Why do people plan HP goals and build around them?
 

I have been wondering this as I try and piece together a build and research.

It seems more logical to me to find parts that collaborate well together, that are in your budget, and then find out how much power your car has made after you have finished building it. (Granted by that time you will have a good idea of how much you should be making)

Rather than saying I want XXX WHP and then choosing parts accordingly?

-Dave

I have a setup that can produce over 300rwhp, but a motor that cant support it.

Having a power goal in mind is a smart idea. If I had a 300rwhp power goal, I'd have a built 1.8L motor in my bay with one-off parts made for efficiency.

Since my goal was always around 200rwhp, I have a stock 1.6L motor and off-the-self parts.

So its like the "Chain is only as strong as its weakest link"

You have a 300RWHP set up but your motor can't handle it.

Is that how power plans work? You pick a power goal and make sure all of your components meet or exceed that standard? Maybe the reason I can't grasp this concept is because I have only modified cars, not built entire engines matching turbos, fuel systems, the right turbo, etc... I have always found X part works with B, lets slap it on and see what kind of power we get.

I had always thought it to be more simplistic to just find things that are in your budget and build around them.

I think the critical issue is not just that there will be a weak link, but that if you don't plan toward a power goal, that one weak link might be vastly weaker than the rest of the chain, and much more expensive to fix.

In our case, rods seem to be the big barrier between 220-240 WHP and jumping right up to 300 WHP or higher. So, you plan accordingly -- if you're going to crack your motor, you can plan for over 300 WHP or more, and if not, you figure out the most efficient way to get your 220-240 WHP.

With a turbo, power mostly depends upon boost. And, yes, some setups flow better than others and some turbos are larger and can boost higher, etc.

Back on point, boost is a number WE control. So, unlike an NA build where you bolt it on and go for it, here we "semi-intelligently" select a boost level that we think will give us a desired performance and reliability. You see everything from my conservative 5psi (~150HP) failsafe/10psi (~200HP) with water injection to Leatherface's epic "ALL OF IT" experiments.

Because in this community most setups that "work well together" have been tried and therefore you can safely pick a number/goal and buy to suit. Barring the variable pieces (IM, TB, manifold type, etc) you can effectively reduce the amount of "collaborating of parts".

Probably better to build to purpose - i.e. fast spool, top end, etc and pick a setup/curve that fits your goal.

yeah, purpose build makes more sense. But if you know you're going to run over 300rwhp or so, a lot more things beyond the turbo setup itself need to be taken care of.

Alright, thanks guys

I am going to keep building my plans, price everything out, and if it is in budget I'll post it up to see if you guys can help spot any problems or tweak the build.

Thanks guys
-Dave

My power goal has always been 235 whp. I came up with that as my car weighs 2350 empty, so 10 whp per 100 lbs. I also based my setup on reliabilty and cost effectiveness.
It turned out that I recently made 225 whp.
My turbo is capable of more boost then was dyno'd, and a better tune would easily yield my original goal.
I realized though that for a daily driver as my car, 225whp is pretty F'n fast. I pulled my 460's, threw in my stock injectors, and bolted on my adjustable wastegate actuator. I am now shootin for 200whp, better idle, and simplicity.

I like the quick spool of my car too, but then I also know it lacks up high. Besides, when was first going to turbo my car, all I cared about was 200whp, now I need MOOOORREE. I listened to everyone preach about how smaller turbo's are awesome, but now I have ridden in a large turbo car, my mind is changed. If a 200whp miata is good, a 300 whp one is better. I am taking baby steps now toward about 300, which is where I think I want to be. Once I get internals, I should be well on the way.

Good to hear, I like looking at other miata builds and getting insight on what they would have changed and why. If anyone else has things to add please chime in.

Thanks
-Dave

We do it becouse the average person who just slaps a 16g or 2860 on there car and runs 12-15 psi does not realize how well i say impressive, but others that have ridden in my car and similiar cars say scary these cars are at 250+whp. + If you actualy read the flow maps for the turbo you will see some turbos just dont make effecient horsepower at lower psi's when compared to what they make at higher psi's. Take a big and small 16g for example, the big 16g flows 15 less cfm at 2 bar than the small but once you venture out a few psi higher the 16g is a capable of a good 20 cfm more flow. So given a horsepower gaol and our knowledge of revlimit etc, we can estimate wich turbo will be useable and make power that can be enjoyed on a day to day basis. Not to mention 5 speeds dontlike hella torque, and neither do 1.6 rear ends, add to this the fact that a 6 speed and 1.8 swap can equal or exceed the cost of the turbo system or car in some markets and some people decide that a power limit is better than a poverty limit when building there cars.

Well, I wanted 300whp, then I experienced 300whp on the track and quickly dropped power to 232-240whp and man is it a better place in terms of funds, tinkering, and life-safety.

Arrrgh. You're wrong. All turbos can boost as much as you want them to. Larger turbos are not necessarily manufactured to tolerate more boost.

You're supposed to choose a turbo that can efficiently make your power goal. You're not supposed to choose a psi/boost level.


Parts that collaborate well together really only applies if you are building your car for a specific purpose, e.g., track, drag strip, hard parking, daily driving. A lot of those collaborating parts don't necessarily have to do with one's HP goals.

Regarding HP goals, as I said above, you pick a turbo that can efficiently make the power you want. As you may have noticed, there is a rather large difference in building a 300+hp miata and a 200hp miata. You mentioned budget, and thousands of dollars will disappear into that 100hp gap. If however, you have a minimalist budget, sure, you can just pick whatever parts come your way cheaply and build and drive your car. There's nothing wrong with that at all.

My goal is 600 whp, if I didn't have a goal I wouldn't know what parts to buy or what turbo to get.

Would you have built your engine (bottom end) if you had known you wanted around 230whp?

I'd rather have a built motor running 230rwhp on the track than a stocker.

We dicker. You're correct in that the turbo you choose needs to efficiently support the boost level and flow that hits your HP target. However, saying that all turbos can boost as much as you want them to is just plain stupid. OTW, why not put a 16G compressor onto a 777 engine? Sure would take a lot less HP to run than the gigantic fan that they have.

Anyway, the point I was making is that, once you've selected the parts that efficiently meet your goal, we have mechanisms to then control our boost and hit that number. This is a lot different from NA tuning.

I sincerely hope I'll never again have to "try a setup". I spent more time working on my car than driving it because I tried to go cheap on many things, never defined my goal, and constantly broke things as one part after another failed... including the motor.

My next car will be done with a VERY CLEAR GOAL in mind. I'll have the money up front to buy the parts I need to get there. I will buy quality parts designed to work together that complement eachother. I will reach my goal within my budget and on time.

I get sick when I add up all the time and money I spent on my '93... a great and indespensible learning expeience yes, but my car sat on jacks in the garage for many months while I tried stuff. I figure I spent around $7k on just turbo'ing... and in the end, had about 210-220whp on a $50 turbo.

This time I will spend the $7k up front, install once, and drive many thousands of happy miles and never have to raise the hood.

You don't wanna live like Faeflora: One broken part/dream at a time?