ok, since i have question on 243s and everyone keeps putting 317 info on it, ill ask about these as well so that info can make its way over here.

Ok,
I know that 243/799s are the same casting for the most part.
i know that 243s and 317s roughly flow the same.
i know that 317s have bigger combustion chambers which lower the compression ration to somthing like 9.0:1 or somthing like that.
i know they can be milled but you probably have to fly cut your pistons

ok, my general question is, if these are put on a completely stock 98LS1
that has the bigger of most cams in the F-body family, without milling or porting, what is the N/a drivability like?

then add a turbo to it building roughly 8psi (everything roughly in a perfect world) what is the drivabilty like with a T76 .81 turbo (front and rear mounts)

i want to know what exactly is it like to not have boost, then it finally spools up, fills the chambers, and then gets going? what kind of driving is this like?
how is this 317 head with lower compression but lose of initial power better with more boost and more PSI to create the same power of the 243/799 heads? i know this has alot of turbo involved questions, but the heads are the highlight of the thread not so much the Forced induction science so lets keep the topic top heads specifically.
im neutral on the subject right now due mostly to the fact that 1) im ignorant and dont have them lol and 2) alot of threads are putting too much random hearsay info and its hard to follow and dig through.

 

I'm not sure exactly what you're asking. If I'm understanding you, I'd say just go take a ride in a turbo'd car of any kind. When boost builds (and it does not take long at all), it's like a slingshot (depending on how much you're boosting). It pulls hard all the way to redline. As far as driveability, it's not a problem in a properly built turbo setup. Yes, with the higher compression heads in a n/a build, you might have a little more initial low-end "grunt" than a lower compression F/I build.....but so what? When boost builds (and it does QUICKLY), any potential "disadvantage" of the lower compression head evaporates as the boost comes on hard.

Hope this helps.

 

it helps alittle. ive riden in turboed cars before. even turbo vans here in germany. the vans do that fall on face then throw you in the backseat thing.
i liked the Evo VIII's acceleration, but all wheel drive kinda helps with that violent turbo rush.

sorry for the confusion, what im trying to say is,
how do these heads respond out of boost compared to like 243s or even the 241s?

 

All I can tell you, is that one of my cars is a T76-fed 5.3 with ported 317's and a 3400 stall and 3.70 gears.....drives just fine to me. If you're planning on decent boost (10-15psi), forget the 243s, IMHO. Does my car boost instantly? The answer is no....but it builds pretty fast.

 

im expecting it not to build boost instantly due to the rear turbos nature. but with a 228 cam and 317 heads, would low rpm/no boost driving show any signs of lose of power due to lower CR? and how much does it lower the CR when going form stock ls1 heads to 317s on a ls1 (5.7L)? with stock gasket? with .040 cometic gasket?

sorry for the bombardment of questions but im trying to get a very clean piture before i start to get too far into it.

 

Uhhh... I think I know where you're going with this. I'll try to tackel them one at a time. For clarification though, I'm assuming a few things. A) you bring up turbo a lot so you've decided a procharger doesn't fit your bill; B) you've done a budget and know that a turbo build hits the $10k mark in a heartbeat and you can do without this car for a while; C) by turbo you mean a real turbo that pushes wayyyy past 500whp. Because let's face it, going turbo costs serious money and serious money is worth serious power. Nobody wants to drop that much money to sit next to a H/C/I car.

The sole reason to lower CR is to reduce cylinder pressure. FI is basically trading ENGINE cylinder pressure for FORCED INDUCTION cylinder pressure, two different animals. You can run a higher CR motor for less lag, but boost will be restricted because of it. So you have a choice between a 10:1 motor (easy number to use) or 9:1 (again, easy number). Without boost, the lower CR motor will reduce cylinder pressure and lose power. Add some boost though and you start increasing cylinder pressure in factors

You can see how a higher CR right off the bat will reach the motor's limit faster (I say motor because the limiting part will change depending on the setup). That limit will not be the same between a 10:1 and 9:1 setup with boost! Common sense tells you "700hp is 700hp so it doesn't matter how I get there." No sir, the truth is that your engine will take more psi with a lower CR and psi is what makes real power. Boost increases cylinder pressure and cylinder pressure makes power.

Your choice, higher CR for more power out of boost and spool faster. OR lower CR for less power out of boost and run higher psi (more power) up top. It is very much like getting a cam setup for top end versus stock cam setup for broad powerband from idle up. If you want to road race I suggest the higher CR for a wider powerband, straight line stuff wants the lower CR for a freight train top end. Its a trade, low end for peak power. This is the same trade off between small vs large turbos and low vs high boost turbo setup.

Next, the cam isn't a good place to spend money when going turbo. Does it help? Yes, but its your call if the gains are worth the price. Same with headwork. Forced induction will cram air down your intake ports whether you like it or not, simple physics. Exhaust side work will show more gains than anything because you need to let the dirty air out.

