candlelit

iTrader: (21)

Hey guys. I recently bought a forged 347 longblock that has -16cc dished pistons & exhaust side ported LS1 heads. Compression is around 8.7:1. I think I have changed my mind for the last time and just want to do a N/A setup instead of turbo and save some money for other mods. How would I be doing if I used this motor for a 430-440 rwhp setup, 230/230 type cam, ported heads, FAST 90, or something along those lines? Is the lower compression going to kill me? Or generally, what's the difference between a 10:1 and a 9:1 N/A setup? This motor is BUILT, semi low miles, and I got a great deal on it. Should I sell it already and use my stock 90k ls1 longblock and build it instead??

TransAmcoupe98

iTrader: (10)

With that low of compression and staying naturally aspirated it will hurt pretty bad. Nitrous wouldn't like that c/r either. I think if you spend the extra cash it would be well worth it with boost. Just my .02

candlelit

iTrader: (21)

hmmm well, if anyone's interested I'm tossing up a trade motor for motor idea...

https://ls1tech.com/forums/showthrea...39#post8998739

ShevrolayZ28

iTrader: (4)

About 2% less HP for 9:1 compared to 10:1. (Roughly 8 hp less at 400 hp.)

I'm no epxeprt but I imagine with those pistons you could run a large cam and mill the heads quite a bit before your P/V clearance becomes too tight.

candlelit

iTrader: (21)

8hp really isn't anything then... I was disliking the idea if it was like 20-40 hp difference will I need to mill these heads with a larger cam? or can I just figure a way around it?

magius231

iTrader: (8)

HP will be slightly down, TQ will likely be way down, and it will feel soggy while driving around. I wouldn't do it personally.

ls1leadfoot

iTrader: (1)

i would get a THIN .030 cometic gaskit....as long as the cam will clear..see if you can maybee get more comp. outta it..


i am running a lq4 at 9.5.1 and am pretty sure n/a i will be happy....if not..
n2o it....boost is too damn expensive....(to do it right)
i would rather have something that runs "good" than have a bunch of pretty/cool parts that look cool and the car doesnt run as it should....to go FI you need to know your crap....cant just jump into it.......found this out the hard way

slow trap

iTrader: (22)

i was thinking a 1 point drop in scr resulted in 4% loss of power ? either way you will leave quite a bit of power on the table. for n/a depending on cam size to figure out your dcr and if 93 is available i would try to get over 11:0 scr which won't happen with those soup bowls. imo if you are wanting to stay n/a or spray it i would optomize it and get the right scr/dcr because you will be pretty dissapointed in the results with that low of compression.

ShevrolayZ28

iTrader: (4)

Yep it is closer to 4% at lower ratios ~7:1. The relationship is not directly proportional or linear. 1-4% per point depending on what level we're at. The difference is less at higher comp ratios.

Here's some info and a rough calculator:

http://www.442.com/oldsfaq/ofcrc.htm

http://www.bgsoflex.com/crchange.html

candlelit

iTrader: (21)

but is 15-25 HP loss really that big of a deal? for example, on a stock compression I'd be throwing down 450rwhp with certain mods and with this 8.7:1 setup I'd be throwing down around 430-435rwhp. I can't get 93 anywhere so the best I could do is 91. however with the lower compression I can run 87 & 89 right? cheaper to fill my car up. plus, would the motor last longer on less compression? I'm not trying to squeeze out extra hp for a dyno queen. this goal would be to run low 11's without turbo & nitrous at full weight. and does anyone have an opinion on building the 90k LS1 (no piston work) and selling this 8.7 setup?

landonew

Why don't you get a set of AFR 205s with a 58cc or smaller if possible Combustion chamber. This would raise the compression ratio, get you a great set of heads, and be cheaper than selling the block and building a new one. This is my suggestion. Then if you do decide to go turbo in the future, swap out the combustion chamber (I assume this can be done?) and badda bing, low compression turbo motor.

slow trap

iTrader: (22)

well you could re-ring the 90k shortblock and put in new bearings,or better yet put in some good flattops in the lo-co shortblock. a local machine shop should be more than capable of file fitting the rings and getting it together for a reasonable price.
decisions,decisions.

s346k

iTrader: (4)

sell your 90k ls1 short and put a good set of flat top pistons in the forged motor.

candlelit

iTrader: (21)

a shop is going to charge me at least $1000 to do the machine work, and that's not including the extra $600 for pistons. and I can't even get $1600 out of the 90k mile LS1 longblock.

chevynation

iTrader: (8)

15-20 peak HP might not be a big deal, but you gotta remember compression plays a big part in low end torque, throttle response, and overall efficiency as well.

I'm going 11.7:1 on my heads/cam setup, 93 octane (8.7 DCR)

candlelit

iTrader: (21)

agreed. hmmm. I have no idea what to do now. I can sell it for what I bought it for. and have $4600 to spend, possibly put that into the 90k motor? any ideas what I should do if I go that route?? keep in mind my car is completely stock right now. and it needs an upgraded clutch & a rebuild on the trans.

Rambo06

iTrader: (6)

To start with nitrous,turbos,superchargers,blowers all love low compression because they all feed on volume and more piston for compression means less volume!!! You won't lose that much hp but you will lose quite a bit of torque which could be countered with nitrous because it creates massive amounts of torque and horsepower,if it was me I would use it and spay it because it sounds like a stout short block, but you could use a thinner gasket and have the heads surfaced to increase compression but you need to check the piston to valve clearance first.

slow trap

iTrader: (22)

if you can sell the forged longblock i would check on having your 90k shortblock rebuilt with a decent set of rods/pistons. a set of mahles with a set of scat or eagle rods should be under a grand. check with all the local machine shops and see what a reputable one would charge for shortblocking/longblocking it for you.

candlelit

iTrader: (21)

would I really need to do internal work (besides cam) on a 90k stock LS1 motor? my last TA had 107k or so, 415rwhp heads/cam/intake, and ran great. I was thinking of a vindicator, g5x3, cartek x3, ms3, 23x/23x type cam, patriot valvesprings, pushrods, timing chain, ported pump, lifters, fast 90, and 59cc 205 or 215 heads to build that 90k motor. am I asking for it?

slow trap

iTrader: (22)

there has been a crapload of motors last alot longer than 90k miles with work done so you won't be asking for it by no means butttttttttttttttttttt....... there have been numerous mills last alot less than that also. while the motor is out if it was at all possible and funds permit i would put in a set of good rods/pistons with something like a -2 or at most -4 valve reliefs . that way it would be more reliable and also have better ptv among other things.also if you decide to spray later on or even f/i you could just bolt on the jug or take off the small cc heads and go with a 72cc and be set.

in reality i guess it comes down to what you feel safe about doing but it would really suck to do all that work and a few thousand miles later the rings go south ,or you change your mind and want f/i or spray but your shortblock won't be able to handle it.