[chuckspeed]

There have been numerous discussions about motor performance, motor swaps, car performance, and overall HP improvments in the last few weeks. I'm going to take a few moments to set the bench racing record straight for future discussions...

There are five real figures that need to be clarified when discussing vehicle performance. These are:

SAE Gross HP
SAE Net HP
Advertised HP
Dyno HP
and...
Power-to-weight ratio.

SAE Gross HP was used up thru 1971, and was quite literally a 'gross' exaggeration of engine HP. All accessories were off the motor during the test, and the test cell was set up to 'favor' the motor. In the case of one manufacturer, high static fans were installed on the exhaust side to remove spent gases - this acted as a kind of 'polish supercharging' to inflate the HP values.

SAE Net HP was initiated in 1972 after the abuses mentioned above. As a general rule of thumb, these SAE net values reduced reported HP by approx 27%, and the system is still in use today.

Advertised HP is the numer manufacturers use for marketing purposes. This is the SAE Net HP generated by a 'perfect' motor - balanced, blueprinted, and tweaked by the best of the best to get the highest possible HP rating for advertising puposes. Real-world motors make about 20% less than advertised HP.

Dyno HP is what you see with your own two eyes as YOUR motor is bolted up to a dyno stand. Assuming a stock motor, it is ALWAYS the lowest of the four HP numbers. Remember, figures lie and liars figure.

Power-to-weight is a ratio of the vehicle's weight divided by its HP. This is a leading indicator of its performance, and is quite reliable - I've won many a street race by estimating power-to-weight. Where folks get goofed up is when they use different HP figures to factor power-to-weight. Let's put this into practice...

a 1966 Mustang coupe with a 289 2 bbl makes 200 SAE gross HP weighs 2500 lbs (prox). The power-to weight ratio is 12.5:1. Conversely, an Opel GT in 1973 makes 88 SAE net HP and weighs in at 2100 lbs (prox.) for a power-to-weight of 23.8:1.

No contest, right?

Whoa, buddy! SAE gross to SAE net is an apples-to oranges compraro! To make it 'fair', the Mustang should be 'de-rated' to SAE net - more like 146 HP. This provides a power-to-weight of 17.1:1. But wait - we're not done...

If we were to hook both motors up to a dyno, we'd see that the 289 is actually closer to 115 HP, and the Opel 1.9 is around 70 HP. Solving for power-to-weight nets out 21.7:1 for the 'stang, and 30:1 for the Opel.

This is important, as the ratios are getting closer as we reflect reality. When we started, the Mustang's power-to-weight was 50% better - when we made it apples-to-apples, it was only 30% better.

Now...We add in Weber, some porting and a low restriction exhaust to pick up approx 20 HP. The power-to-weight of th GT drops to 23.3:1 - this is within spittin' distance of the 'stang. At this point, gear ratios and driver's reaction win/lose the race.

Soo...keep this in mind when yer friends start bandying about HP figures inna bench racing session, and keep a calculator handy!

 

[Kristi]

Wow

SOMEONE ate his wheaties this morning..... (of course I'm still getting beaten off the light by a chevy cavalier so its time to give Emmy a major tune-up....)

 

[davegt27]

I don't think you will here any Opel people bragging about HP numbers

there are a few (very few) getting power out of an Opel


My 72 street car started out at 19.2 in the 1/4 mile

and ended with a Bob Legear ported Head at 17.3 (32/36 carb)

a 1.5 head and 75 FI was 18.5

a 75 FI manifold and a pacesetter header was very little difference

but there was a loss of low in TQ

also 2.0 FI set up lost some low in TQ also, as compared to the 75 FI

I was told by a top Opel engine builder that i could expect 140HP out of an $8K SCCA FP race motor

no i don't think you will here many Opel people bragging about HP numbers


Davegt74

 

[chuckspeed]

There's one other bit I forgot to mention...

Auto transmissions.

