to think the worse.

I spoke to the customer on the phone and said from what he had described in the email, it sounded like a simple question that the butterflies had potentially closed down or gone out of sync, this lets in less air at tickover and means that the engine runs richer on the cylinder or cylinders where this has happened. This causes the spark plug to soot up and even if the spark plug is removed and cleaned when tested outside the cylinder e.g. laying on top of the engine will get a good spark. Unfortunately when the spark plug is placed back into the cylinder again, the pressure created within the cylinder increases the resistance and the spark inside of jumping the gap tracks down the side of the plug. The process that the spark plug has gone through when it has been playing up quite often prevents the spark plug from recovering. If the spark plugs are replaced with a brand new set, check that all butterflies are synchronised and that the correct kgs of air per hour is going into each cylinder correctly and that the TPS sensor voltage is correctly set up. This will normally rectify most problems.

His worry that the injectors plugged in incorrectly could have caused some damage, this would not be the case as the fuel being supplied was the same to all cylinders.

Obviously you can see from his final email, his problems are now solved and everything is running perfectly. This is a mistake that is regularly made by customers with engines that are perfectly programmed and then take them to a rolling road and end up spending large sums of money having the engines reprogrammed to rectify a fault which had nothing to do with the programming. Simply a small issue with the throttle butterflies going out of sync causing a rich mixture which gives very sooty plugs, when all that was required was accurate resetting of the butterflies.

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Please check our customer cars section which may help answer your questions
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