1914 turbo bug

[bazibbo]

This started out as a post about a few issues I was having, but quickly turned into a build thread. Nearly all the initial problems came from a single issue, a hidden exhaust leak that gave us incorrect lamda readings, that became apparent 6 months into the build..... enjoy



Well after a sad end to the year (2011), where I managed to kill my 1914 turbo bug all of 3 miles up the road from being set up on a rolling road..... I'm gonna check things pretty carefully.

Can you take a look at this map and let me know if there's anything obviously wrong please.





A bit of background...

I only got the turbo itch about a year ago and I started off with a standard 1600 and slowly built it up, based on a cb performance hideaway header, a massively oversized t3 turbo, a restricted 009 dissy and Renault 5 turbo carb and fuel system. It was fun but a hopeless drive.. No boost until about 2 seconds before I needed to change gear... Horrible.

So I'd managed to sort all the basic turbo plumbing out and just needed to sort a decent engine and that's where we are now, I got the engine in place and run in, and then as we started too apply a bit of boost... KaPow... read on

The engine went pop after 500 miles of careful run in, after a final set up on a rolling road. In the few miles I drove it, it was detonating just as boost started to come in, and on a light throttle, though it was a few weeks ago and i didn't have time to take note before it died. It hickuped and started to lose power, then ran on badly as I stopped at a petrol station before starting to run on 3 cylinders by the time I arrived home, about 12 miles from the rolling road. The engine is coming out shortly but I'm expecting burnt valve or piston damage.

Its a pretty low spec 1914, 8.57:1 compression and was properly built, as opposed to being thrown together by me.

I'm running a CB hideaway header, a T3 turbo and a group A Renault 5 carb. The ignition is a DTA S40 ignition with a VW speedshop crank driven ignition setup and a MAP sensor. CB wastegate and running at around 5 or 6 psi.

My biggest fears are that although I thought I'd done everything by the book, the motor was detonating badly and I can't afford to break it again.

Any thoughts appreciated.

thanks, Barrie

[miniman82]

First impression: detonation=lean mixture, do you have a wideband? If not, strike 1. Detonation can also=overly advanced timing, but looking at your timing map it's obvious whoever set it up had no clue what they were doing. What rolling road was this, and did the operator have any clue how VW engines react to boost? The 100 kpa line looks OK and so does everything to the left of it, but at only 110 kpa you've lost 10* of timing already? At 7 PSI you're at 15*? Really? That's 2.1 degrees per lb of boost pressure you're losing. That thing had to be a soggy runner on boost, it was practically begging for more timing. FYI, my 1915 is at 22* timing at 12 PSI. There's no way it needs that much retard, unless they were trying to cure the pinging issue (which in reality is probably a fuel issue) with timing.

Sorry, but that's the cold truth. I have no experience with the carb you're using, though I do know about the R5. I suspect it's not giving you enough fuel, let's remember that the R5 was only a 1.4 liter engine and you have a 1.9L. The fuel requirements are going to be different, have you done any jet changing?

[MarioVelotta]

I agree with mini, with the timing so retarded in boost you are creating lots of unwanted heat in the engine for no reason.

[bazibbo]

ta guys.

The car spent some time on the rolling road and I know they were checking fuel pressure, jetting, AFR (exhaust probe, I haven't got a 'bung/boss' in yet) and so on, though I only arrived to take it away. They've got a good reputation, (though some thing is obviously amiss) and whilst they're not aircooled experts, they should know the basics.

So, the carb was pretty extensively modded and reconditioned. It initiallly came set for a Renault 5 GT turbo running 25psi of boost and came with the larger venturi, gassflowed and de-choked. (totally not relevant to the bug jetting I know, but should be capable of well over 200bhp on the renault, though I appreciate the carbs got to cater for off boost as well) But the guys definately had it apart, changed the jets on a few occasions and were checking AFR all the way through. I'm told it's hard to check small throttle work on a rolling road.

I guess I was supprised to hear the detonation within a few hundred yards of the shop. I thought they would have picked this up.

before you ask the obvious.. it was a friday night at 6.pm and they all left at the same time as I did..... so I thought I'd gently get the few miles home and return monday morning (lesson learnt!)

Next step is to get the engine back to my builder and get it sorted. He'll let me know what happened internally and I'll have to revisit the carb option. I'm not a million miles away from efi... BUT I'm not ready yet!

Just a bit of reliability will be a start

[seabeebuggy]

Stuff happens. Don't put so much faith in a builder. My first set up was put together by a VW shop that builds turbo engines. It lasted a short time. The next one was done here and myself. it is now 4+ years old and runs great.

[joosep]

it must be the lean mixture and broken pistons.
Eaven the detonation you can't hear break engines....next time you should use some deto-headphones for listening.....for extra quarantee.

[CobraJet]

It's stories like this that put real questions into a non professional's mind. After spending loads of money on my toy I'd hate to have something like this happen to me.

What would be a failsafe way to prevent this from happening? Knock sensor on a Megasquirt setup?

[bazibbo]

It's stories like this that put real questions into a non professional's mind.

I think that's the biggest problem I've got at the moment. I know I haven't got the skills so you end up putting all your trust, (and money) into other people...... still, as a positive it stops the kids n wife from spending it.

[bazibbo]

Quick question..... kpa vs psi.

I'm a little unsure as to how to convert kpa to psi....

the easy bit is that 7 kpa is about 1psi, but I have to take into account that 100 kpa is about atmospheric. So does this mean I can only apply the conversion after 100kpa?

For example on my ignition map... is the 100 kpa column actually 0 psi ( or could be read as 0 psi ) so 170 kpa is about 10psi of boost.... (atmosphere + 70kpa)

[Clonebug]

A quick formula for ya..

http://www.turbobuick.com/forums/perfor ... boost.html

100 kpa is basically Atmospheric pressure which is 14.7 lbs of air pressing on you at sea level.

Here someone did the math.

http://turbobikes.org/forum/index.php?topic=895.0

Clonebug

[bazibbo]

Ta Clonebug, that second link sorts it.

107kpa (atmospheric + 7) = 1psi
114kpa = 2psi and so on

[Buggsy]

To tune a new daily driver turbo engine, start rich and work toward lean with fuel, on timing, start a little retarded and work toward advanced. Small changes, one change per test drive. You'll never hurt your engine if you take your time. Once you get it pretty close, you can drive it, but plan on tinkering and fine tuning it all summer. If you don't have the patience for this, this ain't the hobby for you.

[bazibbo]

Ta Buggsy, engine's at the builders now so I'll find out how bad the damage is in a few days. We spent quite some time discussing carb and fuel injection options. I suspect I'm at the top of a very slippery (and expensive) slope as I think I'm going to go for fuel injection.

Which one kinda depends on how much the engine costs to fix.

[seabeebuggy]

talk to miniman about his set up. or call CB. do be afraid of carbs. Some are a bit over the top with their advice. I expect a good EFI is better for sure.

[miniman82]

EFI doesn't have to be expensive, you can do a simple MS system for 325p: http://www.extraefi.co.uk/MS_All_products.htm