hey folks, fairly new to this tech board but have been lurking for a little while. i wanted to get your opinions on maximizing the lowend power from my ls1 and share the ways i've come up with to do this. this engine is going into my custom rockcrawler. my previous engine was a tb 350 .060 over with an rv cam, mild tune, stock heads, and headers. nothing special. it never had enoug power/torque for me. high rpms are of no concern. i don't want to have to spin my motor up to 4000 rpms to get to my power.

for starters, i cannot afford to go bigger heads, big bore, or a stroker crank at this juncture. the rebuild of my crawler is sucking my funds dry rapidly. going from maybe 275hp to 425hp (and similar tq) or so through 4:1 gear reduction and 42" tires requires the strengthening of my drivetrain which is also costly (cromo shafts, billet 300m ujoints, x2 steering axles as this thing is 4 wheel steer). so i'm trying to find that happy medium. running a built 700r4 with a 2000 rpm stall.

that being said, this is where i am to date. stock 5.7 ls1 from a '99 bird w/ a supposed 70k miles. compression tested and all 8 holes at 175 psi (fairly dry motor, hasn't run for awhile). i'm building my own custom long tube headers with low end in mind. they are 1 5/8" primaries about 34" long, to 2 1/2" collectors. i'm debating on dual exhaust vs merging to a 3" pipe to single exhaust for better scavenging/backpressure. open to ideas here.

engine has 853 casting heads and i'm thinking of doing a mild port job, as well as milling approx .030 along with .040 gaskets which in theory should get me close to 11:1 w/ a .036 quench. i plan on running 91 octane. to keep things economic, i'll leave the valve train stock as there will be no high reving. one of my concerns here is i don't know what those springs have been through in their 70k life. there wasn't a clear reason as to why the 21 yr old i bought the motor from pulled it and put a built engine in place. i could just be paranoid. i've heard stories of stock push rods being a weak link but this only seems to be when reving to the moon and missing a shift or accidental downshift. so, for my application, would the stock pushrods be acceptable?

my biggest ? lies with cam selection. while i'm sure alot of folks can recommend a descent cam, who's really going to "know" about a non street driven applicaton where low end is paramount. it seems my application is at the other end of the spectrum compared to 99% of folks here. open to suggestions. edit: cam specs have never made sense to me. i'll call one of the cam companies but wanted to get feedback from some folks here first.

another ? i have is regarding a mafless system. what's the advantage other than the obvious, no need for a maf, as i don't have one yet. is this something that would work for my application? if not, why? how necessary is a wideband o2? i have EFILive flashscan V2 and plan on tuning myself. but i only have experience tuning dmax diesels. also, fwiw, this engine will have no smog. 425hp is my goal, pending cost. i've attached some pics to give you a better idea of the application. i plan on doing most of this work myself, excluding the milling of the heads. any thoughts are valued. thanks in advance.

this is the original buildup thread for anyone intersted in the build:
http://www.pirate4x4.com/forum/showt...ht=wheel+steer

David

 

buuuuuueller, buuuuuuueller

 

Rusty,
You want something with a relatively small duration. I'm running a custom Comp Cam that's 200/206 degrees @ .050" on a 109.5 degree LSA and it's a great cam for low to mid-range torque. The lift at the valve is right at .525", Intake and Exhaust. If you want more information, send me a PM. My truck weighs about 6,700 pounds and I tow an 8,600 pound trailer, so torque is the name of the game for me.

Steve

 

sounds like you got your bases covered and you know what your doing but if its off road only i would get the compression as high as i could and run some 100 or 104 octane choices for cam i would suggest something around the stock ls6 cam with a low lsa your best choice would be to call crane or comp and talk to them they would be able do a custom cam that would give you everything you want got a question on your header setup i thought long tubes were more for top end scanenging if it were me i would build some shortys to keep that chylender pressure up for that low end grunt you want

 

thanks for posting up your #'s. did you have to upgrade your valve springs for this cam? would there be different specs for a big block cam vs a small block cam? i may shoot you a pm later.



i have a toy hauler w/ a fuel station onboard that is also used to fuel dirtbikes, generator, start bonfires, etc. i couldn't see filling it with race fuel and "wasting" it elsewhere. not to mention it's cost in addition to my other hobbies. this is why running 91 octane is a more realistic choice for me.

as far as the headers, you're saying the shorty's are better for low end torque and long tubes are for high rev torque? i've never heard this before. i've heard it's not uncommon for shorty's to produce less hp/torque then the same engine with manifolds due to the shorty's inherent design. i could be wrong but i don't think so in this case. anyone else.

