hey dino

[DeftwillP]

So I'm looking at your web page specifically at the 4.6L Low-buck, low CR "rockcrawler" recipe. I like this one because it it keeps the CR stock and rebuilds the engine maybe allowing for forged pistons(I'll get to that in a minute). Is that horsepower and tq estimate with all the standard ancillary mods? I've done homebrew intake, bored tb and bored spacer, dual electrics, msd coil with magnecore wires, etc. I'll be p'n'ping the head as well as a good exhaust manifold.

The reason I'm interested in low CR and putting in forged pistons is for future turbo applications. While I'm no genius on this subject, I know these are two things that will help immensely with a turbo setup. I'm still waiting on my book from corky bell which can help enlighten me further.


I know there are a lot of details that aren't quite put down to paper yet, but if I first set up mild boost, say ~ 5 to 6 psi, what would this setup be making?

 

[Dr. Dyno]

You could easily use a 6psi turbo even without an intercooler and gain ~45% more HP and TQ, but an intercooled set up would be even better and would allow you to use 8psi of boost. The stock cast aluminium pistons are strong enough to sustain 8psi.
The estimated HP/TQ figures for my "rockcrawler" recipe are indeed with all the ancillary performance mods (intake, bored TB, header, exhaust, etc.)

 

[DeftwillP]

Well according to your hp gains sticky on JU, all of the external bolt-ons puts a 4.0 around 225. If you figure in the cam and pnp'ed head(as included in this stroker recipe), it would put you ahead in hp and tq compared to the stroker which includes all of the same things. So what is the point of increasing the displacement in this case??

As far as the pistons, should my boost ever spike more than I wanted it to, I don't want to fry my pistons. I realize that forged cost more, does anyone make a forged piston in the required dimensions for this recipe?

Intercooler is still undecided as I have not set any real boost numbers yet.

 

[Dr. Dyno]

Well according to your hp gains sticky on JU, all of the external bolt-ons puts a 4.0 around 225. If you figure in the cam and pnp'ed head(as included in this stroker recipe), it would put you ahead in hp and tq compared to the stroker which includes all of the same things. So what is the point of increasing the displacement in this case??

As far as the pistons, should my boost ever spike more than I wanted it to, I don't want to fry my pistons. I realize that forged cost more, does anyone make a forged piston in the required dimensions for this recipe?

Intercooler is still undecided as I have not set any real boost numbers yet.

For the benefit of everyone else reading this thread, here's my "rockcrawler" stroker recipe:

Jeep 4.2L 3.895" stroke crank
Jeep 4.2L 5.875" rods
Keith-Black Silvolite +0.030" bore pistons
Increase piston dish volume to 30cc
8.8:1 CR
Crane #750501 192/204 degree camshaft
Ported HO 1.91"/1.50" cylinder head
Mill block deck 0.035"
Mopar Performance 0.043" head gasket
0.058" quench height
2.25" exhaust
Ford 24lb/hr injectors with stock 39psi FPR for '87-'95 engines, stock injectors with stock 49psi FPR for '96 and later engines
231hp @ 4400rpm, 327lbft @ 2000rpm

A 4.0L engine with the same cam, ported head, and ancillary performance mods will be producing 228hp @ 4800rpm, 282lbft @ 3000rpm. OK, so the stroker is only 3hp ahead of the 4.0 but more importantly, it's also 45lbft ahead of the 4.0 and the HP/TQ peaks are at lower rpm, making the power far more accessible.
The turbo should have a wastegate (or blow off valve) to prevent spikes in boost. There are no off-the-shelf forged pistons to go with the 4.2 rods. The 23cc Accurate Power forged pistons only go with the 0.25" longer 4.0 rods and yield a ~9.5:1 CR. If you really want forged pistons, you'll have to get them custom made and use 4.0 rods. In that case, the piston specs would be as follows:

Dish volume 30cc
Compression height 1.365"
Pin bore diameter 0.931"

You would not need to mill the block deck at all with these piston specs.

 

[JeepSpeed]

What people need to realize is that engine power curves are the real measure of performance, not single peak numbers. Advertised hp gains are at peak, so if something actually nets 20hp at peak, it could give much less at other points in the curve, even losses. To add to this point, if you have a 190hp engine, and two mods give you an actual gain of say 10hp and 15hp at their peak, you do not have a 215hp engine. Because they probably added those gains in different parts of the power curve.

 

[renegade_z71]

that makes a good poit about how peak number mean nothing... ever seen a 5.3 chevy race a 5.7 hemi? it is embarassing to say the hemi have 40+ advertised hp.