The torque converter of an auto trans 'eats' HP and converts a portion of said HP into heat. The fudge factor for an auto trans is approx 10% power to the torque convertor - this is why manual transmission cars are usually a tad quicker than their automatic counterparts.

Don't recall the 'zact # off the top of my head, but SAE net on a stocker (non Z24) Chevy Cavalier is about 122 HP. Factored down to real world dyno HP, the Chevy clocks in at 98 HP (more or less). Assuming a base model at about 2500 lbs, the power-to-weight is 25.5 against the Opel's 30. Factor in an auto trans, and the Chevy Cavalier is *around 28:1.

Assuming Emmy already has a Weber (most Opels do these days)
means you've picked up 4-5 HP on a motor in good tune. This puts Emmy at a power-to-weight of 28.3:1, right on the Cavalier's mark. All things being equal, you should run doo-to-door with said Cavalier - if not, it's time for tune-up!

Maggie the Opel was put toghether carefully to minimize frictional losses, has some mild porting and a low restriction exhaust. She will run door-to-door with a Chrysler 3.0 liter V6 inna Dodge Dynasty - not much to write home about, but better than a stick in the eye!

 

[chuckspeed]

Dave-

The discussion was aimed more at the folks who need to put big motors in little cars when a little motor in a little car will often outrun the big motor in the big car.

17's aren't bad for a street car. A buddy with a late 70's Z28 could only clock high 16's as a personal best - another friend with a fairly well-built 307 Chevy Nova could only get into the low 15's.

A turbocharged Dodge Shadow driven like it was stolen (WOT shifts) will only clock mid 16's in street trim.

On the other hand, if you know what you're doing, you can build fast motors on a budget. The key is prep - as opposed to bolting stuff on. Rally Bob's head was mostly prep, and it shaved a buncha time off your ET.

Going to your 140 HP example...this would have the same power-to-weight as a 351 Mach I Mustang or a hottie 350 in a Camaro.

that's the point of the discussion - make a lot with a little.

 

[Travis]

Dave,

$8k seems like alot of cash for 140hp. What mods are allowed to the motor in FP?

-Travis

 

[opelmark]

Did that $8K number come from Roger Wilson in California? By all accounts, Roger is one of the best Opel engine builders anywhere, and a great guy--he answered a few critical questions for me last year, regarding piston-to-valve clearance, when building the 2.0 engine--& I understand he has more work than hours in the day. The best are usually very busy, priced accordingly.

 

[RallyBob]

Dave,

$8k seems like alot of cash for 140hp. What mods are allowed to the motor in FP?

-Travis

*****It's easier to list what's NOT allowed than what IS allowed.
Same bore restrictions as SP or Prepared autocrossing (.047"). Stroke can't be changed. Rod length can't be changed and must be ferrous (i.e., no titanium). 40 DCOE Webers are the largest carbs allowed...I *think* the choke restriction is 30 mm, but that may have recently changed. Exhaust valve size must be stock diameter, intake valve size must be 2.0 litre diameter (42 mm). No roller lifters. That's about it.
Essentially it's a GT-4 engine with small valves, smaller carbs, and stock length rods. In fact Tom Drake's GT-4 engine is nearly identical in spec (Stan's cam has more valve lift though), but Tom's engine has 5.5" length rods, 1.85"/1.55" valves, and 45 DCOE Webers with 41 chokes (custom). As is the case with most Opels, the induction is restricted. With the larger valves in Tom's GT-4 engine, the engine gained 6 hp with a 1 mm increase in choke diameter. That engine would LOVE a set of 48's or 50 Webers, but they're not allowed.

A fully prepped (and dyno tuned) Opel engine for F Production could theoretically probably make around 165-170 hp, based on the airflow I got out of the head when I did the development for Stan's engine originally. I don't know how closely Roger followed my recommendations though...every engine builder likes to do things his own way. Also, the cam choice will decide EVERYTHING in a restricted engine such as F Production. The original cam in Stan's engine was one of mine, but he's changed it since then, to a similar grind by another manufacturer. Cam timing is critical too, getting a couple of degrees off in your cam timing can drop cylinder pressures by 30 psi. The hardest part is not building the engine, but getting everything working well TOGETHER. I guess that's why engine builders in Europe are called tuners...it's really a better description.

