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PostPosted: October 2, 2020, 7:26 pm 
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Joined: October 1, 2020, 3:22 am
Posts: 48
G'day guys, So early stages of planning a build which will be based around Miata/MX5 suspension and a inline 4cyl OHC built motor infront of a R154 5-speed gearbox which I already have.

Just wondering how much power is good for this style of car (weight/suspension etc) Basically I could set the motor up in naturally aspirated form and id expect around 200rwhp or I could run a turbo setup (what the engine was originally built for) and have about 300+ RWHP with boost control this would be variable.

I do not have any intake/exhausts manifolds yet, just the block/head. I would be fabricating everything from scratch to suit. If N/A it would be EFI with individual throttle bodies and custom headers. If turbo id use a front mount intercooler, single throttle body with plenum and custom exhaust manifold and a relatively small turbo as my local track is relatively small with the straight only being 600m so response is most important.

Obviously a turbo setup would make things more complicated and tight space wise. I'm wondering for such a light car would it be overpowered and just be loosing traction all the time?

Would making it able to handle more power just be a matter of designing the suspension around a wider Tyre?

Would I maybe need to step up tubing size? At this early stage im thinking 0.65wt 1.25" DOM round tube.

The gearbox I have will handle it, im not sure how strong the Miata diff's and axles are?

Any other complications or considerations you can forsee?

Thanks again!


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PostPosted: October 3, 2020, 8:14 am 
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Joined: September 22, 2005, 8:12 am
Posts: 1830
Location: 4AGE in S.E. Michigan
Hermit
First add your location to your profile. This is a friendly group that can assist in your build.
I would build with what you have. If the block and head are in good shape, use them as is. These project take long enough to build with out adding engine / trans rebuilds, unless they need them. Once on the road if you feel you need more power then you can up grade. Even adding a turbo to a 4 cylinder you really do not need to increase the frame tube size. I you want added torsional strength, add triangulation to the sides, engine bay, and floor.
Davew


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PostPosted: October 3, 2020, 9:49 am 
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Joined: July 17, 2008, 9:11 am
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Location: West Chicago,IL
I you are building a traditional Locost, then any power level can be fun. If you are road racing you have to follow the rules for the class you want to compete in. A lot of guys build with the Miata power train and simply love the setup. Others have as much fun with their V8's. Stalker builders have built with supercharged V6's. The range of possibilities is endless. My build was with a stock RX-7 powertrain. With 160 HP, it would get me 0-60 in <5 seconds. That was really a thrill when the power band came on around 4-5k RPM. Was it the most powerful car I've owned? NO Was it the quickest? Yes. Was it the most fun? Again, yes, by a long shot! As mine was a street build, I seldom made use of the full acceleration capability. (OK, I did quite a bit, but only for short distances). If I built another, I might try a MG Midget (AH Sprite), maybe the bigger brother MGB. I like the handling more than the knock-you-back-in-the-seat power. Any power level can do that in a Locost. Trying to build the "fastest" car is a fool's goal IMO. Somebody can be, and will, always be faster.

I would say, build something that brings a smile to your face every time you get behind the wheel. Only you can say what power level will do that for you.

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Visit my ongoing MGB Rustoration log: over HERE

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PostPosted: October 4, 2020, 12:39 pm 
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Joined: October 24, 2008, 2:13 pm
Posts: 4863
Location: Carlsbad, California, USA
My perspective when deciding on my engine power, was creating a very high performance street car. I looked at a lot of sources, and read quite a bit about it, including a lot of remarks from this website. My conclusion was that 150 HP would be fun, over 200 HP would be an absolute blast and anything over 300 HP would be undrivable, and probably a little dangerous given the light weight of a Locost.

If you want a track car, different reasoning might apply.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: October 4, 2020, 2:50 pm 
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Joined: April 26, 2008, 6:06 pm
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Location: Under the weather. (Seattle)
A reasonably designed chassis and suspension will handle either power level just fine. To me it comes down to the character you're looking for from the car and how you want to use it.

