BumpHeadRacing

Long time [intermittent] listener, first time caller here. I'm planning a BP engine build to go into an MK Indy RX5 (locost-ish thing, silly little British tube framed self propelled coffin) track car, and I've got a few ideas of what I'd like to do. I'm targeting (but if I end up with more, great! all-motor 100hp/liter from a BP would be an awesome brag, but keeping goals slightly more modest for the time being) 170-180hp NA, 8,000RPM, from a square engine (to give myself a bit of extra meat in the cylinder walls to facilitate an eventual bore to 85.5mm when this engine eventually needs a rebuild) on a BP6D block with a Maruha 85mm crank, with likely a loose clone of Der_Idiot's head that sixshooter ended up buying a few years back, with ITBs, and header (due mostly to working around clearance issues packaging the pedal box and steering shaft and exhaust on the left side of an MK Indy chassis). I know I could likely make more power easier if I built a VVT engine, possibly being able to get away without buying cams at the power level I'm aiming for, but I don't anticipate having trouble making that power with ITBs/cams/extra displacement on a ported BP4W head, staying non-VVT does get me a little bit of hood clearance (a flat hood will clear a non-VVT valve cover, whereas a pretty sizable protrusion is needed in order to clear the VVT components on top of the valve cover), and honestly in a car that should weigh roughly 1500lbs with my lardy self in it, on track, I don't think that I'm going to really miss a little extra midrange power in a car that will already be knocking on twice the power-to-weight of the Spec944 (~2700 with me in it, I'll be lucky if it's hitting more than 140hp) I'm tracking now.

First, I really like the idea of building a long rod BP. Back in 2012, JKav put together a long rod BP for a turbo build. Given that I'm planning to spin this engine to 8,000 regularly (or at least give myself the safe headroom to do so if it makes more sense to stretch a gear vs upshifting just before a braking zone), the benefits of going to a better rod ratio (along with the fact the rods and pistons that were used in that build are both lighter than stock and more consistent in weight from component to component) sounds real real appealing, right up until time to start actually sourcing components. It would appear that Mil Spec is no longer in business (or at least no longer has a web presence reachable from the links in the Inside Line/Edmunds blog posts, which themselves were somewhat annoying to come across, since the site structure and name have both changed since those posts were made). Is there another connecting rod manufacturers I should be looking at, or hopefully one of the other manufacturers bought Mil Spec in part or in whole and may have the knowledge used on those squirreled away in a filing cabinet or server somewhere? Pistons concern me much less, as JE is very much still around, and their memory could very likely be jogged by a quick reminder of this project.

Second (and first among my cooling questions), I'm planning to use an oil-water heat exchanger on this engine, rather than a standalone oil-air cooler, plumbed in line with a remote oil filter kit (likely downstream of the filter), with a coolant reroute kit installed (either FM or Supermiata, or cobbling something together from other OEM parts, since I won't have the constraint of a Miata firewall directly in the way), and absent any guidance to the contrary, am planning to use the heat exchanger in lieu of the long section of rad hose from the rear of the head back to the radiator. Any particular issue with doing it this way? I very much like the idea of letting the engine coolant regulate oil temps, rather than playing around with taping up a cooler or messing with a cooler bypass controlled by an oil thermostat to avoid over-cooling or under-cooling my oil.

Third, I'm real intrigued by the idea of running an electric water pump, completely omitting the thermostat, and PWM controlling the water pump by the ECU to manage temperature. This would let me get rid of the potential failure/leak point on the front of the engine and either just remove the impeller from a stock water pump and weld up the hole, or remove the impeller from the stock WP shaft, weld up a cover for whatever stub was left, and retain the stock WP pulley to make alternator belt tensioning (and purchasing of an alt belt, since I can just get a standard belt for a Miata) easier. This also introduces the possibility of reversing the coolant flow, bringing coolant into the engine from the back of the head and out the front of the block, since doing this would be as easy as installing the electric water pump backwards (as compared to how it would need to be installed to maintain stock coolant flow direction). In this case, it would be very likely that the oil-water heat exchanger would end up downstream of the radiator and upstream of the engine, which seems good for oil temps but perhaps not quite so good for coolant temps in the head, since I'll effectively be preheating the coolant before it even gets to the head, although probably to a lesser extent than stock coolant routing would (coolant will make it through the heat exchanger to the head quicker than it would make it through the engine block up to the head, and will be exposed to less surface area while doing so). In either case, standard coolant flow direction or reversed, since I won't have a heater to worry about, any connections that would be used exclusively for the factory heater core are getting blocked off. The cooling system of the MK Indy does also locate the pressure cap on a firewall mounted header tank, rather than the radiator, for what it's worth.

I understand this project won't be cheap, and the route I'm going to achieve my goals probably isn't the easiest (DEFINITELY compared to what I could get out of it power wise if I went turbo), and that a number of my questions would normally fall pretty squarely into the realm of "just stick with the factory stuff or buy XYZ proven aftermarket part, don't try to reinvent the wheel" on a Miata, but since I'm starting more or less from a clean sheet and can build these decisions into the initial setup of the car, I might as well. Also, I'm waiting to enter the build queue for the MK kit, and am holding off on acquiring engine parts until I have my shopping list pretty well sorted, so currently the only part of this build I have is an NB 5 speed that just came back from getting a rebuild+upgrades from Walter Motorsports, so no cool kit car **** to post quite yet!

curly

iTrader: (25)

Have you considered starting with a simpler engine build? Basic I/H/E with a built head and cams can get you 160whp on a used stock bottom end. You're only wanting 10-20hp more, but going to extremes to get there. I know it's only bench racing, but if I had rebuilt that engine with high comp, slightly larger pistons, I feel like 165-170 would have been possible.

