Looking For Performance Ideas
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Thread: Looking For Performance Ideas

  1. #1
    Member My location West Coast GT is on a distinguished road West Coast GT's Avatar
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    Looking For Performance Ideas

    Here's what I'd like to achieve:
    Using the 1.9 liter engine in my GT, I'm looking to get 50 more hp.
    I would also like to keep the engine streetable & civilized.

    Can these two objectives be met simultaneously, or are they mutually exclusive? If they can be met, is the following strategy sound?
    1. Swap out the solex for the Weber DGAV.
    2. Go with larger valves.
    3. Increase either the cam duration, or ramp it up quicker? (I'm trying to stay away from a 3/4 cam because it'll idle too roughly)
    4. Port the intake.
    5. Add an exhaust header (and maybe increase exhaust diameter?).
    6. Add electronic ignition and performance coil.
    7. I would rather not, but if necessary, bore it out for more displacement and plane the deck to bump compression.

    So, again, is the consensus that this is attainable, or do I need to alter my strategy, or expectations?

    To all of you who have gone before me, thanks in advance for any guidance and insight you provide.

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    Pending Member opeldave
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    One thing to keep in mind is what will California allow you to do. If possible valves and carburator are a good start. Higher compression pistons would help. Never deck the head unless you want to start playing with trying to get your cam timing back. Electronic ignition will help with whatever you decide to do. 50 horses is a tall order for a 1.9 20 or 30 might be a better figure depending on your stae requirements.

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    Member My location West Coast GT is on a distinguished road West Coast GT's Avatar
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    California Requirements

    Unfortunately, California is very restrictive on fuel system and exhaust system modifications.

    Fortunately, being 1972 vintage, it is now exempt from the bi-annual smog testing & certification requirements. I don't know that this means the car is exempt from modification itself, merely that I don't have to take it in for testing or inspection.

    Also, I can still obtain octane boost if necessary. Forget about lead in the Bay Area, but that's really a non-issue here.

    The GT is a hobby car, and the intended use is for weekends. So fuel milage isn't a big issue. Hey, I don't want to get poor milage, but I'll probably be lucky to drive it enough to go through 6 tanks per year. I work from home and am lucky to get to drive my every-day car 5 days out of seven.

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    Opel fan Jim Branham
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    modification

    One thing about being a 72, with the low compression engine, it has more room for improvement that the earlier engines with the higher compression. What you are saying is youd like an engine with about 120-130 hp, not an impossible dream.
    Jim B.

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    1450 Seeker... My location madhatterpdc is on a distinguished road madhatterpdc's Avatar
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    1) Swapping the Weber is a great idea that most of us have done. Cost <$400. The only reason not to swap is lack of $$$ or if you are trying to maintain stock. If you are looking for a bigger cam, valves, and pistons, you may want to consider the 38 instead of the 32/36

    2) Larger valves - This is a modification that is not to be taken lightly. I am going to upgrading here soon, and will let everyone know my results. Spend a little extra time searching past posts on this topic.

    3) Cams - Spend some time looking at the specs that are available from http://www.opelgtsource.com and http://www.tgsi.com (TGSI Racing is a user that frequents these forums, but is having a littany of computer issues right now, hopefully we will see him again soon).

    4) Ported intake - I am sure that you are aware of Rally Bob's intake porting guide. 'nuff said.

    5) I don't personally know of any off-the-shelf headers for the GT (If anyone knows different... let me know). A hard-to-find but worthwhile upgrade might be a "Sprint Manifold" or a stock exhaust manifold modified to behave like a Sprint (as recounted here Modified Exhaust Manifold , this is my plan if I am not able to fabricate a suitable header)

    6) Electronic ignition and coil - I haven't done this yet, but by all counts this makes sense, if only for the ability to not ever have to set your points again

    7) Deck the Head - The only time to deck the head here is to gain a flat mating surface for optimal seal. Take off the bare minimum to attain that goal. Otherwise you are risking your cam timing and valve clearance as a sacrifice. Overboring - this is something else that has been performed numerous times on the 1.9L, this is a good time to look at raising your compression through a flat or domed piston. Chevy 305 pistons come in 34 flavors and will get you where you need to be.

    *) Brakes (necessary), suspension (including front and rear sway bars), 5-speed trans, S-10 clutch. electric cooling fan, roller rocker arms, 15 inch aluminum rims...

    Sorry about that, got carried away there.
    Keep it Blitzed

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    Senior Contributor Travis
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    Unless you plan to stroke the crank, the Chevy 305 pistons are NOT going to work for you.....

