Mark 4 VW 1.8T GTi Build - RallyCross - MF Class

Correct. I've been looking at SCCA RallySprints, as well as Sprints run at The Firm in Starke, Florida. Some of our local competitors in RX also run the Firm events, and have reported 75-80 as max speed.

So if I keep standard gear ratios, less labor and parts costs, and fine shift points at 6200-6500 rpm.

RX will all be 1-2 events, and the Sprints would be 1-2-3 events.

So far, so good. Now to save up for the lsd, and pick a good clutch for the 2.0 trans on the TT turbo engine.

Thanks, guys.

Don't forget that you will have wheelspin under power, always, and you also won't ever really get to use the theoretical top of a gear if the surface is at all rough.

For example, my 2nd gear is theoretically good for 70-75mph but practically speaking I have to shift to 3rd at about 50-55mph actual, lower the rougher it is. Engine zings from 8k to 11k+ REALLY fast when it unloads the tires at WOT...

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Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.



Edited 1 time(s). Last edit at 08/01/2016 11:54AM by Pete.

Good to know. The experiences like that are why I came to this site. My Rovers off roading set ups, are all low end, low gear on the transfer case; and crawling through mud or sugar sand. So nothing like this will ever be. A 3 ton truck fully loaded, at 15-20 mph top end, and usually 10 mph does not translate to the rally or even RX world.

Luckily when we set up the tune on the dyno, I will be able to set the turbo up so the power is coming on over 3500-4000 rpm. Hopefully this will allow the tires to grab and be biting, before the turbo tries to break them loose.

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DanielSL
Luckily when we set up the tune on the dyno, I will be able to set the turbo up so the power is coming on over 3500-4000 rpm. Hopefully this will allow the tires to grab and be biting, before the turbo tries to break them loose.

So your goal is lag? If so why?

Throttle pedal is how you control power output, not turbo sizing/geometry or boost controller settings.

No, not lag. That's the nice thing about the Maestro tune on the dyno. I'll be spooling up, and power on, around 1800-2200 rpm, but not on full boost until 3500-4000. The sweet spot would be to have the boost building as the tires are gripping and pulling the car forward, out of the corners. That way it is "shooting" into the straights.
But too much boost, too soon, and even with a lsd, I'll be spinning tires and wasting time. I will have the ability to go between 2-3 maps, so I am hoping to eventually design it to have a sand tune, an overall dirt tune, and a tarmac tune. That's one of the reasons that from the beginning I went with a turbocharged car.

It doesn't work that way. The tires are never "biting" in the way you're thinking. The surface is rough and loose, if the grip is tenuous then when the tires get unloaded...

This is why suspension damping and geometry is so critical, you need to make sure the tires FOLLOW.

This is why my personal car has a rotary engine (absolutely flat and predictable torque curve) and rear suspension geometry that drives the tires into the ground for max grip.

My turbocar experience is less than enthusiastic. My personal turbocar I just turn the boost down so it doesn't break the tires loose much if any. My friend's turbocar, I can't get the hang of driving, it just sort of goes and then the boost hits at 3k-ish and then it's on the rev limiter. Which is entertaining, to be sure, but very frustrating personally because I can't finesse the car, it's more like playing darts with a sledgehammer.

FWD would be easier to deal with this because you can at least vector the drive wheels...

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Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.

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john vanlandingham
looking at the results...Badass class: 6 runs average 119.1 second-per run
and the P class................................6 runs average 120.5 seconds per run..

about 1% difference

Clearly modding CARS in any way is meaningless for this kinda of hooning..
Driver driving cleanly and as I said 1000 times driver avoiding MAJOR BLUNDERS is key.
Not vented 17" discs and crazy tires and mucho turbos or anything much.

Just don't fuck up.

I was looking through this thread to make sure I didn't already post the embarassingly bad videos of me trying to drive a turbo Miata (but I did post the picture of the tire carnage from turbo throttle response * gravel, which was awesome, and oh well the tires were getting bad UV cracking so it was a Viking funeral for them. they died with HONOR) and I thought I'd point out that at last weekend's Ohio rallycross, on a soft and loose dirt "power course" with a steepish down and up hill, two idiots (myself included) in an Impreza 2.5i wagon on street tires (not even snows, with a heavy '07 chassis...) dominated Stock class to an embarassing degree.

