Learning how to build Lotus Seven replicas...together!
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PostPosted: August 6, 2008, 12:24 pm 

Joined: August 15, 2005, 10:13 pm
Posts: 7043
Location: Charleston, WV
The info below was condensed from this thread. For those who don't want to read through four pages here are the cliff notes. I do however recommend reading the whole thread, I left out a lot.

On Turbo Selection:
Me wrote:
I was told I should run a "Disco Potato."

Junior wrote:
The disco potato is really a GT28RS. Great turbo to make 250 whp. It can make 325 but will run out of steam doing it. If I had a 1.8L miata motor I would go for the GT28/71. It has the same exhaust wheel, 53.8mm as the GT28RS, but has a larger 71 mm compressor wheel. The turbo can easily support 350 whp and will have ALMOST the same spool characteristics as the disco potato.

Keith Tanner wrote:
First off, the Disco Potato is a bad choice for a Miata engine. Bad. It spools like a big turbo and makes power like a little one. Seriously, if it wasn't for the super-cool name that turbo wouldn't be well known.

The GT 2560 is a good mix of power and spool in my opinion, and in a Locost I'd probably prefer the smaller GT 2554 because I think response is more important than ultimate power in our application. But packaging is also a concern, and the Mazdaspeed manifold for the 1.8 helps a lot - get the compressor and intake wheels changed out and you can get a good bit of response out of the little IHI used in that application. Feel free to give us a call at Flyin' Miata and we can help sort you out. It might make sense to choose your manifold first due to the packaging considerations. On a 1.6, the manifold from the 323 GT and 323 GTX might actually work nicely.

Junior wrote:
Never heard anyone say the disco potato spools like a big turbo. Even its big brother the GT30/71R spooled TO FAST on my 2.0L S2000 for my taste. Full boost by 3700 with 5300 rpm of boost to play with. Was a great street set-up, but no matter what I was always boosting. Even when just trying to cruise around that turbo was ready for action!

I can't imagine with the tiny GT28RS it spooling slow on a 1.8L miata. Keith you have way more experience here then me so I have to trust you. I will run the flow numbers on a GT28RS flow chart, but the characteristics you describe with that turbo would lead me to believe you are running a poor log manifold with a small down-pipe.

A GT25 is the turbo that is on the SR20DET that I have in the lotus now.

Keith Tanner wrote:
...An S2000 engine has a lot more available energy to spin up a turbo - 11:1 and 2.0 beats 9:1 and 1.8. The numbers don't work out that well for the Miata engine, it's a fairly narrow sweet spot in that application regardless of manifold or downpipe design. We've found that the 3071 offers the same spool but with a lot more headroom, or the 2560 is far better for spool and is nicely sized for the power level the rest of the drivetrain can handle.

Keith Tanner wrote:
...boost is not the goal, power is the goal. You choose the turbo that's best suited for your needs, and the amount of boost is a byproduct. It's my opinion that it's power levels and tuning that kills engines, not simple manifold pressure.

A Miata engine running 200-250 rwhp doesn't need anything unusual, it just needs to be a healthy stock engine. If you want to reinforce anything, reinforce the rods. But even that money is better spent on excellent engine management and/or professional tuning if power, response and longevity is the goal.

By itself, "boost" is a meaningless piece of information. But, like peak horsepower, it's a simple, single number so people focus on it. And also like peak horsepower, it's not really very useful.

When people call Flyin' Miata, they always want to know how much boost the various turbo systems can run. The answer is "whatever it takes to reach the power level you need". The first step is to choose the correct turbo, and that's done with power levels.

Want 180 hp at the rear wheels? Well, maybe that's 11 psi on a GT2554 with a Voodoo box, or maybe it's 8 psi on a GT2560 with a Hydra. Or 6 psi on a GT3071 with a Hydra, never tried to run that low on one. "25 psi" is a meaningless statistic without knowing anything else, but it does impress the sort of "tuner" who likes to wear his baseball cap sideways. To many people, boost pressure is the goal. They want a "12 psi" turbo kit, not a "250 rwhp" turbo kit. Or that's what they think they want.