Bob

 

[RallyBob]

You know, getting back to Chuck's talk about racing and 1/4 mile times made me remember to mention that the DRIVER is the most important thing of all! My old 139 hp street Opel did a best of 15.0 @ 94 mph in the 1/4, but it was a VERY fine balancing act between rpm shift points and wheelspin off the line. I had a close ratio ZF tranny which dropped rpms by about 1000 between shifts, and the engine made peak power at 6700 rpms. BUT, with some experimenation, I found the best shift rpms were at 7200, so the car was 'fat' into the power band in the next gear. I mean, with the exact same car/tires/driver, I started at a 16.2 1/4 mile time, and whittled it down bit by bit.

This holds true for any kind of racing, as I found out last fall at the Skip Barber driving school. I was the heaviest driver by far (about 210), and with the exception of two experienced kart racers who were taking the school, I pulled everyone down the long straight at Lime Rock. When the other students asked why I was so much faster there (must be the car, right?), the instructor said it was my corner exit speed, which placed me higher in the rpms and let me pull past 4-5 cars on every straight. But on our rolling starts (all cars traveling at the same speed), EVERY other student's car pulled mine, because most other people were in the 140-160 lb range, and those racecars weighed 1100 lbs with 132 hp. But, entering the first corner at the end of the starting straightaway, I usually got past 6-8 cars, because I was braking deeper in the turns. Consequently, I was faster on the NEXT straight again, since my corner exit speed was higher.

Bob

 

[Kristi]

Ok, speaking of RPM shifting... in daily driving, around what RPM range should the driver be shifting? I've noticed my GT seems to shift at higher RPMs then any other car I've had (or maybe I'm just not "getting" it and shifting at completely wrong timing)

 

[johnbran]

Ok.....since we seem to be on the HP topic here, I have what may be a redundant question, but here goes. I apologize, but this may be lengthy. I know it has been addressed a hundred times already, but I was wanting to know what HP mods you all would suggest for my '70 GT with a currently bone stock 1.9L/4 speed? From what I've read, these early motors are fairly stout to begin with (higher comp, forged internals, etc), although their stock HP ratings do little to reflect that. Anyway, I'm getting everything mechanically sound on the car now, but I figure by next spring or summer at the very latest, it will be time for a complete engine rebuild. Now, what I'm interested in is a little different than what most have been asking about because I am looking for just some minor to moderate increases in power. No engine/trans swaps, blowers, turbos, or anything else that would require major surgery, modifications, or big $$$ to accomplish. This car will never be more than a daily driver. But, while I am not looking to make a high dollar race machine, I would like to get a little better performance out of her for those occasional "stop light races". I'm mostly interested in improvements that do not require major machine work as well, although I am hoping to port/polish the intake when I install hardened exhaust seats. I realize that the first big improvement would be to swap out my origional Solex for a Webber, but as you've probably noticed from my past posts, I've spent many a weary hour on the Solex and have finally got it working extremely well (thanks for all the help!!!). As for the exhaust, I am currently running a stock manifold/head pipe with no muffler straight back to a stock resonator/dual tips. Is eliminating the muffler actually gaining or hurting my performance? Would a header really provide any "noticable" HP gain without major engine mods? What about camshafts? What kind of lift/duration would be my best choice, keeping in mind that I will probably be running stock pistons, valves, springs, and solid lifters? Are there any other areas that can be improved fairly cheaply that would provide some worthy gain? Also, does anyone know what is the largest size (widest) tire that I can safely run on the stock 13" rally's while still being relatively close to stock tire height for the speedometer reading? I've read articles about upsizing to larger wheels, but nothing I've seen has addressed running the 13" stockers. I realize that my interests may be on the opposite end of the performance spectrum from what others desire, but I am building this car on a fairly tight budget and I am going to attempt to achieve a balance between looks and performance and not get too carried away with either aspect. I plan to have my GT for many years to come, so the more radical mods will come on over time. Right now, I just can't wait to get all the bodywork done so I can get her out on the road. That's going to be one great day!!! Thanks for taking the time to read all of this and sorry it's so lengthy. I just can't help myself when I get talking about GT's............

