Jeff_Ciesielski

iTrader: (10)

It won't apply to about 99% of your setup because you have a 1.8. The relevant part is the timing map, which is also not entirely accurate because the VE curves of the two motors are similar, but not perfect.

hustler

iTrader: (6)

that spark table is 6-8* back from MBT at 184kpa+(crappy CAS and headroom for heatsoak on the track) and made 254whp at 11psi, and like 305 or whatever at 16psi on a gt2860rs with an 8.6:1 compression 83.5mm bore. If I ever get a crank wheel I'll put that spark back in it.

na8psi

iTrader: (1)

Holy spark map! I see why hustler is god.

So, water/meth injection for my purposed setup would essentially be overkill for a car that will at most see the drag strip on weekends? Basically, that I should make my goal of 280whp+ on just the hardware of the setup alone, not using the methanol as an essential octane boost to grab more timing?! Im also intrigued to discussing what is a proper/efficient CR to choose from for pistons and the effects of said? Picking 9.0 vs say 8.6 will this essentially effect power under the curve, overall power capabilities, or what essentially does one take into account when trying to choose between the two? I've heard many a rumor of people ranting that lower compression is just an all around better choice when looking for peak power numbers vs say 9.0 CR giving you better power under the curve?

Guys, elaborate all help is appreciated criticism likewise. Anyone who contributes gets free beer!

hustler

iTrader: (6)

No one who's driven my car around town made a mention of a lack of power in vacuum. FM stands by 9.0:1 compression, and even on Matt Andrews' car it works all the way up to 400+whp on the racetrack. I'm somewhat ignorant to how engines work compared to engineers but the low comp certainly gives me headroom and allows for a ton of spark angle. It wasn't a better choice for me on peak power...it was better all the way around or at least good enough for the large AR turbine and lots of spark.

miata2fast

iTrader: (2)

For what I have learned, low compression really becomes critical when you are going for mega high boost. I always thought that if you had the ignition, ECU, and proper fuel to handle it, higher compression would make more power when boosting with lower pressures.

With my nitrous experience, the smaller shots made more power on high compression engines, but if you wanted to make the most power possible, a lower compression engine coupled with a very large amount of nitrous was the way to go. Does it make sense that it would apply to all boost applications, or is there more going on than I am aware of?

Jeff_Ciesielski

iTrader: (10)

This is correct. You will make more power per pound of boost with a higher CR all other things equal. The big deal with lower compression is that it allows you to make more power on a given octane of fuel. You'll have to run more boost/timing to get that power though.

webby459

iTrader: (8)

I'm surprised at how agressive hustler's timing table is, especially compared to mine. I'm 9.5:1, actually wanted 10:1, but weren't available in a timely manner. I was told we were at mbt for the most part throughout, no timing was pulled back out. E85, 2560R. I wanted high comp plus the smaller turbo to make it mean for autocross. I still didn't get quite the spool I wanted. If it ever goes back together I'm in for a lot more tuning.

WonTon

iTrader: (17)

i know im a lil late on this but you can go 20 over and still be able to use the OEM head gasket. 20 over is about as much as you would want to go on when running boost. anything more and you have less cylinder wall thickness ( no brainer )

i talked with the guy who is building my engine the other day about this stuff. he is doin a 40 over but he is going to be NA with sidedrafts, running like 13:1 compression ratio OEM style pistions and corrilo rods.

hustler

iTrader: (6)

The main reason I went low comp was for headroom on the track. Its probably hurt my output below 16psi, although I make 234wtq at like 3800rpm at 11psi, but its super safe and I would do it the same way again. Its worth it for pizza-mind when I'm on the track focused on driving.

Once again, that spark table is 6-8* behind mbt at 11psi+. I'm leaving 10-15whp on the table for the sake of safety. I had it 2* back from MBT but after a friend did a rebuild from detonation in his 300ztt from heat-soak detonation, I pulled time. When you consider that we have 2-tooth CAS, no real knock control, and a stretchy timing belt, you have to be overly cautious.

miata2fast

iTrader: (2)

You can go .030.

Maybe with a gigantaur amount of boost, but come on.

