ADM

Just took apart my engine for a freshening up, and was wondering about bumping up the compression some.

Its a 97 with a CC503, Pro Magnum 1.6, Comp 918 springs, full bolt ons and Transgo HD2 shift kit. No stall or gears at the moment, but will do that whenever funds are available.

I was considering the Victor Reinz 5898 0.026" head gaskets, or the Mr. Gasket 5716G 0.026" http://www.summitracing.com/dom/part...716g/overview/

Should I go with just the gasket swap? Or also mill the heads?

What quench area should I aim for with this build? And whats the highest compression I can run safely with pump gas? I run 91 octane.

Car is my DD, will never see the track. I do like to drive it hard every now and then but no racing.

bowtienut

iTrader: (1)

If it were mine, with that fairly small cam, 91 octane, and not going for track numbers, I'd just run a thinner gasket.
With that cam, 91 octane, and the hot climate, I wouldn't target more than 11:1 CR.

bufmatmuslepants

iTrader: (3)

Stock I think is about 0.022 in the hole, optimal quench is between 0.030 and 0.040, so do what you need to get there, closer to 0.035 if possible. I can never remember his username, but someone did 0.026 gasket and milled the heads 0.010 (cant remember what his chamber came out to) and got 11.5:1 with a AI 228/232 cam and made 370rwhp. I priced out milling heads 0.010 and it was I think $100, and decking the block 0.010 was $150, decking the block adds more cr since its more volume being removed. You need to do some math, but decking 0.010 would get you 0.012 in the hole, plus 0.026 gasket gives an optimal 0.038 quench, but you'll need to calculate your cr as that 503 may have too high of a dynamic cr to be really happy in the mid 12s. Take all I'm saying with a grain of salt you need to do your own calculations.

ADM

Considering the heads were never milled before (I will measure the combustion chambers to confirm), calculations state that a mere gasket change to 0.026 results in 11.3:1 compression ratio.

Bore 4.000"
Stroke 3.480"
Gasket thickness 0.026"
Combustion chamber volume 54cc
Deck height 0.025" (worst case scenario?)

With a deck height of say 0.020" or 0.025" and a gasket thickness of 0.026" that puts me at 0.045" - 0.051" quench. I wouldn't worry about 0.010" away from optimal as this is not a max effort build.

Dynamic compression ratio with the CC503 will be 8.925 with the gasket change. Is that too high for a DD?

bowtienut

iTrader: (1)

VERY smart to measure things as you're doing.
Deck clearances vary from .023" to .03X" in production motors and chambers will probably show more than 54cc.
I think your CR estimates at this point are high. But yes, 8.9 is too high for 91 pump gas and daily driver environment considerations.

DUDCOUPE

Lmao 11.5.1 compression

93M6Formula

I don't see a problem?

jaycenk

iTrader: (1)

I had lots of problems with the Mr. Gasket 5716's.
First they failed on my engine and then when I went to replace them I got 3 different sets of gaskets from summit racing and all of them pulled parts of the gasket material when I removed them from the packaging.
I tried chilling them freezing them and heating them and each time they failed to come out of the package correctly. A real stupid problem to have with a critical part.
I would spend the money for a good reliable gasket.

ADM

bowtienut, you were right. I found my deck clearance to be 0.030". So even with a 0.026" gasket I will still be at roughly 0.056" quench.

I will measure my combustion chambers tomorrow.

Have a feeling this block has already been rebuilt not long before I purchased the car because the head gaskets were in excellent shape, the head bolt threads are shiny clean and the head decks are dead on flat! Even the gasket has not printed itself on the block deck or heads yet.

Also, the oil pump I removed is a Melling 155. I installed a GMHPP standard volume, high pressure pump I had installed on my previous car.

Must say I am lucky to have taken this engine apart because when I pulled the pan I found the pick up tube swinging easily and almost fallen off. Explains why I started getting low oil pressure suddenly.

LT14LIFE JT

iTrader: (1)

Me either considering it's 10.5:1 from the assembly line. I've heard of factory block/heads getting near 13.1:1 with 0 decked blocks, shaved heads, and thin gaskets. I'm planing on close to the same recipe with my cam only convertible. I'll admit that it's not exactly logical for a "street car", but I've seen much more radical setups out there that had longevity.

ahritchie

iTrader: (1)