If you're looking for outright lap times, the 300hp build will be faster...But that comes with a catch. The faster the car, the less margin you have for error. Consider that 200whp gets you 8.5 lb/hp or better, while 300whp gets you 5.67 lb/hp or better. Those are like a Mustang with at least 460whp and 690whp respectively. There is a point where more power start to make it less fun and more work to run the car hard. This point is different for every driver, and is heavily dependent on their skill level. Get on the brakes a fraction of a second late with a lower powered car and you can scrub enough speed with a bit of extra tire slip. Get on the brakes a fraction of a second late with a higher powered car and you're suddenly a passenger on an off-course excursion praying not to hit an immovable object. The 300hp car will also require a more capable brake package, that will need more frequent consumable replacement.

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PostPosted: October 4, 2020, 3:40 pm 
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Joined: January 11, 2017, 11:06 pm
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Location: Alberta
I guess another point to consider is responsiveness. These cars are so light and nimble that IMO a quick-responding engine makes it a whole lot more fun. I like your idea of an ITB setup, and that would probably get my vote.


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PostPosted: October 5, 2020, 1:37 am 
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Joined: July 29, 2006, 9:10 pm
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Location: Oregon, usually
rx7locost wrote:
I would say, build something that brings a smile to your face every time you get behind the wheel. Only you can say what power level will do that for you.
There is a remarkably broad range of power levels that can satisfy that standard, depending on the driver and mood. For example, I currently have a smile brought to my face on 32 horsepower (Kubota) and also had a smile brought to my face with a hundred+ more horsepower (Honda CBR1000). I don't know if I, personally, would smile bigger with 300 horsepower...in fact, I might smile bigger with a little less than that.
rx7locost wrote:
As mine was a street build, I seldom made use of the full acceleration capability.
Actually, that's one of the reasons my turbocharged Kubota-powered car is such fun. With 32 horsepower, I get to use full acceleration capability quite a lot!

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PostPosted: May 16, 2021, 11:03 pm 
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Joined: May 16, 2021, 10:42 pm
Posts: 15
For the ae86 guys 250whp is commonly the useable but not quite scary range. (Which goes right up to 1500whp drag setups that are downright terrifying for a caged car, lol. See 6 second passes for tire shaking silliness... ~2100lbs or so stock.

Short wheelbase cars get scary fast. They can lack that... "this end forward" instinct.

There was someone here with a 300+whp sr20 build that ended up going for a slip angle adjustable traction control setup after a friend lost it on a short test drive. Obviously, they're all different so baselines are generalized.

I'd think the miata differential would go before the 154 - see them used behind 1/2j and 1uz plants with reasonable success.


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PostPosted: May 8, 2022, 12:26 pm 
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Joined: November 26, 2012, 2:29 pm
Posts: 153
Location: Sioux Falls, SD
Nick94tt wrote:
There was someone here with a 300+whp sr20 build that ended up going for a slip angle adjustable traction control setup after a friend lost it on a short test drive.


Got a link to how he accomplished this at all?

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PostPosted: May 8, 2022, 2:39 pm 
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Joined: April 1, 2010, 10:26 am
Posts: 512
What engine are you planning on using? You say you have the head and block but you do not say what it is.

What do you plan on using the car for? For me 200rwbhp was fun, next evert will be 225 and a 6 speed box. Ask me after my trip to Pittrace.

If your planning on running track days hp is important, the are a lot of 400+bhp car around even 600+bhp now. As they do not allow you to dive bomb them on the brakes your in trouble. If you have to follow some one through a corner, they have traction control and can just mash the throttle, your in trouble. If you just street driving 200 is perfect.

Turbo is an interesting problem, turbo cars produce a lot of mid range power, making the transmission to boost smooth enough is very difficult. Even so getting a car to rotate when you have a flood on mid range power is difficult.

Graham


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