I am an old fart & old school chevy guy and have no experience building LS engines. My project motor build is for my '02 Tahoe which has already been retro-fitted with a JW Performance 4l80E & converter along with a 14 bolt SF rear end fitted with 4:10 gears and a NP263HD transfer case. I am running 33" tires. I want a big torque motor for towing a rather heavy boat and for 4WD adventures. I am NOT building a race motor but do want durability.

Here is what I have acquired so far:

New stock L92 heads
New stock Lq9 block
Used L92 truck intake manifold w/stock injectors (has fuel reg. retro-fitted)
Fast 92mm TBC air door
Used Crower Sportsman 6.125" LS Rods
Yella Terra 1.7 ratio non-adjustable roller rockers

Here are my questions:

1) Will the LQ9 block take a 4.1 stroke crank? How much modding?
2) 4.0 or 4.1 stroke, pros & cons?
3) What compression ratio to shoot for?
4) Long tube headers...... what diameter?
5) Cam Specs? (I have read enough that cams seem to be an issue with L92 heads plus I want fuel consumption to remain reasonable)
6) Do I need larger injectors and if so, which ones?

Please bear with me on this. Any and all help is greatly appreciated!

John

 

The lq9 block can take the 4.1" as far as i know, but you are not going to get the durability that you want. The long stroke in that block is going to cause more piston rock since it will be coming that much further out of the bottom of the cylinder. If you are not building a race motor, I would sell the rods and the rockers, a set of stock lq9 or 05 up lq4 rods will be more than you need. The rockers are not going to gain you anything either for a dd/low stress application. If I were you (which I am not, so you may have another route you want to go), and you want a motor that will last 200k, I would build a 370 around 10.5:1 compression, a set of 243 or 317 heads with a mild porting job, a cam somewhere in the 21X/21X .56X/.56X on a 114-116lsa range. I wouldn't run the l92 heads, they are not known to have the best low end power you want due to their larger port volume, and run a tbss or 07 or newer truck intake with a 90mm tb. This combo or something similar will net you some very satisfying low end power, good fuel economy and last a very very long time. I had a setup similar to this only with a slightly larger cam, and I towed an 8000+lb trailer with my mud truck, atv, and various tools etc that was tall and had alot of wind resistance. My truck with 3.73's and a built 4l60 towed this quite well, able to tow in OD at 70-75mph no problem. Made my 5.3/small cam feel like a 4cyl as far as towing. If you want headers, get smaller primaries, 1.625 to keep the velocity for torque. This is just my suggestion, others may agree or say different, but I believe you would be satisfied. Obviously a stroker would yield more torque, but I don't think the durability could compare, the stock 6.0 can last several hundred thousand miles and still run strong.

 

Thanks for your suggestions Joey. I knew a 4.1" stroke would be pushing it in the dependability department but am thinking the 4 x 4 being a 'square' ratio similar to the 8.1L truck motor would be a better choice. I have quite a bit invested so far and don't really want to sell off parts to re-buy. My thinking was that with the 402 ci, the stock L92 heads would be small enough (not much more than mild ported 317s) and with a 92mm TB would be in the same ballpark airflow vs cubic inches ratio as the combination you suggest. With proper pistons made for a 402 application, is there still excess skirt coming out of the bores? As for the roller rockers, I only got them because they were a bargain, didn't really need them.

Hypothetically, if I stay with the 402 ci route, would the 1.625" primary headers be too small or would 1.75 be a better choice?

How about cam specs for this combination?

Sorry for the many questions. Just trying to narrow down the specifications.

Thanks!

 

Ive had two stroker motors in my truck and they both had 4.1 strokes in them. They both didnt last long due to piston rock at BDC. The cylidners egg shaped and lost compression and started drinking oil. This was going on 6 years ago so ALOT has changed in technology since then. It can be done but will need a longer rod, but then youre looking a VERY small compression height piston and will not be good for anys ort of power adder at all.

If I were you, Id run the 4" stroke, with your heads but get Richard at WCCH to do atleast a stage one type job on them. Cam choice is going to be very subjective. Do you plan on using any sort of power adder later? Also what stall speed converter do you have? If its a typical reowrked stock 80e verter and youre going to stay NA with a 402 Id go with something around a 216/226 on a 112+4 to keep the power low. Id recommend contacting Patrick G(his sn on here) and getting him to spec a custom cam for your app as he has the cam software and vastly more experience with cam combinations that anyone on this site.

CR Id shoot for low 10s if youre running 93 so you can still keep some timing in it while under load aka towing.

Id run a set of LPP headers since they are 1.75 primaries but still retain a 3" collector to let that big motor breathe.

You will need bigger injectors, Id pick up a set of the good ole 8.1L marine injectors which are 44#ers and will take you as far as your longblock can take you NA.

 

1slow01z71 - Thanks for your input. Well, I have decided on the 402ci (4"x4") choice. It is going to be straight up NA with the stock truck L92 intake. Those headers you mentioned also appear to be a good choice and makes sense. I sent a PM to Patrick G to see if he is willing to do a cam spec. for me.

Are you sure about the 44# injectors? I thought that size would only be needed on a 402ci if it was boosted. Also, I wasn't planning on modifying the stock fuel pump unless I have to.

Thanks for your help!

John

 

Unfortunately there isnt much in between the stock injectors and the 44s, there is only the 8.1l injectors but your engine will need more fuel than those will provide as they are only 31lb injectors. You may be able to get away with the stock pump depending on how strong it is but if it were me Id get a walbro 255, theyre only 120 bucks and take about two hours to install. Its a good piece of mind mod IMO.

 

After sitting down and looking at how much towing I would actually be doing, I realized it is not that often. It is just that when I do tow with my anemic 5.3L, it is easy to dream about a monster torque motor. Actually I would be doing far more off-roading than towing. So after much soul searching, I sent my motor specs and realistic vehicle use to Patrick. Here are the results:

228/238 .571"/.585" 113 LSA, +4

This is based on 1.75" long tube headers into true dual baffled turbo mufflers with cats. I will have to upgrade my springs to PAC1518 units.

So we shall see how this works out!

 

Sounds like it is going to be a stout set up. Are you having Patrick grind the cam for you?

 

On Patrick's cam sheet, it says a cam can be ordered from Engine Power Systems. I e-mailed them and they gave me a call back. They seem to know their stuff but I was a little surprised that they actually order a cam grind from an outside vendor. Or at least that is the way I interpreted how it works.

However, doing due diligence, I also sent the spec. sheet to other companies for price comparisons. I was surprised that Crane Cams responded that they couldn't do the grind unless they made some new master tooling. Cost to me would be $1,700+. Or I could settle for a .335" lift for $468. That eliminated them. Crower responded with a decent price under $400. Adding shipping would put them on par with EPS.

I will place an order Friday which gives me a couple of days to decide.

 

Fair warning, EPS will take 3-4 weeks to deliver your cam.