turbo

[BradGTV]

i have decided to run a turbo on my 2ltr gtv, i just have a few qustions, i dont really want to run fuel injection (to much messing around) and i am looking for a smart improvment in power, i have seen the alfa turbodelta and lotus espirit that run a blow throught set up with dellortos,
was just wondering:
is this way of turboing efficent in power?
will the dellortos need modifications (diffrent size jets ect..)?
have others put there done it this way?
cheers, brad

[Duk]

The only way to use carbies and turbo's is in a blow thru set up.

You can, and should use an intrcooler.
No sane person would ever use a an intercooler with a draw thru set up. 1 back fire (more likely to happen with harder to tune correctly carby/mechanical advance ignition), and you have yourself a pressurised container that will go off like a bomb . "Funny, unless it's your car!"

The fuel from the carby has a lot less distance to travel, so there is a lot less chance that it will drop out of the air stream. This is especially bad when the engine is cold and when there are low airflow rates (idling and cruising). Cruise fuel ecconomy of draw thru carby turbo cars suck very badly because they tend to run rich just so they behave themselves (a mate has a factory Mitsubishi Sigma Turbo, it's highway fuel consumption is/was disgraceful!)
Having the carbies in the factory positions will also impruve throttle response.

Tuning is a must (jets and emulsion tubes but also ignition timing).
Also, the carbies won't work propperly in a blow thru set up without modifications to seal the throttle shafts and pressurise the float chamber.
A rising rate fuel pressure is also needed.
Some people will tell you that this is why a draw thru set up is better, but that will only add more compromises to an already compromised set up.
http://www.alfabb.com/bb/forums/carb...urbo-help.html

[BradGTV]

hi duk,
if i had the turobdelta spec dellortos, stock engine, intercooler, t28 turbo running 8psi what ruffley would my power be? also what bennifits are an intercooler?
cheers, brad

[Duk]

Hi Brad,
It's only a guess, but if ou can keep detonation at bay without running overly retarded ignition timing, run decent air/fuel ratios (not to rich and deffinately not to lean) and have a decent intercooler and well made exhaust manifold and exhaust, then a conservative 50% increase in power over standard should be very real.
You could well see higher, but I stay with a conservative figure.
The mid range torque would be a lot of fun in such a light car .

Intercoolers do 2 things when they reduce the compressed air temperature (any time you compress a gas it heats up).
1: The cooler air is more dence (more air molecules per unit of volume). More air allows more fuel to be burnt = more torque and power.
2: The lower inlet air temperature helps to keep detonation under control.
When I added the turbo to my twincharged MR2, I also added a bigger and better flowing intercooler (a modified Pulsar GTiR unit). The AW11 MR2 intercooler is in 1 of the worst places. It has air that has already been flowing over the engine/exhaust going thru it (read: hot air!).
Initially I didn't have any ducting that made sure the cooling air flowed thru the intercooler and out the engine cover. This allowed the cooling air to bypass the intercooler. The end result was audable detonation. By adding the duct, no more detonation.

[BradGTV]

wow, 50% increase on a stock engine sounds pretty cool,
as for the exhaust maifold - i was planning on making my own out of steam pipe in this sort of layout (pic below) is this classed as a good flowing manifold ro should i reconsider my design?
also what size exhaust i was thinking 3" or 2.5"?
i will ask my mate about bying his intercooler tonight and get the mesurments to check if it fits,
what cars have a decent intercooler is medium size to fit in my 79gtv?
cheers, brad

[Duk]

Ye Olde Log manifold.
Simple to make but poor flowing.
The real problem with them is that cylinders 1 and 4 pretty much point at each other with the turn into the turbine housing being more work than it should.
The end result is a manifold that will cause a lot of heat retention within itself due to their poor flowing design. A lot of heat retention within the exhaust ports and valves. And higher potential for detonation and/or pre-ignition.

Trust me (and I hate it when people say "Trust me") I have 1 on my MR2. It was built like that due to space issues and being able to position the turbo while making the manifold. Basically I couldn't holt the turbo in place above my head (working under the car) and get in there to make any sort of jig.
The MR2 is deffinately being held back by something and I'll bet my steel capped work boot that it's the log manifold.
Fortunately I made a jig from the manifold itself, so when I get off my butt, I'll finish making my decent merge-collector type of manifold.

Put the effort into making a propper manifold and reap the benefits.
The end result will be well worth the exstra effort. It's something that nags at me with my car, don't let it nag at you now that you know.

BTW, some people may try and tell you that most factor turbo engines use log manifolds. But if you look with an objective eye at engines like the RB20/25DET and the XR6 turbo manifolds, you'll see that there is much more effort put into getting them to flow towards the turbine housing rather than pump into other cylinder exhaust ports.

[gattia86]

2.5" exhaust should be plenty for 200+ hp, and will be MUCH easier to route under the car and over the rear axle, especially around the rear axle/CV joint. 3" pipe really takes up a lot of space and is un-necessary at your power levels.

Cheap, medium-sized intercooler? How about a Volvo 240 or 740/940? Very big for an OEM unit, easy-to-route inlet and outlet pipe orientation, and a dime-a-dozen at auto wreckers. They have plastic end tanks that tend to crack or blow off, but at 8psi, you don't have to worry about that.

Isn't 8psi a bit much for a stock Nord engine? I mean with un-supported wet cylinder liners, and detonation-prone domed pistons and single spark plugs? Isn't this a recipe for intermittent head gasket leaks and detonation?

