4.2L swap

95CaliSC

Registered User
I have heard some rumblings about the 4.2L 6cyl from the later model trucks can be swapped out in place of the 3.8L. Can you do a direct swap of the blocks and bolt up our heads, sc , etc.? Or is it just that you can put a 4.2L in our bay without the sc?

I am somewhat curious because if my poor 95' ever kicks the bucket, I would like some options that could prove more reliable/less work to get a shop to work on it. Some shops won't touch the SC engine and the few that do sometimes don't know what they are doing. Would be somewhat nice to just put a N/A engine in her and call it a day. But would still like a little oomph without going nuts on bolt ons.

If it is already discussed here somewhere , please forgive me. I am still waiting on my membership to process and searched the public forums to no avail.

Thanks
 
The factory 4.2 crank is not up to the task of the pull from the roots style blower. If you wanted to put the 4.2 in the car with a different intake and a turbo, you could bolt your SC stuff right to the top of it.

Chris
 
I've been doing a little more research into the 4.2L engine. I have heard some real horror stories regarding the 97'-99' or so years. I am assuming that the later model years 4.2's have been fixed? Alot of those motors failed at 50k miles or less from coolant leaks(internal). bearing problems, etc. I am hoping later model 4.2's were better.
 
Based on what facts? There are several running around making plenty of HP.

Okay...What are the limits of the 4.2 then? I dont mean to sound crass, but there have been a few guys who have broken them, or just disappeared after they got them together. I understand if it is stock and tuned it works okay, but what of a higher performance engine?

Chris
 
Based on what facts? There are several running around making plenty of HP.

How many are with a roots blower? I'm curious as we know the limits of a stock SC bottom end have signifigantly decreased recently then what was proposed to be true not to long ago. What power are these m90 powered 4.2's making>??

I'm still a firm believer in Ford not spending money where they dont have to and when all other ford cranks were nodular iron to create a steel one for SC specific applications...Knowing what I know about crank issues on roots blown applications I would pesonally forego the extra displacement in place of the extra security of a steel crank. The jackshaft system helps a bit but I'd go steel all the way when I have the option...Which I do
 
Of course forged is always better and if you can afford it, billet even better than that in most cases. But that doesn't mean that a cast steel crank can't stand up to decent amounts of roots generated boost. The 4.2's that I know of which "blew up" were subject to extreme abuse. SC motors have blown up under similar circumstances. The 4.2's that are running around with roots blowers disappeared mainly because of all the grief they get around here. Anytime someone does anything out of the ordinary around here they get lots of hassle. Most people have better things to do than defend themselves on the internet against people they don't even know.

I'm curious as we know the limits of a stock SC bottom end have signifigantly decreased recently then what was proposed to be true not to long ago.

I'm curious upon what you base this statement? If you are referring to Ira's motor then your statement is false as his motor was making significantly more power than anyone has ever made before putting it in very uncharted territory. I have no doubts whatsoever that a stock SC motor can handle over 400rwhp, the only thing with that is your margin for error is reduced.
 
I'm curious upon what you base this statement? If you are referring to Ira's motor then your statement is false as his motor was making significantly more power than anyone has ever made before putting it in very uncharted territory. I have no doubts whatsoever that a stock SC motor can handle over 400rwhp, the only thing with that is your margin for error is reduced.

Dave, what about the limits of the crank and block. Not factoring in rods and pistons, how far can you push the two pieces of the engine that can't be affordably replaced?
 
Dave I have a stock 5.0 shortblock that has handled over 700rwhp...How long is the question. As far as Ira is concerned I'm not mentioning names however he doesnt exactly drive like a madman. If anyones 400rwhp plus stock bottem end SC motor would hold up it be his. Just my opinion of course

A few people have done the 4.2 swap here and I have yet to see any super spectacular results and recall a few mishaps. So I'm SERIOUSLY curious who has had great results because I have yet to see them. And this isnt a wise*** remark. I'm being serious
 
Damon, we don't know what happened to Ira's motor. Remember his red car blew up at less than 300rwhp and I've rebuilt plenty of motors that scattered in nearly stock condition. Ira has absolutely driven the snot out of his car. Ask him how many times he has hit the factor rev limiter....

I haven't changed my opinion which is to state that 400 +rwhp is reasonable on a street driven SC. Probably a good place to put an expectation is around 425rwhp but again, we don't know what happened to his motor and his is the only one I know of that *seems* to have failed due to HP at over 400rwhp.

The stock block and crank have made over 600rwhp on several occasions but what needs to be understood and has not been mentioned above is that all parts have a life cycle expectancy. For racing if you have a perfectly capable combination of parts you simply do not continue to use them forever because eventually they will fail. If you don't know at what point in the lifecycle your parts are at then you simply can't say how long they will last.

