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Discussion Starter · #1 ·
Hello all! I'm thinking of adding a turbo to my GT 1.9(bored to 2.0). Would really appreciate any suggestions or advice form anyone who has tried this. Would rather learn from your successes or mistakes than beat my head against a wall or spend money unneccesarily.
Engine has some mods: 9.5:1 Mahle forged pistons, oversized valves (I believe the mach. shop said Chevy 1.84 I & 1.50 E), head port/pol, .445 lift/280 degree hyd. cam (Small Car Parts), intake plenum reworked, Weber DGAS, header, Pertronix HEI, MSD 6AL w/coil, 8mm. wires, Bosch +4s :confused:
 

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Cliff said:
Hello all! I'm thinking of adding a turbo to my GT 1.9(bored to 2.0). Would really appreciate any suggestions or advice form anyone who has tried this. Would rather learn from your successes or mistakes than beat my head against a wall or spend money unneccesarily.
Engine has some mods: 9.5:1 Mahle forged pistons, oversized valves (I believe the mach. shop said Chevy 1.84 I & 1.50 E), head port/pol, .445 lift/280 degree hyd. cam (Small Car Parts), intake plenum reworked, Weber DGAS, header, Pertronix HEI, MSD 6AL w/coil, 8mm. wires, Bosch +4s :confused:
Well, a couple of issues stand out here. First, that compression ratio is rather high for a turbo engine. You will HAVE to use an intercooler if you run 9.5:1 and probably will need racing fuel as well, depending on the boost level you run. Second, that camshaft won't be very well suited for a turbo, too much overlap. Third, a carbureted turbo engine is pretty rough to tune, so you will likely have to deal with an all or nothing power curve with spotty fueling control or you will have to spend the cash for programmable EFI.

What are your realistic power expectations? Generally, a small turbo = good response and minimal lag, but with modest power. A bigger turbo will give the higher hp levels, but at the expense of some turbo lag which can make the engine less than ideal for point-and-squirt driving.

HTH
Bob
 

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Discussion Starter · #4 ·
Turbo tips

Thanks for the response RB! Yeah, I figured that this cam duration would be unsuitable. I had this engine in another GT and the power came on around 3500 rpm. I aniticipated using a donor setup that included an intercooler. I'll relocate my oil cooler to the nose and put the intercooler on the front of the rad.(Flex-a-lite 12"/1650cfm behind) As far as turbo impeller size I think smaller with a quicker spool-up would be more practical and realistic for the hp gain I'd be looking for. I'm not sure what I've got right now, but to go through the trouble I'd like to end up around 175-185 hp. Do you think with the compression @ 9.5 I'd experience any knock using 92 and an intercooler? I don't want to fight a turbo mod, so why is carburetion a problem? Hit me with any other questions please!
 

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First off, it's a bit impractical to use an intercooler with a carbureted engine. You can't do it with a draw-through system, as the air-fuel would be cooled by the intercooler to the point where the fuel would settle out from the airstream, which is bad. If you use a blow-through system, it can be done, the compressed air goes from the turbo compressor housing through the intercooler, and then through the carburetor and intake. However, as you may have read on this site, pressurizing a carburetor is iffy at best.

In order to maintain 3.5 psi of fuel pressure into the carburetor, you must use a rising rate fuel pressure regulator. Otherwise, the minute boost pressure rose above 3.5 psi, the fuel flow would stop. No fuel + boost pressure = no pistons! Okay, let's say you get the fuel pressure figured out, and now at 6 psi boost you have 9.5 psi of fuel pressure being fed to the carburetor to compensate for boost. Next is the sealed carburetor issue. The carburetor, quite simply, was never designed to accept pressure above atmospheric. I suspect that if you pressurize the carburetor enough, the gaskets will eject themselves! I know for a fact that even at modest boost levels the pressurized air will leak past the throttle shafts...

Another issue is the power valve. At high vacuum levels, the valve is closed. When vacuum drops as engine load/rpm increases, the valve opens to administer extra fuel to prevent a lean-out condition. With a blow-through system, you will work this diaphragm opposite the design intent. Failure is fairly common. Again, no fuel....no engine. A draw-through system is another scenario altogether, the vacuum is so low at idle, the carburetor thinks it is at full-throttle all the time, and dumps extra fuel constantly.

You could however build a pressurized box to completely surround the carburetor, but that naturally has its own set of issues. Gale Banks used to do this on all his twin-turbo small block Chevys back in the '80's, but even he has a lot of failures due to fueling issues from using a carburetor.

