Can a high compression engine be Streetable?

[Christos Adam]

During the last Autox event my clutch was slipping and I couldn't get any power to the ground... I was completely bummed but to my surprise the car was extremely smooth (since only limited torque was going to the rear wheels) and fast (I got the first spot).

All these put me in thoughts about building my engine as NA for next year. The problem is that I still want to be able to drive the car on the streets, therefore I'm looking for a build that won't have very limited lifespan.

Are all of the high compression motor a disaster ready to happen?
Would a 13:1 compression motor live long if its been driven on the streets?

Which are the things that I need to be careful about and which the things to avoid in a motor build to be streetable?

Currently the car has a flying Miata stroker (2.0 not 2.1) built on a 01-04 block with 99 head and it's been running for the last 3-4 years exclusively on E85.

Here is a very initial plan:

Crank: I'm planing not to lighten the stroker crank.

Pistons: 13:1 or 14:1 pistons - same bore probably keep it 2.0 so I can go back to FI if I ever change my mind. Obviously I plan to keep running E85.

2001 Vvt head (already purchased)
- what do you have to suggest for camshafts and springs?
I noticed some E production miata are running the ones below:
http://www.epmiata.com/store/Engine/WEB37-022.html
- would you do oversize valves and if yes by how much?

Header: I'm planing to get a Maxim header as a starting point. Custom headers can be as good as their creator and I don't know any good shop that I would trust.

Exhaust: I probably need a 2.5" but I might just keep the 3" that I have right now for simplicity. Hopefully it won't hurt the power too much.

ECU: probably would get an MS3 with vvt control unit.

TB: I'll either use my JB welded TB or get the new one that everyone uses in CSP. No time or money to play with IRTB at this point.

Intake: I have a Turbo intake manifold from BEGI with velocity stacks inside which worked wonders in my turbo car. I believe NA need even longer runners.
I don't want to spend any money there so my options are either the turbo or the stock manifold.

Thanks,
Chris

[Bobby Beyer]

I'm not a Miata guy but to answer your first question...Yes high compression engines can work very well on the streets. Now for the big issue most engines require more octane when the compression ratio climbs so a 13-14:1 engine will probably require more octane which it seems you have figured out by running E85.

The compression ratio has no bearing on engine life aside from death by detonation, your piston alloy selection and bearing materials have a much greater impact on longevity, going with a piston of 2618 alloy will wear out the ringlands sooner than say a piston made out of 4032 or a hypereutectic or cast material. As for the bearing materials the softer the material the more capable it is at embedding particles but its more likely to suffer excess wear from use. Aluminum will last a long time but doesn't hold materials as well, where as babbit(sp) can embed dirt very well but doesn't last all that long.

So if you're piston selection includes very soft bearings and a soft alloy piston I'd be shocked if the motor wasn't clapped out after 30-40k miles. If its a race only engine that shouldn't be an issue but a street engine that might be an issue.

[Jayson Woodruff]

Remember, its only really high compression when you're hard on the throttle.

Jay W

[Christos Adam]

You are right I didnt realized that up to now... I was thinking that the piston goes always up to the same point and of course the compression ratio is always the same but obviously the amount of air stuffed in there (and the actual compression) isn't always the same.

[Marshall Grice]

I think a high compression engine is going to be harder to drive in an autox setting because it is not going to achieve what you think it will in terms of power delivery. meaning a higher compression engine will not drive like a turbo motor with a slipping clutch just because it makes less power. a high compression NA motor will have very immediate throttle response and crazy high engine braking abilities making it very sensitive to throttle application, aka the opposite of what i think you're looking for.

a turbo with a good boost control strategy is, IMO, the way to go. ...of course I might be biased. ;)

[Christos Adam]

I think a high compression engine is going to be harder to drive in an autox setting because it is not going to achieve what you think it will in terms of power delivery. meaning a higher compression engine will not drive like a turbo motor with a slipping clutch just because it makes less power. a high compression NA motor will have very immediate throttle response and crazy high engine braking abilities making it very sensitive to throttle application, aka the opposite of what i think you're looking for.

a turbo with a good boost control strategy is, IMO, the way to go. ...of course I might be biased. ;)

OK, I'm sold , turbo it is, let talk when you have some time, I need you brain }:)

[John Coffey]

Marshall is right, but immediate throttle response can be an advantage if the the throttle is setup with enough throw and the driver has good control over his/her right foot. At the cornering limit most cars are steered with the throttle so a more sensitive and quicker reacting throttle (engine) will aid a more skilled driver. BTW... A heel brace helps keep the throttle foot steady.

