Go forged

Hi all,

My coop is eating 1lt oil for about 3 or 4 thousand kms so I went and checked engine compression. The result shows 2 cylinders with less compression than the other 3 (which I assume is from the effort for those 2 to accomplish the "easier" work from the other 3), so I'm planning a nearby rebuild, even if the it shows 3 bar when cruising, 2 bar when standing (hot), and 1,5 when standing (hotter as it can be).

For the obvious reason, I'm planning to go forged, even if I don't have the money to invest in larger turbos and fmics at this time.
The original turbo is running strong and keeping boost even in higher gears and revs and stalls just a little in those circumstances so I think it's capable of doing many more kms.

I've seen that many mantes are using different kinds and makes of forged internals, so the 2 questions I have are:

- What is the best option to simply swap pistons and rods for forged bits without messing around too much?

- What are the pros and cons of lightened and polished flywheels?

Thanks in advance

What were your compression results and what kind of power are you planning on running in the future?

You also have to see what state your bores are in to decide whether you can have the standard size 82mm pistons.

Well... It was a friend of mine that did the test and he simply told me that 2 of the 5 cylinders were around 65% and the other 3 about 75.

I was planning to run a gt2871 in the future, so about 360hp.

I assume that only after opening it the mechanics can say about boring right?

The ammount of oil that you are using is not too bad at all...I would leave it until it gets very bad.

Personally I would go for 83mm pistons, which would require the block to be re-bored - then you know the block is also sorted. Accralite and CP seem to be popular manufacturers

You can also choose a compression ratio depending on how you want the car to drive - most seem to think 9:1 works well on a 20VT.

For 360 bhp you will not need forged rods, though you will notice that the engine feels smoother if you run them as they are balanced and lighter than the standard rods.

You will also need to consider the condition of the crank + shells and replace this if it looks worn.

A lightened flywheel means the engine feels more 'revvy' though personally I dont feel that it make too much difference.

Dont forget that if you are going for 360 bhp there are a lot of other modifications to consider rather than / as well as forged internals - a forged engine does not mean that it is indestructible.

Yes, only way to be sure is opening it up. If they have an engineering endoscope you can get a good idea tho without opening

I was thinking simpler mods would do it, like fmic and sip, and the needed v-band and downpipe plus live map. Any more than these?

clutch, fuel pump, full exhaust, standard injectors with 4 bar fuel pressure will be pushed to the limit, not to mention the internals of the engine depending on the boost you want to run. That is before you look at handling...

You could get there, but be prepared for the engine to let go...it could last 5,000 miles or 50,000, but I dont think anyone has got more life out of a highly tuned engine on standard internals (350bhp+)

Yes, I've forgot those.

Nevertheless, I'm not in the mood for a full exhaust. I hate the noise and want to keep the coop's exterior as original as possible.

Forgot the clutch because I'm replacing it very soon so it was already on my plans. I don't know if a gt2871 will put out about 350/360bhp with 1.2bar but that was the boost I was planning to use.

I'm also using billies/eibach, powerflex bushes, and upper strutbrace. Planning to update to osravs and get eibach ARBs. Running 3g grooved with blue pagids already so the handling department I think is sorted out for that kind of power (but willing to ear your input on that also, as you kindly did on the engine tweeks).

Sorry if I didn't understood your last statement. Are you saying that the engine will not last even if modded right?

On standard internals at 360 bhp you have to be prepared for the engine to fail, and certainly have a shorter life than it would on a standard car. the likelyhood of failure at 1.2 bar of boost is less, but it is still there...

It is a complete waste to run a big GT series turbo on a small exhaust, as it will not flow well, you may also see the the EGT go a lot higher than with a free flowing system.

"1lt oil for about 3 or 4 thousand kms"

That is fantastic. The manual says 1 litre per 1000 miles (1600 km) is within range.

"It is a complete waste to run a big GT series turbo on a small exhaust, as it will not flow well, you may also see the the EGT go a lot higher than with a free flowing system."

Hi suba, whilst I bow to your superior knowledge of tuning coupes, I think your comment is a little too wide sweeping. I have an RSR turbo with standard dp plus quite free exhaust (decat/sports muffler) and the car is very quick and smooth, but FC custom map made all the difference.

Sure, I'm nowhere near 360 (c.300) but its very flexible throughout the revs and hopefully good longevity for the standard engine internals. No idea whether it would run equally as well with a lower powered turbo, but this is a great combination if set up correctly. :-)

Sure, but with all the supporting mods in place and a good 3 inch full system you would be running 350bhp at 1.3-1.4 bar or so.

Your RSR is a comparetively small turbo - it becomes more critical as you go from a bigger one, as the engine can only flow as well as the weakest link. Once the engine is flowing nicely you will make power using less boost....which in turn helps with safety.

My 20vt made the same power at 0.9 bar of boost with a full 3 inch system than a 3 inch downpipe with a V-band, then a 2.25 supersprint mid + rear box and 1.4 bar - the head had been ported, which accounts for some of the extra flow, the exhaust was clearly a restriction though. This was on a meager GT2560R 0.64 housing (the RSR has a bigger compressor wheel)- the difference would have been more on a bigger turbo.

Sure, but lets not forget that I'm planning those figures after swapping internals for forget bits. I assume that it will be safe then, right?

So if I'm not choosing the right turbo, what do you suggest to make around 350 with a healthy engine safety margin?

