interesting turbo engine build

[turbotim3]

Well guys, Thanks for your comments, I have taken it all on board. I have today received my inlet back, its been crackle blacked and looks great. I am going to get the engine back together over the weekend and hopefully on the dyno for next weekend. I'm going to start by mapping it on the Garrett Stage 5 turbo and see if altering the cross-over pipe as helped things. I would like to see 30 psi, but if the back pressure is to high I'll have to tail the boost off. I also have the loan of a gt35 which if I have time I may pop on.

Thanks again for the comments and I hope to meet you all sometime, when I get the car done.

Cheers Tim

 

[George Elliott]

Tim,
can you comment on the bore stroke ratio of your engine. I was advised the 100mm bore of the std 2.5 was better with the 3.0 crank stroke as regards the B/S ratio (which provides a 2.8L capacity). The assumption would have been an 8v head. May be that is then correct?

You have gone the opposite route with 104mm bore and 2.5L short stroke crank. Perhaps the improved breathing of a 16v head is the enabler for this.....?

Not sure if you are aware, but there are cars in the states with offset ground 3.0L long stroke cranks which are offset ground to increase the stroke! They run Mitsubishi rods, increased bores (sleeved) and have enormous swept volumes of about 3400cc I think.

Interested in your comments as I have no expertise of the subject, but a great interest

Thanks
George
944t

 

[turbotim3]

No problem George. The bore of mine is 104mm and the stroke is 78.9mm which gives you a ratio of 1.32. The rods are 150mm long so as a rod ratio of 1.9. The higher the rod ratio the less rod angle you have, so less force on the bore wall when the piston is pushed up. This makes my engine ideal for revving. I would confidently take it to 9000 but for one thing and that is the crank driven oil pump, which I have been told cavitates and can causes oil pressure problems at high revs. We tuck the engine to 8000 on the dyno and it sounded like it was on holiday and still had 640hp.

Tim

 

[George Elliott]

Is the shorter piston travel at a given rpm of greater or less benefit than the increased rod angle. I am thinking the slower travelling pistons in a short stroke engine at a given rpm means the rods have an easier time?

As you opted for a short stroke, I am guessing that rod angle is not a massive issue in your opinion. (subject to correct warm up routine and oils)

Also, you removed the balance shafts and then talk about 8 and even 9k rpm on a 2.7L four cylinder........

....on holiday...!

apologies for all the questions.

George
944t

 

[TTM]

As far as I understand engine basics, less stroke means pistons decelerate harder when nearing TDC and spend less time there, which means using more ignition timing before TDC.

Tim said he went short stroke indeed to reduce the rod ratio, or rod angle as you call it.

Where things remain a bit hazy to me is whether increasing bore should allow increasing ignition timing further, all other things being equal.

Tim, would you mind telling us how much ignition timing you are running at peak torque?

 

[333pg333]

ORIGINAL: TTM



Tim, would you mind telling us how much ignition timing you are running at peak torque?

[]

 

[944 man]

The dyno figures (676bhp!) are extremely impressive, but what sort of power will the engine be able to reliably make when its fitted into the car?

 

[turbotim3]

ORIGINAL: George Elliott

Is the shorter piston travel at a given rpm of greater or less benefit than the increased rod angle. I am thinking the slower travelling pistons in a short stroke engine at a given rpm means the rods have an easier time?

As you opted for a short stroke, I am guessing that rod angle is not a massive issue in your opinion. (subject to correct warm up routine and oils)

Also, you removed the balance shafts and then talk about 8 and even 9k rpm on a 2.7L four cylinder........

....on holiday...!

apologies for all the questions.

George
944t

Hi George, The fact that I have gone for a short stroke crank means I have reduced the rod angle not increased it. I suppose reduced piston travel and speed will help with stress on the crank, bearings, conrods and bore walls.

Cheers Tim

 

[turbotim3]

ORIGINAL: TTM

As far as I understand engine basics, less stroke means pistons decelerate harder when nearing TDC and spend less time there, which means using more ignition timing before TDC.

Tim said he went short stroke indeed to reduce the rod ratio, or rod angle as you call it.

Where things remain a bit hazy to me is whether increasing bore should allow increasing ignition timing further, all other things being equal.

Tim, would you mind telling us how much ignition timing you are running at peak torque?

Hi TTM, I must say mate that it all gets a little confusing when you start reading about stroke, rod angle, piston speed, bore size, flame front burn time to ignition timing etc, but it all boils down to trial and error and and at 7500rpm 28psi of boost and 675bhp on the monitor its hard to add a couple of degrees to see if it will be ok. I think you are right about more ignition for bore size, I'm sure I read it somewhere but doing it is another story when your engine is at risk of melt down.

I'll tell you timing figures when its finished, if that's ok I want to tell you right not guess.

Cheers Tim

 

[TTM]

Thanks Tim. I will be happy with temporary value too, my engine is always more or less undergoing different tunes so i know all too well what you mean.

Looking forward to hearing of your progress!

 

[turbotim3]

I got my manifold back in the week after being crackle black, so I have been in to work today and fitted it back on the engine. Here are some pictures of the manifold and the turbo in its finished position.





This one shows inside the manifold and how I have made the trumpet part of the back plate.

















Hopefully back on dyno for next weekend.

 

[TTM]

Nice... Are you using a vaccum line from the turbo mount to the oil fill tube?

 

[turbotim3]

ORIGINAL: TTM

Nice... Are you using a vaccum line from the turbo mount to the oil fill tube?

Not quite sure what you mean

 

[TTM]

Do you have any vacuum line in between the oil feed line to the turbo and the oil return line to the sump?

 

[turbotim3]

ORIGINAL: TTM

Do you have any vacuum line in between the oil feed line to the turbo and the oil return line to the sump?

No. Just oil return pipe to sump and oil feed from filter housing

 

[George Elliott]

Thanks for the comments TT3, I am amazed at the boost figures you work with, can't wait to see it turning wheels.

You will produce a step change in 944 turbo tuning if you get that working reliably.

hope the foot is recovering well

george
944t

 

[nick_968]

Worth noting as I read back through the spec is that this engine is fairly low compression for a 16v. With the 16v head as opposed to the 8v, it is much more efficient and resistant to detonation. Running this engine at 8.2:1 compression is probably similar to running an 8v at 7.2:1 compression in terms of det resistance. Assuming I have read things correctly this does allow a much higher boost threshold and should aid with some of the problems associated with running such high boost levels on an 8v engine.

This low comp 2.7 big bore 16v setup is a great move and makes a lot of sense to me now I have read and understood it all, especially in the context of the learning curve I have been through with my own engine. With the right modifications to the air, oil & water cooling system and assuming a free flowing exhaust this setup should run and prove reliable.

The drivetrain may still prove to be the weakest link but only testing will show the true impact. The driveshafts & bolts will certainly need to be monitored closely as these are a known weakness on high power cars, albeit more of an issue on track cars that are lowered running on UK tracks with mostly right turns!

This thread has turned into one of the most interesting to follow threads for me in a long time, cant wait for the next installment