compression
02-19-2007, 01:53 PM
#1
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compression with 317 heads on a stock 99 ls1, i think my cr should be 9.5-1. what kind of boost ( with a good tune) could be run on pump gas before i get into detonation problems? i would like to have 7-8 psi, so im wondering if the heads would be enough or do i need to go with pistons as well? even if the cr is fine for that boost level, is the stock piston good enough or should i just go ahead with a good forged piston? just thinking a head swap would be pretty simple as compared to getting into the shortblock
02-19-2007, 04:17 PM
#2
CR is determined by your pistons. Not your heads.
Some guys have managed to run 6-8#'s on the stock bottom end, while others (like one I used to know) lasted a whopping 2500 miles on only 8#'s of boost (he was intercooled as well) before he fried a piston.
Basically you're only going to be able to run low boost on the stock bottom end. Even then you are risking it, and will probably still run into issues eventually. Most of the stock bottom end boosted guys even with 6#'s of boost are getting at best 25,000 miles before something goes wrong.
You are better off saving up the money to build a motor that lasts under boost rather than skimping and only getting minor power increase by running low boost and still being unreliable. Most things that deter people from going FI is the sheer price. To build a motor right, you'll on average spend a good $10,000+. Not to include everything else like the blower itself, the fuel system and supporting mods like clutch, rear, driveshaft, tune, ect., ect., ect. If this isn't something you can afford, I reccomend just going with a good heads/cam/and intake setup. When compared to the price of even a cheep blower setup and only being able to run low boost, its more cost effective just to keep it N/A.
Just my 2 cents.
Some guys have managed to run 6-8#'s on the stock bottom end, while others (like one I used to know) lasted a whopping 2500 miles on only 8#'s of boost (he was intercooled as well) before he fried a piston.
Basically you're only going to be able to run low boost on the stock bottom end. Even then you are risking it, and will probably still run into issues eventually. Most of the stock bottom end boosted guys even with 6#'s of boost are getting at best 25,000 miles before something goes wrong.
You are better off saving up the money to build a motor that lasts under boost rather than skimping and only getting minor power increase by running low boost and still being unreliable. Most things that deter people from going FI is the sheer price. To build a motor right, you'll on average spend a good $10,000+. Not to include everything else like the blower itself, the fuel system and supporting mods like clutch, rear, driveshaft, tune, ect., ect., ect. If this isn't something you can afford, I reccomend just going with a good heads/cam/and intake setup. When compared to the price of even a cheep blower setup and only being able to run low boost, its more cost effective just to keep it N/A.
Just my 2 cents.
02-19-2007, 06:07 PM
#3
Originally Posted by CALL911
CR is determined by your pistons. Not your heads.
Last edited by gi8e7oi825; 02-19-2007 at 06:16 PM.
02-19-2007, 06:43 PM
#4
The point I am making here is that you can change the heads all you like. But until you change the pistons to some low CR forged ones, you aren't going to be able to run enough boost to make much more power than a good H/C/I combo will make. Furthermore, its still risky running any boost even if its low boost with running the stock bottom end.
02-19-2007, 06:52 PM
#5
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what i was getting at with the 317 heads would be the bigger chamber, which would drop the cr. i'm already in this money pit to far to back out, and i really like FI, so i don't mind spending some $$$ on the internals. i had planned on putting a good set of pistons in, but i keep hearing people talk about how much power they get out of a stock bottom end. i'm new to the ls1, so im not sure what they'll hold. its going in an old chevy truck, already has a good th350, 9 inch, etc. i want to make 6-700 hp, daily driver. from what i've been reading on here, i should be good with some forged pistons and arp throughout the motor stock rods and crank, plenty of fuel and a safe tune. what do you guys think? sound good or sound like a mess?
