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Old 01-20-2008, 12:24 PM   #1
kb58
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Default Low boost K20 or lower boost K24?

As some know, I'm currently designing a one-of-a-kind car. It's going to be mid-engine and very light, <1400lbs. For trackday events I don't want any "issues" with pesky Z06s, heavily moded STis, or Evos, and that means >250whp. IMHO, somewhere around 220-230whp is where a turbo becomes cheaper than NA, so I'm thinking of going that route, a low-boost setup between 250-300whp.

Liking torque I immediately got interested in the K24A2, but between the high prices and questionable sellers ("what VIN?") I wonder if I should reconsider. What I mean is, if I'm going to turbo anyway, should I just start with the the more common and cheaper K20.

The catch is that this turbo setup will only use 91 octane gas, so the smaller 2 liter will need more boost to reach the above power goal, pushing it closer toward detonation. Regardless of engine choice, I will likely change pistons and rods, backing it off to 9:1 for safety.

Your thoughts on this, and input on which K20 to use as a base?
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Old 01-20-2008, 12:58 PM   #2
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Default Re: Low boost K20 or lower boost K24?

if your gonna go with a k24 go with a crv bottom end and a k20a2 head. The compression is around 9 something to 1.
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Old 01-20-2008, 01:09 PM   #3
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Default Re: Low boost K20 or lower boost K24?

Ah, very good point, and the extra expense of pistons and rods that I would have needed has to be factored into this, too. Thanks!
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Old 01-20-2008, 01:23 PM   #4
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Default Re: Low boost K20 or lower boost K24?

thats the setup i am currently running. I have yet to put the turbo kit on it yet though. i'm lazy.

if you look around you can get a good deal on a crv motor. I got a great deal on mine. I bought a complete 05 crv motor for $800 shipped. I just changed out the heads and put the type-s oil pump in.
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Old 01-20-2008, 01:53 PM   #5
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Default Re: Low boost K20 or lower boost K24?

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Originally Posted by kb58 View Post
As some know, I'm currently designing a one-of-a-kind car. It's going to be mid-engine and very light, <1400lbs. For trackday events I don't want any "issues" with pesky Z06s, heavily moded STis, or Evos, and that means >250whp. IMHO, somewhere around 220-230whp is where a turbo becomes cheaper than NA, so I'm thinking of going that route, a low-boost setup between 250-300whp.

Liking torque I immediately got interested in the K24A2, but between the high prices and questionable sellers ("what VIN?") I wonder if I should reconsider. What I mean is, if I'm going to turbo anyway, should I just start with the the more common and cheaper K20.

The catch is that this turbo setup will only use 91 octane gas, so the smaller 2 liter will need more boost to reach the above power goal, pushing it closer toward detonation. Regardless of engine choice, I will likely change pistons and rods, backing it off to 9:1 for safety.

Your thoughts on this, and input on which K20 to use as a base?
First, I must congradulate you on your excellent mid-engine mini project. As your buddy said, "It's nice to see someone complete a project". Second, I must say, Nice driving at laguna seca. Even the porshe waved you by.

As to which k20 to choose. I would suggest the k20a2. the k20a has a higher compression ratio which isn't the best candidate for turbo. The k24 makes quite a bit more torque than the a2 and in most cases I would suggest it. But since you're building a car that's going to weigh less than 1400 lbs... traction is going to be an issue.

Just my .02 cents

edit: oh.. and as for turbo.. I would definately go with the fullrace kit if you can make it fit. If money is an issue. Peakboost is what I went with and I'm lovin it
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Old 01-20-2008, 05:08 PM   #6
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Default Re: Low boost K20 or lower boost K24?

Would you use the high-compression K20A2 as a base for forced induction? I'm now tempted to go larger displacement again, especially since the K24A1 + K20 head = 9:1 CR...
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Old 01-20-2008, 07:52 PM   #7
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Default Re: Low boost K20 or lower boost K24?

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Would you use the high-compression K20A2 as a base for forced induction? I'm now tempted to go larger displacement again, especially since the K24A1 + K20 head = 9:1 CR...
go with the k24 u won't regret it. But either way it will be fine. Your not going to be running alot of boost to get 300hp. The compression wouldn't be a problem.
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Old 01-21-2008, 06:10 AM   #8
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Default Re: Low boost K20 or lower boost K24?