Then we get to the lag part.... This entirely depends on you and your car. Lots of factors go into this your driving habits, road conditions, fuel and weather conditions, auto or manual trans, vehicle weight, etc. Lag and drivability are completely subjective. My turbo car is manual so I can slip the clutch, drop a gear, or brake boost to spool immediatly. Sorry bud, nobody can tell you what it'll be like because there are too many factors involved.

Hope that helps. Are you just trying to learn or do you have specific goals?

 

thank you and both. Im trying to learn more but do have some what of a goal in mind. Im just trying to get a more clear understanding wiht the lower compression heads and turbos and vise versa, especaily with rear mounted turbos. and then where the cam fits inbetween the two.

im torn between leaving my motor as is and running the rear mounted turbo or help it abit with a head and cam combo better to deal with boost. hell at this point im almost ready to just do a Head and cam swap and call it a day! im trying to get all my ducks in a roll before i shoot em' lol

definitly have help alot with it. Ive been asking some sponsors as well about what i should do and get to make my car perform well.

 

What are your goals with the car? Current mods? Driving habits? We can help more if you point us in the right direction.

Head/Cam/Intake will be a mean machine. Rear mount turbos are cool and all but they just aren't worth the time and money, IMO. I would recommend a procharger way before a rear mount setup. No lag, very nice powerband, MUCH easier install, simpler system means fewer parts to fail, and cheaper.

 

my goals for my car are pretty modest. Aiming for about 600HP with roughly 8-10 psi. not looking for alll out drag car but getting low 12/high 11s would be nice. Mostly drive on the street since I dont have all the time in the world to go to track unfortunatly.

ive thought abuot procharger, but the initial cost is high. Plus ive always loved the sound of a rear mounted turbo. and the cost, if done right, can be cheaper.

im starting to consider the 317s more and more. ive been playing with a engine compression ratio calculator and with stock 317s, .040 gasket, and everything else stock the CR comes out to about 9.8:1 CR
and with the LS9 gaskets it 9.6:1.
Two this
1) is that even noticable drop in CR compared to 10.1:1?
2) is that a good safe drop in CR to run 10psi with preimuim and no meth?

 

Procharger will be cheaper overall. Plenty of good used head units and kits for sale on here. It'll hit your goals and have killer drivability across the board.

For your CR, yes that little drop is very important! Remember this is a multiplication thing like AFR. If you can run with premium and no meth depends on your fuel over there. What octane is it? Convert to US octane rating if yours if different.

Boost psi will be different depending on what size turbo or blower you run. Bigger turbo or procharger will run more air per psi, just dig around in the Forced Induction section to see what will or won't work.

If I were trying to do what you stated with an LS1.... forged pistons/rods, 317 heads with upgraded valvetrain, no headwork, hardened pushrods, LS9 head gasket, blower cam, good full exhaust (whatever you think sounds best), D1 procharger or a small F1, FAST intake and matching throttle body, fuel upgrades galore, and a laundry list of supporting mods.

 

well just for updates ive decided to go with 317 heads and LS9 head gaskets. still trying to get a cam between 224-228 range. looking more and more at the 228 but if a 224 cam pops up ill go with it. I just want to do the cam since ill have the heads off and might as well get that little baby cam out of there lol since im gonna be there anyway installing an LS6 oil pump in the process. I got one brand new for very cheap. I got most of everything else so i might as well get the cam and since ill be doing vavles springs and stems i might as well. it just makes since

ive pretty much narrowed down what i want, just time to piece it together is the problem.

 

I'd run a Thunder Racing 220 with a 112 or 114 lobe separation which will be
a bit more drivable in non boost situations than the 228. You should still hit
your HP goal with 10-12 lbs. of boost when properly tuned on large injectors.
Also if you have good drag radials...prepare for high tens....not elevens..

 

yeah, im thinking i might go with a slightly more mild cam like a 224 or a TU1 225 cam. Still trying to locate a few other things right now, but for now i got the 317 heads sitting in my garage. I think a slightly milder cam will be more of my driving style anyhow lol i dont rev my motor to the moon lol

 

ok so which head gasket would be best suitable for this, the LS9 gasket or a cometics .040 gasket with 317 heads?

 

LS9 gasket is the best for all applications IMO

 

I picked up ls9 gaskets and the TU1 cam for my 347, and I'm sending my heads for a clean up mill as we speak, pretty similar build to you

 

nice, with my my moderatly low boost levels and meth, im im only sacrifcing alittle compression to get my goals where they need to be at. im leaving the heads untouched and cleaning them up. i might to a polish on them by hand, but im not gonna port them or anything.

 

i know its waaay later but im stuck and have the same questions u had did u make ur power gols and how did the 317 heads perform and where did u get them

 

well i havnt installed them on my build yet. still waiting on a cam. i got my heads off of ebay for $80. dont even know ho i got them that cheap but i did lol

 

AiAiAiiiii, caramba