Advice on Normally Aspirated BP Engine Build

[CrazyRacer]

I’m looking to build a normally aspirated BP engine to go in an NB. It's for a road dríven track car, but not a daily driver...weekend fun only, so road manners can suffer a little. I would like to target something around 120 rwkw and reliable, running on 98 fuel. Could settle for a little less if it's going to get too difficult/expensive.

I guess I’m looking for advice on where it’s worth spending and where it's not. I’d like to do it on a budget, but realise that some areas just do require money to be spent and don’t want to skimp on something that will cause me grief down that track.

I guess I’m looking at:
- After market ECU, I like the look of Adaptronic but would consider others
- Cams, how big can you go while keeping the standard shim over solid buckets
- Mild head work, a bit of a clean up on the ports and chambers but retain standard valve sizes
- Standard inlet manifold

What’s the best base engine to start with?
Are any of the BP blocks and cranks better to use than others?
Which head?
What sort of RPM are the standard rods/pistons/valve springs good for? Are some better than others? Are forged pistons and rods advisable at this power level?
What compression ratio would be required for this?
What valve springs?

[Magpie]

165 RWHP is not cheap. Have a look at Madjack's build thread for suggestions. There are some other people on here who have built some serious NA engines.

Compression - 11.5:1 is probably the max on pump unleaded.
Block - BP
Head - NA8
ECU - gslender has helped install a Megasquirt into a NA engine, check his Megasquirt build thread for information.
Intake - 2 choices either ITB's or Honda (see Madjack's thread).

Whilst written in the states this is still worth reading.

http://forum.miata.net/vb/showpost.php?p=5704021&postcount=24

[QUOTE=emilio700;5704021]= ~200whp. Andrew is quoting wheel horse power.

I've heard more like 185-190whp for the best EP motors but we're all in the same neighborhood. You guys must know of Terry Barnard. Retired now but it's safe to say he knows of what he speaks.
________

InfernalPlacebo,

Decide on a few things up front and it'll be easier for the rest of us to offer useful advice.

-Autocross, what class?
-Wheel to wheel racing or HPDE only, what class?
-Street only?
-Does it need to be emissions legal in any state? (what state)
-Must it be able to run on pump gas and if so, what octane?
-Must it run in a street car, (A/C, OEM alternator, col start driveability etc) ?
-Actual budget for everything connected to engine/power making hardware?
-Tuned by a pro or semi-knowledgeable amateur?
-You cool with the additional tuning/set up hassles of an IRTB set up?
-Does the car need to be quiet?
-Do you have a shop in mind that is familiar with race BP series builds?

Cost no object, I suspect someone could build a 300whp grenade that runs on exotic fuel. In the real world 150-190whp is doable within the budget of the most of us.

150whp is bolt-ons and a good tune. Above that you need to go into the motor.
160-165whp is just a little bowl work and compression.
170whp requires more substantial head work or mild cams or lots of compression, pick one.
185whp requires mild cams (still streetable in a VVT), compression, porting. Pick two.
195whp full head work, lots of compression and mild to medium race cams.
205whp+ is pretty much a full race engine with cams that would probably never idle for street use.
225whp+ so and the life expectancy begins to shorten. Perhaps 15-30 race hrs and you're looking at a $15-20K long block.

We have just touched 180whp on stock cams with an NB2 motor but it was not cheap. Based on the data from that experiment, I know 190whp on stock cams is possible with IRTB's, more compression and E85. At that point however, you should just feed it the cams it wants. We played with stock cams to gain a higher BFSC for endurance racing.

For most guys, I think a stock-ish cam NB2 build makes the most sense. Run as much compression as your fuel will stand, get the best ECU you can, build a Honda B series manifold grafted onto the Mazda flange, RB/Maruha/Maxim works header, fully port and polish the head. Forged everything, SUB's and heavier valve springs. That should net and easy 175whp or so, be safe to 8000rpm sustained, idle like a stocker and last 100 race hours.[/QUOTE]

[CrazyRacer]

Thanks for the response Magpie.

Yeah, I have seen that write up before but it didn't answer some of my specific questions.

165 RWHP is not cheap. Have a look at Madjack's build thread for suggestions. There are some other people on here who have built some serious NA engines.

