1991 4.0HO FUEL INJECTED STROKER WHATS NEEDED? 300 HP

[kkchevy3]

My motor is going to need a rebuild soon and i figure the winters a perfect time. This is my daily driver so it needs to be reliable. This is my daily driver so it needs to be reliable. It get about 90% road and 10% off road. I would like to keep all the stock drive train. My friend builds race engines so machine work really isnt a problem. Im looking to get towards the 300 hp mark. With keeping the cost down what could I make here? i have heard that the stock computer probably wont handle this. What do i need to do in order to make this work. Thank you

[Alex22]

By giving yourself a HP number to meet you are rapidly on your way to ignoring the all important torque, it happens to quite a few of our customers. 300 HP is going to be a lofty goal for a budget build. To start off, you're going to need at least a 4.2 crankshaft and a 4.0 engine to start with. Since your buddy is a machinist, the KB944 pistons may be a good candidate for you. Although they do cost more than a cast piston, but you won't have to buy a set of 4.2 rods and your friend can get them at the dealer cost. The next thing you will need is a good cam that is designed for HP at upper rpm ranges. There are cams out there for 4.0's that will pull right to 6500rpm so you might be able to get 300hp out of your stroker. How much porting experience does your friend have? A quality port job and the use of a flowbench will go a long way to producing max HP. The rod studs and bolts should be replaced with ARP hardware. Your stock cast rods will need some attention to make sure they are as strong as possible; Magnaflux, stress relieve, shot peen, ARP hardware and resize. Cryo treating the rods will also make them stronger, but it will raise the cost of your build. Balancing the rotating assembly to race spec as well.
I'm probably forgetting something but i'm sure a few members will chime in to help you out.

~Alex

[1bolt]

The stock ECU will keep up with an average 250 hp (crank) Stroker, after that you'll want to look into aftermarket fuel managment, to help make the power you will need both fuel and spark custom tuned to your engine. Plan on 98 octane and 11 to 1 compression (or better use E85 if available and even higher compression).

Besides that I can think of several things that will help meet the 300hp goal. First of all realize you will be sacrificing some long term reliability to make more power. Don't expect a max power build to last 200K miles... 100k maybe but the number gets lower the more power try to make. Build with tolerances just loose of factory specs, looser tolarences = less friction within reason (in other words where a range is specified, .010 to .014 use .014 or the looser of the two and spend the time needed to actually GET that tolerance the same from bore to bore or bearing to bearing. get the bores done with a torque plate, and pay your friend (or bribe him with beer) to get your bores as perfectly matched to the pistons you will use (not a mock up set) as possible. Need I mention keep the Beer away until the days machine work is done? Balance everything. It shouldn't take that much to get any 4.7L engine into the 300 crank hp territory... Obviously flip the piston orientation, use bronze valve guides, a 3 angle valve job, as big an intake valve as you can fit using an offset guide. hand polish all your journals, including cam, and cam lobes, use a fairly radical Cam. use a big ported throttle body, the 99+ intake, and make sure the intake is getting OUTSIDE air, not engine bay heat (either through some custom ram air ducting or a cowl induction hood). If you throw in all the racing inspired build tricks you practically can it should come away with more than 300hp without any crazy parts or drastic measures (like offset ground cranks, or big overbores).

300 is only 40 more than HESCO's off the shelf 4.7 Stroker... I bet a good porting job, a windage tray and close attention to all the build factors and machine work I mentioned above would make that 40hp with ease. All that without spending crazy money on bolt ons, or power adders. The close attention to detail and tolerance machine work will be the big expense, but since you have a buddy

[kkchevy3]

okay if the computer isnt going to handle the power what are my options. This is the one thing that im worrying about

[Cheromaniac]

Realistically 270hp is as much as you're gonna get out of a 4.7 stroker and maintain reliability, but the 335lbft of torque that'll go with it is very handy indeed. Check out my 4.7L medium buck "recipe" on http://www.jeep4.0performance.4mg.com/stroker.html

[1bolt]

As Dino said if you build it on the tight side for reliability, 270 even 250 will be more realistic....

[kkchevy3]

yea i guess my hopes were a little too high. and who am i kidding, when im i going to get up to 4500 rpms for peak power? i want torque

[crustodd]

What about just adding a "Stupor Charger"?

[1bolt]

that a whole nother ball game, and some important build parameters change drastically (like compression ratio). Where you put it, how you intercool it (and where you put that) and engine management system become extremely important and much more expensive.