mx5cartalk.com

I will be interested in replies to this topic.
Not owning an SE but a NB8A turbo'ed.
Have run from 7-14psi for nearly 18 months.
Currently running rich at 12 psi 168kw atw.
Has put out 187kw atw on dyno but struggled to run smoothly
at cold start.
No bottom end work done. Admittedly in that 18 months I have never
stomped on it in first gear or dropped the clutch at high revs. Oh yeah
the clutch has been built up to 1780 lb pressure plate clutch, 700 standard.
Only once has another driver gunned it in first and second gear. If I had known he
was going to do it I would have said don't do it:)
I only ever use the torque once I am into 2nd gear and have got past the wheelspin stage.
How long will the engine last no idea. Should you run less boost and less power. I am sure the answer to that question is Yes. A lot of people have commented that they are surprized that my car as not blown up. With so much power I find no need to boot it.
I believe the gearbox is probably the weakest link in the chain. Touch wood sofar no problems. I have heard it is good for around 165kw atw. The cost of building up the engine and the length of time off the road has deterred me from going down that route.
Cheers Novice1

If Familia engines are anything to go by, then pushing more then 14psi regularly, will result in bent rods and holes in blocks. 17psi would kill the engines pretty quickly.

doesn't matter what turbo it is. you push too much pressure into the engine, it will go kaboom!

SE10S

Where are you based?

All the info you need about SEs (MSMs) is here
http://www.mazda-speed.com

and here
http://www.flyinmiata.com/tech/MSM_upgrades.php

No need to reinvent the wheel.

project.r.racing wrote:doesn't matter what turbo it is. you push too much pressure into the engine, it will go kaboom!

PLEASE,

If you dont know what your talking about dont give advice in thread relating to peoples engines.

Boost isnt just boost.
When the air fuel mix combusts the engine sees well over 1000 psi during combustion, this is how the engine makes power, even just turning the motor over to start it makes 200psi just cranking with no spark. Its doesnt work "like 17psi will blow it, hurr durr".

Its combustion pressure that will break things, combustion pressure is what dictates torque, more pressure, more torque.
If you have a small inefficient turbo pushing 17psi with no intercooler, it might only be flowing as much air *MASS* as a larger more efficient turbo with water injection and a large intercooler does on 5 psi. This air MASS is the actual amount of molecules of air that your engine uses to burn with fuel and make power.

More air mass equals more torque (by adding more fuel and making more combustion pressure...yes thousands of psi).
The limit of B6 and Bp bottom ends is the rods first, both engines use the exact same rods, and they both have a safe limit that you can get away with for years of about 250rwFT/Lb. If you have big cams and make this torque at 8000rpm, you will make double the power of the bloke who only makes that torque at 4000rpm.

TL,DR Its not horsepower that breaks bottom ends, its torque. PSI and horsepower does NOT equal torque.

Dann

Lots of things break engines, but I think you will find that the real killer is detonation, especially the sort that you can't hear (or don't recognise). Don't go for a highly agressive tune with as much timing advance as you can. Run a knock sensor if you really must push the limits, preferably one that pulls timing on knock, and be careful about the fuel you use. I assume you will be cleaning up the combustion chambers to (amongst other things) eliminate hotspots that might trigger detonation.

BPs are known for (relatively) weak rods, so best to play safe. I see you are planning a built bottom end, I suggest that you do it sooner rather than later.

The next weak link will be the gearbox. Do a search on here, but the short answer is an SE box and/or Redline Shockproof. Or a new gearset, 300kw (at the wheels?) is probably too much for an SE box, but I am only guessing. If you are going drag racing, the whole drive train will need a good look - some of Minx' sites should have some answers for you, but also see miatanet.com and miataturbo.net

Davex3 wrote:15psi limit on any turbo on the stock rods. Rods will start to go at 200rwkw pistons at 220rwkw.

A 3076 is way too big for a stock 1.8 bottom end, even on a built 2.0 it will be laggy. Unless you are shooting for 400rwhp+ its way too much turbo, a 2560 or 2860rs is a much better choice for a stock bottom end.

What is your horsepower goal?

