Okay, I made an intro thread awhile back, saying that I was doing an Built/Stroked LQ9 engine in a Cobra. My original plans were to fit my existing 3.4L whipple, to the LQ9 engine, but I have since changed my mind. The first thing I am doing it rebuilding my 5.1L Stroker DOHC, and then selling it. As mentioned previously, there already exists the proper k member for the lsx swap, and nelsonperformance is making me a custom wiring harness for the swap. I will be using the stock GM computer. I just wanted to get some input on a couple of things.

First of all, I decided to ditch the whipple. I will be selling my whole stroker/heads/cams/whipple/t56 set up all together. I have a fabricator that can fabricate a turbo kit for me, at a good price, with me providing the main parts (intercooler, turbo(s), wastegate, bypass valve, etc...).

I am doing a 408 lq9, with a turbo cam, and ported l92 heads...

What kind of intake manifold has proven reliable at over 20lbs of boost?

Just how good are the stock ls1 coils? I know the individual coils on the Cobra, started failing me past the 600rwhp level. That's when the dyno graph started to get "bumpy"...

Also, what kind of turbo(s) would you recommend...

I was thinking twin 76's.... How much lag would that be, on a well put together kit, running a built 4l80e with around a 3800 stall?

OR single turbo?

I assume the max psi I could run, on pump gas, is around 14lbs? Anyone running anything higher than that on pump?

The set up that I am doing, is in no way unique (besides that its going into a Cobra, I'm sure there are hundreds of fbody guys running about the same thing)... So I hope my questions aren't too vague...

Also, just as a plus, I have already seen what the ls based engine looks like in my car, and not to be arrogant, but it SEEMS to fit SOO much better in a Cobra, than in an F-Body. There is tons of space to work with. Definitely a lot smaller than the modular engine that used to be there...

 

Maybe cuz the 4.6 is the size of a freggin big block!! lol...Some one will chime in on this. I think some people are using the edelbrock intake with the elbow, I heard the FAST isn't good for forced induction. Good luck with the build.

 

Sorry of topic... but you are a very smart man my friend! get rid of that ford and drop in a gm! brillant!!! haha

 

20psi?!? how much power are you looking to make/. a tc78 will make 750rwhp. i thonk twins that size would be pointless. wats your motor and cr? give us some details

 

A forged/bored/stroked 408 lq9 block... 8.8:1 CR...

How much hp or boost can the stock coils handle, before they start failing?

 

more than 20

 

I think LMR or the Ohio boys have run 30psi on stock truck coils.

 

A factory manifold will hold you to over 20psi: I'm running a stock ls7 mani to 25-29psi.

On my last car (TT TransAm 6.0) I ran 17psi on 93oct with only a FMIC.

The stock coils are good to 1K plus. I'm venturing to the 1300rwhp+ realm and chose to go with the 6.0L mitubishi truck coils.

The problem you will run into with a 408 and twin 76s is head lift. It would be laggy and way overkill for you. Most with a 408 run 88-91mm singles for the strip. If you HAVE to do twin I would recommend 67s: not laggy and capable of over 1Krwhp.

 

I know the search is messed up but if your trying to make good numbers(800-1000 or more) you should do a lot of reading. Its not all that hard to make that kind of power, just need to know what your doing. If your new to the LS based motor, search back on old threads in this FI forum. Your going to learn a lot more by doing that then what 20 people are going to teach you in one thread. There's all kind of valuble knowledge that guys discussed here in the past that makes your job 10000 times easier if you stick with what works.

 

The heads will lift, even though they are studded?

 

The heads will start to lift with 4 bolt heads. L92's have thinner decks as well, thats why most guys dont use them. DOnt worry about coils either. The stock ls1 coils are way better then Ford coils. You wont make enough power. You can make 1k on a 4 bolt setup but it will push water even if you have studs(Tghe tune has to be done right). You can get the block o-ringed to help with that.

