Intercooler sizing and proper practices thread.
 

Hi guys,

I am going to post a few threads like this over the next few days where Ill try and learn what my personal unknown unknowns are about a few things.
Ive built an absolute tonne of turbo everything, 80% of them have been mx5's and lately I've come across some challenges that I can't just power through with knowledge, hard work or ingenuity, at least not in the ways I want to so I need to learn more.

First thing, Ive built heaps of 300+whp MX5's with what are essentially 'undersized' intercoolers, the common 550x140mm core from ebay, but these days a lot of my customers are asking for an honest 350whp.

A couple of challenges Id like to attack are how to achieve 350whp with virtually zero lag on gasoline, which Ill start another thread to discuss, and in this thread Id like to learn if some of my trouble has been with lack of flow through these small intercoolers, how to calculate intercooler and piping requirements with better accuracy and how things like total boost vs flow (ie a 1.6 on 30psi vs a nice Bp4w head with cams on 20psi etc) affect requirements.



Here is the intercooler which is on most of these. (centre)

https://www.miataturbo.net/attachmen...ine=1464363147


Rough guides suggest that its actually about half the vertical size that it needs to be, assuming that the rest stayed the same, which is an easy fix because that exact cooler is easily available.

The other question is while I typically use 2" on the hotside and 2.5" from the intercooler to the inlet manifold, the car that was short on power tonight has 2" from turbo to throttle body, and while the math that I know says that 2" is ok for the power (aiming for 350whp) I believe that it needs to be larger from the intercooler to the inlet manifold.

As a good example this car is an na8, 11.5:1, 272*/10mm cams, Disco potato 0.86 internal gate, absurdflow style manifold, 3" exhaust, e85 and makes 325rwhp on my dyno dynamics 2wd analog dyno. I expected 350 or so, and to be able to get more boost out of it (21psi) based on previous experiences, but this has the small intercooler and 2" piping throughout.



People who actually know both the real world facts and the physics behind these questions, please school me and provide relevant links.

Thanks,
Dann

I'd put temperature sensors in the inlet and outlet and investigate intercooler efficiency. You're most concerned with temperature into the manifold (IAT). The smaller 1.6 engine at 30 psi is likely going to be in a lower efficiency part of the compressor map and generate more heat, have a higher intercooler inlet temperature and will likely need a larger intercooler to keep the same IAT than the 20psi bp4w.

for tube sizing I'd look at finding someone with a flow bench to find the flow vs pressure drop for different piping and intercooler combinations. You know what CFM or mass airflow is required to achieve 350 HP, with that info you can find exactly what pressure drop the charge air cooling system will require to move that air mass. by graphing CFM vs pressure drop you can see exactly where the intercooler maxes out on airflow and the system has reached it's limit. Tradeoff for bigger inter cooler and tubing is boost response so don't oversize if you don't need to.

Finally, ducting ducting ducting! I think that's where the easiest improvements can be made. A larger intercooler core is useless unless the air actually is traveling through it. I'd try ducting your current core size and datalog with temperature inlet and outlet data vs un-ducted first before looking at increasing the core size. I bet you'd find a big temperature improvement with good ducting. Look at trackdog intercooler kits for good ducting ideas.

Yeah that all makes sense.

Temperature control is no issue, thats confirmed during dyno testing with an ait sensor right at the throttle body. Only 30*c during a few big long pulls on a 20*c night. Datalogs on track on hot days also confirm temperatures are in check. However, I was considering putting a boost gauge before and after, significant pressure drop would surely be seen if the intercooler was a major restriction to flow, yes?

Dann

a little off topic but
"how to achieve 350whp with virtually zero lag on gasoline"

efr efr efr efr for that small of a hp goal..


If iats are a issue due to running smallest turbo possible and cranking it out maybe consider a non off the shelf ic, like a bell core with custom endtanks.

Im fairly well completely certain the issue is flow and now cooling efficiency.

As for the 350 with zero lag, I ran a 9.5:1 motor on premium, GTx2863r with really good flowing everything (this small intercooler though, but its made 330 for me in the past a few times soo...) and only could make 315ish due to being det limited. But thats another thread.

Dann

Didn't know @codrus shipped his car to Australia for a tune :party:

Add a pressure sensor at the compressor outlet. Make a math channel of (charge air cooler system delta pressure = Compressor outlet pressure - Manifold absolute pressure). Plot that math channel vs mass air flow and you should get a curve that looks like this. Repeat with other configurations and overlay the graphs and make engineering decisions of where the diminishing returns of IC piping size is. or keep IC piping and change different intercooler cores out to see which is the least restrictive.

https://www.miataturbo.net/attachmen...ine=1464366844

Yes.

:)

Mine is 9.0:1 (nominal) and det limited to around 270 on 95, 340 on 100. I haven't even bothered trying it on 91.