If you buy a complete K20a2 swap (RSX-S) you will get everything you need to do your swap (tranny, wiring harness, correct TB, 3 lobe vtec head, etc). It is a great motor with a lovely 8600rpm redline stock, and people have made upwards of 500-600hp on the stock block. So your goal of 300whp should not be hard and should still be as reliable as any other stock block turbo setup, assuming it is tuned properly and has a well setup cooling system. Starting this way will also give you the opportunity to get the car running with a complete OEM untouched factory motor. At that point you can throw on the turbo, build a 2.4L short block, or whatever else you may want to do and not have to worry about piecing anything together before you can get the car running. The RSX-S motors are also more common than the golden child of the 2.4Ls the TSX, and finding a clean complete motor and trans should not be to hard (look for something in the 3000-3500 price range complete with motor/trans/shifter/harness etc, if not cheaper)...
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Old 01-22-2008, 12:35 PM   #9
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Default Re: Low boost K20 or lower boost K24?

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...Starting this way will also give you the opportunity to get the car running with a complete OEM untouched factory motor. ...
I'm aware of that... and between that and price, it may be what causes me to go that way. I am surprised though that people are boosting that much on an 11:1 K20A2 block. Remember that I'm using a self-imposed requirement of running only 91 octane. Even 300whp seems like too much for 11:1. Is my thinking right about this?

Regardless of engine, I'd really like to avoid swapping pistons and rods. The head, maybe, and if the K24A1/K20A2 head gives 9:1, that seems like where I'd want to be. OTOH, I completely agree about the price. With the K24 being the new thing, K20 setups should start showing up with decent prices.
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Old 01-22-2008, 01:58 PM   #10
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Default Re: Low boost K20 or lower boost K24?

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I'm aware of that... and between that and price, it may be what causes me to go that way. I am surprised though that people are boosting that much on an 11:1 K20A2 block. Remember that I'm using a self-imposed requirement of running only 91 octane. Even 300whp seems like too much for 11:1. Is my thinking right about this?
With the right parts you can make this on 5-8psi.

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Regardless of engine, I'd really like to avoid swapping pistons and rods. The head, maybe, and if the K24A1/K20A2 head gives 9:1, that seems like where I'd want to be.
Yes.. I just don't know about circuit racing it though, I imagine pushing the stock internals that hard for that long on boost (even as low as it is) might snap a rod or damage something in time. I'd swap in forged internals to be safe.
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Old 01-22-2008, 02:33 PM   #11
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Default Re: Low boost K20 or lower boost K24?

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I'm aware of that... and between that and price, it may be what causes me to go that way. I am surprised though that people are boosting that much on an 11:1 K20A2 block. Remember that I'm using a self-imposed requirement of running only 91 octane. Even 300whp seems like too much for 11:1. Is my thinking right about this?

Regardless of engine, I'd really like to avoid swapping pistons and rods. The head, maybe, and if the K24A1/K20A2 head gives 9:1, that seems like where I'd want to be. OTOH, I completely agree about the price. With the K24 being the new thing, K20 setups should start showing up with decent prices.

The VTC and the great ECU options available to us make tuning even the semi high comp FI setups very easy. The thing you are really going to have to watch is the heat and the expansion of parts due to the heat (I.E. the stock cast pistons). The oil squirters found in the K20a2 and the K24a2 will help with keeping the OEM cast parts cool, but the K24a1 block you speak of does not have these comodities and would be much better off with a set of forged aftermarket internals. The rods in the CRV block are also not the beefiest around and may give out on you sooner or later (although I am sure you could get some quality use out of them before they let go). Look around at some of the members on the forums signitures, there are plenty of guys running around with low boost setups (8-10psi turbo setups making around or above 300whp, and plenty of non intercooled SC guys pushing 6-9psi making 260-280whp) and also a hadnfull of guys pushing the stock 2L blocks up to 14psi or above and making gobs of power more than that and still running strong!

a nice tubular manifold and an intercooler and 8-10psi will put you above 300whp effortlessly, you just need a quality tune and a setup that can handle the abuse of regular stints on the road course...
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Old 01-22-2008, 06:20 PM   #12
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Default Re: Low boost K20 or lower boost K24?

Nuts...

So, regardless of engine, to do things right, I have to install rods and pistons (I knew this... but was hoping for a cheaper answer.)

In this case it seems like I should go for a cheap block, K24A1 or A4, change rods and pistons, add pistons squirters if it's not too hard, and leave the head stock. I'd leave the head stock because as light as the car is and as much torque as it will make when turbo'd, I can't see any reason to "need" to rev it high.

Also due to the anticipated high torque is using a 5sp instead of a 6sp, both for strength and because I think shifting isn't very important when there's tons of torque on tap. With a small turbo, the torque band should be really wide.
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Old 01-23-2008, 08:41 AM   #13
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Default Re: Low boost K20 or lower boost K24?