Quite frankly, if you saved your pennies and did a programmable EFI system, you might just end up doing it for cheaper than if you carbureted it and you ended up burning a piston or valve and had to start over. There's a reason manufacturers stopped producing carbureted turbo engines. They are finicky at best. You will have more power, a smoother idle, WAYYYY more usable torque and better mileage if you go with fuel injection. Just my .02....

As far as turbo choice, are you going junkyard shopping or buying new? A T28 would probably be all you need to make that power, and it will spool up quickly. Or you could go the route I went and use a Mitsubishi TD04 turbo from a WRX, they're cheap and plentiful and more importantly: newer. Nothing like a worn, bad turbo from a 15 year-old junkyard engine. They're also water-cooled, so they last longer. It'll make the power you want at modest boost (under 10 psi), and have enough reserve to make 275-280 at 17-18 psi if you ever go the EFI route. That's too dangerous a boost level for a carbureted engine, the fueling control is simply not accurate enough to ensure proper fuel distribution.

Don't forget, you WILL need to drastically rework your distributor for any turbo engine. Forget the vacuum advance and retard units, they don't like boost pressure! And you must limit the total timing, probably to no more than 24-25 degrees total with that carburetor, and maybe 28-30 if you go with programmable EFI.

Bob
 
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Discussion Starter · #6 ·
Turbo toast

Thanks Bob, you obviously are the person I was looking to talk to about this! I guess for now I'll just concentrate on putting this configuration in the car and getting IT right.
This morning I read the post about your current endeavor with the Mitsu blower and EFI. Would really be interested in how this works out for you. Maybe copy off your paper if you don't mind. Are you expecting to get hp in the hi 2s? Amazing! I will follow progress as you post.
When this car is assembled, driven a little and I start to get hungrier and its time for a change, I'll know where to go for pointers. What tranny and clutch will you be using with that much hp? (I swapped 3.44 rear for a 3.67 a while back). Will an Opel diff. withstand the kind of power your engine will make?

Cliff
 

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OK, I have a question now... What if you use a TBI system instead of the carb? From what I remember TBIs use the same fuel pressure as MPFI, 80+ psi, which would make up for the boost. TBIs are also a lot easier to set then an MPFI system: only 1 injector, use the same mounting system as a carb, etc. Might be another, cheaper, option for Cliff too.

To answer Cliff's last queston (the only one I know how to answer), an open differential can handle the same power output than any other type of differential. The question here is if the shafts are going to handle, which I have no idea since I know nothing about Opel's differential. A bullet proof rear for 200+ HP would be using at least a 190mm ring gear diff for more contact area and 28 spline shafts. Like I said, I don't know what opel had going on under there.
 

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A TBI system using the stock intake manifold would be giving up a lot of potential power compared to using the standard Opel EFI manifold. The airflow through the stock carbureted intake is simply not as good. Most of the TBI systems I've seen use 17-21 psi, and most multi-port systems use 36-44 psi. True, the pumps are usually capable of 60+ psi, but they don't operate at those levels. But with either system, it's enough to feed most turbo engines.

Regarding the rear differential, the axles are not usually the weak point, with one exception (more on that later).

The first thing to break is usually one of the spider gears or side gears in the stock differential. They are, quite simply, incredibly brittle. Every Opel diff I've 'exploded' had these gears broken in half, laying in the bottom of the diff housing. By comparison, every non-Opel diff I've broken usually sheared or twisted the edges of these teeth off these gears. A 'simple' cure for this is to install an aftermarket limited slip differential, such as a ZF or Quaife. These, however, are very pricey and hard to come by, costing about $1000-$1300. But, the diffs are nearly bulletproof at this point. Then the next weak link....

The next area to break is normally the torque tube input spline at the pinions gear. I have sheared them off all splines on numerous occasions. Having a limited slip and soft-compound tires increases the loading on this part, as you now have the traction of two tires instead of one putting the forces through this weak part.

If you have enough power, the other part that can self-destruct is the torque tube shaft itself. It is small enough in cross-section that a combination of tire grip and hp can shear it cleanly in two. There are aftermarket parts available from Europe (particularly Sweden and Finland), which are larger in cross-section and they are made from stronger material as well. Alternatively, I have welded large diameter tubing over these shafts (sleeved them) and had them rebalanced.

