98 Vortec 350 - comp ratio

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Diptenkrom

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I have a 98 Suburban K1500. I think i have a leaking HG, as i have replaced the lower manifold and gasket, after a failed attempt at just the gasket, and i am still losing coolant and getting rough idle. I was thinking about adding some grunt while i was at it. motor itself is stock and low mileage as it is 4 years old and not driven at all for 1 year. I was aiming at 300+hp and 400ish tq.

LT4 Hotcam or Ramjet Cam
1.6 ratio roller rockers
LS6 springs and comp retainers

the question is deck the heads and/or run cometic .030 MLS HG to increase compression? and if so how much. I was wanting to get to 10-10.5:1 - but then i read that may be an issue with running on pump gas. now i was thinking about fill up cost and those trade offs.

So short version - how much compression can i get away with running midgrade gas (89 octane) and would i be fine without getting it decked and just run the .030 gasket kit? i read that the standard is around .041 compressed.
 

Diptenkrom

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by math i found on another forum and extrapolation it looks like the .030 MLS Cometic would put me just under 10:1 or so. i like that number, and i think it would wake her up a bit. but i dont want to HAVE to run 93+ octane in the 42gal tank, lol

which means skip the decking and just have the thing checkd for cracks/true and slap it back together?
 

L31MaxExpress

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by math i found on another forum and extrapolation it looks like the .030 MLS Cometic would put me just under 10:1 or so. i like that number, and i think it would wake her up a bit. but i dont want to HAVE to run 93+ octane in the 42gal tank, lol

which means skip the decking and just have the thing checkd for cracks/true and slap it back together?

Stock head gasket is 0.028" compressed. With stock heads and stock pistons, works out about 9.4:1. A 0.016" head gasket would put it about 9.6:1. I say about because the stock chamber size and deck height varies a little bank to bank and cylinder to cylinder.
 

Diptenkrom

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so i am safe to deck the heads a little, and use GM Performance HG set? i am still debating on the cam setup as there is a lot of "opinionated" information out there. I would like to run the ramjet cam, and not mess with valve springs, but there is no definitve answer to whether or not that is possible. - i am just trying to get a little more grunt in my suburban, and minimize downtime. headers/exhaust will happen later, but not right now.
 

Schurkey

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You'd be WAY better-off to deck the BLOCK, so that you tighten-up the quench distance. The quench distance is probably too huge as-is.

More compression, more power, better efficiency, less detonation.
 

Redneckgeriatric

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or, install new cometic gaskets (to ensure no leakage) and a cam that will keep compression bled enough to enjoy 87 octane. this will be close to stock! decking is usually done as part of a real engine build, and is done AFTER measuring installed NEW piston height. the new pistons are decided AFTER cam selection. cam selection is done to make power band where you want it, and how much power you want realistically speaking.

engine is built around the camshaft. if there is no ability, or hardware/software, to tune a build, you just wasted tons of time/money.
 

b454rat

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Stock Vortec compression is 9.4, so even if it gets bumped up some it will still run 87...
 

CW73

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You can run 87 or 89 with just decking the heads to true them up and the .030 gaskets. My 98 has had the heads decked .010 and .015 steel gaskets and have ran 87 with no problem but I normally try to run 91 due to tune. As far as the cam, I would go with the Ramjet because of the weight of a 4wd suburban. You can run that cam with stock springs and tune. The hot cam will move torque up higher in the rpm range. I run the hot cam with 1.6 rockers in my 98 C1500 with 4:10s, a 4l80 and a 3000 stall 10 in converter.
 

Schurkey

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Hard to say what octane rating will be required, IF THE KNOCK SENSOR IS PULLING TIMING to prevent detonation.

You'd have to connect a scan tool, and watch the knock sensor/ignition retard data. It's entirely possible to run an engine that "needs" 93 octane on 87, if the computer is pulling timing like mad, and the vehicle is lightly loaded. Doesn't make it right.
 
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