Let talk 2.5L motors

[13204u]

Let me start off by saying I picked up my 84 SVO for $500 as a salvage title car, not running from a local tow yard. Car was more or less complete not running. There had been a slow oil leak coming from underneath the car but I wasn't really concerned considering the price. I finally got to looking where the leak had been coming from under the car yesterday evening. Turns out the pan is punctured from the interior out so more than likely the bottom end came apart on my car and is totally gone. I figure that is why the previous owner finally gave up on the vehicle as the body was more or less straight. Anyways, if I am going to be putting a new bottom end in this car or a whole top to bottom engine assembly I might as well just go with a 2.5l. Assuming the block isn't chowed, is this just a matter of new rods, custom pistons, and a 2.5 crank, or is there more involved? I also have a spare long block assembly that needs a rebuild but does not have the issues this may have.

[MikeFleming]

... is this just a matter of new rods, custom pistons, and a 2.5 crank, ... That pretty much covers it.

What are your power& RPM desires, budget and engine building capabilities? Got good local machine shops that are experienced with the Ford 2.3/2.5 OHC?

If you stay with the stock 2.3 turbo block (large main journal) you will need main inserts to fit the 2.5L crank (small journal). Rod journals are the same.

If you stay with a stock compression height piston, you will need shorter rods (not recommended). Otherwise you will need stock (not recommended) or longer rods with a shorter piston.v It's more better - and easier to assemble/disassemble) to have full-floating pistons and pins but that requires a non-stock rod (since you're already going with custom pistons).

There are a few of us here that have moseyed down the 2.5L path and recently gyrhead went with a small journal crank/block configuration.

You need to get that engine out and do a tear down and inspection to know where to go from here. And start saving some $$.

[13204u]

Honestly at this point I am looking for a good streetable combo. The car is dead stock at this point, which makes me think it was heavily abused and never maintained in order for it to come apart like it did since these motors tend to be pretty bullet proof. I had picked prior to this revelation a stinger 3" full length single exhaust, was planning on picking up a boport 1.5 cam, running a manual boost controller to about 20psi , a large NPR which I have my possession. I also have a new walbro 255 in tank pump, rebuilt 35lb brown top injectors, a kirban FPR, and a LA2 series ecu. I also planned to have the head rebuilt to stock specs and have the E6 manifold I have ported. Basically I want a really fun but reliable street car. 300RWHP or slightly more is the goal. The reason I bring this up is because if I am going to rebuild the motor I might as well do it right and gain some more base horsepower and torque from the get go.

[MikeFleming]

If you're only looking for 300HP, you do not need to go to a 2.5. But you will still need some head work, good intake, exhaust and fuel to match. Personally I'd go straight to MAF and 52# injectors and completely bypass the 36 Lbers - but that will require learning a QH and the MAF code tuning methods.

Which adds a bit of scope creep in the tuning area versus doing lots more mechanical stuff to the engine.

[13204u]

Well at this point I am kinda stuck at rebuilding the motor anyways so I figure I might as well go for the gold. What are my options on rods in terms of manufacturers? Also what else am I looking at in terms of head work?

[Stinger]

While I agree with Mike that building a 2.5L is far from "necessary" and not often "worth it" from a time/money vs power gains standpoint, it's your car and you can do as you wish. Certainly if you've already got to replace the crank, rods, and pistons, it makes it a more affordable option (since the price difference is minimal compared to replacing perfectly good 2.3L parts with the 2.5L version).

The most common (and affordable) quality rods are Crower Sportmans. They can be purchased in all the common lengths and pin diameters for $430 or so.

As for head work, I've not found many stock heads that have exhaust seats that are still sealing. Once the exhaust seats wear out and are re-cut, they typically cut through the factory hardening which means they won't last long at all unless hardened seats are installed. It's also common to find a cracked head on these engines. Fortunately in many cases, the cracks are removed when the hardened seats are installed, killing two birds with one stone.

[13204u]

Fair enough. You have highlighted the main issue, that I HAVE to build a new bottom end at this point so I don't have the option of just running the stock bottom end. As far as head work is concerned I already planned on going through that as well. Is it worth it for me to send it out and have port work done while it is down or for my power goal is that necessary?

[MikeFleming]

In either case - to reach your goal of 300WHP+, you will need a head that can flow at least 360HP IHP of airflow. And either a slightly mod'd 2.3 or 2.5 can do that but the head will still need to be capable of that much airflow.

Head & block machining are probably the longest lead times. You need to decide on crank/rod/piston configuration and have the pistons in hand to do the block bores. And have decided what ring package to use to define the bore finish. And use a shop that has - or borrow/rent - a head torque plate for boring and honing of the block.

I recommend a thin moly-coated top ring (normal gap type), a medium second plain iron scraper and a chrome 3-piece PC-style oil control ring set. Naturally they need to fit the pistons.

Most important on an engine that has fragged: CLEAN EVERYTHING AT LEAST FIVE TIMES. Especially after any machining. Remove (and replace) all the oil galley plugs and run brushes in ALL the oil passages.

And *replace* the oil cooler.

[Meotchh]

And *replace* the oil cooler.

Which will also require you to replace the oil cooler o-ring (and not with an oil filter gasket). I might know where you can pick them up without paying the NOS $30 price that some vendors try to charge...

[MikeFleming]

^
Shameless plug from Meotchh!

[13204u]

^
Shameless plug from Meotchh!

Out of curiosity what is the general cost on building a ground up 2.5 vs a 2.3l?

[MikeFleming]

The 2.5 will always cost more as you need custom pistons at the minimum since there were never any factory forged turbo pistons for the 2.5 engines. And most people use longer rods (than the 2.5 engine used) so that adds more cost to the build for custom rods.

But if you're doing custom rods and pistons anyway for either, about the same then.

[13204u]

Well even if I rebuild a stock block, I was going to put in good rods and pistons regardless. So now I am kinda at a cross roads in terms of what I want to do.

[MikeFleming]

Go 2.5.

The 2.5 will eat more air - especially in the mid-RPM range. So, in theory, that should help with the bottom end power. Now it all comes down to rod/stroke ratios and compression ratios.

I went with a 5.5" Crower rod, short piston, floating pin, a 0.030" overbore and a static CR of 8.5:1. I also used a lightened 2.5L crank from Race Engineering. And studed/straped mains. And painted it all red.