This still isnt right, read my post, it may be that 15psi on the stock turbo is the limit (yeah thats about right), but with water injection it might be 13 psi, a bigger turbo and water injection it might be 10 psi.

Dont just deal in absolutes with someone asking advice about his engine, if he throws a large frame garrett on there and boosts 15 psi with his new upgraded intercooler that is NOT the same as 15psi on a hot day from his stock turbo. Its much more.

Dann

SE10S wrote:

Davex3 wrote:15psi limit on any turbo on the stock rods. Rods will start to go at 200rwkw pistons at 220rwkw.

A 3076 is way too big for a stock 1.8 bottom end, even on a built 2.0 it will be laggy. Unless you are shooting for 400rwhp+ its way too much turbo, a 2560 or 2860rs is a much better choice for a stock bottom end.

What is your horsepower goal?

Cheers thats what i wanted to know, yeah it is a bit big for the standard bottom end but i wanted to get all the fab work done before i get a built bottomend, the goal is 400 whp+ should make it a bit of fun

Ok rods at 200rwkw , pistons at 220rwkw. What about gearbox?
I have a eboost2 installed and can choose from 6psi or 12 psi. 99 percent of the time car runs on low boost. I may go months without hitting SP2 or high boost.
Currently my car puts out 168rwkw at 12 psi and 417 newton metres of torque. Perhaps my car has not detonated as a) high boost is very rarely used b) even on high boost I never throttle it from a standing start. Recommendations for what gearbox to use if I am pushing the boundaries. Can't see myself going over 200rwkw but 180 plus is well within my cars reach.
Cheers Novice1

350hp or so on the 6 speed. The worlds highest power 1.6 makes well over 400 on a 5 speed, but he only does highway pulls.

Dann

mt.net full web address please.
Novice1

Novice1 wrote:mt.net full web address please.
Novice1

Ron,
www.miataturbo.net/

In particular there is a DIY turbo FAQ:
http://www.miataturbo.net/showthread.ph ... bf4&t=4288

Mate I spend ages on there. Its not power that breaks ANYTTHING, its torque. And 15psi on any turbo is NOT the same as any other.

Dann

Maybe I need to clarify this, torque is how hard the pistons gets pushed down by combustion pressure, power is merely a factor of the torque and the rpm which you can make that torque. Rods in MX5s break by bending, that is, they are broken by too much combustion pressure pushing down on them, ie its the torque NOT the power that they fail from.

Secondly, PSi is a measure of restriction of air NOT air flow. So stop telling people that 15psi is 15psi, it isnt that simple.

Dann

really? i thought torque was a measurement of the force required to turn/rotate an object.

Correct, the downward force of the conrod levers on the crankshaft, producing torque.
Apart from helping determine capacity (which helps determine combustion pressure) the bore of an engine determines downward force, since pressure is force over an area the larger area the more force is generated against it (this is piston/bore size).

Apart from helping determine capacity (which helps determine combustion pressure) the stroke of an engine determines the length of the leverage arm the piston and rod has against the crank, think about it, when the piston is halfway down the bore the crank arm where that pistons conrod is pushing is at 90 degrees to the downward force (look up an engine gif if you still dont follow), so there fore the longer the stroke the larger the leverage on the crank, producing more torque.

Now imagine that there are 2 engines that both produce the same amount of torque, but one does it at double the rpm, we can gear it down to the same rpm as the other engine (2:1 reduction drive), now the output torque after the gearing is doubled and both engines output rpm's are the same, hence that engine makes more power. It makes the same torque at twice the rpm, therefore it makes twice the horsepower due to its ability to be geared lower, for a greater output torque, but still at the same rpm.

As for PSI isnt just PSI, psi is a measure of RESTRICTION. If you put a boost guage on a turo outlet thats not connected to an engine, it will still flow huge amounts of air but now your guage will read 0psi, because there is no restriction to airflow. 2 identical turbo engines, but one has cams, it produces more power at the same boost pressure as the stock cams engine. Therefore it can produce the same power with LESS boost. This is because with the cams its head flows better, and the same air MASS can flow through with less restriction, therefore less boost.
Its less boost pressure but its easy to see how it is the same airflow. Therefore ANY 15psi is NOT any 15 PSI.

i hope thats clearer to everyone.

Dann