 

SBF motors have 4 head bolts as well. I've had no problems running over 22psi and ~ 700hp. I'll soon find out if these motors are worse or better than the old SBF

 

The only time I've seen people upgrade the coils is for aesthetic reasons. Otherwise people making alot more power than you plan on making are still using them.

As far as what I've seen on here the problem with pushing water seems to be hit or miss up to a certain point. I would venture no further than 1,000 but that in of itself is a flawed argument as you're trying to nail it down on a static number. veee8, who I'm partly modeling my build off of is using the so-called "thin decked" L92 heads and had problems pushing water. He recently switched his head gaskets and has no problem holding 1,000 hp with ported gm castings.

The stock intake has been proven to be "reliable." But switching to a different setup is up to preference, and to work congruous with the rest of your build. With the L92 heads you have limited options. The L76 will be alright, but there will be alot to gain on the top end by switching to a different intake like the carb style and an elbow.

Guys with single turbo's make comperable hp with the twin guys. Seeing as how you are going with an automatic you won't have the spooling problems associated with a big single turbo that manual guys do. I would look into an 88+

Again one of those things that you can't give a static number to. It's going to depend on your engine. My personal engine is 8.5:1 with a progressive meth system. I plan on pushing as close as I can to 1,000hp on pump gas as I can. But with your low compression and assumed fueling needs taken care of I don't see why you can't push 20psi on pump gas.

 

Any reason your using L92 heads over 317's? I'm just curious. LS6/2 manifolds will hold together for what you want to do. If you've got the $$$ look into a sheetmetal intake, that would be the best. As everyone has said, the stock coils kick ***, you'll have no problems with them for what you want to accomplish. I'd reccomend a single 88mm turbo. And depending on your cr, what octane rating your premium gas is, and if you plan on running meth or not, high teens/low 20 psi should be no problem. If I were you I'd also check into FIC 80lb injectors. Good luck on the swap/build.

 

I'm guessing he went with L92's because his compression ratio has been taken care of with the bottom end. So he went with them for cheap, great flowing heads. Sheetmetal intake is overkill, IMO. For the money I would buy an LSX block before I boutht a sheetmetal intake. 88mm would be a great turbo but he has yet to tell us what flange he is going with, so turbo's can't be spec'd out to great detail.

 

Agree'd, he left alot of info out. I read it as he is still planning the motor build, not that it is already built. I'd never go with a SM intake myself, he asked what intake has been proven to hold over 20psi and I've never heard of one of those blowing up

 

As stated I had some pushing water problems a while back, that has been fixed for now with the new GM LS9 ZR1 head gaskets, I gave them a spray of copper coat when I installed them too. My heads are L92's with Rich at WCCH magic stage 2 cnc port work and 75cc chambers.
For intake manifolds, the choices are limited with rectangle port heads. I use the GM single plane and Aaron's elbow. I would be a little leary of the L76, not because of boost pressure ( it will hold 20+ psi), but the hp/rpm limits especially on a 408. Why have great flowing heads, and top them with a crappy intake? There are a few choices coming to market, but for the money and looks to me, it is hard to beat a GM or Edelbrock single plane.
The 6.0L truck coils will be fine for 1500+ hp.

 

Wow guys, thanks for the abundance of information... As far as how deep I am into this project, I'm not deep at all. All i got is a bare lq9 block, and have yet to sell off my modular crap. I got a chance for some good deals on internals and the crank. I don't have heads yet, but it seems as if I am better off going with a cathedral style port, so I have better options on my intake...

As far as fuel system goes, I'm using my existing one, minus the fuel rails... I got a dual walbro 255's, amp'd up by a Kenne Bell Boost A Pump set at 50%. Good for over 1000rwhp. I was already running 92lbs/hr low impedance fuel injectors...

What brand of turbo would you recommend, comparable to a y2k 88mm? The Turbonetics units are hella expensive, but is it worth it? I know a couple of LS guys go with Borg Warner, because their AR'S are rediculous (in a good way)...