I think a boosted k24 may cause problems in such a lightweight chassis. Have you considered a supercharged k20? I'm not a fan of turbos in a track vehicle due to the non-linear powerband. However a SC gives you a flat torque curve from low rpms up. Power is smoother and always there.

Add lightweight rods and the piston of your choice (I would want to keep a higher CR piston) and you should be golden in such a lightweight vehicle. How does your desired power/weight ratio compare to that of an atom?

As for how high you need to rev, you need to see what speed you can obtain in each gear with your desired tire size. That will actually determine what rev range you need to work with.
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Old 01-23-2008, 07:46 PM   #14
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Default Re: Low boost K20 or lower boost K24?

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I think a boosted k24 may cause problems in such a lightweight chassis. Have you considered a supercharged k20? I'm not a fan of turbos in a track vehicle due to the non-linear powerband. However a SC gives you a flat torque curve from low rpms up. Power is smoother and always there.

Add lightweight rods and the piston of your choice (I would want to keep a higher CR piston) and you should be golden in such a lightweight vehicle. How does your desired power/weight ratio compare to that of an atom?

As for how high you need to rev, you need to see what speed you can obtain in each gear with your desired tire size. That will actually determine what rev range you need to work with.
I think common has an excellent point here. A 2.4 is huge for a rwd car, even with such balance. You are going to have major traction issues with 2.4 and even a 2.0 turbo. I would suggest staying all motor honestly, but if your heart is set on turbo I would focus on the upper portion of the powerband to keep the most power higher up in the RPM and stick with a 6 speed box. You'll have to learn how to drive a peaky car but I think you'll be much faster in the end.
2 cents.
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Old 01-24-2008, 06:49 AM   #15
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Default Re: Low boost K20 or lower boost K24?

All good points.

Remember that's it's mid-engine. I currently have an mid-mounted H22A1 in my 1600lb Mini. Starting in second gear I get to 60mph in 3.9 seconds. There's very little wheel spin, only for the first 10 feet or so, and then it just hooks up and goes. Tires and clutch fight each other, resulting in a stinky stock clutch - drag race starts aren't something I like to do.

The NA H22 puts out 190whp, so 250whp doesn't seem like an uncontrollable amount. About the NA vs FI thing, I see NA getting really expensive well before the 250whp goal, never mind anything higher. The turbo's not as expensive (especially since I'd make everything myself) and the sky's the limit, power-wise. NA requires great expense on every part of the engine. Crank, rods, pistons, valves, valve springs, cams, head porting, intake replacement/porting. Going turbo means rods and pistons, and that's it, but you guys know all this.

Also, I'd design it to be anything but peaky. With 8-10psi boost and a small turbo like a GT28RS, I'd like to have full boost as low as possible and I think that can happen by around 3000rpm.

All that said, I'm fully aware that a turbo setup tends to be unreliable in a roadracing environment, and not very drivable. I suspect that this is due to high boost and peaky turbos, exactly what I plan to not have. I recently saw an in-car video of a kid who took his 400hp FWD Honda to a trackday event. That thing was completely useless on-track, as the boost would hit like a freight train and he was getting wheels spin all over the place. If he'd cut the boost in half he would have been much faster, but I digress.

A supercharger is a viable option, too, but that decision's still a ways off. There's a car to finish designing, and I sometimes wonder if I'll ever find an engine. Seems like the "VIN word" scares away sellers. What, are all these engines stolen?
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Old 01-24-2008, 03:18 PM   #16
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Default Re: Low boost K20 or lower boost K24?

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All good points.

Remember that's it's mid-engine. I currently have an mid-mounted H22A1 in my 1600lb Mini. Starting in second gear I get to 60mph in 3.9 seconds. There's very little wheel spin, only for the first 10 feet or so, and then it just hooks up and goes. Tires and clutch fight each other, resulting in a stinky stock clutch - drag race starts aren't something I like to do.

The NA H22 puts out 190whp, so 250whp doesn't seem like an uncontrollable amount. About the NA vs FI thing, I see NA getting really expensive well before the 250whp goal, never mind anything higher. The turbo's not as expensive (especially since I'd make everything myself) and the sky's the limit, power-wise. NA requires great expense on every part of the engine. Crank, rods, pistons, valves, valve springs, cams, head porting, intake replacement/porting. Going turbo means rods and pistons, and that's it, but you guys know all this.

Also, I'd design it to be anything but peaky. With 8-10psi boost and a small turbo like a GT28RS, I'd like to have full boost as low as possible and I think that can happen by around 3000rpm.