Didn't all OEM carb/turbo engines have boost-retard distributor ignition? (First-gen RX7 turbo, for example) Kind of vacuum advance in reverse; under boost, a mechanical actuator on the distributor rotates the timing plate and retards ignition to avoid detonation. Is this possible with an Alfa distributor? Might be possible to adapt a wastegate actuator to do this.

George

no turbo Alfa experience, but lots of Mitsu Evo experience

[Duk]

Quote:

Originally Posted by gattia86 Cheap, medium-sized intercooler? How about a Volvo 240 or 740/940? Very big for an OEM unit, easy-to-route inlet and outlet pipe orientation, and a dime-a-dozen at auto wreckers. They have plastic end tanks that tend to crack or blow off, but at 8psi, you don't have to worry about that.

[BradGTV]

i will soon be making up a plenum/airbox, now does it need to be made to evenly as possible share the air between the two carbies/4 inlets? or do the carbies suck enuf air them selves to get an even amount of air if it was a simple box?

also is this intercooler anygood?
Apexi Delta intercooler kit S14 Silvia 180sx legal 100% - eBay Engine Modifications, Performance Parts, Car Parts, Accessories, Cars, Bikes, Boats. (end time 06-Oct-09 22:48:01 AEDST)

cheers, brad

[Duk]

If it was my project, I would build the plenum chamber with the intercooler pipe attached in the center at the bottom.
This way air flow can't favour #s 4 and 3 cylinders as much as it would if the pipe were attached to the front of the plenum chamber.
Moving air doesn't like to change direction unless it has to. 'Has to' being the form of a side of a plenum chamber.

The intercooler looks good. Really speeking, the most important aspect of intercooler design is the end tanks. They determin how well the air is destributed thru the core and again collected to send into the pipe.
I couldn't give you any clue as to wether or not it will fit and allow you to get pipes and tools in to mount it and do up hose clamps.
You could suck it and see, or you could get some dimension from the seller and have a look at your own car with a tape measure. Use your the old imagination to help visualise wether or not you think it will fit.

Be realistic and realise that an intercooler hanging out the front of your car is just going to be a Police magnet, it makes you look like an attention seeking tosser and probably won't work as well as an intercooler that is behind a properly designed air duct (grill and bumper bar air inlets) as the air tends to flow around the intercooler because it represents more of a flow restriction than going around it.

[gattia86]

Quote:

Originally Posted by BradGTV i will soon be making up a plenum/airbox, now does it need to be made to evenly as possible share the air between the two carbies/4 inlets? or do the carbies suck enuf air them selves to get an even amount of air if it was a simple box?

[BradGTV]

cheers guys, i will try and buy some materials for the plenum,
can you paint an intercooler, say black?
cheers, brad

[Duk]

The reason I would use a center entering plenum chamber is to do as much as I feel you can to prevent cylinder to cylinder mixture variations. 1 or 2 cylinders may run rich and the others may run lean, but an air/fuel ratio meter will only provide an average of the lot as a read out unless you are able to do individual mixture or exhaust gas temperature monitoring.

Agreed with keeping plenum chamber (and pipe volume) down, but the intercooler should be as effective as possible.
Surface area rather than thickness is probably more important, but that is rare in off the shelf intercoolers. I have seen some thin, tall and wide factory 'coolers, from a Saab I think.
Radiator upgrades could be done to help maintain coolant temperatures that may be strugling with the new air flow restrictions thanks to the intercooler. Also, making sure that all the air that goes into the front of the car must(!!!) go thru the intercooler and radiator is essential.
Also agree with effort put into the exhaust manifold design and dump pipe.

Effort in design of a series of small things will achieve a good total result. It will never be 1 success that will achieve.

And yes, painting an intercooler black is good for 2 reasons, stealth and black surfaces disapate heat better (but rumor has it the paint can act as an insulator). The big 600 x 300 intercooler in my Silvia is satin black and you hardly notice it. The cops hardly notice it too

[gattia86]

The coolest turbo intake plenum I've seen was on a Porsche 911 race car, and the fabricator said he copied design ideas from Audi's R8 (turbo V8 LeMans car, not the street car) race car.

Audi spent a huge amount of development on thier turbo rally cars in the '80s, where a priority was not just outright power, but throttle response. They also had to work with their inline-5 cyl engine, which created even more of a design problem with a long, 5-throttle body long intake plenum.

The basic idea is a tapered shape (tapering down from the throttle body, so the farthest cylinder gets the smallest plenum volume). This equalizes the pressure seen in front of each throttle body, since without the taper, pressure would drop as air got to the farthest throttle body. The taper compresses the space, keeping the pressure up.

The coolest part about the Audi plenum is the "dual plenum" or "split plenum" design, where the air enters the tapered section first, but the throttle bodies are in a second, adjacent plenum, connected to the first by a small slot. The slot re-directs or "normalizes" the airflow to the throttle body trumpets, further improving response.

Since this is all kind of hard to put into words, I did a quick Google search and came up with this very cool Audi website.

Photo Album

Check out the pictures, especially the cut-away of the dual plenum with the slot clearly visible.

At any rate, you don't have to go nuts with the fabrication, but you could incorporate some kind of tapered plenum to get much of the same benefit.

George

[oz3litre]

The Turbo Delta Alfetta GTV ran about 170 BHP according to Luigi, who was working on it when I was in there last week.