2tgte comp Qs + backyard anti lag Q

[cooter]

hey guys the new engine for the levin is going to be a 2tgte hybrid and i was wondering if im gonna have some trouble with comp levels.
im going to be using the 3tgte bottom end with 3tgte forged pistons and a 88261 2tgeu head. i was hoping to be able to use a stock 3tc h/g.
seeing as how if you use 3tc crank + pistons in a stock 2tg you get 10:1 comp, will i have too high comp for turbo if i use 3tgte forged pistons + bottom end with the 2tg head.
if so would i have to go aftermarket h/g (metal) to raise it meaning ill need to have the block o ringed?
or is there another type of h/g that will just bolt straight on to lower comp.
if im not gonna have trouble with comp can i use the stock 3tc head gasket with some gasket paper and much sealant around the timing cover?

now for the backyard anti lag.

i was rather bored yesterday and started thinking about the anti lag systems in rally cars. theyre obviously good to keep the turbo spooled but are very life shortening.
and i was thinkin bovs work when they see vac from the intake yeah?
which brings me to my question.
do you guys think itd work if ya plumbed a plumb back bov into the inlet of the exhaust housing on the turbo so that instead of the woosh of air going back to your intake when coming off throttle it goes straight into the turbo to keep it spooled?

any help on these Qs is greatly appreciated.
cheers
craig

[TwentyTwo]

The pressure coming our of the wastegate (BOV) would have to be above the pressure in the turbine housing, which might be hard with a closed throttle. Also dunno if blowing cool air onto a hot turbine is a great idea... I'm not any expert by any stretch of the imagination though, sounds like an interesting idea!

[Toycrash]

It's been tried to make valves between aehaust port and turbine housing.
These valves open in free air same time BOV valve opens. Some worked some melted
Other option is to feed raw fuel to turbine and ignition retard up to 45deg.

But allways you do these, you shorten the life of your charger. Many stock turbos wont last a day with setup like this. Better axial thrust bearing would be nessesary.

This is for antilag, but launch control boost up can be made with ignition retard and launch rev limiter + enrichment. Even plain rev limiter can be used to get pressure up.

[YelloRolla]

hey guys the new engine for the levin is going to be a 2tgte hybrid and i was wondering if im gonna have some trouble with comp levels.
im going to be using the 3tgte bottom end with 3tgte forged pistons and a 88261 2tgeu head. i was hoping to be able to use a stock 3tc h/g.
seeing as how if you use 3tc crank + pistons in a stock 2tg you get 10:1 comp, will i have too high comp for turbo if i use 3tgte forged pistons + bottom end with the 2tg head.
if so would i have to go aftermarket h/g (metal) to raise it meaning ill need to have the block o ringed?
or is there another type of h/g that will just bolt straight on to lower comp.
if im not gonna have trouble with comp can i use the stock 3tc head gasket with some gasket paper and much sealant around the timing cover?

You wont need to lower comp. In fact I would NOT use a thicker head gasket to lower comp. I am unsure of the 261 head's combustion chamber volume, but with my set up I run 8.8:1 and add 25psi to mix just to make things interesting (std dome, 86mm forged pistons and 2TG). This set up is run on pump fuel and has done so for 2 years. I just use the std 2TG head gasket with O ringed cylinder head. I recently (last wed) damaged the gasket, boost went out of control (dopey me fault) to over 30psi and it detonated (this is the first time that I have heard this combo ping). The result was 3 tiny little leaks (under boost) to the coolant on the exhasut side of the block.

Use the 2TG head gasket (available everywhere) and save yourself the grief of trying to seal the timing cover.

Don't forget the search function - practically all of this info has already been made available right here in these forums.

[sillycar chick]

seeing as how if you use 3tc crank + pistons in a stock 2tg you get 10:1 comp, will i have too high comp for turbo if i use 3tgte forged pistons + bottom end with the 2tg head.

Hi, I was just wondering where you got the 10:1 figure from? I have just recently put an 88261 head on 3T bottom end, and will have the enigne running this week, and had to use a 1mm head shim to reduce the comp back to standard (according to my calcs and research) to use with the "lower" octane standard unleaded fuels.

[SRacin]

This is my basic setup, with standard rebuilt 3tgte bottom end, standard 2tgeu head rebuilt, t3 50trim, VR4 intercooler, etc. Made 185hp at wheels at 8psi. More tuning and power to come.

YellowRolla. How much timing are you running at 25psi? Ive noticed even at 8psi they can take mamoth amounts of timing, especially in the mid range! What sort of power are you getting?

Cheers
Logan.

[YelloRolla]

If my memory is correct I think that it runs ~15deg :?

edit/ about 260rwhp

[cooter]

cheers yellow rolla thats exactly what i was after. is it nescessary to o-ring the block for my engine with 2tg h/g? im not planning on running anywhere near the psi you are. reliability is the key but so if its gonna make it more rliable ill do it. something like 15psi max.
and as for the 10:1 comp its somewhere about what u get. or 10.5. cant really remember. dont hold me to that tho.
and toycrash wouldnt the pressue in the intake tract be more than in the exhast turbine housing? seeing as when u close the throttle all the pressurized air builds up against the tb and then the bov lets it go in one big woosh. also at this time the exhaust turbine would be seeing vaccum because the tb is closed so the engine cant injest anymore air and not give the exhaust turbine any more but itll still be spinning thus making vacuum. is that right?
cheers for the answers guys
craig

[TwentyTwo]

There will be sudden drop in pressure in the turbine housing, but not vaccum (below atomspheric pressure). If im thinking the right way around, on closed throttle (gear change) there will be positive pressure built up against the closed throttle, pulses of roughly atmospheric pressure and vacuum between the throttle and the chamber, then roughly atomospheric pressure after the exhaust valve.

If you were to vent the +ve pressure from the wastegate into the turbine, you would increase the pressure there and therefore the speed of the turbine.
Could well be wrong, but thats how i picture it...

A guy called Eddy Tassone had a different but sort of similar setup on his HP Hero's TT 383ci aussie motor. It was designed to create a massive boost spike under load on the dyno. At a pre-determined rpm the ECU would dump fuel into the turbine and slam the wastegates closed, the fuel would burn in the turbine housing and the resulting pressure spike sent the boost pressure through the roof and shot a metre long flame out the tailpipe.
When i read about that it was making 1582rwhp, but you probably dont want that going on when you try to chage gears, hey.

[cooter]

If you were to vent the +ve pressure from the wastegate into the turbine, you would increase the pressure there and therefore the speed of the turbine.
.

i cant see how the waste gate will have positive pressure seeing as how if theres near atmo in the exhaust manifold and the turbine then the wastegate will be seeing near atmo too cause its connected right at the inlet of the turbine housing. did you mean the positive pressure from the intake/bov?
im getting a spare turbo manifold with the new turbo so i might try a backyard turbo setup (suk thro carby) and try the wannabe antilag on that.

[TwentyTwo]

Sorry yeah, I meant blow off valve.

[TwentyTwo]

Mabe another idea is creating a reserve of compressed air in something similar to a surge tank. You could have the wastegate (not BOV ;-) ) pushing the excess boost normally bled into the atmosphere into this tank while under heavy load/full boost, then have a valve that opens up under +ve intake pressure and lets the stored air into the turbine. Might be the long way around but it should work i guess...

Or go buy a supercharger.