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Tom Drake's Opel GT to have fuel injection for the Runoffs

5025 Views 36 Replies 9 Participants Last post by  davegt27
I just got off the phone with Tom Drake, noted Opel GT racer, and he finally got a chance to fire his GT-4 Opel GT with his new fuel injection system, and run it on a chassis dyno. The good news is, the car makes more power than before, with an extended power band, and has far better low rpm tractibility. In fact, Tom says the car now idles smoothly at 1000 rpms, where it used to idle rough at 2000 rpms.

Tom is running a basic SDS (Simple Digital Systems) programmable fuel injection system, with 45 mm TWM throttle bodies. With the previous carburetors, the intake tract was restricted by the venturi size (41mm), but with the 45 mm throttle bodies, there is no restriction, only a smooth 45 mm bore. That, plus the superior atomization of the fuel injectors versus a carburetor, and the car picked up an appreciable gain in power throughout the rpm range.

For those who want to witness Tom in action, he will be at the Mid-Ohio Sports Car Course for the SCCA National Runoffs, which is being held from September 15th-21st.

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I take it that he isn't using the stock opel FI intake then? What are these "throttle bodies" that you speak of and how do they mount?
As I said, he is using the S.D.S. system, which is the programmable ECU. Nothing is original Opel as far as FI goes. It has sidedraft intake manifolds (as you would put DCOE type Webers on), it has 45 mm thottle bodies (which essentially mimic DCOE carburetors), a custom fuel rail, larger aftermarket fuel injectors and regulator, a custom wiring harness, aftermarket Bosch high pressure fuel pump, a custom airbox, etc. Figure about $2500 to replicate.


so i am guessing they changed the gt-4 rules to allow the use of fuel injection and 45 mm throttle bodies.
Yup, they allow FI, as long as it's individual runner, no plenums allowed. They didn't change 'carb' sizing either, so we still have to run 45's, but with no venturis it frees up some airflow. Tom's the first Opel driver I know of to take advantage of the new ruling, and he's the Opel guy with the best shot at finishing well at the Runoffs, having already run well in the past. We'll see...

The FI is one of my "not so secret" secrets to getting a lot more HP and torque from the Opel. We are using essentially the same set-up as Tom except that we are going with the Electromotive engine management system. (I think the Electromotive will be good for another 5-10 HP at a cost of another $2000 over the Simple system).

We used TWM manifolds and air horns for our previous engines, are using TWM throttle bodies for the FI. (I don't know of any one else that makes FI throttle bodies that can be used in place of DCOE Webers.)

Rally Bobs cost numbers are not too far off. We are a dealer for TWM and RC Injectors. So, anyone considering an equivalent set-up from scratch get out your wallet. Here are the almost current prices for the TWM stuff and the RC Injectors

Manifolds $550
Throttle Bodies $300 each (2 required)
Air Horns $55 each (4 required)
Fuel Rail kit $155
Fuel Pressure Regulator $217.00
RC Injectors $95 each
Some alternate sources of throttle bodies:

good info Bob thank you.

if i remember right Jenvey did the setup for QED's F 3 Opel Motors

the reason i bring it up is QED had some very interesting info on there web page before they changed it

seems they had Jenvey develop a Taper bore setup where the quad TB's bolted right to the head

and reported amazing results
its may opinion that this taper bore setup resulted in Laminar flow

a friend argues "you don't want Laminar flow" i say you do

some pretty long haired math is involved (way over my head)

so what am i saying

the ideal setup would be a taper bore setup starting at the air horns with a 6% taper (i hope i remember that right from QED's info) going right down to the smallest choke point in the head (that's where the CNC'ed head comes in)

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i think jenvey has the best tb setups
they have the DCOE style in a standard length and a size that is half the lenght of that which i believe would help in tuning by changing the lenght of the air horns
also for a fuel injected turbo application it allows alot more plenum volume with out cut into your gt

i have never heard of the sds computer systems
are they descent priced easy to tune?
can you give me a link
72opelguy said:
i have never heard of the sds computer systems
are they descent priced easy to tune?
can you give me a link
The link is in my second post above. They are very inexpensive. They don't have a lot of the capabilities of more expensive aftermarket ECU's, but they are relatively simple to tune. Still need a dyno with appropriate fast-response O2 sensor for tuning, but you don't need a laptop PC.