I don't really want to get too serious at the moment, so if 110kw/150hp is going to be a whole lot cheaper and easier to achieve than 120kw/160hp then I would probably settle for that at this stage.

I'm trying to get a gauge on what trouble and expense its worth going to.

I'd probably prefer to go with an NB head at this stage as I think it will require less work to get into this power range.

Considering whether it would be better to start with a complete NB8B motor for the extra compression, but then some say they're a pain to get cams for them.
Do any of the cam grinders do weld up and regrinds on the VVT cams (which I'm fine with, I've happily used regrinds on competition motors in the past).
Then again if I need to go forged anyway, there's less benefit in the VVT engine...???

I don't really want to go to ITBs if I can avoid it. Its still road registered and I would prefer it to look stock(ish) on a cursory inspection under the bonnet. And while I could probably get a good deal on some ITBs from EFI Hardware (I used to work there) they would still be expensive and I suspect I can get away without them.

I don't know much about Megasquirts, so I'll check out that thread. I've used a MoTeC M4 in the past and still have it sitting in a drawer, and while still a good unit, I don't think its going to be as MX5 friendly as some of the PnP ECUs that are out there now. So the M4 might go up for sale to fund a new ECU.

[NitroDann]

Unless you absolutely have to be n.a for class reasons turbos will always be way better and easier and cheaper especially for these tiny power levels.

If you have to go n.a I'd just buy a crate engine no question from 949.

Dann

[CrazyRacer]

Unless you absolutely have to be n.a for class reasons turbos will always be way better and easier and cheaper especially for these tiny power levels.

It has crossed my mind and is an option.

I have a rebuilt HKS GT2510 sitting in the cupboard that I reckon would be perfect. It was destined for another project, but it might suit the MX better.

Something to think about...

[Magpie]

NitroDann is right if chasing cheap power then turbo is the way to go. However unless you drop a SE motor in you will have to have the replacement engine emissions tested to be 100% road legal.

[The American]

Turbos are cool, but this:
[youtu]http://youtu.be/80gAtOD1hPQ[/youtu]

[zossy1]

Cost per HP is soooooo much lower with a turbo. Dann's right.

I love aspirated power though, especially for a track car.

[zossy1]

Further to this, here is an article we wrote recently providing some more guidance:

http://gwracing.altervista.org/factors- ... 2015-.html

165whp doesn't need to cost $20K. It can be done for a lot less, especially if the car isn't a full time track weapon. Obviously, like anything, the more you spend, the more power you will make and the longer it will last.

Firstly, here's what is mandatory for a build like this:

* Higher compression pistons - either NB8B or aftermarket pistons. A head shave and/or block decking will help boost compression further.
* Lots more flow - either bigger cams, or significant port work, or a bit of both. Making 165whp on stock cams is, I'm told, doable - but bloody hard (we have never tried). I'd suggest big cams in any event, preferably with some port work and +1mm valves.
* ECU and a good tune from someone who knows what they are doing.

Yes, bigger cams will need SUB lifters. I'd suggest anything at or above 9.5mm lift should be considered unsafe for shim-over-bucket, depending on the ramp and profile of the cams. Even stock cams have been known to spit over-bucket shims at 7800rpm. You might get away with stretching lift to 10mm lift if you kept revs below 7400rpm or so and ran double valve springs, but it's risky. SUBs are fairly cheap though - you can get a set of Mazdaspeeds for $300 or so landed from Bill at Miataroadster (less if you patiently wait for a secondhand set to come up). Budget $100 or so for shims.

From here, it's a question of how much you want to spend and how hard you will push it. I've seen these power levels made on stock rods, but extreme care must be taken to avoid money shifts or over revs. Anything over 7600-7800rpm puts the stock rods in danger of failure.

Decent valve springs are also strongly advised, in particular as stock springs with big kms are probably rooted anyway. Supertech singles will be perfectly fine for any engine running stock rods. If you're looking for bigger revs though, at least light duals are advised.

Remember the stock TB is a time bomb waiting to destroy a big HP aspirated engine with lumpy cams. Either do something to prevent it spitting a screw into your big $$ engine, or replace with a Skunk2. Stock NB8B oil pumps are OK for your type of build, but consider a boundary gear for safety.

As you can see, the money adds up quickly depending on how far you go. You can also sink big $$ into balancing, lightening crank, decking block, boring the engine, and the like. All will yield power but the law of diminishing returns applies. ITBs are for the serious players.

