falcon

iTrader: (13)

Compression ratio is not measured with PSI from a compression test. All that does is tell you how well your rings are seated.

To get your "true" compression ratio you need to cc the head and measure how far the piston is below or above the block deck. Then do some fancy calculation and you get your true compression ratio.

miata2fast

iTrader: (2)

That would be correct. You will notice that in the ports there are little scratches left by the sanding process. You do not use too fine a grit with your polishing scrolls.

The combustion chamber itself however, often has a more polished appearance.

TNTUBA

iTrader: (1)

You don't want a polished finish on the intake side. You want the exhaust as smooth as you can get it. The reason you don't want a smooth surface on the intake side is the mixture going into the chamber has liquid fuel suspended in the mixture. If the boundary layer of air against the port wall is not turbulent the liquid fuel can "fall out" of suspension and pool against the port wall. The rough surface of the wall creates that turbulence much like the dimples on a golf ball. The exhaust port has somewhat the opposite problem. The burnt gasses leaving the combustion chamber are carrying carbon. That carbon can deposit itself on the port if the boundary layer of air isn't kept at a high velocity. Secondly the smooth surface doen't give the carbon something to hang on to. You want the combustion chamber as sooth as possible and you want all the sharp edges in the chamber to be softened. Any sharp edge in the combustion chamber can get extremely hot creating a source of detonation. The second reason you want the combustion chamber smooth is the same as the second reason for the exhaust ports. You don't want to give the carbon in the combustion exhaust a rough surface on which to deposit itself.

mx594m

iTrader: (1)

Eric - and all this time I thought the fuel injectors injected directly through the open valve port into the combustion chamber, little did I know that the air flow coming out of the intake plenum and through the head passages was a fuel-air mixture [FFS excepted].
I think that satin finish logic is now an old wives tale, a carry-over from carburetor days.

For me, I want my intake and exhaust passages as smooth as possible, but I want the passages for the charge air to have the satin finish to aid in heat transfer.

But I do admire your work, and since you are so close I am tempted to bring a head to you to duplicate the effort again -

TNTUBA

iTrader: (1)

No worries. I will need the head, 2 intake vales, 2 exhaust valves, the intake gasket you are going to run, the exhaust gasket you are going to run and the head gasket you are going to run. I work with a machine shop down here that only does head work so if you bring me a complete head that is what you will get back. If you are serious let me know and we can work something out through PM's

miata2fast

iTrader: (2)

Just a note of interest, if you want to go larger than the manifold gasket, you can easily expand the gasket with a die grinder by a reasonable amount.

I guess you would need to stay far enough from the raised portion that is designed to crush when torqued.

I have not explored the limit, but I had to cut the gasket so it was not protruding into the intake tract. I have not encountered issues with sealing.

TNTUBA

iTrader: (1)

Just finished CC'ing the head, measuring the deck height and a compressed head gasket. It looks like the final compression ratio is 9.9501:1

I love how inaccurate advertised compression ratios are.

vehicular

iTrader: (3)

1.) Polishing the exhaust ports and combustion chambers will net you some gain in heat rejection, but the gains will be immeasurably small. Endyn did some testing with port finishes once upon a time, and published dyno data showing that for all the work involved in polishing/ finishing the CCs/ exhaust ports, they produced no measurable improvements over the same port left at carbide cutter finish. Think about it, after 30 seconds on a running motor, no surface rougher than WPC treatment won't be so covered in carbon deposits that the surface finish itself will be totally obscured.

2.) The difference between 10.13:1 and 9.95:1 could easily be lost in the casting variance/ headgasket/ machining tolerance mix. You're talking 1cc difference. You also lost a little compression in the chamber porting process. I won't disagree that compression ratio numbers from piston manufacturers often seem to be totally arbitrary. I've even found that some of their own advertised dome height and compression numbers don't agree. I'm just saying that I wouldn't sweat that tiny bit of compression ratio difference.

Faeflora

iTrader: (2)

It's been about the same across three different gauges. Who knows, maybe they were all HF gauges though.

Maybe my rings never seated that well. My engine had a hard first 5 minutes of it's life where we were trying to run it on 6 month old atmosphere-exposed gas. I did put boost in it and suck a lot of vacuum as soon as it was on the road with fresh gas though. Maybe I will do another test. I haven't done one since I ran 30psi.

TNTUBA

iTrader: (1)

I should prob have the title of this thread changed to Head porting and a few other projects. I know it's "off topic"...but hey it's my thread. So here are some pics of the new wing and splitter.

Bought this wing off a now wrecked XP car that has trophied at Nationals a few times. I rebuilt the end plates out of Alumalite and added the greyhound stickers.


Homemade gurney flap. I "stole" this idea from Brian Johns


And the first stages of the splitter. Building it out of Alumalite too. I have moved some things around since this pic was taken...but my cell battery was dead.

vehicular

iTrader: (3)

Gangster.

Just out of curiosity, why XP instead of Street Mod? Seems like it would be even harder to keep up with the FDs and Corvettes when they can legally lose even more weight.

TNTUBA

iTrader: (1)

Oh the car is a SSM car. The wing just came off a XP car that has since been wrecked.

vehicular

iTrader: (3)

Got it. What do you weigh, and what kind of power do you make?

TNTUBA

iTrader: (1)

Right now the car is about 1370lbs and makes 0hp and 0ft lbs.

At the Nashville "Road Tour" it was 2163lbs and the goal with the new motor is 325+ on C16

Miater

StratoBlue1109

iTrader: (1)

Just out of curiosity... why C16? E85 is a much cheaper solution.

C16 is leaded so it eats oxygen sensors pretty quickly, and has an octane rating of 117, and has a cost of about $17/gln.

E85 is unleaded, easy on O2 sensors, has an average octane rating of 113, and costs less than $4/gln.

Not to mention the evaporation rate of the ethanol helps to lower charge temps, which basically makes up for the slightly lower octane rating. I dyno tune cars for a living and can honestly tell you that I'm usually within 5%, power wise, between C16 and E85. Food for thought....

If you really have to run race gas, I'd recommend Q16 over C16. It's basically a highly oxygenated version of C16. Tends to be easier on sensors and consistently makes more power than C16, for about the same price. Also if you're going to be touring nationally and visiting sites with varying altitudes/climates, Q16 will perform more consistently due to the higher oxygen content. It also has a wider range of "acceptable" AFR's, which can cut down on the need to re-tune for different weather.

vehicular

iTrader: (3)

I'd guess availablility and consistency. E85 isn't nearly as common in the south as it is in most of the rest of the country. As such, turn over on gas station tanks is slower, and batch consistency isn't as good around here. Plus there's all the fuel system contamination and corrosion issues to keep up with, especially on a car that sits for long periods of time.

And where are you getting your octane numbers? I've NEVER heard or read anything reliable claiming more than ~105 octane from E85, and you usually see more like ~98.

TNTUBA

iTrader: (1)

The closest station to me with E85 is over 120 miles away...the closest BP dealer to me is 2.6 miles away. Second I have never seen published, repeatable tests showing E85 with motor octaine ratings that high. Third. O2 sensors are cheap...that said I have been using the same sensor for the last season and a half with ZERO degradation in performance. On Q16...go read how corrosive that stuff is. You should mpletely drain your fuel system after every race and for the extra cost of the fuel, coupled with the added maintenance required it isn't worth is for the less than 2% increase in power it MIGHT net.

TNTUBA

iTrader: (1)

And here is more off topic in my own thread. Got the splitter finished tonight.

flier129

iTrader: (7)

Looks like a gay uncle's miata to me!!