All that said, I'm fully aware that a turbo setup tends to be unreliable in a roadracing environment, and not very drivable. I suspect that this is due to high boost and peaky turbos, exactly what I plan to not have. I recently saw an in-car video of a kid who took his 400hp FWD Honda to a trackday event. That thing was completely useless on-track, as the boost would hit like a freight train and he was getting wheels spin all over the place. If he'd cut the boost in half he would have been much faster, but I digress.

A supercharger is a viable option, too, but that decision's still a ways off. There's a car to finish designing, and I sometimes wonder if I'll ever find an engine. Seems like the "VIN word" scares away sellers. What, are all these engines stolen?
This is all true, however, its not HP that creates wheelspin, its torque. The H22 stock is a great motor for this car, but it really doesn't sh!t out trq (150-160 ft pds?) the way a turbo will (300 whp will land you in the low 200's for wheel trq depending on what k series you use). However, it can be controlled with a proper suspension setup I would imagine. Try the turbo and focus on getting the power to ground afterwards if you are gonna go this route. Use a really small turbo that wont wind out (K20's will take you to 8k+ rpms, 24's to 7ish) at the upper end of the power band with a conservative tune and I think you will be ok. Good intercooler placement seeing as you are not stock honda body =D(I would imagine you have great spots with the front being so empty) is also key.
Be sure also to match your upshift landing points with your powerband and step up your FD to compensate for any wheel torque lost.
That and a little experience with pedal modulation (not being able to smash open the throttle on corner exits) will net you some nice times at the track if you plan to go turbo.
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Old 01-25-2008, 08:10 AM   #17
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Default Re: Low boost K20 or lower boost K24?

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All good points.

Remember that's it's mid-engine. I currently have an mid-mounted H22A1 in my 1600lb Mini. Starting in second gear I get to 60mph in 3.9 seconds. There's very little wheel spin, only for the first 10 feet or so, and then it just hooks up and goes. Tires and clutch fight each other, resulting in a stinky stock clutch - drag race starts aren't something I like to do.
Even being mid-engined, you may not have enough weight and mechanical grip to effectively put down the power. If the wheels are spinning, thats lost power The short gears of the 6-spd trannies might make 2-3 useless for you.

Quote:
The NA H22 puts out 190whp, so 250whp doesn't seem like an uncontrollable amount. About the NA vs FI thing, I see NA getting really expensive well before the 250whp goal, never mind anything higher. The turbo's not as expensive (especially since I'd make everything myself) and the sky's the limit, power-wise. NA requires great expense on every part of the engine. Crank, rods, pistons, valves, valve springs, cams, head porting, intake replacement/porting. Going turbo means rods and pistons, and that's it, but you guys know all this.
Actually you can get much closer to your goal than you think while staying N/A. Ported head, ported IM, cams, and custom header should put you very close to your goals. Some of the items you are going to have to do regardless of boost/na just for reliability on a road course (valvetrain & light rods). Anyways, the cost to go n/a would probably be ballpark the same as building a small reliable turbo setup.

Quote:
Also, I'd design it to be anything but peaky. With 8-10psi boost and a small turbo like a GT28RS, I'd like to have full boost as low as possible and I think that can happen by around 3000rpm.

All that said, I'm fully aware that a turbo setup tends to be unreliable in a roadracing environment, and not very drivable. I suspect that this is due to high boost and peaky turbos, exactly what I plan to not have. I recently saw an in-car video of a kid who took his 400hp FWD Honda to a trackday event. That thing was completely useless on-track, as the boost would hit like a freight train and he was getting wheels spin all over the place. If he'd cut the boost in half he would have been much faster, but I digress.
I think the spool and torque steer would be big issues as well. Engine braking into a turn, quick downshift, rolling into throttle mid-turn, turbo spools, torque steer, and car kicks to the side.

Quote:
A supercharger is a viable option, too, but that decision's still a ways off. There's a car to finish designing, and I sometimes wonder if I'll ever find an engine. Seems like the "VIN word" scares away sellers. What, are all these engines stolen?
eh, buy from a legit place like www.hmotorsonline.com . It will save you a few headaches down the road. I have pretty much decided I'm not dealing with another individual seller for anything that moves or can wear. So unless I need a rock with a k20 sticker on it, I'm buying new oem and saving myself unnecessary headaches.
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Old 01-25-2008, 12:10 PM   #18
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Even being mid-engined, you may not have enough weight and mechanical grip to effectively put down the power. If the wheels are spinning, thats lost power The short gears of the 6-spd trannies might make 2-3 useless for you.
That's why I'm going with the 5-speed tranny.

