How Much Boost Can a Stock Jeep 4.0 Handle

Whatsoever 1 know a rough hp effigy that the four.0L tin can safely handle?

Post by **CobraMarty** » August 8th, 2012, seven:26 pm

I accept read most every postal service here and other sites and the guys who were racing these engines were using stock rods and up to 450-500HP and 7000 plus rpm and never had talked about a rod problem. They had other problems cam harmonics at higher rpm, that is kinda wierd. 505 has a 600+hp turbo but I don't know what rods. Good oiling and build and reasonable rpm and no detonation and they sound like they can terminal.

Post by **five-xc** » Baronial 9th, 2012, 5:41 pm

CobraMarty wrote:I have read near every post hither and other sites and the guys who were racing these engines were using stock rods and up to 450-500HP and 7000 plus rpm and never had talked almost a rod problem. They had other bug cam harmonics at college rpm, that is kinda wierd. 505 has a 600+hp turbo but I don't know what rods. Skilful oiling and build and reasonable rpm and no detonation and they sound like they can last.

There is an consequence with cam harmonics in the range of 6000-7000rpm, as Barney Navarro plant out in the 1960'southward (he raced a destroked twin turbo AMC 6-199 at Indy for a few years.)

Below or above that range, the engine will live forever.

It may have something to practice with the vii main bearings - I don't know if anyone experimentally opened upwardly some bores to make it a 5- or four-primary block, merely that may prove instructive, if someone has the time... (Eliminating main bearings will change the harmonics from firing impulses, by irresolute how the crankshaft is supported.)

Even so, no 7-main configuration would survive in the 6000-7000rpm ring - I recollect the Navarro team went through a few engines to figure that out...

Post by **SilverXJ** » August 9th, 2012, 6:28 pm

I believe the harmonic is closer to 5500 RPM. The problem was the driver wanted to concord the engine there nether ability. Snapped the timing concatenation. Twice. Hesco has the info virtually that.

Also, digging around on Hesco yielded the stock rods support 400 HP.

Post past **coincidental** » August 15th, 2012, iii:39 pm

I was going to pipe in with 505 telling me around 425Chp every bit well.

I believe turbo tom was effectually 400 hp with his stock 4.0 when that motor permit go. Stock motor, mileaged just addeda turbo & dynoed it. Vid's are on youtube.

August 15th, 2012, 3:56 pm

I believe his head gasket failed though.

Mail past **casual** » Baronial 15th, 2012, seven:51 pm

SilverXJ wrote:I believe his head gasket failed though.

Yes he pushed the headgasket out around 13psi? Correct me if I'thou wrong, only also snapped 2 pistons or rods.

Post by **Cheromaniac** » August 16th, 2012, v:25 am

CobraMarty wrote:505 has a 600+hp turbo but I don't know what rods.

Hawkeye forged 6.150" length rods.

SilverXJ wrote:Whatever one know a rough hp effigy that the 4.0L tin safely handle?

The stock iv.0L rods can easily handle 400+hp and 6000+rpm. Other components in a stock four.0L engine are likely to fail (e.g. snapped timing chain, cracked crankshaft rod journals) before the stock rods or rod bolts, and the stock blended caput gasket volition fail if subjected to more than 8psi of heave.
Shotpeening the rods, using ARP rod bolts, nitriding the crank, using a MLS head gasket, and accelerating through the ~5500-5700rpm cam harmonic should take intendance of the most likely points of failure.

Post by **SIXPAK** » August 16th, 2012, i:03 pm

Tom cracked the pistons in the wrist pin area with 13lbs of boost. I had a fix of mill rods final me 17yrs, my engine guy threatened me and I replaced them. Many years of standard transmission abuse followed by many years of 5300 stall converter action besides.

Post past **casual** » August 16th, 2012, nine:49 pm

SIXPAK wrote:Tom croaky the pistons in the wrist pin area with 13lbs of boost. I had a set of manufacturing plant rods last me 17yrs, my engine guy threatened me and I replaced them. Many years of standard manual abuse followed by many years of 5300 stall converter action too.

Aww ok. I thought it was the rods that went.

Curious how much could you lighten the stock rods? I know mine were all off balance..a few grams variance between them. Would it exist worth information technology to try and lighten them upwards? Could you drop 50 grams per rod easily? That'd be a lose of 300 grams which is over half a pound. Is this possible?

Post by **Cheromaniac** » August 17th, 2012, ane:forty am

coincidental wrote:Curious how much could y'all lighten the stock rods? I know mine were all off balance..a few grams variance between them. Would information technology be worth it to try and lighten them up? Could you drop l grams per rod hands? That'd be a lose of 300 grams which is over half a pound. Is this possible?

You're asking a lot to drop 50g from each rod without compromising forcefulness. What you could do is polish the rod beams to remove stress risers, grind abroad the balance pads on the pocket-size ends, balance them to equal the lightest rod, and shotpeen to add forcefulness.
The stock 4.0 rods, at ~660g each, are non exactly heavy in the kickoff place considering that they're long at 6.125". The 4.2 rods are ~30g heavier yet 0.25" shorter.

Postal service by **casual** » August 17th, 2012, 8:52 am

Cheromaniac wrote:

coincidental wrote:Curious how much could you lighten the stock rods? I know mine were all off balance..a few grams variance betwixt them. Would it exist worth it to try and lighten them up? Could you lot drop l grams per rod easily? That'd be a lose of 300 grams which is over half a pound. Is this possible?

Yous're asking a lot to drop 50g from each rod without compromising force. What you could practise is polish the rod beams to remove stress risers, grind abroad the residue pads on the small ends, remainder them to equal the lightest rod, and shotpeen to add strength.
The stock iv.0 rods, at ~660g each, are not exactly heavy in the start place because that they're long at 6.125". The 4.2 rods are ~30g heavier all the same 0.25" shorter.

Ya I sympathize. I judge I'g trying to make whatever gains where ever possble..even if it takes extra fourth dimension! My lightest rod currently untouched weighs 663g, heaviest being 676g'due south. These are out of an 87 motor. I simply call up thats far too much of a deviation to be a polish running motor..I approximate getting them all to 660g would be much better than having them 13g apart. Perhaps I should focus more than to go them all together.

Mail by **Cheromaniac** » August 17th, 2012, 1:26 pm

casual wrote:My lightest rod currently untouched weighs 663g, heaviest being 676g's. These are out of an 87 motor. I but call back thats far also much of a divergence to be a shine running motor..I guess getting them all to 660g would be much better than having them 13g autonomously.

Definitely. I worked on the 4.2 rods to get them all inside 1g of each other before putting them in my stroker and yes, it runs smoothly right up to the 5200rpm rev-limiter.

Dino is that normal for the rods to be that far out? I've seen maybe 5g or and so...but these are virtually tripple that!

Would it be a skilful idea to go a 2nd set up of rods and try to find a prepare thats more evenly matched? Equally in combine two sets and get them all much closer? Or do y'all think its possible to become the heaviest even or at least within a gram of the lightest?

Post by **Cheromaniac** » August 18th, 2012, three:15 am

casual wrote:Dino is that normal for the rods to exist that far out? I've seen mayhap 5g or so...but these are near tripple that!

Would it be a skilful idea to get a second set of rods and endeavour to find a prepare thats more than evenly matched? As in combine 2 sets and get them all much closer? Or do you think its possible to get the heaviest even or at least within a gram of the lightest?

That'due south too much of a variance in rod weights and so I agree it'll be a good idea to buy some other set of rods, choose six that are most closely matched in weight, and become from at that place.

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