i found the site
its not all that expensive but it looks like a very simple setup
why would you need a dyno you can just get the base settings and then go drive the car
and if yoou wanted to tune you car at the track the little programmer is alot easier to deal with than a laptop
Well, in my case, I would rather tune on a dyno. If I spent, say, 5 G's (or more) on an engine, I'd rather have access to a wide-band O2 sensor, with all operating parameters (coolant temp, EGT's, manifold vacuum, audio knock sensor, etc) being documented during a dyno pull. You can't do this driving on the road. Plus, 'seat of the pants' tuning rarely gets the best power and a safe air/fuel ratio. I wouldn't risk it. What's another $300 or so in dyno time at that point? I'd be looking to optimize the tuning without risking engine damage.

please excuse my use of words but for a budget efi conversion that you can tune you cant beat it
you will be fine tuning by the seat of you pants as long as you have the air/fuel and spark advance right
and to get full potential out of it you could go to a dyno
Well, it's not budget EFI if you blow your engine up tuning it....

The truth is, most people don't know what the correct air/fuel ratio is supposed to be for a particular engine, particularly for performance use. Do you know what Opels like for CO percentage for maximum power? Do you know what turbocharged Opels like? And as every engine out there has different needs, you can't randomly pick an air/fuel ratio and use an off-the-shelf air fuel meter (slow response, mind you) to tune it. You could get away with it for a low-performance street engine sure, the stresses are low.

But go high compression/high rpm engine, or worse yet, turbocharged, and you'll be guessing. And it only takes about 3 seconds of full-throttle, full-boost application with detonation to melt a piston. Can you honestly say you'll respond that quickly and add fuel to the map while it's happening?

I'm simply making the point that it would be somewhat foolish to spend all that money on an engine and engine management system, and then *think* you're saving a few bucks by not going to a dyno. It'll end up costing you in the end, either in lost power, or in broken parts.

Anyway, I don't want a pissing contest here, I'm trying to make my point that the tuning of the engine is not the place to take shortcuts. You can turn a $5k engine into junk in seconds if you're not careful.

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I'll second what Bob has said about melting a piston, or in my case two. A co-worker driviing his Honda 250, single carb, twin cylinder, got about 50 feet when the engine died. Teardown revealed the carb mounting bolts vibrated loose and in seconds the lean mixture put dime size holes in each piston top. With all the engine sensor pickups available with computer readouts a dyno is the only way to go for super fine tuning. The gofast big boys use telemetry sending the info of the engine to computers and the crew can send and make adjustments during the course of the race.


Since you mentioned you have a little time off, any chance
you planning on going to the run-offs in Ohio? Or anyone
else for that matter. It would be nice to have some Ohio
and W. PA opelers cheer on a GT. I see the GT-4 main
race is Friday afternoon at 3:20pm. Too bad it won't be
on Saturday or Sunday, it may have gotten a bigger Opel
cheering section. Do you know if any other Opels will be
racing in the other classes?

Tom C
No can do. Besides the lack of money to travel, I have a ton of projects to catch up on here.

Besides Tom Drake in GT-4, there's Stan Czacki in another Opel GT in GT-4, and perhaps the 1.1 H-Production GT may show up again...

John Mills parted out his GT-4 Manta, and will not be racing an Opel any more.

I'll be there in spirit....

i fully back you but for street its nmot that critical as you say and that what i mean
i plan on using a haltech computer and spending way too much time and money on a reliable high hp engine
but for a carb to efi conversion that kit takes alot of things out of the picture to simplify it
and i back your idea fully i just wasnt meaning the hipo part
stock manifold?

That SDS system looks like a fairly cost effective alternative to the Megasquirt I was planning on building. By the time I got everything built I probably would have wasted enough time to justify the $500 difference in price.

Now about the throttle bodies. I know Tom has to run the individual throttle bodies to meet his class requirements, but I don't for the street. Does the stock EFI manifold flow well enough to make it worth my time to hook-up one of those systems to it? If so, someone could then cut the cold start injector boss so the manifold will fit into a GT and greatly simplify that install. I would also have the greatly simplified option of a turbocharger, which would be just plain yummy!

I mean, really, $750 for the SDS system, a stock EFI intake manifold, a custom exhaust manifold, and a $300 rebuilt Saab turbo, and the Opel 1900 would be a fairly cost effective option to keep in the car and smoke some "rice rockets." I may just have to scrap the 2.8 I was planning on swapping in.....
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