[CrazyRacer]

I think I'm really looking for the easy cheap power rather than going too nuts on it. This is supposed to be a toy to do some track days and sprints for the next couple of years to get my racing licence back while a slow build on a IPRA car takes place. But I know I'm going to want more than stock power. My last track car (a Datto 1600 with a Toyota 3SGE) had about 130rwkw and that was too slow.

The car I have now is a little rough, very high km NB8A which I picked up cheaply from a mate. But my daughter is about to get her licence and is very keen to have it so I might pass it on to her and look for another nicer one.

After some of the comments posted here I think my options might be:
1. Buy an NB8B and drop some cams and an ECU in it and just live with whatever power it makes.
2. Buy an SE and mod it lightly to make 150rwkw or so. There are a couple around for reasonable $$ at the moment.

[NitroDann]

The first option doesnt work so easily because there arent really any cams available, certainly not a lot of choices. Youd also want to CRANK the compression, do a little port work and run E85.

The second option sucks, its just hopeless shitty value, youll be putting money into a poor value turbocharger system, on the heaviest worst geared and most expensive chassis available.
I should also point out that more than 50% of the SE builds I now do include removing the SE turbocharger system to replace with with a low cost and very basic garret turbocharger setup, because it performs so so much better.

If you want a couple hundred hp slap some boost into whatever the hell it is that you have, keep the power within an easily manageable amount (within th elimits of your supporting mods) and enjoy dumb level of performance for a pretty reasonable cost.

Dann

[CrazyRacer]

Is there a problem with getting weld up and regrinds done on the VVT cams for the NB8B?

The turbo build topics seem to be filled with tales of woe, long build times and big $$ around developing turbo setups on normally aspirated cars. The advice seemed to be to start with a factory turbo setup and work from there.

Happy to be pointed in the right direction if there's a proven turbo path to follow that's quick, reasonably priced and reliable.

[oztrackdays]

You are basically asking for a close to 100% increase in engine output in a 1840 cc naturally
aspirated engine that much of which was designed in the mid 80's.

If you are not stripping the car down by the extra hundred kilos as a dedicated track
car, the extra few kilowatts will cost you heaps and you won't go that much faster.

Shoot for 95-100 rwkw with an unopened motor strap the best tyres on it you can,
and you will enjoy that more.

I had around 135 rwkw in the engine Zossy bought off me, and make about 220 rwkw
now with the Honda Frankenmotor but both of those cost more than they are worth
in terms of performance.

[NitroDann]

The biggest issue with turbo builds is spending the right money in the wrong places. N.a builds that suffer from this issue end up making low power, and the owners are usually pretty tight lipped about how slow those builds really are.
The secondary issue with turbo builds is that its so easy to crank the boost up and break it if you dont have self control.

At the end of the day intelligent selection of parts and experienced setup and tuning is key in both cases, for a turbocharged build its simple. Basic thick walled manifold, big high flowing exhaust, inconel exhaust studs just like factory cars use, braced exhaust with a flex pipe just like the factory uses, a small intercooler, enough fuel, a cheap HD clutch, a big radiator with all the factory ducting in place, and a flexible ecu with a competent setup and tune. Thats 200 odd rwkw on a stock engine, exceptionally reliably.

E85 is yet another layer of protection if you are really worried.

Dann

[davekmoore]

The second option [modify an SE] sucks, its just hopeless shitty value, youll be putting money into a poor value turbocharger system, on the heaviest worst geared and most expensive chassis available.
I should also point out that more than 50% of the SE builds I now do include removing the SE turbocharger system to replace with with a low cost and very basic garret turbocharger setup, because it performs so so much better.
Dann

.... unless you can find a decent SE for NB8B/C money, in which case it might be easier engineering-wise to throw away the IHI and put a proper turbo on it than it would be on a car that didn't come with a factory turbo. Still got to deal with the other SE downsides though, as Dann says. Mind you, if you got Dann to do the build, even the factory SE gearing might turn out ok if he makes it produce enough power. My SE only just needs 6th at to get to 208kmph at Phillip Island with only 150rwkw. If it had 200rwkw and less weight the gearing might be ok. Of course, if it had a decent driver it would be going faster with the present 150rwkw.