I tuned another ITB 2.0, some exotic JDM Mazda race engine that still only made 175whp.

Oh here ya go, it was one of these: https://www.miataturbo.net/miata-par...ssories-85018/

Fell a bit short of their advertised 192hp, which is probably crank hp, not wheel, but still a data point for you.

I won't comment too much on the water pump, only that you'll most likely replace any known failure points with just as much complexation as the factory system. You won't be able to drive the water pump from the ECU, you'll have to drive a solid state relay, which in turn would drive the high amperage loads of the pump. While I don't think I'll be able to convince you otherwise, I do want to warn you from creating what I call a "science project", which is to blaze your own trail for the sake of blazing your own trail. I work in an aftermarket focused shop, and have been tasked with bringing customer's science project ideas to life many times. They always end up taking way longer than expect, or not matching what their cocktail napkin math said it would do, or costing way too much more, or any combination of the three.

While you don't have the firewall constraints a Miata has, also keep in mind our cooling system is not limited by the size of our reroute housing. it's designed to be compact to fit back there, and works amazing.

Good luck with your project!

sixshooter

iTrader: (12)

I wouldn't add more failure points to a track car if it could be helped.

jedd

If all you have is a transmission so far I would just use a Honda K series. Stock it makes the power you want.

sixshooter

iTrader: (12)

He said it is going in a Lotus 7 copy. K motor won't fit

emilio700

iTrader: (3)

I've never been convinced a long rod conversion will help much in a BP without significant increases in airflow. Motor that have long rods tend to have a better CFM (head flow) to displacement ratio. So that extra dwell time matches up with high rpm, high overlap, high CFM operation. The BP has low flowing, low velocity ports. To get even modest power requires radical cams and porting. A handful of SCCA EP motors made around 220whp with dry sumps, billet cranks, 12-13mm lift 310° cams and massively hogged out ports that still barely squeak out sub OEM K20 CFM numbers. And they use stock rod lengths and have nothing below about 6,000. Having driven a balanced blueprinted 1.9L long rod BP on stock cams, I can say that they are a bit smother than stock, no surprise there. But having it on the dyno, there was nothing special there.

I agree with Josh, keep it simple. Mild cams, modest compression if not running E85, deshroud and bowl blend, +1 O/S valves and a square top. Forged bits, HD valve springs and it'll make 160whp for 200-300hrs if not over revved and has an oil cooler. I recommend shimming the oil pump and running a bit thicker oil like 10-w40 or 20w50 depending on oil temps and usage.

BumpHeadRacing

Partially correct, it is going in a Seven, but more of an evolved and tweaked Locost chassis than a true Lotus 7/clone. MK Sportscars (the manufacturer of the kit) does have a well-documented build formula for a K20-engined car otherwise using NB running gear, but probably against "press the easy-button" logic, I will be sticking with the BP platform, even in the face of knowing the kit manufacturer has sold and built a few K-engined cars and has the process well-documented. If this isn't already evident, "actively and bull-headedly disinterested in doing things the easy way" is a common theme with who I am as a car-loving human being and is not a trait about myself I intend to ever change; if I wanted to just smash the "quick track car easy button" I'd forget anything that used any portion of a Miata driveline and buy the Hayabusa-engined early Radical SR3 that just went up for sale in Maryland.

Oiling is going to be taken care of by a Boundary BP-S3 (high flow VVT pump with billet gears and shimmed to 70psi), and I will be taking steps to control oil temperature, in the form of an oil to water heat exchanger (let engine coolant temps stabilize oil temps and let the radiator deal with all of the cooling needs of the car, rather than stacking multiple heat exchangers in the nose), so I should be fine there.
I may play around with a flex-fuel sensor, and will be making sure everything in the fuel system is ethanol-safe just to deal with fluctuating E levels in pump gas, but the overwhelming majority of the time I'll be running dino squeezings. The hassle of E85 for a track car is a bit more than I'm interested in dealing with, as only one of the tracks in my area has E85 semi-readily available and even then it's just from the Sheetz just outside the track. 93 is common as the highest octane pump gas out here, then 100 unleaded and I believe 105/110 leaded at the pumps at VIR, I would be tuning the car for 93 as the lowest common denominator.
In the realm of "in order to make more power, go out and buy an intake other than the one that came bolted to the engine", is there a compelling reason (other than cost by itself) why I wouldn't want to get ITBs for a naturally aspirated application, given I will be doing head work (the recipe you gave, plus port matching on intake and exhaust as required), cams (Maruha 264deg 10mm lift, unless there's some massively compelling reason not to), and 4-1 header (by virtue of a factory Miata exhaust manifold of any generation being confirmed by MK Sportscars to be unusable in a left hand drive MK RX-5 chassis due to the steering shaft needing somewhere to go)?

sixshooter

iTrader: (12)

Many sevens only have a 6 gallon fuel tank so E85 would definitely be a non-starter. Yes, I was unaware you were using a larger chassis that could accommodate a k engine.

The BP is a rather agricultural engine, lol. It is sturdy and cheap in the front wheel drive economy car configuration for which it was originally designed. Hardening some of the soft spots in its design help its longevity on the track but there is not a lot of additional power to be made without incorporating forced induction.