    -Travis

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    Moderator jimsky jimsky's Avatar
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    One of the things I really like about this site is it's "self-serve friendly". The information that is contained in the forums is really just amazing. Many of the items and issues raised here have been commented on and discussed before by very knowledgable indivuduals like RallyBob and the like. Recommendations of best bang for the buck, what's acheivable and what's not, it's all there. Do a forum search using appropriate keywords, the results will provide reading material for hours. Good applicable information provided by people who know. We keep adding to this wealth of information everyday with new threads, but there is SO MUCH that is already here; it's mind blowing. Seek and ye shall find.
    lovinight likes this.
    Jimsky
    '73 GT

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    5,000 Post Club My location namba209 (R.I.P.) is on a distinguished road namba209 (R.I.P.)'s Avatar
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    Because your car is of 72 vintage, it is totally exempt from all CA emission requirements. To verify this watch for all the hot rods on the road that are 30s-40s vintage with modern V-8 engines in them. My 72 GT is in the process of a V-6/T-5 transplant. As the others have stated, run a search for the mods you want to do, there is a wealth of information on this site pertaining to engine modifications.

    Ron

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    Site Admin My location Gary will become famous soon enough Gary will become famous soon enough Gary's Avatar
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    Originally posted by jimsky
    One of the things I really like about this site is it's "self-serve friendly". The information that is contained in the forums is really just amazing. Many of the items and issues raised here have been commented on and discussed before by very knowledgable indivuduals like RallyBob and the like. Recommendations of best bang for the buck, what's acheivable and what's not, it's all there. Do a forum search using appropriate keywords, the results will provide reading material for hours. Good applicable information provided by people who know. We keep adding to this wealth of information everyday with new threads, but there is SO MUCH that is already here; it's mind blowing. Seek and ye shall find.
    Thanks Jimsky. That was the intent when I was searching for a high quality forum program for OpelGT.com. I bought a vBulletin license because of their features, continual upgrading, their hack community and their support. While the default display for forum messages is 30 or 100 days. (settable in your User CP) there are over 15,000 posts in the database going back a year and a half. So a lot of the posts may go unnoticed and that is where the search feature comes in.

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    Opeler lowkey is on a distinguished road lowkey's Avatar
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    My two cents

    Newbie,
    I would worry less about horsepower, and more about reliable, usable, torque. Here's the low buck approach to it.
    1. a weber 32/36
    2. Electronic ignition
    3. remove the stock fan for an electric
    4. get a 75 Manta, or so called sprint exhaust
    5. Don't make the exhaust bigger (kills your torque) if anything go inch and seven eights max, an aftermarket mufler, and leave off the resonator at the end.
    6. set the timing halfway between the pointer, and the bottom of the window at idle.
    7. semi synthetic oil
    8. Port match the carb to the intake
    9. have a machine shop take a pound or so off the flywheel.

    If you have any money left, then talk to Gil about a very mild cam, but there is no point in doing that unless you change the timing chain and dampers too.

    Now this is just my two cents, but these are all easy, and inexpensive things to do first, if you decide to play with pistons, and valves, these things will all help if you decide to go that route, but bear in mind pistons, and valves are expensive items that need a lot of other thing done to get the full benefit from.

    James
    I'm just another Opel Rehab Failure.

  12. #11
    Project 1450 supporter... Site Supporter My location RallyBob has a spectacular aura about RallyBob has a spectacular aura about RallyBob has a spectacular aura about RallyBob's Avatar
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    Here are a couple of 'recipes' for improving the performance of your engine without investing a ton of cash. I've broken it down into two categories, bolt-ons and internals.

    Bolt-ons.
    >38 DGAS Weber carb. It will work on a mild engine, even a bone-stock engine, but must be rejetted accordingly.
    >Ported intake manifold, preferably '73-'74 smog-style. Easiest to port and get good results.
    >1975 'Sprint' exhaust manifold from fuel injected Opel. You'll have to grind the triangular nub off the center pipes to clearance the intake manifold.
    >Custom 2" exhaust pipe. GT's only have a 1 5/8" pipe, while Manta's come stock with a 1 7/8" pipe, yet they're rated at the same power (? I never understood this...). Even a stock engine will benefit from this mod, you will not lose torque, and it will help the entire power band. Use a perforated-core, straight-thru design muffler up front. For a GT, use resonated rear tips, and a custom 2.5" over-axle pipe splittting into two 1.75" pipes out back. Nice sound, not too loud, and looks good. A Manta can use a second straight-thru muffler (round body) and it will emulate a resonator nicely.
    >Electronic ignition. At least a Pertronix unit, with an upgraded coil. Another upgrade would be a Crane XR-700, but for a few bucks more a Crane XR-3000 is a lot nicer, and you can eliminate the resistor wire in the ignition with this system. Use a Crane PS-91 coil with this, it works well. Lastly, another option for the ultimate in 'trick' bolt-on ignitions, the Compufire DIS-IX 'distributorless' system kicks butt.
    >Electric fan.....much quieter, and adds a few hp in the upper rpm range.
    >Tuning! Having the parts is one thing, but getting it setup right is another. Most cars are not getting nearly 100% of their part's capabilities, so setup is crucial. Consider having it dynoed on a chassis dyno. These days, $75-$100 will get you about 6 pulls on a dyno, and tell you more about your setup than a month's worth of driving on the street. If you can get 6-8 hp from tuning, then you just got more power than a 38 DGAS is worth, and for a lot less money. Not to mention, you will get better gas mileage, and save $$$ in the long run. Well worth it.