Thanks,
John

 

[RallyBob]

On a limited budget, this would be my recommendation for a rebuild.

*Invest in some Total Seal gapless rings
*Deck the block to bring the pistons flush with the top of the block
*mill .050" from the head. This, combined with the block milling will get you a true compression of about 9.5:1. Opel's listed compression ratios were optimistic and inaccurate.
*Install hardened exhaust seats, and get/install some 2.0 litre intake valves. Have the machinist mill 1/4" off the valve guide protrusion in the intake port, and blend the bowls of both the intake and exhaust ports.
*Slightly hotter camshaft. I'd recommend a split profile to pump up the Opel's inefficient intake port. A nice profile I've used a lot is Cam Techniques' F-270 profile for the intake port (.405" lift and 220 degrees @ .050") and their F-265 (.398" lift and 214 degrees @ .050" duration), ground with 109 degree lobe separation and 5 degrees of advance. The ground-in advance will compensate for the head milling, plus give a little more advance than the normal 1 degree retarded stock installation
*Ported intake manifold. Best thing you can do for the engine
*38 DGAS Weber. It's the best for the street, what can I say. A Solex flows 190 cfm, a 32/36 Weber flows 270 cfm, and the 38 DGAS flows 330 cfm. The Opel NEEDS it, and even a dead-stock Opel with an automatic will have better power and driveability with a 38 DGAS. The key is the setup, if it's not properly tuned and rejetted, it'll lend credence to the myth that a DGAS is 'too big' for a stock engine. Not true, they run great if setup right.
*1975 Exhaust manifold and 2" exhaust system, with a 2.5" over-axle pipe. The 2.5" over axle pipe might seem redundant, but I've seen 4 ft lbs of torque EVERYWHERE in the power band from this mod. It's the most restrictive area of the exhaust.
*If you feel the need for a header, and can't afford a proper custom built one, then take the Pacesetter (or whatever brand), and have someone (or yourself) lengthen the primary tubes by about 10". The primary tube diameter is fine (1.5"), but the length of the primary pipes is WAY too short for the rpm range a street Opel runs at. You'll get more torque and better response.
*Restrict the mechanical advance of the distributor, but for a street engine with a mild cam, I'd leave the vacuum advance intact. This will allow you to increase the baseline timing a bit for better response and a smoother idle and better starting, but will restrict total advance so you don't ping under load with the higher compression. You'll have better top end power to boot (Opels lose power FAST when you surpass 36 degrees total timing...see the Tech FAQ's section for the timing curves of the various year distributors). I'd shoot for 8-10 degrees baseline and 35-36 total timing.
*Pertronix ignitor and a hotter coil (The Crane PS91 is a decent coil for a decent price), or a Crane XR-3000 ignition and the PS91 coil. The Crane ignition costs more, but it also has a WAY hotter spark.
*Lighten the flywheel. This will make a huge difference in lower gear acceleration, and is very cost effective.

As far as the tires, a stock 165-13 is about 23.39" tall, and a 185/70-13 is about 23.19" tall, but will fit the stock rims. I would not go any larger, you'll end up with a lot of sidewall flex and no better tread contact area. You have the option too of widening the stock rims. I'v done this for about the past 15 years. They look stock from the side, but they're wider. A 7" rim with a 205/60-13 looks and handles GREAT and will not rub with proper offset. Most non-Opel people will never know they're not stock.