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Actually you can get much closer to your goal than you think while staying N/A. Ported head, ported IM, cams, and custom header should put you very close to your goals. Some of the items you are going to have to do regardless of boost/na just for reliability on a road course (valvetrain & light rods). Anyways, the cost to go n/a would probably be ballpark the same as building a small reliable turbo setup.
I realize I CAN get there - it's a cost/benefit thing. For a low-boost, low-rpm FI, I see $3-4k over the cost of the engine. For NA, geez, where do I start? Virtually every piece of the engine has to be modified for reliable high rpm. And when it's all said and done, what whp can I expect on 91 octane? I'm not putting down the NA solution, but I do feel it can't get where I want to go (without spending way more than a turbo solution.) I suspect to reach even 250whp will cost quite a bit more going the NA route. However, I'd love to be proven wrong on this, but I've yet to see an NA solution that doesn't involve E85, race gas, or 9000rpm. (I also think high rpm kills engines faster than boost, but that's just me.)

Also, I don't need hp, hp is for top speed, I have no need to go >145mph... but I'd like to get there quickly, with torque.

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I think the spool and torque steer would be big issues as well. Engine braking into a turn, quick downshift, rolling into throttle mid-turn, turbo spools, torque steer, and car kicks to the side.
I'm aware of this and agree it may be an issue, maybe even a big issue. It's something that I've never gotten a good consensus on. Half the people I talk to say it's an issue, and the other half say it's fine. I'm hoping to avoid trouble by staying low boost and a wide torque band. If I never fall below full boost, I shouldn't have lag issues... that's the theory...

I have a theory that 90% of the people who say a turbo on track is a problem are the same ones with really high-hp peaky setups. I think they get sucked into the peak hp bragging game, have fun dragracing, then think they can clean up at trackday events. Totally different situation. But like I say, it's just my theory.
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Old 01-25-2008, 02:43 PM   #19
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That's why I'm going with the 5-speed tranny.


I realize I CAN get there - it's a cost/benefit thing. For a low-boost, low-rpm FI, I see $3-4k over the cost of the engine. For NA, geez, where do I start? Virtually every piece of the engine has to be modified for reliable high rpm. And when it's all said and done, what whp can I expect on 91 octane? I'm not putting down the NA solution, but I do feel it can't get where I want to go (without spending way more than a turbo solution.) I suspect to reach even 250whp will cost quite a bit more going the NA route. However, I'd love to be proven wrong on this, but I've yet to see an NA solution that doesn't involve E85, race gas, or 9000rpm. (I also think high rpm kills engines faster than boost, but that's just me.)

Also, I don't need hp, hp is for top speed, I have no need to go >145mph... but I'd like to get there quickly, with torque.


I'm aware of this and agree it may be an issue, maybe even a big issue. It's something that I've never gotten a good consensus on. Half the people I talk to say it's an issue, and the other half say it's fine. I'm hoping to avoid trouble by staying low boost and a wide torque band. If I never fall below full boost, I shouldn't have lag issues... that's the theory...

I have a theory that 90% of the people who say a turbo on track is a problem are the same ones with really high-hp peaky setups. I think they get sucked into the peak hp bragging game, have fun dragracing, then think they can clean up at trackday events. Totally different situation. But like I say, it's just my theory.
Well, think of what track cars weigh sub 1800 lbs and are turbo. Cart, F1, protoype style racers, and they can put that kind of power down due to 2 things.
Low trq/high hp and aerodynamics.
I say try the turbo though and prove us all wrong.
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Old 01-25-2008, 05:32 PM   #20
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Originally Posted by zerotraction View Post
Well, think of what track cars weigh sub 1800 lbs and are turbo. Cart, F1, protoype style racers, and they can put that kind of power down due to 2 things.
Low trq/high hp and aerodynamics.
I say try the turbo though and prove us all wrong.
So if turbo engines give low torque and high hp, I'll have no problem getting that "low torque" to the ground. However, another post a bit higher says I won't be able to get all that torque to the ground... Just messing with you.

Prove you wrong? What am I saying that's contrary to what you guys are saying? Is it that I think that I can get the traction to the ground and you guys think not? How much weight's on the front of a FWD Honda under full acceleration at 300whp? I'm guessing I'll have about twice that weight due to load transfer on my back tires, so roughly twice the traction. That seems like a good thing.

Aero doesn't help below around 120mph, so that's not their solution for low-speed traction. They fix that with crazy-wide chewing-gum-soft racing slicks.
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