1st Time Post- Newb Help

[hvacman]

I have been researching and studying.

I think I have this right. For those of you that have done this, please let me know.

I have a 4.0 H.O. from a 1996 XJ. This is the preferrable engine becasue it has some extra "ribs" for support.

I also have a 1989 258 4.2 L.

If I take the crank from the 4.2 and install it in the 4.0, I could get a 4.5L. If I bore out the cylinders I could get (depending on bore size) up to a 4.9L.

Does that sound correct to you guys?

The good thing is that I have both engines and they are operational. I think I have a heck of a start, but am needing a little advice on where to go with the build.

[dwg86]

That sounds right. Now you need to decide what rod/piston combo you are going to use.

[hvacman]

I was thinking of boring the 4.0 out about 20 over.

But I just cannot grasp the terms quench height and decking the block. I have rebuilt many engines many years ago. But I never had to figure out these calculations, so I don't know what it means.

It appears I have the proper parts to do a budget build, but I am still trying to decide which rods to use. Any advice?

[dwg86]

Well a longer rod is better, but if you are on a tighter budget and you already have the 4.2 rods, you could get a hypereutectic piston with a 1.592 compression height. Ebay has a set with cast rings for about $160.00. I think they are engine tech brand, which i do believe is a silvolite piston repackaged. Get in touch with oletshot on this forum. He can dish you pistons deeper to lower the compression so you can run a tighter quench and lower octane gas. He does great work, fast turn times, at a good price.

Quench is how close the piston gets to the head. The closer the piston gets to the head, the better. I've read .040 to .060 quench is good. Personally I would try to get it around .040 to .045. When the piston gets close to the head it forces the fuel to the center of the piston and causes turbulence in the fuel/air mixture, for a better and more complete burn. You can think of it like putting shaving cream in your hands and smacking them together, if that makes sense. If your quench is too wide, some of the fuel may not burn right away causing detonation. You can a higher compression with a tighter quench on lower octane gas without detonation.

You deck the block to get a tighter quench. Milling the head will not increase quench. Your machine shop can install the crank, a piston and rod and measure how far down the piston is in the block, and then mill enough off to get the desired quench. So if you left the piston .002 in the block and your head gasket was .043, you would have .045 quench.

You will also need to take in consideration the cam you are going to run to see what the DCR is(dynamic compression ratio). This is different from the SCR(static compression ratio) and is affected but the intake valve closing...but that's another story...

[hvacman]

That really explains it well. Thank you. I will be taking the block to the machine shop next week.

Also, I planned on using the stock camshaft so I hope the ratios will be right. Everything I read says it should be fine. That along with some after market cams breaking is steering me to stay stock.

[dwg86]

Just make sure you measure all the lobes to make sure it's not worn bad. I have had several conversations with the smaller camshaft companies(Reed, Engle, Racer Brown). All have said the same thing...That they aren't having any camshaft problems. I would hope they are being honest. But each one also said the same thing about camshaft failures...the mass produced cams from the big companies could be failing because of thier grinding process, as well as the newer oil. I chose to go with a custom ground cam from Engle, but I would have used any of the smaller cam companies. I have also used Reed before.

Reasons I like the smaller companies...1) The customer service is better. Most of the time when you are talking to someone on the phone, it's the owner of the company. He probably takes pride in his work because he may have built the company from ground up and his reputation is on the line. 2) You can have a cam ground to your specific needs, not some mass produced cam that is ground to fit many needs of many people. 3) Each cam is hand ground and inspected, not just thrown into an automated machine with preset values. Well at least I know at Reed they are. I have toured their shop.

[hvacman]

So do you know of anyone that has ground their own?

In the meantime I will be searching.

[Sighman]

Hi Charlie, sounds like you're moving in the correct direction! These guys know everything there is to know about building your motor so you're in good hands. I'm glad you found the site! Let me know how it goes and if you find you need a part let me know as I might have one sitting around!

[dwg86]

So do you know of anyone that has ground their own?

In the meantime I will be searching.

I used a Reed cam in my 401(intake [email protected]/512 lift, exhuast [email protected]/.518 lift). It runs great. Thats more of a mid to top end cam. I had Engle grind me a cam for my stroker, 214 [email protected]/ .501 lift (intake and exhaust), ground on 112 lobe center, 3 degree advance ground in the cam. Engle suggested not advancing to far, just enough for cam chain stretch. Their opinion was that its a small cam built for low end torque. Advancing a cam brings the power in lower rpm's. So you aren't really helping the low end ,you are just hurting the top end...if that makes sense. I haven't got my stroker built yet, so I'm not sure how it will perform. It's similar to comanches build, so I am hoping to get similar dyno numbers.

If you start researching cam grinds, you will find different opinions about split lift/duration cams vs. straight lift/duration cams. Isky likes a stright lift/duration cam. They have a write up on thier web site about it. The crane cam(to me) seams as if the spread of the intake/exhaust duration is too wide. Its a small cam with a lot of valve overlap, that would bleed off cylinder pressure. Most applications where a small cam is used(low torque), the compression ratio is smaller. Then you through in a cam with a lot of valve overlap, you are bleeding of even more compression, affecting performance. If I where going to run a split duration cam I would keep the duration spread about 4 degrees.. But I'm not an expert on cams, I'll leave that up to the cam grinders.

[Djmack]

WOW! thanks for all this info, i have a long way from building my stroker, but im beginning to hear some struggle in my 95 4.0 at almost 228,xxx and im about ready to search the junk yards for a moderately used 4.0HO to tear down, bore and hope to achieve between a 4.7 and 4.9 stroker

BUT! i have ALOT to learn about engines, and even more that they probably dont teach you, such as building a stroker.

i will continue to search forums and read as much as possible before making my decision. and read up on as many terms as possible.