Bob

 

[chuckspeed]

Rally Bob's comments are spot-on.

The key to making power is MATCHING componentry to the engin ebuild and vice versa. A short non-Opel story:

When I started building 2.3 liter Ford motors, I had no idea how fast they'd go - only had some SAE books on engine theory and math (I wanted to engineer chassis and/or powertrains for Ford as an aspiring mech engineer), and had a VERY limited college-student budget.

Over half of power mods can be accomplished with minimal cost - assuming you have time, patience, and a little bit of experience. After two years of 2.3 liter tuning (and that is the appropriate word), I had a Pinto that flat flew.

Meanwhile, a pair of buddies went the 'bolt-on' route with their Camaro and Torino. The Torino guy went the mail order route - cam, carb, headers, and exh. None were matched - the completed motor was actually SLOWER than stock! The Camaro guy went the 'buy HP' route, and had an engine builder make up a motor for him, complete with a wild cam so's he could do the 'rump-rump' thing at the light. The motor made lots mor power - but it was WAAAY up the rev band.

In street racing, tho, it's the LAUNCH that counts. Drag strips post 60 foot times as part of the printout - it's that 60 foot time that wins/loses on the street. In the case of the Camaro, the 60 foot time stank, although the motor made good power at the big end of the track.

How'd it do against the Pinto?

Well...the Pinto sucked his headlights out in 1st gear, held its lead in 2nd, and eventually gave up its lead late in 3rd - at about 90 MPH! Since street is all about the first two gears, the Pinto was the hot ticket. Corvettes, Cougars, Mustangs, Maseratis, Posches & Pontiacs - they all fell to that bitty 2.3 whose build sheet was virtually identical to Rally Bob's suggestions! (I used a much modified 350 Holley whose bolt pattern matched the EGR plate)

About the only things I'd add to Rally Bob's build sheet is a heat shield between the exhaust and intake manifold, along with some sort of cold air induction for the carb. The best place to get cold air is off the base of the windshield - it's a natural high-pressure area. The cooler the intake charge, the more power you make. The Opel GT motor is in a highly constrained area, so underhood temps are more than what you'd normally see on a comparable displacement vehicle. Proper intake charge temp management can boost HP by 2-3%, and ram air induction may add another 2-3%. If you're at 120 HP, that's a good 5-6 HP for free!

Finally, I'd add a thermostatically controlled cooling fan so as to eliminate the parasitic loss of the belt-driven fan. If you REALLY want to get trick, add an electric water pump and reverse cooling flow (cold water to the head first). it's a bugger to vent, tho - don't recommend the reverse flow to the average Joe. These last two mods will free up approx 5-6 HP.

You'll have a runner if you do alla these things. The 2.2 Shelby I did for my brother was estimated at 160 HP (130 dyno). It outran his Porsche 944S, and his favorite street race was a normally aspriated 300ZX. He raced the guy three times - the third time he beat the guy, he could see the driver beating on the steering wheel in frustration!

Remember - you're not constrained by SCCA class rules in building a streeter, so you can do things that make more power for less. Just take your time getting the setup 'right' - it's the key to going fast with a small displacement motor.

 

[oldopelguy]

1.1 Opel Kadett

Just to throw in a peanut from the gallery, I do have some neat timeslips from a 1.1 Opel Kadett smoking everything but a funny car one evening at the drag strip.

Don't get be wrong, the car topped out at 6300 RPM at 72mph, with a single Weber IDT carb and a 2" exhaust on a pair of the tiniest slicks you will ever see. The car launched like noone's business. Weight was down to 1475# including the driver, and with the 1.1 engine the Opel was handicapped part way down the track to "even things up," so the race wasn't really fair. Nothing at the strip that evening could post a better 60' time.

Sit back, if you will, and think about the satisfaction in a $200 car with a $600 engine (that displaces 66 cubic inches) as you beat a Hemi Cuda. Then follow that with a drive home getting 42mpg.