The car was also used by another friend, same friend who lets me drive his Miata or 2.5RS every now and then, and he chose to run it in Mod class against the turbo/rally tire/strippo guys, just for shits and giggles. He placed first in class. And he wasn't downshifting to 1st at the start of the hill even though I was shouting at him "DOWNSHIFT YOU WUSS".

It isn't so much what you use but how you use it. And when people are using it correctly, a lot of people aren't MODIFYING correctly, they're doing all the wrong things. Reducing spruing weight while increasing unsprung weight. Running big giant tires that don't have good side bite compared to tires of the right size. Running turbo engines that have undriveable power response.

Corner workers from during my run heat noted that my car's owner and I were braking a car length or two later than everyone else. Well no KIDDING, the brakes are to set the chassis not to slow down, you turn in a little, stomp the brake once or twice to get the car rotating, and power through as soon as the car is aimed in the direction you want to go. We only had maybe 170hp and the course layout had us in the annoying section between gears for most of the runs but grit and determination and BOTC got us through.

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Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.



Edited 1 time(s). Last edit at 08/01/2016 07:54PM by Pete.

Pete; Excellent advice, and I am listening...

I will be paying very close attention to the torque curve on the dyno, when we're tuning. We might actually be able to pull some power out of it, to make the curves flatter, or at least more linear. The last thing I want is Hp or Torque spikes anywhere in the powerband I will be using.

I am thinking I will be needing between 2,000 and 7,000 rpm to be as linear as possible in the 1st through 3rd gear realms. Luckily, I will be able to spend enough time, and get my dyno curves in all gears. Even if I have to do multiple runs in each.

I am not planning on doing the tuning like a drag car or street car, where your dyno runs are in 3rd and 4th gear only. I want to see what this engine package is going to do, where I am going to be using it.

The Scion (Toyota) factory team spent a lot of time trying to get power down in their FWD turbo stage rally car and despite a lot of time and money spent, it remained a massive challenge in any corner under say 45mph.... After years of development, racing, and testing with multiple drivers, setups, etc..

I am not doubting that it can be done, but I wouldn't be at all sure that you and your tuner can sort it out even with a whole day on the dyno.

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____________________________________________________________-

One. Class -- 2WD

www.quantumrallysport.com

http://www.facebook.com/home.php?#/pages/Quantum-Rally-Sport/281129179600?ref=nf

The place to shoot for linearity is not at WOT but in response at, say, 20%, 40% throttle. THAT is what needs to be predictable, if you're at light throttle then you're in a finicky situation and the car needs to do exactly what you want it to.

If you're able to go WOT then you probably have enough grip that the powerband can be whatever.

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Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.

USRT has a boost controller that works in-line with the ECU. Maybe I can use that in conjunction to make sure the boost doesn't come in too early in the powerband. Basically creating the car to react like a NA engine until 3,000 rpm or so. I will have to look into it more with the staff over there.

i wonder if you could use a boost controller with a steering angle sensor, so the boost would not come on full until the wheels are straight under a given speed

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I would rather drive a slow car fast as a fast car slow!
first rule of cars: get what makes you happy, your the one paying for it!

So much effort for a rallyx... so much wasted time and effort. 1.8t if you must, but spend all that extra money you're wasting on boost controllers, ecu tunes, gear sets and random bits and spend it on rally school, tires and seat time.

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DanielSL
USRT has a boost controller that works in-line with the ECU. Maybe I can use that in conjunction to make sure the boost doesn't come in too early in the powerband. Basically creating the car to react like a NA engine until 3,000 rpm or so. I will have to look into it more with the staff over there.

The VW ECU is WAY WAY WAY more capable than you know. There are tables in the factory ECU that can be unlocked for launch control and torque management.

BTW, a naturally aspirated 1.8 low-compression engine below 3000 rpm is going to make like 30hp and 40tq...

It seems you may be bench-racing well above your engineering knowledge base.

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____________________________________________________________-

One. Class -- 2WD

www.quantumrallysport.com

http://www.facebook.com/home.php?#/pages/Quantum-Rally-Sport/281129179600?ref=nf

Josh; That's an understatement. I was a Marine Biology major at an Engineering school. Left my senior year because they wanted us (Bio majors) to take Calculus 3 to graduate. Told them where they could stick it, and never looked back. I absolutely hate math, mathematics, technology, all of it.

That's the major reason the shop will be doing the install, tuning, and dyno work. If I tried to do any of that myself, there would be shotgun holes all throughout the shiny race car. I'll stick to wrenching on the body work, plumbing, seats, brakes, and wheels. And then concentrate on driving and seat time, as soon as its rolling.