    Internals.
    >Bore block .020" over, install flat-top pistons. A small increase in power from the displacement, another small increase from the compression, and yet another increase from the 'newness' factor. It's no longer a 30-year old engine. Use Total Seal gapless rings on the second compression ring. Relatively modest investment but the engine holds compression nicer.
    >Lighten flywheel. No power increase, but acceleration is improved. Stock flywheels weigh 22.5 to 23.25 lbs on average. You can very safely lighten to 17-18 lbs.
    >Recondition the head, install hardened exhaust seats, larger 2.0 litre intake valves, and mill .050" off the head. This will increase compression a bit, to about 9.5:1 true compression. Still workable with pump gas. Don't worry about cam timing, I'll get to that in a moment. The head's ports can be cleaned up a bit. Don't enlarge the actual port area, just blend the bowl areas, and have the machinist mill about 1/4" off the intake valve guides and 1/8" off the exhaust guides where they protrude into the port. Blend the edges of the guides slightly.
    There, you just improved airflow by about 10-12 cfm per intake runner, and 8-10 cfm per exhaust runner with minimal effort. If you do any more to the head, then you'd better know what you're doing, or you may do more bad than good! After the head is milled, make sure to deburr the edges of the combustion chamber to reduce the chances of hot-spots.
    >Performance cam. Nothing crazy, if you are using stock valve springs (you should be), then you are limited to .425"-.430" max valve lift anyway. I usually keep it to .420"-.425" max, but that's just me. If you are not gonna rev it hard, use hydraulic cam/lifters. Less maintenance. Shoot for a custom profile, with split intake/exhaust duration. This helps the Opel's notoriously weak intake flow (note the trend? Most modifications are aimed at intake flow). For a truly mild driveable cam, I'd go with around 212-214 degrees of intake duration @ .050", and around 6-8 degrees less on the exhaust lobes. Grind at 110 degree lobe separation for a smoother idle and broad power band. Now, to correct for the milled head, have the cam guy grind the cam with 4-5 degrees of advance. This will correct the retarded cam timing, and give a touch of advance for better torque. Stock Opel cams are ground 1 degree retarded for comparison.

    If you decide to put a bigger cam into the engine, expect to have to modify the distributor to get good throttle response. This mild cam I've recommended would run well with 3-4 degrees more initial ignition advance than stock, but can use a stock distributor. I'd use a later distributor too, a 72-74 model.

    Anyway, just some ideas/feedback from someone who's built a LOT of Opels over the years, and has just about seen/tried it all.

    Bob

  13. #12
    Senior Contributor My location calvin calvin's Avatar
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    Wouldn't a set of say a set of properly jetted for the 1900 DCOE webers 40ies give you more bolt on HP than a DGAS?

    Oh and you will not only have to add to the crank (if you go the 305 piston route) but will also have to recruve the distributor.

  14. #13
    Project 1450 supporter... Site Supporter My location RallyBob has a spectacular aura about RallyBob has a spectacular aura about RallyBob has a spectacular aura about RallyBob's Avatar
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    Yes, a set of sidedrafts will add quite a bit more power. But as you've found out Calvin, they are a bit more finicky to tune. They are also a lot more expensive (a new set with manifolds and filters can cost over $1k). Plus on a GT, the heater box will likely have to be modified/removed unless you happen to stumble onto a set of short Irmscher intakes. A 38 DGAS is a more economical and simpler approach to improving power, especially for a weekend cruiser.

    The reason your distributor had to be recurved is a combination of the twin Weber sidedrafts, and the hot cam. A mild or stock cam would not have required the distributor rework. A larger displacement engine such as yours does not need a recurved distributor by nature. The hotter the cam, the greater the need for a modified distributor.

    Bob

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    Opel fan Jim Branham
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    opel mods

    copied and saved RallyBob, I just love good sound advice.
    Jim B.

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