I really loved that car, too bad the heater never worked in SD.

 

[chuckspeed]

tellyouwhut...

I really want an Opel Kadett. After the GT's and the Mantas, the Kadett is the last undiscovered country for me. I'd like to do the whole rally thing with it, complete with Steinmetz flares, widened steel rims, and a hottie 1.9.

Assuming a 130 HP motor and 1500 lbs, the Kadett (lightened, of course) would have the same power-to-weight as a late-model Corvette. If anyone got *close* to running with it on the street, a light shot of nitrous would shut them down fairly quick.

Yah - that's a fun car. Anyone got one they need outta their driveway?

 

[RallyBob]

I've got a Kadett wagon sitting there waiting for a 2.0 block with a 1.5 big valve head (11.2:1 compression), hot cam, Holley 390 4-bbl (custom intake) and custom exhaust. Should be around 160 hp, plus I've got a 50 hp nitrous kit too, a 4500 rpm stall speed converter, and a 4.22 final drive...all just waiting to be put together. Those of you who went to Carlisle LAST year might remember the custom headpipe I brought with me and the big-valve 1.5 head...those are for the Kadett.

Bob
'Gonna keep the roof rack on the wagon too'

 

[chuckspeed]

oh, man!

Paint me green with envy!

I've done motors both with the 350 and the 390 - the 390 had a off-the-shelf Offy dual-plane manifold available for the 2.3 Ford motor. FWIW, the motor (mild Crane cam, forged TRW's, a skosh over 10:1, custom header 2" custom exh and a buncha other stuff) was happier on the 350 than on the 390 - which made no sense, as the 390 should have been more tractable and powerful at the same time.

The trick was to balance the power valve/pump shot/shooter combo to offset the signal drop on tip in...the motor went fat if the settings weren't 'just so'. When they were right, the whole car lifted 4" and LEFT the line HARD. Took 3 weeks to sort it all out, as the three were interlinked. It wasn't a matter of making a change and running the trap - the three variables were interlinked with about ten choices each. Woulda took nearly 1000 passes to check each iteration, so some intuition was needed.

Great fun.

If I were to build one again, I'd like to experiment with long runner steel tube manifolds so as to cut down on the hard right angle turn the intake charge has to make after it leaves the throttle body. Imagine half a tunnel ram manifold that was cross bred with a Chrysler octopus tunnel ram, and you get the idea. So the carb sticks outta the hood! MUCH easier to explain to the poor slob you just blew away when the carb's hangin' off center!

 

[RallyBob]

I like the 2-bbl holleys for the Opels too, but they just don't have quite the range of adjustability the Webers do (especially emulsion tubes and idle jets). We've always used 500 cfm Holleys with 2.0 Pinto carb adapters on the stock (ported) intake and Lokar throttle cables for circle track Opels. In fact that 192 hp 2.1 litre circle track motor I spoke about previously used a 640 cfm Holley 2-bbl (reworked 500 Holley with Motorcraft baseplate and reworked choke towers.).

The biggest problems using them on Opels is getting the power valve orifice correct (they're about 80% too large), and the idle circuit passages too, are too large. So I epoxy them up and redrill based on my Weber experience, and then the idle mixture screws actually work, and the power valve doesn't suddenly dump excess fuel in. Gotta remember they're made for small displacement V8's, so the idle circuit and power valve circuit is literally sized for twice the amount of cylinders and over twice the displacement. The rest of the game is simply tuning...power valve vacuum values, pump cams, and jetting.

Of course, the 500 is too large for anything other than a racing 2.0 litre, or a hot 2.2 or 2.4 litre. My friend's 2.5 uses a 500 Holley and it's VERY driveable and has excellent power, far better than L-Jetronic fuel injection. I've never used a 350 Holley, but seeing as it's only 20 cfm bigger than a Weber 38 DGAS, it should be a good matchup with a ported intake.

