turbo 4.8 compression ?s
turbo 4.8 compression ?s I have a low mile 4.8 with a vsracing 7875 turbo. Its a L20 motor with 8.8 compression with 243 heads and I am worried it will be a dog out of boost. I have a 4l80e with 4.11 gears which will be swapped for 3.31 gears when funds permit. The pistons have valve reliefs and I have a set of gen 4 flat top pistons and rods laying around and was wondering if they would raise the compression enough to be worth it. Thanks for any help.
I have a low mile 4.8 with a vsracing 7875 turbo. Its a L20 motor with 8.8 compression with 243 heads and I am worried it will be a dog out of boost. I have a 4l80e with 4.11 gears which will be swapped for 3.31 gears when funds permit. The pistons have valve reliefs and I have a set of gen 4 flat top pistons and rods laying around and was wondering if they would raise the compression enough to be worth it. Thanks for any help.
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Joined: Jun 2010
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From: Alberta, Canada
That 4.8 isn't gonna want to swallow a cam that requires valve reliefs. If you want to bump up compression a bit, I would suggest looking for some 862 heads. The cam should stay conservative. I would suggest an intake closing event no later than 35-36 degrees. Even with the stock cam, those engines don't want to do much under 2500-3000 rpm. The faster you can get that cam making torque, the earlier that turbo will spool.
I would of recommended the Stage 2 4.8/5.3 cam at the largest and only if you just absolutely have to hear the cam at idle. If you want the best performance and can live with the idle that comes with it, I'd of recommended the Stage 1 4.8/5.3 camshaft.
I reserve the Stage 3 being used in 4.8's for all out racing applications with S480 or larger turbochargers, trans brakes and 4000+ RPM stall converters.
It will probably be even doggier out of boost with the Stage 3 cam than it would of been with the stock cam. The Stage 1 cam would of really helped get it to spool quicker.
I reserve the Stage 3 being used in 4.8's for all out racing applications with S480 or larger turbochargers, trans brakes and 4000+ RPM stall converters.
It will probably be even doggier out of boost with the Stage 3 cam than it would of been with the stock cam. The Stage 1 cam would of really helped get it to spool quicker.
I would of recommended the Stage 2 4.8/5.3 cam at the largest and only if you just absolutely have to hear the cam at idle. If you want the best performance and can live with the idle that comes with it, I'd of recommended the Stage 1 4.8/5.3 camshaft.
I reserve the Stage 3 being used in 4.8's for all out racing applications with S480 or larger turbochargers, trans brakes and 4000+ RPM stall converters.
It will probably be even doggier out of boost with the Stage 3 cam than it would of been with the stock cam. The Stage 1 cam would of really helped get it to spool quicker.
I reserve the Stage 3 being used in 4.8's for all out racing applications with S480 or larger turbochargers, trans brakes and 4000+ RPM stall converters.
It will probably be even doggier out of boost with the Stage 3 cam than it would of been with the stock cam. The Stage 1 cam would of really helped get it to spool quicker.
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Everyone's definition of "dog out of boost" is different. A 4.8 isn't a power house NA, so it's going to feel like a turd out of boost if you don't make radical changes. Tiny bump in compression won't even be noticeable IMO. Buy a custom cam setup to give you a healthy bump in DCR if out of boost response is a big deal to you. Loose converter can also make a big difference. IMO leave it alone and make up for the lower CR with boost, converter, cam. The trick is to light the turbo off as quickly as possible. That way you'll spend very little time "out of boost". PTC 9.5 with the 17 blade stator worked really well on my 8.6:1 5.3. Plenty of slip down low and still coupled hard up top.
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Verdad Gallardo Recently put together a turbo 4.8. 500HP and a mean aggressive idle where the goals. I went with the edelbrock 2215 cam. It's a very low lift design has the aggressive idle while maintaining a -2 overlap at .050. So it shouldn't be too horrible for mild boost. Cam was $312.
92 s10 4.8 swap edelbrock 2215 cam - YouTube
92 s10 4.8 swap edelbrock 2215 cam - YouTube
For a low boost 500-600HP goal I think it would work just fine on a 6.0.
Come up with a power goal and a desired RPM range. I’m sure Martin could hook you up with something a little more ideal. I literally just wanted to show boat this build around to sell it. The crowd I’m targeting doesn’t’ care about an ideal cam… they just want it to sound mean! My 8 second car idles like a minivan at 750RPM
Come up with a power goal and a desired RPM range. I’m sure Martin could hook you up with something a little more ideal. I literally just wanted to show boat this build around to sell it. The crowd I’m targeting doesn’t’ care about an ideal cam… they just want it to sound mean! My 8 second car idles like a minivan at 750RPM
4.8’s are gutless as it is. Easiest to get rid of that with a loose converter and boost. Then cam it for the top end. 6500 is on the low side IMO for a 4.8. Seems like guys are buzzing them to 7k+ pretty easy. Low RPM and big boost don’t seem to get along with the SBE LS engines. I always thought limiting RPM was the way to go as well, but with the LS stuff I don’t think your doing yourself any favors... especially with a 4.8.
6.0 has a lot more grunt down low. IMO you’d build that setup opposite. Tight converter, less rpm, “small” cam.
This guy runs his 4.8 up to 7500rpm… with a lot of converter slip. Not optimal with ls6 cam and factory intake, but the engine doesn’t seem to mind.
$220 Gt45 turbo maxed out at 17lbs...
6.0 has a lot more grunt down low. IMO you’d build that setup opposite. Tight converter, less rpm, “small” cam.
This guy runs his 4.8 up to 7500rpm… with a lot of converter slip. Not optimal with ls6 cam and factory intake, but the engine doesn’t seem to mind.
$220 Gt45 turbo maxed out at 17lbs...
FYI before you buy the 6.0. You're kind of doing the same thing as before, only in a differant way. That 78/75 is going to max out pretty fast on the larger 6.0 then it would on the 4.8. It should make 700whp, but don't expect much more. That may seem like plenty to you now but sooner or later, you're going to want more and that will mean buying another turbo. Much more expensive than a JY motor. A 4.8 might not have much grunt down low, but your an auto so that's easily delt with, and that cheap 78/75 will make much more on the smaller motor.
Just don't get impatient and ask around. Know what you want and be willing to make nessecary sacrifices, because nothing is going to excel at everything. It seems like your looking at this from a NA perspective but turbos are a differant animal. I don't think a little soft at low rpm is going to matter much to you at 7000+RPM and 800+whp.
Also, the 4.8's are popular because the short stroke and small bore allows them to take a ton of boost absolutely stock. Doing nothing but throwing in some ARP rod bolts and 20lbs is cake walk, with a good tune of course.
I remember watching this build. This guy ment to get a 5.3 but the JY gave him a 4.8 by mistake. So he said **** it and used it, untouched bottom end.
Just don't get impatient and ask around. Know what you want and be willing to make nessecary sacrifices, because nothing is going to excel at everything. It seems like your looking at this from a NA perspective but turbos are a differant animal. I don't think a little soft at low rpm is going to matter much to you at 7000+RPM and 800+whp.
Also, the 4.8's are popular because the short stroke and small bore allows them to take a ton of boost absolutely stock. Doing nothing but throwing in some ARP rod bolts and 20lbs is cake walk, with a good tune of course.
I remember watching this build. This guy ment to get a 5.3 but the JY gave him a 4.8 by mistake. So he said **** it and used it, untouched bottom end.
Last edited by Mongoose350; May 23, 2015 at 05:15 AM.