As for the 4.2L thing I know of more than a couple making 350rwhp at 13-14psi and well into the 450rwtq range. As expected the 4.2L makes significantly more torque than a similar 3.8L and requires less boost to do so. I do not know of any which have failed after being properly tuned. There are a couple reasons why you can't just toss a 4.2L in an SC, abuse it, and expect it to live. We can start with a nonfunctional knock sensor, then talk about timing curve, and what parts exactly have been used in it. All the 4.2L failures I've heard of involved significant abuse and/or suspect parts use.
 
I dont mean to sound crass, but there have been a few guys who have broken them, or just disappeared after they got them together.

Who has broken a stock 4.2L crank?

How well was their motor balanced?

I researched this and couldn't find any cases of broken 4.2L cranks :confused:

Dr. Fred broke a cut and welded SC crank that was stroked similar to the 4.2L truck crank. Though, he believes it was due to harmonics and a poor balance job by the shop that did the balancing.

He now has a billet crankshaft that was made by Moldex. It has a slightly longer stroke than the 4.2L truck crank I believe. Has to be one of the nicest looking crankshafts I've seen. The engine is currently dis-assembled due to a cracked block, which we belive was a poor casting. It had only been bored .020 and was leaking coolant into the #3 cylinder.

Jeramie
 
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Dave,

Have you ever considered building a 4.2L block?

Yes, I intend to build at least one for myself but beyond that people seem to be scared of them so there's been no call for it from anyone else yet.

Jeramie, where did the crack form? I have my suspicions as I've sonic checked a few blocks and they tend to be very thin in one particular place...
 
Jeramie, where did the crack form? I have my suspicions as I've sonic checked a few blocks and they tend to be very thin in one particular place...

I don't recall exactly where. His motor has been apart for a few years now. We know the crack formed after it was running for awhile. We thought it was a headgasket, so we replaced headgaskets twice, then discovered the crack. If I recall correctly, you could BARELY See it, but it was there.

Jeramie
 
The crank and rods shouldnt really suffer from fatigue. I'd more concerned with the actual strenght of the factory rod bolts and the rods themselves.

Ira is the constant hititng of the rev limiter due to yer slow shifting?:D
 
The crank and rods shouldnt really suffer from fatigue. I'd more concerned with the actual strenght of the factory rod bolts and the rods themselves.

Ira is the constant hititng of the rev limiter due to yer slow shifting?:D

Don't give Ira a hard time. I didn't mean to suggest that he is a maniac behind the wheel but the motor did see high boost many times, was drag raced (much of it untuned), and dyno'd, etc.

On a forced induction motor connecting rod bolts are not subject to high stress, I've never seen one fail, even on connecting rods that broke. The OE rod bolts are 180,000psi 9mm bolts, not exactly weak and in fact stronger than the ARP rod bolts that some people use. The rods are a different story. On most motors that toss connecting rods the damage can be traced to cracked pistons or bent rods.

The crank and rods are subject to fatigue (that's why they break ;)). Even cylinder heads are subject to fatigue (they don't crack due to the weather).
 
Has anyone had a SC 3.8 crank ground, heat treated , polished.
To fit the smaller diameter Chevy connecting rods.For a lighter
crank,rod assembly, for racing use?

If I was building a stroker motor. I would use the stock
SC 3.8 crank ground,heat-treated, polished to my stroker specs,
and the use of smaller diameter, lighter rods.

Randy
 
Has anyone had a SC 3.8 crank ground, heat treated , polished.
To fit the smaller diameter Chevy connecting rods.For a lighter
crank,rod assembly, for racing use?

If I was building a stroker motor. I would use the stock
SC 3.8 crank ground,heat-treated, polished to my stroker specs,
and the use of smaller diameter, lighter rods.

Randy

Randy,

Chris Wise did an offset grind and used a smaller diameter rod journal to increase stroke about .200, then bored the block .050 over to get 4.2 liters. As I recall the width of the rods and bearings was a problem, and required remachining of all the rods and the bearings to make them the same width as an SC rod. The crank was ground and polished, but not heat treated.

The crank did fail about a year after the car was sold to Bob Simms. When I last checked, the motor was not yet taken apart to determine where the crank failed and if the failure was related to doing the offset grind.

David
 
What Casey said. Aluminum fatigues however. I love Ira btw. Hes a great guy even though I may give him a hard time now and again and perhaps make his blood boil.

I cant comment on the factory rod bolts however I cant see them being stronger then an ARP or the quality control being quite as good. Besides important factors such as thread pitch bolts/studs experience stretch. Rod bolts moreso then a head stud due to diameter. On a high performance application I am not so sure a factory SC rod bolt should be reused under any circumstances as proper torque values are probably never reached due to those factors. An aftermarket bolt such as an ARP with a stretch rating and proper thread pitch IMO should be used. And always use a stretch gauge rather then a torque wrench when dealing with rod bolts as torque values are generally way off even when using the proper lube. Add that to the typical torque wrench being out of calibration (even good onbes) amd its a recipe for disaster.

Bolt stretch and various types of performance thread pitches can perhapsbe talked about by Casey as I havent dealth with this stuff in over 10 years.

And of course the number one reason for rod bending/breaking is detonation.
 
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