Now, getting back to the axles. IF the car has enough hp and grip, they can twist as well. This is less common, and usually only in competition cars which have repeated high-load cycles forced into the axles. They eventually fatigue and either twist just inboard of the splines at the diff, or more scary....they shear the fusion weld at the outboard hub (the axles are not one-piece). This is also common on rear axles that have a welded 'spool' type differential, and that run high-grip tires on asphalt. The constant twisting action of the non-differentiating axle will eventually break a hub off. This happened to a low-powered ITB Opel Manta at Nelson Ledges a few years ago, and once the axle broke, 100% of the drive torque went to the other axle, putting the car into a high speed spin and completely destroying the car. 'Nuff said.....

So, you can see why I like the idea of using an alternate rear axle for high-po Opel applications. The cost of a new Opel LSD, new bearings, stronger torque tube, and the installation can easily break $2000. A much-stronger Toyota/Ford/Chevy axle can be built for around $800-$1000, not including labor to install it.

Bob
 

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Cliff said:
Are you expecting to get hp in the hi 2s? Amazing! I will follow progress as you post.
What tranny and clutch will you be using with that much hp? (I swapped 3.44 rear for a 3.67 a while back). Will an Opel diff. withstand the kind of power your engine will make?

Cliff
With the new, larger IHI VF22 turbo I just picked up, I expect power in the 275-300 hp range from this engine.

This car has a ZF limited slip with a 3.67 final drive, which should be okay for a while anyway. The transmission is a Getrag 240 (5 speed), but I know that it won't last for very long. I have been on the computer all day looking at options. I had been considering one of the Quaife/Ford-based gearboxes, but the exchange rate has really driven the prices up, and they would be borderline as well for torque capacity.

So far, the best bet seems to be adapting a G-Force modified Borg-Warner T5. The ratios available are more suitable than stock Mustang/Camaro ratios, and the tranny is rated to 550 lb feet of torque. Should be adequate! I would need an adapter to fit to the Opel block of course, and a custom driveshaft, and a custom clutch disc.

http://www.g-forcetransmissions.com/tran_t-5_price.asp

You'll see that the price for an assembled synchro-type tranny with a used case supplied by G-Force is about $1600.

Bob
 

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Axles & G/boxes

I used to scribe a line down the length of the axle so any twist could be seen easily when they were pulled at the track ( not on Opels though - Fords)

Have you considered the Toyoata Celica RWD iron case gearboxes? they are extremely strong and will hold V8 torque to 300 lbs/ft plus. Got a range of ratios too.
 

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GTJIM said:
Have you considered the Toyoata Celica RWD iron case gearboxes? they are extremely strong and will hold V8 torque to 300 lbs/ft plus. Got a range of ratios too.
Yes I have. I'm an old-time Toyota enthusiast as well (still have my '72 Corolla wagon and my '87 pickup with convertible top and roots-type blower).

Problem is, there aren't any commercially cost-effective ratios available (I have only seen Quaife and Housemann Gear list them$$$$$), they are rather heavy, and I simply can't find any here! Seriously though, the old-school import drag racers snag them all up at the wrecking yards over here. Still a lot of old Corollas running nitroused/turbo's 3TC's and cast-iron W57's in drag racing cars in New England. Oh well.

I have been considering a 3rd-gen Supra turbo tranny though....

Bob
 

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Imports!

Lots of those gearboes are directly imported from Japan to here for use in Aussie Ford Falcons and Holdens - I had one in a Holden and it lasted very well behind a 3 litre six.
 

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Bob,
These are certainly impressive HP numbers that can be achieved through the use of boost. I realize that the engines you are hanging these turbos and EFI on are also well modified engines. What kind of HP could be expected from a bone stock (rebuilt) 1.9 with a WRX donor turbo and aftermarket programmable EFI? Is there a good reference for this type of modification? It appears that there is a great deal that has to be considered for these mods to work correctly, what cam, what valves, EFI setup, distributer setup and on and on. Can you recommend a way for an amateur gather all the correct combinations before spending his hard earned money on parts? Thanks
 

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Even a stock engine could be made to make impressive HP, the difference is the relatively low airflow through a stock engine means that a bit more boost is need to achieve those HP numbers. So those parts that are already stressed from boost will be placed under even more stress, but those parts will be stock. In theory you could make a stock engine make 500-600 hp if you had a big enough turbo, but the stock parts would fail in short order from the thermal stress.