Those of you considering adapting a 4-bbl, remember than 2-bbl carbs and 4-bbl carbs are rated at different flow depression values, so a 390 4-bbl flows at around 551 cfm (multiply times 1.414). Too much for anything except a VERY hot street engine! That's 2.9 times more airflow than a Solex!!!

Bob

 

[chuckspeed]

Right on about static pressure ratings. 2 bbl carbs are rated at a higher static pressure, so a similarly rated 4 bbl has a much higher capacity due to it's lower SP rating.

The 4 bbl off of the 62-63 Buick also works well, but they are tougher than all get out to get parts for these days.

Back in the day, I could buy brand-new 350 Holleys for $20 off the clearance table of Gratiot Auto Supply - the hot-rodders avoided them like the plague. Since I was on the 'no budget racing' team, I could afford the $20 and three weeks to futz around with the Holley, as opposed to the then $200 for the Weber - a no brainer.

I adjusted power valve flow with a gasket cutter - made the power valve gasket wider, thus cutting down the amount of available flow. Yeah, non-scientific, but it worked. Trimmed the tip in with teeny long nozzle pump shooters and cut the amount of accel pump flow by going to the orange pump cam - if I remember right. The whole deal started to work well with the addition of the orange cam.

I remember calculating carburetor size before making the switch. Discovered the motor would pull 190 CFM at max BMEP and the stocker was *around* 220 CFM. The 350 really woke up the motor...if your motor has been 'hotted up' with the addition of cam/header/port work and you're running a small-ish carb, swapping out to the bigger carbie is like adding a blower - the power difference is HUGE! After having the street-start down on a modified stocker carb, the Pinto did a donut inna intersection the first time it went head-to-head on the street!

The way to 'rule of thumb' diagnose the capacity of the carb against the motor (with free-flow exh) is to LISTEN to the note. IF, as the motor builds RPM's, the volume remains the same, then you've more or less matched carb to motor. If the note's volume drops as the RPM's build, then the motor will tolerate more carb.

Maggie the Opel has some mild head work and a 2" exh running thru a turbo muff and 2" resonator behind the rear axle. Real pleasing engine note from idle to 2500 RPM. After 2500 RPM, she starts to get quiet. By the time 4000 RPM comes along, the motor sounds like it's muffed by a stocker exh. of course, she's running the stock solex.

Discovered the 'tone check' when I added an Edelbrock manifold and Holley 4 bbl carb to my Nova SS. It already had dual exh and some head work - while the exh note was pleasing, the top end was kinda quiet. After going up in carb size - BAM! The motor got LOUDER, and sounded strong all the way up to redline.

Unscientific as all get-out, but most of us have limited access to flow benches...

 

[johnbran]

This question is really a follow up to a part of Chuck's earlier answer, but is open to anyone with some ideas.

You have the option too of widening the stock rims. I'v done this for about the past 15 years. They look stock from the side, but they're wider. A 7" rim with a 205/60-13 looks and handles GREAT and will not rub with proper offset. Most non-Opel people will never know they're not stock.

In regards to widening the stock 13" wheels to 7" or so, like you mentioned, what is the best method in doing this? For instance, what equipment do you prefer to cut the wheel apart with and what size/kind of metal do you prefer to use for the spacing material to widen it out? Also, where do you usually cut the rim apart at or is there any particular place on the rim that is better to cut and won't chance weakening the wheel? I am very interested in performing this mod to my GT wheels and want to get as much info as possible before attempting it. I'll probably "practice" on some scrap rims first just so I don't risk damaging my good GT rallys. Can all 4 rims (front/rear) be widened to about 7" without clearance problems? How about taking the rears to 8" or possibly more? Would this present any problems if only done on the rear wheels? I really like the idea of keeping a somewhat "stock appearing" car by running the rallys, but with the better handling and looks too from running wider wheels/tires. It's the best of both worlds. So, any info or tips you or the others could pass along about this particular modification would be greatly appreciated.

Thanks,
John