compression ratio / Paging infomaniac & Fiat48

[hbhallett]

Gentlemen,
I recently aquired a procharger set up with 5-8 lbs of boost. The pistons which I believe are installed in the 454 BBC standard bore/stroke are TRW 2399F with a .095 dome. I have been only to find one number inside the piston and that is 269 99 under the head of the piston. I've researched the web and found similar style dome configuration on a web page which look identical and the user states they were the TRW number quoted earlier. I the went to Flatlander Racing's website and looked up the TRW piston page where I approximated the CR based on the the psiton part number.
The heads are GM 6272990 rectangular ports with 118 cc. I presume that I'm probably at about 9.5-1 CR.
If I don't change the boost, intercool, and keep the engine with it's current direct from the Berkeley jet cooling system [no thermostat and it runs pretty cool say 150 F] can I get away with 91 octane pump gas.
I don't plan on mashin' it [under 5000 RPM] and I thought I could also decrease the CR slighly by replacing the head gasket with a thicker one.
Can I keep these pistons?
Your sage wisdom would be much appreciated as always! THANKS

[Fiat48]

The compression ratios that are shown at Flatlander racing are not correct. Some are misprints..IE..they are showing some smaller chambers with lower(?) compression ratios.
Last catalog I have showing part # 2399F shows 8.73 to 1 with a 119cc head. They measure with a .0385 thick head gasket but do not mention deck height. Since they don't give me a dome CC, I can't calculate whether they are figuring the compression ratio at 0 deck or not. TRW used to use .020 in the hole for calculations but no mention in this catalog.
Since you are at sea level and want to use pump gas, I'd think you would want to lower the compression ratio. If you were at 4500 ft like I am, I'd say o.k. I would definately use some sort of octane booster.
Here's some ways you can do this. The piston dome of .095 is no doubt solid, so you could machine the dome off in a lathe. Since you would be lightening the pistons all equally, a slight overbalance(engine balance) would occur. You wouldn't need to rebalance your engine. Using a 4.350 bore size gasket .040 thick and assuming you have 0 deck would get you to 8.28 to 1. If you wanted to go lower (future use when you want to add more boost), then a .062 thick copper gasket (you have to O ring the block) at 4.500 bore size gasket will get you to 7.93 to 1. All these calcs assume 0 deck. If you are .020 in the hole, that's worth a drop of about 1/4 point in compression.
This is just food for thought. Many engine builders have many combinations, but my thought is to get a lower compression ratio due to todays junk gasoline and the fact you are at sea level, which means a lot. Plus the fact guys with blowers like the idea of being able to turn up the boost later on.
Infomaniac (unless he got blown away by a tornado) is sure to have more input and probably a whole lot more experience with gasoline. The number one reason I went to alcohol years ago is not to worry about octane or elevation.

[Infomaniac]

I think that about covers it.
How many CC's is a .095 dome? Anyone know?

[Blown Lavey]

INFO...
How is the quad rotor coming along? I have been checking H.B and I havent seen any new info. Just wondering if it has made its way to the dyno?

[Fiat48]

Best math guess on the .095 dome is 8 cc's. Figured that by using L2377F which is flat, no dish and 1 valve relief.
[ May 09, 2003, 11:02 AM: Message edited by: Fiat48 ]

[hbhallett]

Info /Fiat-
Thanks as always for your help!!
Based on your comments, I think I would be running at about 9:5-1.
I have a set of custom JE pistons 4.255 bore size which are flat top forged aluminum. Given that the TRW pistons are usable and I'm on a budget would you suggest I have the TRW pistons' dome milled to reduce the CR or bore/hone the block to fit the JE flat tops?
Thanks again for your expertise!

[Infomaniac]

Blown Lavey:
INFO...
How is the quad rotor coming along? I have been checking H.B and I havent seen any new info. Just wondering if it has made its way to the dyno? Dyno next week. In the boat soon after. Speed runs by Memorial Day.

[Infomaniac]

hbhallett:
Info /Fiat-
Thanks as always for your help!!
Based on your comments, I think I would be running at about 9:5-1.
I have a set of custom JE pistons 4.255 bore size which are flat top forged aluminum. Given that the TRW pistons are usable and I'm on a budget would you suggest I have the TRW pistons' dome milled to reduce the CR or bore/hone the block to fit the JE flat tops?
Thanks again for your expertise! 8.8:1 on a stock bore and stroke 454. .0385 head gasket and 0 deck.
[ May 09, 2003, 01:07 PM: Message edited by: Infomaniac ]

[hbhallett]

Infomaniac-
I the 8.8-1 CR the value you calculated with the current pistons (i.e. .095 dome)?
Thanks as always! By the way your write up on assembly in the Havasu Barney site is awesome!! Good Job!

[hbhallett]

Infomaniac-
What I menat to say was Is the value of 8.8:1 the value calculated with the current .095 dome pistons??
Sometimes my fingers are faster than my brain-

[Infomaniac]

hbhallett:
Infomaniac-
What I menat to say was Is the value of 8.8:1 the value calculated with the current .095 dome pistons??
Sometimes my fingers are faster than my brain- Yes

[hbhallett]

Info- last question of the day before I wish you a good weekend. Presuming I'm at zero deck height same .095 dome pistons at standard bore x stroke, if I use an .051 compressed height Felpro head gasket I calculate a 8.62:1 CR. Any problems with using this type of gasket {intake manifold mismatch, valve train etc...)?
What type of deck heighy would you expect to see on an engine which has never encountered machining? .030, .000???
If I do have .03 deck I calculate an 8.34:1 CR with an .041 gasket at 110 CC volume and 8.2 CR with a .051 gasket. This 8.2 to 8.34 CR would certainly seem to be an acceptable range to add a 5-8# Procharger correct?
Thanks and have a good weekend

[Infomaniac]

That compression should work OK
I am not familiar with those pistons. I guess they are forged?
It is intercooled? If anything else , back off of the boost a pound or so and keep timing conservative.

[Fiat48]

If the block has never been machined, odds are it is not O deck. Just guessing, it's probably .020 in the hole or very close. Buy the thickest and largest bore diameter gasket Fel Pro makes. The TRW piston is forged and very adequate.

[hbhallett]

Thanks to both of you for your insight. I really appreciate your comments.