02-19-2007, 07:02 PM
#7
sounds like a mess, I popped mine at just under 500 on a mustang dyno, you absolutely need excellent pistons, stainless top ring, aftermarket rods with really good rod bolts (arp 2000) Ive just about finished my complete setup with methenol injection and Ive got about 13000 invested doing all the work myself. you can spend close to 18000 if you have someone else do your motor. you did not mention what kind of blower/intercooler setup you will run, this will determine how much boost you can safely run due to overly hot IAT temps. thats why im running the methenol injection because I dont want to cut my car up to put in a front mount intercooler.
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02-19-2007, 07:16 PM
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i already have a holset hx35 that will be mounted behind the cab, similar to a sts setup. its a 67 chevy truck, so theres room up front for a huge intercooler when i get to that part. you think i should definatly go with some rods too, as opposed to just putting arp's in the stockers?
02-19-2007, 07:16 PM
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Originally Posted by jdime20
with 317 heads on a stock 99 ls1, i think my cr should be 9.5-1. what kind of boost ( with a good tune) could be run on pump gas before i get into detonation problems? i would like to have 7-8 psi, so im wondering if the heads would be enough or do i need to go with pistons as well? even if the cr is fine for that boost level, is the stock piston good enough or should i just go ahead with a good forged piston? just thinking a head swap would be pretty simple as compared to getting into the shortblock
You can get a complete forged shortblock for around $3,600 (no core charge either) utilizing great components like Wiseco pistons, Callies Compstar Rods, All arp fasterners and a new to newer LS6 block. If you don't believe me call BRIAN at LME as they build a GREAT MOTOR at an affordable price! The stock LS1 crank is EXTREMELY STRONG and no need to forge that in a stock cubed application unless you are looking to exceed 800rwhp. Builiding a good stout forged shortblock is not as expensive as some would have you believe. Also, the 317 heads will drop you closer to 9:2 to 1 compression and this will help you out quite a bit in running 6 to 8 lbs of boost. There are MANY vette guys I know who are running 10lbs of boost on stock LS1/6 motors without any issues. You need an EXCELLENT TUNE and GOOD GAS and alky injection also helps BIG TIME.
I myself have run 7000 miles on my stock LS6 motor (10:5 compression) and see anywhere up to 5 to 10 lbs of boost on the street with 0 issues with my D1SC procharger. I also run straight alcohol injection for safety that sprays into my cylinders anytime i make 4 lbs of boost of more. For what your trying to do up to 7 to 8 lbs of boost is a no brainer with a GOOD TUNE but when going f/i you have to be prepared to go forged b/c the motor could let go if there is any detonation caused by bad gas, bad tune, heat, etc., etc.!
02-19-2007, 07:34 PM
#10
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i think i'll be fine with forged pistons, arp, will probably find some heads as well. 7-8 pounds with a good tune should be pretty reliable. i'll probably talk to ed wright about the tune, everyone in my area speaks very highly of him, so i feel pretty confident that all this should be a pretty good package. i might check into some kind of alky injection too, sounds like some good motor insurance thanks for the info
02-19-2007, 08:37 PM
#11
Originally Posted by jdime20
i already have a holset hx35 that will be mounted behind the cab, similar to a sts setup. its a 67 chevy truck, so theres room up front for a huge intercooler when i get to that part. you think i should definatly go with some rods too, as opposed to just putting arp's in the stockers?
Just my opinion here, but again, if you cut corners and don't get at LEAST the pistons, ARP head studs, and RODS , even with running low boost, and a good tune, there's no garuntee you'll make it to your 3rd oil change before you need to rebuild the motor. Really pistons, studs, and rods are the bare minimun here to be somewhat reliable. Just my opinion. I hate seeing guys try to go cheep, and then end up in a bind a month down the road when their skimping ended up costing them big time.
02-19-2007, 08:39 PM
#12
Originally Posted by lmt0705
sounds like a mess, I popped mine at just under 500 on a mustang dyno, you absolutely need excellent pistons, stainless top ring, aftermarket rods with really good rod bolts (arp 2000) Ive just about finished my complete setup with methenol injection and Ive got about 13000 invested doing all the work myself. you can spend close to 18000 if you have someone else do your motor. you did not mention what kind of blower/intercooler setup you will run, this will determine how much boost you can safely run due to overly hot IAT temps. thats why im running the methenol injection because I dont want to cut my car up to put in a front mount intercooler.