 

whish i had your toys i dont really know on the headers maybe somebody else will chime in but i thought long tubes scavenge better up top because of the long primaries and merge collectors hince why drag cars always have them and shortys and mid lenghts were better for the low to mid range cylinder pressure builds trq and thats what you want apply this concept alot of people say they feal they lose alot low to mid range trq when they run open headers but they get good hp gains up top your not going to be reving this motor to need the scavenging up top thats why i think shortys or some mids with like a dual 2.5 inch exh would be good but dont take my opion im kinda new to the board to post it up in external section im sure yuoll get hits on it

 

Why not keep it simple and cheap?
Stock cam
5.3 heads with MILD port work (or none at all), comparable to GTP stage 1s
Maybe even shaved just enough to bump compression a bit more
Optimized tune
Port the TB and keep the stock LS1 intake
The header/exhaust choice will be key but don't think you need to shrink the tubes a whole lot. LOTS of guys actually improve their torque with big diameters, ask the LS2 GTO guys.

Start with that, you can always change the cam and/or heads (AFRs) later if it's not enough.

Sounds fun, good luck!

 

longer headers emphasize lower power band, get LTs. might want to look into stepped headers or 4 into 2 into 1 designs, not sure how these pan out.

work your DCR up into the 8.4 range with shaved heads to 11:1 SCR and cam events to finish. use a thinner head gasket to optimize quench and avoid detonation.

save som but not a great deal by reworking stock heads. port your small runner heads by short side radius, bowl blending, eliminating the rocker arm stud hump, valve guide blending. smooth combustion chamber and exhaust runners. do not open runners up!

when selecting cam use high lift fast ramp rates to get the most flow out of your shortened time period between exhaust valve open and intake valve close. a narrow lsa will result, and my first inclination is to keep the overlap in check for off-idle response. use all the tricks you can here, set intake closing to maximize DCR, open exhaust later.

 

when you say do not open the runners up, are you refering to the exhaust runners? thanks for the detailed input.

 

i figure since the motor's out, and i'm gonna open it up for inspection and to have the heads worked, why not through a cam in now? the money i'd save buy not buying heads could be used to mill the stockers and pay for the cam/gaskets. 6 to 1, half a dozen to the other i guess.

 

^^ don't add volume by hogging out and increasing runner cross-sectional area for both intake and exhaust. when the volume increases the powerband moves up to higher RPM.

 

Here are my thoughts on the cam. Reverse split seems like an idea for this. You don't need a lot of exhaust to carry the rpms very high. Second, the stock valvetrain really limits your lobe choices and decreases the torque you'll make because the exhaust valve will come off the seat early for a given exhaust duration at .05 compared to a faster ramp lobes. Third, I'd probably keep overlap somewhat limited. Fourth, Is 93 Octane not available in your area? 93 adds a little more flexibility down low. Assuming you hit 11:1 SCR, I'd suggest a 214/210 111 114. If you went with faster cam lobes (i.e. use aftermarket valve springs), I'd put it on a 110 LSA.

Other thoughts; Sticking with 1 5/8" primaries sounds good. Merge collectors may help too.

A 2000 stall is really low for an LS1. I know you will be battling converter heat, but I would really look at a reworked stock truck stall in the 2400 range. The LS1 intake is designed to make power in the midrange, camming it can only do so much.

Looks like a cool project, good luck.

 

nice rig rusty! ive got a built k30 on 42's and a built k5 on 39.5's as well. are you a member of ck5? check it out if your not, lots of built rigs over there, and a ton of ppl from CA. its no pirate, but its just chevy stuff, with lots of nice guys.

hijack off

 

understood. i'll just smooth the runners and port match.

 

interesting. thanks for the advice. i'll look a little further into the stall speed.

 

thanks for the kind words. no, i'm not on ck5. avid member on pirate4x4 though.

 

You seam to know what you want. All i can say is read,read and readup some more.

then pay patricg $25 to spec you a cam that will be just what you need.

the more you read the less you will need to ask. shoot for a static around 11.2-11.6 and a dcr of 8.5-8.7

But like i said pm patg and be honest in the cam help form and i bet you will have what you need

mike