Head compression

**USCG Charger** · 04-21-2007, 12:46 PM

Ok guyz I just wanted to open this question up to the forum. I an going to be doing head/cam install shortly and wanted ya'lls opinion on the FRI street heads and how they mill and shim them to add compression. I've PM a few individuals that have been very helpful and knowledgable in their response. Steve @ Franks has also helped to explain how they do this and what the outcome is after the fact. I do trust all their view on this, but I wanted to get everyones view as well.

When they mill and shims the heads will this effect the longevity of the engine? Meaning is this gonna cause problems later down the road and possibly lead to bigger issuses...if so, what issuse would come from doing this?

Again guys I wanted to stress that I'm not second guessing any info that you have giving me. I just wanted all views good or bad.

Thanks Jason

**USCG Charger** · 04-21-2007, 02:17 PM

bump

**gremlinsteve** · 04-21-2007, 02:18 PM

vary'n opinions on this. some dont like the shims. some dont mind them, some swear by them. you ca always use a pushrod checker, get a pushrod length and buy a set then install them .

the compression wont affect you in the end...remember, you also still have the knock sensor as a fail safe...use premium fuel also.

steve

**USCG Charger** · 04-21-2007, 02:24 PM

Ok.. so when I get this compression done either by milling or push rods, how does that effect denotation (sp?) or what ever it's called and pinging. I already use the highest octane with the super ships as is.

Jason

**HEMI~C~** · 04-21-2007, 02:42 PM

USCG, From what I understand, the milling that some shops are offering will raise compression to around 10.2 to 1 which should be fine with 91-93 octane....especially if you have a larger cam which tends to bleed off a bit of cylinder pressure. Its a cheap/efficient way to gain horsepower. Chrysler/Dodge kept compression at a lower value to allow customers to run 89 octane and for emission purposes. Those that run 93 octane all the time such as you/myself can easily take advantage of the hp/tq increased compression will give you. As long as you are not raising high enough to induce pre-detonation you will not effect the longevity of your motor at all.

**USCG Charger** · 04-21-2007, 03:20 PM

As long as you are not raising high enough to induce pre-detonation you will not effect the longevity of your motor at all.[/quote] How will I know that limit? Also if I'm running something similar to the sidewinder wil this burn off enough so it wont get pre-detonation?

Jason

**Jweezy** · 04-21-2007, 03:21 PM

Originally Posted by HEMI~C~

USCG, From what I understand, the milling that some shops are offering will raise compression to around 10.2 to 1 which should be fine with 91-93 octane....especially if you have a larger cam which tends to bleed off a bit of cylinder pressure. Its a cheap/efficient way to gain horsepower. Chrysler/Dodge kept compression at a lower value to allow customers to run 89 octane and for emission purposes. Those that run 93 octane all the time such as you/myself can easily take advantage of the hp/tq increased compression will give you. As long as you are not raising high enough to induce pre-detonation you will not effect the longevity of your motor at all.

What about your heads, are they milled or whatever is going on here.

**HEMI~C~** · 04-21-2007, 04:10 PM

I haven't touched my heads *yet*. Jason, generally speaking 10.2 to 1 compression and the increased cylinder pressure it would provide is well within the limits of 93 octane, especially given the fact that we have aluminum heads. Hell, the SRT8 comes factory with 10.2 compression. LS-6 is close to 11 to 1 I believe. The compression ratio is only one factory in determining an engines absolute cylinder pressure or dynamic compression ratio.

Bottom line, if you are going to take the time to pull your 5.7 heads off and get work done to them then I would absolutely recommend getting them milled to maximize the power extracted from this head.

**Jweezy** · 04-21-2007, 04:17 PM

omg why is this all confusing...I can help configure a 3 million dollar supersystem, but not understand my engine...AFGGGGHHHH

-Justin

**Shakin** · 04-21-2007, 04:21 PM

in a simple answer to your question..

NO

it will not affect the longevity of the engine. We are not talking about cranking it up to 13.1 or anything like that. Its still streetable and you will probably have to run hi octane gas but other then that it will not affect the integity of the motor.

**USCG Charger** · 04-21-2007, 07:50 PM

Ok kewl, thats what I wanted to know! So just a slight bump of compression should hurt anything unless is done to extremes.

Jason

**USCG Charger** · 04-21-2007, 08:12 PM

so compression it is then...now I just need to find out the most efficient way to achieve it....push rod checker or shims? I guess it's personal preference huh? It seems like shims might be easier plus it's what Lee and Steve mentioned from the get go!

Jason

**PPP-Tech** · 04-22-2007, 01:28 AM

steve, answer me this as I am confused. If you mill heads, you are taking material off of the bottom of the head right? If thats the case, are you not messing with valvetrain geometry. I have attached a picture with the way that I understand it and you tell me where I am wrong. My name is ppp-tech, but I am no engine builder, INDY does all of that. My photo would represent milling on a larger scale, but as you can see the line no longer meets up once I decreased the size of the top rectangle that represents the heads, the botttom rectangle is the block and the line is the pushrod.