[Marshall Grice]

At the cornering limit most cars are steered with the throttle so a more sensitive and quicker reacting throttle (engine) will aid a more skilled driver.

totally agree here too. exactly what I meant by "good boost control". The hardest part about driving a turbo car is controlling the car at the limit as the motor transitions back into high boost. setting boost targets based on TPS make that control much easier, perhaps even easier than an NA high comp motor. If you're running a manual boost controller you're SOL, throttle oversteer is almost guaranteed unless you just don't even try to get on the gas while cornering.

Most throttle bodies are flowing nearly 100% of their max air flow by the time the throttle angle is ~60%. With the tps based boost targets you can add torque control authority beyond where the throttle becomes ineffective at controlling engine torque by ramping up the boost with increased throttle. It yields basically the same outcome as a progressive linkage on an NA motor but is more effective on a turbo motor than the progressive linkages are and you get to keep the high specific output of the turbo setup.

If you wanted to get even fancier, doing traction control based on varying wastegate duty cycle could be pretty damn cool too. Personally I prefer the awd solution to traction problems though. ;)

[Ed Holley]

At the cornering limit most cars are steered with the throttle so a more sensitive and quicker reacting throttle (engine) will aid a more skilled driver.

totally agree here too. exactly what I meant by "good boost control". The hardest part about driving a turbo car is controlling the car at the limit as the motor transitions back into high boost. setting boost targets based on TPS make that control much easier, perhaps even easier than an NA high comp motor. If you're running a manual boost controller you're SOL, throttle oversteer is almost guaranteed unless you just don't even try to get on the gas while cornering.

Most throttle bodies are flowing nearly 100% of their max air flow by the time the throttle angle is ~60%. With the tps based boost targets you can add torque control authority beyond where the throttle becomes ineffective at controlling engine torque by ramping up the boost with increased throttle. It yields basically the same outcome as a progressive linkage on an NA motor but is more effective on a turbo motor than the progressive linkages are and you get to keep the high specific output of the turbo setup.

If you wanted to get even fancier, doing traction control based on varying wastegate duty cycle could be pretty damn cool too. Personally I prefer the awd solution to traction problems though. ;)

Sent at 02:31? Really?? How BAD have YOU got it? This is what winners do boys and girls. And then, they pay it forward....although in small doses.

[Rick Brown]

At the cornering limit most cars are steered with the throttle so a more sensitive and quicker reacting throttle (engine) will aid a more skilled driver.

totally agree here too. exactly what I meant by "good boost control". The hardest part about driving a turbo car is controlling the car at the limit as the motor transitions back into high boost. setting boost targets based on TPS make that control much easier, perhaps even easier than an NA high comp motor. If you're running a manual boost controller you're SOL, throttle oversteer is almost guaranteed unless you just don't even try to get on the gas while cornering.

Most throttle bodies are flowing nearly 100% of their max air flow by the time the throttle angle is ~60%. With the tps based boost targets you can add torque control authority beyond where the throttle becomes ineffective at controlling engine torque by ramping up the boost with increased throttle. It yields basically the same outcome as a progressive linkage on an NA motor but is more effective on a turbo motor than the progressive linkages are and you get to keep the high specific output of the turbo setup.

If you wanted to get even fancier, doing traction control based on varying wastegate duty cycle could be pretty damn cool too. Personally I prefer the awd solution to traction problems though. ;)

Sent at 02:31? Really?? How BAD have YOU got it? This is what winners do boys and girls. And then, they pay it forward....although in small doses.

Marshall is currently working night shift. And it looks like your browser is still on DST.

[Ed Holley]

Marshall is currently working night shift. And it looks like your browser is still on DST.

As if posting at 01:31 a.m. changes my point. As for "working" the night shift, I'm gonna tell on him. Unless, of course, he continues to provide copious amounts of performance enhancing secrets. ;)

[Marshall Grice]

hahahah. yeah i'm working nights, so that was my 'lunch break'. the more impressive feat is that i made it to the practice and championship after working until 6am (although not the nights directly before so it's not really that impressive)