The boost level is simply a parameter, like the timing number at a given load and engine speed. Factor is a good word for it, so feel free to substitute that in my post.

On Water/Meth Injection:

Keith Tanner wrote:
One suggestion - instead of an intercooler, consider water/methanol injection. It's amazingly effective. We're going to pull the intercooler out of the Westfield.

Junior wrote:
KB58 wrote:
evotech wrote:
Keith gave some good advice. Instead of all the piping and expense of an intercooler, a alcohol/water injection kit does a very good job of lowering intake temps. In addition it also effectivly equates to more octane allowing more boost/compression without the need for race fuel. I have used it for years with good results. A 50/50 mix of water and methanol works best.

Until you run out, like with nitrous. How fast is it consumed?

On a viper I did it ran just water/meth and has a 2 gallon container and it will last 2 fill-ups on the street, but on the track it made it through two 30 min runs and then needed a refill.

In reality there is no answer kimini, because its based on the reservoir you go with and the size of injectors you run on the set-up.

Hope that helps

J. R.

Other points/suggestions. (sorry for not crediting all the posters of this info, I don't have that kind of time, but you know who you are and your input is appreciated)

After turboing your car you will likely need a larger radiator, consider that in the design phase.

Money spent on engine management will yeild the best bang for the buck above any other component.

Stock Miata rods are good to around 12psi.

KB58 Provided the following links:
Go to http://www.rceng.com/ to accurately figure what you need for injectors and fuel. 310s are WAY too small. 300hp requires around 660-750cc injectors. And don't forget a larger fuel pump, too.

Go to http://www.turbobygarrett.com/turbobygarrett/index.html to figure out which turbo is correct. Be sure to read the Turbo Tech section.

Keith on the Miata transmission:
The transmission does become a problem at 250hp + if it's abused. I don't think we've ever lost a transmission at FM other than two in a 350hp race car, and there were extenuating circumstances there. It's the weakest point in the drivetrain, but I wouldn't call it weak. Of course, we don't break engines often as well so maybe we're just conservative.

He is a wise man who does not grieve for the things which he has not, but rejoices for those which he has.

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PostPosted: August 30, 2009, 12:56 am 

Joined: August 29, 2009, 3:18 am
Posts: 3
I'm not sure if I can post here but seeing that it's my first post maybe I sneak by on ignorance.

A couple good things to add to this thread is a good fuel pump and fuel pressure regulator, I would recommend a Wahlbro 255, that typically will supply all of your turbo hp fuel needs and an Aeromotive FPR. Both of those i've used many times and are high quality pieces.

Also a better way of looking up what Turbo fits your goals is the compressor maps.

Here is a good link to understanding the maps...

http://www.turbobygarrett.com/turbobyga ... ch103.html



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PostPosted: September 1, 2009, 8:09 am 
Locostering Information Liaison
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Joined: August 17, 2005, 1:30 am
Posts: 2397
I'm not sure if I can post here but seeing that it's my first post maybe I sneak by on ignorance.

Looks like you did.....

Thanks for posting the info and adding to our knowledgebase.

....Welcome aboard.

I'll keep an eye out for you!

To err is human...
I am more human than most.

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PostPosted: September 1, 2009, 11:22 pm 
We ended up putting the intercooler back in the Westfield, by the way. The water/methanol injection was useful, but not as good as both together. Now the intake air temperatures are right at ambient with 15 psi of boost on a small turbo.

I personally prefer Pierburg pumps to Walbros, and since they have some nice external units they're easier to package in a Locost. That's what's in my car. They'll flow at least enough fuel for 350 hp and won't overpower a stock Miata FPR.

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PostPosted: September 2, 2009, 8:45 am 

Joined: July 9, 2008, 11:00 am
Posts: 126
Location: Framingham, MA
So how much power do you want? That will be what helps you pick a turbo.

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