As I have said allready - for 350 bhp the standard rods will be fine. it's perfectly possible to kill forged pistons, they are just stronger than standard ones, and the rings can take more boost. Whether you kill pistons will depend on how the car is mapped rather than your choice of turbo, i.e if the fueling system can't supply enough fuel to match the boost level /air supplied by the turbo. Forged rods and decent rod bolts are required dependant on the torque your engine is producing (if you raise the rev limit then there is also more stress on the rod bolts when you lift at high rpm's...) The general limit on the standard rods and bolts is 350 lbs /ft and 7,300 rpm (though this should be considered a guide only)

Exhaust gas temperature also is a factor, though mostly on cars running 400bhp+ - if you have a restrictive exhaust manifold or a peashooter exhaust then in cylinder temps can get over 900 degrees, which will then burn out an exhaust valve etc.

I would speak to flea on here about mapping and turbo choice for what you want from the car, just make sure that you research what spec you want to build, slapping a big turbo on, winding up the boost, and hopeing for the best will end up in a big oily mess.

I would go with a GT28RSR if I were you, you'd have more lag with the GT2871.

It's safer for the engine to have more midrange boost and tail off at the top than a massive turbo which starts flowing huge amounts of air at high revs.

Suba is spot on with what he is saying here, for those power figures a much larger exhaust is a must even with a RSR I would say it's a must

Addict what EGT temps are you getting now the car has been mapped?

Tricky, how is Addict going know what EGTs he has? Unlesss I tap every exhaust manifold??!

You don't need to know EGTs, they are useful to tune with no doubt but not for the reasons of stopping them going too high.

Hi Flea,

As suba suggested, can you give some tips about best choices when I start to rebuild my engine? It's starting to have low level compression so I'm putting some money aside to repair it.

I was telling that I was going to put some forged internals (pistons and rods) and save for a turbo swap later on.

I know that some mates are running 350/360bhp with 1.4/1.5 bar but I wanted to achieve around that with low boost to prolongate engine's life.

What do you suggest?

I dont think that it is a must - but it certainly would help you to make the most out of a roller bearing setup.

On a 300bhp car I dont think that the EGT's will be a factor unless you are pushing the car hard for long periods of time, i.e. trackdays. But on a big boost, big turbo 2lr car you want to do all that you can to keep them at manageable levels.

I was asking in the small possbilty that they were measured is all, if not then fine but I bet they are very high

as far as I can tell they run rather high EGT's as it is possibly down to the manifold design?

When TurboJ changed his exhaust from a larger than standard to a 3 inch system there was a massive difference, something like 50 bhp, Jason will no doubt be along with the specifics

Its not so simple though is it? If I put on a larger DP and exhaust to maximise my RSR, then I need to spend money to upgrade the fuelling and more.

For me, I think I have good supporting mods for my 300bhp, but the OP obviously wants to go further.

Actually addict I would say it is that simple by running a larger exhaust you can still run 300bhp if you like but with the larger exhaust you will be putting less stress in the form of heat on the turbo, exhaust valves and other associated parts that are affected by high EGT's, it just makes for a more reliable setup

obviously it's difficult to say at what point you need a larger exhaust to help combat high EGT's but I would if your getting consistently above 850 degrees then it's an area that you need to look into

Back on track if you don't mind

What are the best turbo options for around 350bhp after my forged internals then?

Ideally I would be looking to achieve that power with lower boost as possible and good fuel economy (I remember one of the moderators - Nigel IIRC - that posted is findings on better fuel economy on larger turbos?)

GT28RS with 0.86 turbine housing should see you in the 350hp range.

A bigger option would be the GT2871R with 0.64 turbine housing which might have potential for higher than 350hp depending on the final setup.

This might help as well, quoted from the 20VT Tuning Workshop Thread by TurboJ



Good luck with the choice

Reading this post is making me a little unsettled
I have a gt2871r with the larger housing run on standard insides, and it hasnt gone pop....yet!
Flea showed that it can be done,386 bhp at just a small amount of boost, however as everyone has explained previously, you are running a risk.

Good luck with the choice

Are you achieving almost 400bhp with what boost if I may ask?

it made 396 and 330lbft at 1.4 bar

Ben

What do you mean?

Power is torque. (with revs added into the equation)

If you have too much midrange torque you will break the engine, but there are plenty of other ways, most of them involving high revs...

Agreed - a very bland statement from Benny with no explanation offered.

Ben

OK - but why have engines failed at those levels? You can't just make sweeping statements, and there are a lot of factors to consider.

But is it that 330lb/ft at 4500 rpm that kills the engine, or is it the fact that they run lots of boost to get that, which the boost controller hangs onto as much of as it can right upto the redline? I would be happy to run loads of boost if it tailed off quickly. Loads of torque, less power up top, safer engine IMHO.

330lb/ft is seen to be the general limit of the rods.

I tell you what i wont bother to express my veiws .



Ben

Power and torque are just results, not causes. If you can find a way of getting more than that without too much heat / stress / pressure etc on the internal parts then great!

Like suba says, you've got to take into account all the many variables to know whether it's safe or not.

What I'm trying to say is, I dont think you should rely on what the rolling road says your car is making to judge whether the mods you've installed are safe or not.

Nothing untrue in what Benny was saying - too much torque will bend standard rods, regardless of how much boost is being used to produce the torque. The safe limit is estimated to be around 330lb-ft - some engines will take more. Mine bent at around 350lb-ft.

However, there's some truth in the other statements too - you can kill an engine with too much fuel, too little fuel, too much back-pressure, too much heat, detonation, and lots of other things too (although to date, I still reckon the biggest killer is lack of oil - totally avoidable)

Forged pistons and forged rods is ALWAYS a smart move regardless of how much power you have. If you can't afford to do anything else do this, it sets a strong foundation, tuning parts to follow can be easily replaced but the bottom end is your roots. If you’re going to rebuild the engine do it once and do it properly.

Turbo choice will be completely up to you. Everyone is going to have their personal preference even cars with the same turbo behave different so there is NO right or wrong choice. You have to pick one in the powerband you want and see how it suits your setup then make any changes from there.