However, if you simply want to 'make the numbers', the required components are:

>A turbo with enough airflow potential for the HP you want. A stock WRX turbo will max out at about 270-280 hp with appropriate fuel, exhaust flow, and intercooling. Above 18 psi the efficiency goes to hell, it just creates heat, and power is actually reduced. Detonation is a reality once the efficiency drops.
>Fuel injectors that are large enough, 370 cc's are enough for 300 hp
>A fuel pump with sufficient volume, 155 lph is fine.
>An exhaust system that is large enough, at least 2.5"
>A bigger cooling system, i.e., larger radiator
>Large enough intercooler to drop compressor outlet temperatures
>A strong enough clutch and transmission
>A strong enough rear axle
>Oil cooler....don't underestimate the heat created by boosted engine
>bigger brakes, one hard stop from 130 will absolutely cause brake fade that will cause the pedal to hit the floor.....I know this for a fact, and nearly died from it.

A stock cam is fine, stock EFI manifold is fine, stock throttle body size is fine, and stock valves are pretty durable, albeit not ideal. If you want to go with bigger valves but keep them 'Opel', go with 2.2 intake valves (they're 1.77")
, and with 2.0 exhaust valves (they're 1.45"). The flow proportion will improve as a result, and EGT's will drop by about 150-200 degrees. Once EGT's go above 1500-1600 degrees, all bets are off! Gaskets blow, heads crack, nasty detonation leaves piston skirts in the oil pan, etc.

HTH
Bob
 
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Thanks Bob,
That is a lot of information, I'd be excited to get 175 to 200 hp and make it live for a while rather than shoot for any higher. I guess it's time to start dragging the salvage yards. :D
 

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Discussion Starter · #16 ·
EFI Info

Hey RallyBob! I've got a spare engine and thought I'd go ahead and start looking now for parts I'll need to someday go EFI. What years and model(s) Opels will give me a usable system to build on? Also, is there an aftermarket ECU you'd recommend or what would be a good donor? Any problem with hood clearance on a GT going EFI?
Have a great 4TH!
Cliff :D
 

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...looking now for parts I'll need to someday go EFI. What years and model(s) Opels will give me a usable system to build on?

*****Any model US-market 1975 Opel, i.e., Ascona, Sportwagon, Manta.

Also, is there an aftermarket ECU you'd recommend or what would be a good donor?

*****There are a lot of options. Do a search, you'll see at one point I listed about 10 or so different brands of programmable ECU. Price varies greatly with options.
>Found it! http://www.opelgt.com/forums/showpost.php?p=29932&postcount=8

Any problem with hood clearance on a GT going EFI?

*****No hood clearance issues, the only issues are the cold-start injector hitting the cowl area (no problem as you don't use this injector with programmable EFI), and the hood latch will have to be slightly modified to fit.

Bob
 

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tranny option for Bob L

found this article in KIT CAR mag.

there is a new Tremec 5 speed the TKO-500 and TKO-600. shifeter location can adjust from 14 to 27 inches from the face of the bellhousing. rear crossmember fits Ford and GM applications, and comes standard with mech and elec speedo pickups. 31 spline output shaft.

full info is at this link: www.ttcautomotive.com/English/news/20news.asp
 

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Discussion Starter · #19 ·
2.4 fuel rail

Thanks for the link to the old post Bob. Question from someone not familiar with Opel F.I. What displacement are the '75 engines? Will the '75 head fit my block? Will the fuel rail from a 2.4 fit the '75 head? I like the idea of being able to use readily available injectors. If not, is this the essence of your current project?
Thanks, Cliff :confused:
 

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Cliff said:
What displacement are the '75 engines? Will the '75 head fit my block? Will the fuel rail from a 2.4 fit the '75 head? I like the idea of being able to use readily available injectors. If not, is this the essence of your current project?
1975 Opels are still 1900 cc's

Yes, the 1975 head will fit your block, but I don't suggest it. 1973-1975 heads were built for unleaded fuel, and as such have induction-hardened exhaust seats. Getting to the point, the heads crack if you look at them sideways! Really, they aren't tolerant of high water temps, and adding a turbo will compound the problem (high EGT's).

The 2.4 fuel rail will fit the 1975 intake manifold, yes. The stock 2.4 injectors are not enough for most turbo systems, in terms of fuel flow, so figure on having to upgrade to larger injectors.

For the turbo project I'm working on right now I have a stock 1975 intake manifold, a custom fabricated fuel rail, and aftermarket Bosch injectors that flow nearly double what stock injectors flow.

Bob
 
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