Who said you have to hack up the front bumper?
I am running a HUGE FMIC, and I just cut the area behind my fog lights (barely noticable) and then ran some custom ducting from underneath the front bumper. My bumper still looks stock, and my IAT's stay nice and cool. 
02-19-2007, 08:44 PM
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Originally Posted by CALL911
CR is determined by your pistons. Not your heads.
Some guys have managed to run 6-8#'s on the stock bottom end, while others (like one I used to know) lasted a whopping 2500 miles on only 8#'s of boost (he was intercooled as well) before he fried a piston.
Basically you're only going to be able to run low boost on the stock bottom end. Even then you are risking it, and will probably still run into issues eventually. Most of the stock bottom end boosted guys even with 6#'s of boost are getting at best 25,000 miles before something goes wrong.
You are better off saving up the money to build a motor that lasts under boost rather than skimping and only getting minor power increase by running low boost and still being unreliable. Most things that deter people from going FI is the sheer price. To build a motor right, you'll on average spend a good $10,000+. Not to include everything else like the blower itself, the fuel system and supporting mods like clutch, rear, driveshaft, tune, ect., ect., ect. If this isn't something you can afford, I reccomend just going with a good heads/cam/and intake setup. When compared to the price of even a cheep blower setup and only being able to run low boost, its more cost effective just to keep it N/A.
Just my 2 cents.
Some guys have managed to run 6-8#'s on the stock bottom end, while others (like one I used to know) lasted a whopping 2500 miles on only 8#'s of boost (he was intercooled as well) before he fried a piston.
Basically you're only going to be able to run low boost on the stock bottom end. Even then you are risking it, and will probably still run into issues eventually. Most of the stock bottom end boosted guys even with 6#'s of boost are getting at best 25,000 miles before something goes wrong.
You are better off saving up the money to build a motor that lasts under boost rather than skimping and only getting minor power increase by running low boost and still being unreliable. Most things that deter people from going FI is the sheer price. To build a motor right, you'll on average spend a good $10,000+. Not to include everything else like the blower itself, the fuel system and supporting mods like clutch, rear, driveshaft, tune, ect., ect., ect. If this isn't something you can afford, I reccomend just going with a good heads/cam/and intake setup. When compared to the price of even a cheep blower setup and only being able to run low boost, its more cost effective just to keep it N/A.
Just my 2 cents.
02-19-2007, 10:29 PM
#15
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Originally Posted by SleeperZzZ28
there is so much wrong stuff in that paragraph I dont know where to begin.
02-19-2007, 10:50 PM
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Originally Posted by CALL911
CR is determined by your pistons. Not your heads.
02-20-2007, 06:30 AM
#18
I was speaking of my 00 ta, and not having to loose the front licence plate insert and the fog lights. DUDE YOU NEED RODS!!! you can get eagles for under 400 bucks, you WILL kick your self in the *** when you have to pull the motor again because you wanted to save an extra 400 dollars. If you cant afford to do it right dont do it at all till you can. you will wind up wasteing tons of extra money and lots of down time
02-20-2007, 09:13 AM
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Originally Posted by CALL911
Alright, past the heads lowering your CR, what esle?
02-20-2007, 10:44 AM
#20
Originally Posted by 406 'velle
head gasket thickness, deck height, piston compression height, whether the piston is dished, domed, or flat, combustion chamber volume (including any unshrouding of the valves done when/ if you had them ported)
Uh.... I was reffering to SleeperZzZ28's comment on "so much stuff wrong with my statement". I have no idea what you are trying to say here in refference to my quote 406 'velle.
It was my mistake in saying that only the pistons lower the CR. It just seems when you need forged pistons anyway that most people get low CR ones to change their CR as well.