I would agree that it is not necessary to do it, but if anyone later needed to bore larger than .020 because of an engine failure, it is safe to do so.

na8psi

iTrader: (1)

In a nutshell, going with 8.6 persay vs 9.0 is just the difference between making my HP sooner on lower boost vs having a safety net and needing more boost pressure and timing to make the alotted goal? I already have ordered a snow performance water/meth kit thats going on my current motor which is stock 1.8 DD on 10psi. What im gathering from the more experienced heads on here is that water/meth on either setup would be overkill. A good question for the subject at hand is, just how much more power are people making off boost with the higher of the 2 compression ratios vs the lower of the 2? Enough to make the consideration worthwhile, so less of power off boost that I would gripe? Car is practically driven daily for 90% of its life, and 10% at the strip.

hustler

iTrader: (6)

Remember that your tach reads slower than what MS logs, so where it shows 3500rpm on the log, the tach reads like 3200rpm:


This is the AF parts on 8.6: compression in like 3rd gear with the CHRA/turbine leaking enough to make noise. I need to put those Nimonic bolts in or at least tighten the CHRA bolts since the first installation, lol. I saw 220-250wtq from 3500-4000rpm when tuning.

"Off boost" comparisons don't really matter because you're not concerned with power in that range when you're cruising...you just run lower kpa per wheel-speed. You're basically concerned with how soon you can hit target boost. You have good tubular manifold stuffs so you'll probably see results like what I've posted.

If you're cruising around town at less than 3000rpm then you're a tard:

At 2000rpm I'm going over 100kpa, at 2800rpm or so, the car feels like its really starting to move. At 2800rpm I'm already at 120kpa, in 2nd gear at 3200rpm (6psi/140kpa)street rubber starts to break loose on the Nitto Neogens.

I had the same worries you have currently and I'm totally happy with the performance over the entire rpm range.

hustler

iTrader: (6)

The water is overkill, but adds lots and lots of safety. I'd put the money somewhere else but its not going to hurt of course.

WonTon

iTrader: (17)

my post was answering the dudes question with bore and headgasket, the guy that is building my motor has been racing for god knows how long and builds his own engines and has probly done about 50 or so between 1.6's and 1.8's.....im pretty sure the dude knows what he is talking about!

i didnt say you couldnt do it...but me personally, if i went overbore i wouldnt do more than .020 over for peace of mind. (i have intentions of running 17-20psi of boost threw my engine) and more eventually when i get another motor put together with a slight overbore with some H-Beams...

off topic...how much power do you have off the bottle and is your engine stock or built? i cant remember.

miata2fast

iTrader: (2)

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Rennkafer

iTrader: (3)

Has he sonic checked the wall thickness on varying Miata blocks? If not he's guessing. When we need to know how far we can go with a particular engine we check the cylinder wall thickness at 12 spots per cylinder on all bores.

Some engines have very little meat around the bores... others like the engine in my '67 International can do rediculous overbores because it has really thick walls.

1slowna

iTrader: (1)

i personally plan on running higher compression prolly 10.1 but i also plan to use e85. i would stick with somewhere in the 9.1 area seems like a good medium and your power goals are by no means out there you could stick any off the shelf piston in there with less then 11.1 and you could easily meet your goals on pump gas my guess is 16psi 9.1 you will be right at that 280 area, only one way to know for sure though, also considering your power goals there no need to get crazy with the overbore you would be better off leaving some meat in there just in case you melt a piston or break a ring land you will be able to reuse the block, maybe.

WonTon

iTrader: (17)

ill talk to him some more this weekend about the methods he uses and what all he has done. we didnt get a chance to speak a whole lot when he dropped by to pick up the shell and engine parts.

+1

miatamania

iTrader: (9)

A little late to the party but as we talked about yesterday, I still think for what you are wanting to do 9.5:1 would be what you need.

Hustler's motor is overbuilt with plenty of headroom. For the goals you have it just seems like a waste to leave power on the table like that for a car that is going to see more street time than a dedicated track car.

18psi

iTrader: (76)

I'm very happy with my 9.1:1 compression fwiw.
Plenty of response, plenty of headroom for timing, and low enough compression to have headroom in boost as well.

I call it the "happy middle"