Boosted 4 cylinder vs V8 for all around build

Hello!

So, I have an 09 NC Miata that has a 2.5 swap and a M62 supercharger.  Once the car is put back together, I will be adding corn juice to push it over 350 whp.  This will be fun, but I know me and I will want more after this.  
 

Background!  I street the car, I Autocross the car in XA and I have been dying to take it back to the track for some time trials and time attack.  I have not been back to the track since the supercharger has been installed.  (Had problematic track days the last 2 times I went and I wanted to be sure I wouldn't be asking for more)
 

I am dreadfully worried about heat and reliability.   My end goal is to make a small trailer to tow behind the car to events both near and far.  I realllllly want to do an Autocross week and Nationals in Lincoln until my car broke, I was aiming at this year to do it.  
 

Back to the main topic.  The 2.5 duratec is leaving it's reliability window as I push up from 350 whp, and I would rather have a junkyard swap motor than a built one.  I also want the ability to scale up as I can make power more useable via setting up the car and becoming a better driver.  So, a duratec is off the table and I am left with 2 obvious candidates, boosted K24 or LS.  Is the lighter weight K24 worth the heat I will generate with a turbo/supercharger?  (Kinda addicted to the whine). Or is the simplistic LS swap the right answer?  

The nice thing about an LS swap is that the whole drivetrain is overbuilt for your use. Transmission? No problem. Rear end? You'll never hurt it. The engine, at base 430 hp LS3 levels, is engineered to last for hundreds of thousands of miles. It's nice to have a hammer for a track car.

The K won't be as light under hood as you think once you hang a snail and intercooler in there, and the rest of the drivetrain is only lighter because it's not as strong. 

I understand these drivetrain issues... I have RX8 diff, axles, hubs and uprights for more strength, I broke my factory 5 speed back in March and I am trying to make time to slap the stage 3 5 speed in.  The new weak point should be the clutch.  
 

That being said, no matter which motor I plan on using, I plan on a tremec transmission to keep it all tamed

Have you read these?

https://grassrootsmotorsports.com/forum/grm/25-liter-swap-the-secret-to/256406/page1/

https://grassrootsmotorsports.com/articles/25-liter-swapped-nc-mazda-miata/

IMO it already can produce 300+ hp, repair it when it needs it. Buying the same engine for a spare would be less money than a LS swap. 

MyMiatas said:

Have you read these?

https://grassrootsmotorsports.com/forum/grm/25-liter-swap-the-secret-to/256406/page1/

https://grassrootsmotorsports.com/articles/25-liter-swapped-nc-mazda-miata/

IMO it already can produce 300+ hp, repair it when it needs it. Buying the same engine for a spare would be less money than a LS swap. 

I am well versed in the 2.5, but I also know that I am heading towards the issue threshold.  Yes, you can buy another motor for about $500.  But I also don't want to have a duratec graveyard as I destroy one after another

Classy said: I am dreadfully worried about heat and reliability.

V8.  /thread

Do the V8; turbo 4s are every bit as heavy as a V8.

Keith is spot on in his observations.

I do not think an M62 can physically move enough air for 350whp.  By recollection, and it has been a while, you're looking at a 14000rpm maximum sustained speed and 16000rpm absolute max speed on that unit.  Volumetric efficiency is an island peaking in the middle or so of that, but let's say that VE is at 70% at 16k,  That is 62ci times 16k times .7 = 694400 CIM, convert to CFM = 401cfm.  Now, in theory that is good for maybe 580hp, BUT, that air is also going to be extremely hot, so the mass flow is going to be a lot lower.  This is where my math fails because I don't have the figures to calculate that.

VE is also dependent on how much boost you are making, more boost means lower VE.

If you really want the whiney supercharger noise (and who doesn't love it?), what about a supercharged GM 3.6L V6? I used to drive a Chev Colorado for work and that thing had some decent motivation. Add a supercharger and it should comfortably make 400+HP and all the right noises.

Pete. (l33t FS) said:

I do not think an M62 can physically move enough air for 350whp.  By recollection, and it has been a while, you're looking at a 14000rpm maximum sustained speed and 16000rpm absolute max speed on that unit.  Volumetric efficiency is an island peaking in the middle or so of that, but let's say that VE is at 70% at 16k,  That is 62ci times 16k times .7 = 694400 CIM, convert to CFM = 401cfm.  Now, in theory that is good for maybe 580hp, BUT, that air is also going to be extremely hot, so the mass flow is going to be a lot lower.  This is where my math fails because I don't have the figures to calculate that.

 

VE is also dependent on how much boost you are making, more boost means lower VE.

I have ported the supercharger, went to a larger throttle body and the big header also helped, I know I don't have a dyno to prove my theoretical numbers, but I did a dyno with a 1.8" header and 2.8 pulley and made 280whp and 275 tq, calculating the boost I was making then, with the boost drop due to higher efficiency and the 2.6 pulley, I am very confident I am around 325 whp.  I also added a MUCH bigger air to water Intercooler and a higher volume pump, I am working on finishing an icebox/swirl tank for the cooling of the supercharger.  
 

I do plan to put it on the rollers once I have E85 tuned in and see what it makes with everything.  Others have crested 340 whp with this blower on a 2.5, comparing it to an ecotec does not seem a fair comparison for some reason.  I attempted to use it as a base line for comparison, but it always fell much shorter than the 2.5 duratec whether is was the 2.0, 2.2 or 2.4 ecotec.