FWIW, I'm using a standard Flyin' Miata FM2 intercooler and the pressure drop across it at 230 kpa MAP and 7000 RPM (so about 340 rwhp worth of air) was only 6-10 kpa.

MAP and COP are both in the bottom graph:

https://www.miataturbo.net/attachmen...ine=1464367952

--Ian

I'm curious to see where this goes. My first IC was a Precision 350hp, 18x6.25x3.5" (460x160x90mm for those of you who haven't been to the moon). It was perfect, except for being a little too large to play nice with the factory plastics in the nose. I built up a custom IC smaller than anything I could buy, 18x4x3.5" (460x100x90), thinking that if 350hp = 6.25 tall, then a 4" tall core should be able to do 225whp. What I found was ~1psi less boost at only 9-10psi and far higher IATs in boost. No bueno. The pressure drop makes sense, but the high IATs surprised me a little. I wonder whether using a better core in the smaller size would have helped - the baby IC is a Treadstone core which has some turbulator action going on, but it's nothing compared to what the Precision core has inside it. My next experiment is to cut the Precision core down by a row or two and see where it gets me.

This is why I love you guys.

Our 98 is your 93 and we were det limited to 315 odd, and by det limited I mean we left it at 300 because 315 was touch and go, running cool, in a controlled room.

Lets go back to cooler cores, and Ill start the det limit thread tomorrow, its 3am here now.

So with this car:

"As a good example this car is an na8, 11.5:1, 272*/10mm cams, Disco potato 0.86 internal gate, absurdflow style manifold, 3" exhaust, e85 and makes 325rwhp on my dyno dynamics 2wd analog dyno. I expected 350 or so, and to be able to get more boost out of it (21psi) based on previous experiences, but this has the small intercooler and 2" piping throughout."

I can only blame the cooler and the 2" piping from cooler to TB.

I have another few cars making 15-20hp more with worse exhaust manifolds, lower comp and stock cams, however they have flat top manifolds.

Is the NA8 manifold really that bad or is it just this piping/cooler, and again, whats the best testing method that can be repeated on other cars (ie an answer of just swap all the parts and do more runs isnt what I am after)

Dann

Find a flow bench to use and bench test intercooler and configurations. That's how most of the aftermarket world does it along with controlled dyno and street testing with a lot of instrumentation. There are DIY's to build your own flow bench out there.

Find a very competent engineer to run CFD analsysis on setups. This will only give you accurate data with an OEM level of resources.

Or just continue on with your trial and error process based on information from your previous car builds and other similar build thread.


Every intercooler has vastly different configurations and design features and will have different flow vs pressure drop graphs. Size, thickness alone will never give you an idea of how the intercooler will flow without actually testing it. At my job we typically test flow test 6+ different inter cooler cores before vehicle test them.

The na8 intake is bad and the na8 head sucks. Do the same setup on an NB1/2 with a flattop intake and I'd be willing to bet you'll see your 350hp on E85. But seriously forget the disco potato and get EFR for a few hundred $US more. The piping is not your real problem.

This, down to the last detail. I made 350whp at 17psi on a stock VVT head, stock VVT cams, with 2 points less compression. Intake manifold and cylinder head are the choke points. I bet those 272/10mm cams are NA cams which aren't helping anything either.

The cams are Tighe 845c from this link, bottom cam. It was 3am and I mispoke. They are a turbo rally cam. Basically a fast road turbo cam, we also have vernier camgears which we spent some time playing with but didnt find much improvement over the recommended spec.

Is it worth swapping to a flattop (common and cheap here) and porting this head? This would be the most cost effective way to get some flow back, yeah? Also, just to confirm, all BP inlet manifold flanges are interchangeable?

Dann

NA8 and NB bolt patterns are the same, but the ports mismatch by 15-20mm. The 4W/6D heads have a much higher intake port. You are stuck with the NA8 manifold or something custom.

When I put motors together for customers, I basically brow-beat them into upgrading to a later cylinder head. After you spend all the money in the bottom end and turbo system, the extra $300-400 for the later head is some of the most cost-effective power you can buy. In 5 years of building motors for customers, I have done exactly one 94-97 head, and it was required by rules.

No they are not interchangeable. 99-05 only.
You want the better flowing head, and then you want the cams and porting in that. Dont' waste time and money on the na8 head.
2" piping is theoretically good to 400hp assuming little to no bends and no other restrictions (like intercooler). so you're tapped out and need bigger piping and bigger fmic.
tall narrow fmics are more effective for less pressure loss but with a wide short mouth opening on our cars we really don't have many choices.

I currently have Andrews old intercooler. Good to hear it works well :)

Bbundys is running an NB intake on an NA head. Lots of modification to do it. Probably only did it because he had $$$ into the NA8 head and didn't want to redo it.

GM "style" 4bar map sensors are like $15 on ebay. Get a couple of those and test pressure drop over different areas in your piping?