When Premium Fuel is not an Issue

[lcolina]

Dear Friends, I have had a 4.6 stroker for 5 years. Planning to build a second stroker as my current one is in the EoL.

I am not an engine specialist so I am kind of lost in something.

I remember the recipe when using 4.2L connecting rods and now I found the new recipe using 4.0 con rods and forged piston that allow using these rods.

As I have read in the forum, there are 2 main reasons, pinging when low octane is used and angle of the rods will be more reliable when 4.0 rods is used.

In my country (Venezuela) gas price is not a problem so we can run 95 octane anytime.

But even using 95 Octane I have experienced some pinging in my old stroker and had to build a map adjuster. The gas here is cheap but also mechanics always comment is not good quality

Based on said before, my questions are:

Is it worth for 95 octane to use 4.0 con rods and spending that money in the special forged pistons?

Any help highly appreciated.

Is it worth also to spend that money in forged pistons?

Is it worth also to mill the block so I can have a decent CR? or should I stay with the old recipe. I know nothing about CR and deck and so on.

I have a CJ7 but with EFI from a 92 YJ, with 99+ intake, 12 lb crankshaft, 0630 head that will be polished

I am asking this because I am about to buy everything in US to import it to my country.

[Cheromaniac]

You're better off going for Bulltear custom pistons from the outset together with your original 4.0L rods.
By the time you add up the cost of 4.2L rods, hypereutectic pistons, and decking the block, you won't be any better off anyway.
BTW, the 95 octane fuel you have is the RON rating which is the same as 91 US octane.

[lcolina]

Dino,

I really appreciate your help. I have been a reader of your site and comments for years.

Good to know about the octane in my country. That would explain some things around here.

Definitely will go with 4.0 conn rods and custom pistons as you recommend as I want to avoid decking the block, and so on.

Thanks and keep safe,

Leo.

[SilverXJ]

I would definitely go with the 4.0L rods and custom pistons if you can swing them. With custom pistions you can set the dish at what you need for the compression ratio you seek. Also in your previous stroker, it doesn't sound like you have a compression issue with the gas if you were able to tune it out with a mpa adjuster. Your afr may have just been wrong for that load. What was the AFR when it was pining?

[Torqsplit]

I generally prefer long-rod setups wherever possible. I know many here enjoy great success with builds using the 4.2 rods, I just think the the 4.0 rods offer an advantage(theoretical or realized) on our engines when they fit the constraints of your budget. Given the 'rule-o-thumb' minimum rod:stroke ratio of 1.50:1 commonly used for a street engine, the 4.2 rod length has you right on limit. 4.2= 1.508:1
*the standard 258 has a relatively small bore size for engines with this rod ratio=plenty safe for a low-rpm 6cyl*
4.0= 1.572:1 *Using the 3.895 stroker crank*
I'd wager our engines live safely with these ratios due to lower peak rpm's and smaller bore sizes than comparable V-8's.

This offers some great insight on the topic in general, even tho its not directly related to these engines:
http://www.fordmuscle.com/archives/2003 ... index2.php

[lcolina]

SilverXJ,

When pinging the AFR gauge is not always showing the same number. Sometimes it is 12, 13, 14 but sometimes it is more than 16 so I can not tell if it is running lean or the opposite.

When I installed an FPR from hesco and M-9593-AA302 mustang 24 injectors engine started to run a lot better. MAP adjuster was on 5.8V and I set it to 5.2V. Pinging was reduced a lot, but sometimes it does it again, always in highway in 4th or 5th gear!!!!! Never pings uphill at lower gear (2nd) even at WOT.


I know my CR must sucks because I did not solved the deck issue with this stroker when using 4.2 conn rods. (Newbie mistake 5 years ago).

Anyway, I am planning to do this stroke right, and definitely going with custom pistons and long rods.

[lcolina]

Torqsplit, very nice article. Definitely long rod is worth the investment in custom pistons to increase engine life.

What CR would you recommend for my CJ7? It is not a DD, 80% offroad use, but Here in Venezuela I have to drive onroad between 200 and 800 miles to go to good offroad places.

[Torqsplit]

Icolina, there are far too many variables involved with this for me to be comfortable making any recommendations for you. I wouldn't want to steer you wrong.
A quick search here for "87 octane" produced many threads on this very topic with a lot of good info. Give it a try and spend some time reading. Mostly you just need to gain some knowledge of what areas are important to this and weigh them against the environments you expect to operate your CJ in and how it will be tuned. Fuel availability while far from civilization is a good thing to be aware of. Having an engine that demands at least 91RON could get you in trouble if higher quality fuels aren't available near your off-roading destinations (I have to keep a bottle of octane-boost with me now when i venture out to keep my 10:1 monster happy and ping-free if I have to run regular).
Otherwise, read up on Dynamic Compression Ratio's and see what has worked for others here before you spend your $$.
Good Luck!