In reply to edwardh80 :

The LFX is a disappointing engine to me.  Compared to other same size V6's this one does not make power well and has a minimal aftermarket.  Take a 2GR and you can crest the numbers of a LFX easily.  Yes a supercharger would be the I win button though

I agree that 350 rwhp seems pretty optimistic for an M62, folks running them on NA/NB Miatas rarely get out of the low 200s at the wheels.  E85 and perhaps a better-flowing head than the BP is good for some, but 350 still seems like a stretch.

I drove my NB on the track for 19 years, most of them with a turbo on it making progressively more and more stupid levels of power (topping out about 350 at the wheels).  About 5 years ago I switched to my E46 M3 with almost as much power as the Miata (330 at the wheels with intake/header/exhaust/tune) and the difference in reliability is night and day.  Personally I would not go with an aftermarket forced induction system for a track car again.

So if it were me I'd pick the desired power level and swap a naturally aspirated motor that's good for that amount.  If you want 350 that probably means an LS.  I wouldn't go K motor unless you were happy with what an NA one will do.

...of course, an S54 swap would be fun too!   Or maybe a p-port 20B? :)

After 3 stages of supercharging for the track car, finally went LS swap. There is no comparison. 

Oil radiator needs blocked off to get it hot enough. RPMs are kept below 6800 still making 400whp.

Gear changes are unnecessary since it pulls like a train from 2500rpm and up.

If you are serious about running track events (more than a couple), then LS swap it. If it might see one track weekend a year and then some autocross, stick with what you have as you can choose cooler weather and it shouldn't be an issue with e85. But it's a lot of time and money if you are just "thinking about doing it a bit" and WAY overkill for some AX and street driving.

codrus (Forum Supporter) said:

 Personally I would not go with an aftermarket forced induction system for a track car again.

I couldn't agree more. Pick a random turbocharged car, put it on track, and I'll bet a lot of money it has a heat related issue. Even most of the OEM "track specials" quickly suffer from heat soak/pulled timing/limp mode.

Pick a random V8, throw it on track and I bet it survives multiple sessions.

L mean, if you can afford the V8, why not?

Also, I love the idea of an NC with an LS. Kind of roomy (in terms of Miatas), Muscular, can take plenty of tire, etc.

I also vote V8 if you know you're going to keep chasing more power. 1 and done solution.

I have to also vote v8. Now that I have gotten my v8 swapped e36 running slightly better (crate 350, Atomic EFI) the torque all over is absolutely addicting. 

And it is worth the extra weight?

I can't really comment. I never drove this e36 with the inline 6 to know if there is a definite weight penalty. On throttle hard it'll pull the front up (because I need to tackle suspension mostly) and my other e36 coupe is a gutted with roll bar drift car. They both feel about the same at low speed driving. 

I think with an E36, there wouldn't be much if any of a weight difference 

In the Solstice/Sky world we have turbocharged Ecotec 2.0 LNF engines.  They are quite durable, having been built with this in mind and are pretty much dead reliable up to around 400 bhp without swapping out the internals. They also weigh considerably less than a V8, even with the turbo unit included.  

Above that level, new pistons, rods and crank can be added and I think the record drivable 2.0 is this one  

https://www.youtube.com/watch?v=2S6XiC0ZDgE

A Cobalt with 715 bhp at the wheels.

(Engine weight with turbo c. 370 lbs. about 100 lbs. lighter than the LS series V8s)

Classy said:

And it is worth the extra weight?

There is no extra weight; twin cam turbo 4 cylinder motors ,due to all the extra hardware (intercooler etc.), weigh every bit as much as a V8.

The V8 is very underdressed at 350hp.

Here is another consideration: at the BRE open house Peter Brock and I were having a conversation about all the great turbo motors available. I said I was sold on the V8 becuase I could get on Summit or Jegs and have the part I need the next day. He said "good point"

Classy said:

I think with an E36, there wouldn't be much if any of a weight difference 

Some quick searching finds a E36 S52 engine at 330 lbs and an LS3 at 403 lbs.  So roughly 70 lbs more, although it "should" be more central in the chassis compared to the longer I6, so probably a wash performance-wise.  Add forced induction to the BMW engine and it will almost certainly weigh more. 

In reply to wspohn :

A 5.0 Ford with aluminum heads weighs in at 410lbs. Extreme measures will get it to 390lbs. Also the T-5 trans only weighs 75lbs. The weights for the turbo 4 tranmissons are 100lbs.............the weight diference of motors isn't enough to live on.

I give a much higher priority to whichever was the more reliable package and part availability.

In reply to Tom1200 :

I love 8.2 deck Fords but at the power levels already here, they are not the most reliable.  In the Trans-Am days, they had problems with breaking cranks and blocks, and that was with the heavier 60s castings and 28oz imbalance cranks.  The 50oz cranks hang a lot of weight forwards of the #1 journal and will break at the rod journal between 1 and 2 in heavy racing use, and the 5.0 blocks weaknesses are well documented even without forced induction.

On the plus side, there is little need to upgrade the pistons and rods, since they are not the weak point, so you can save money 

Again, I love the 8.2 deck Fords, but an aluminum Chevy is better in every way except for external size, and a Miata engine bay is much larger than an old Mustang's.