NeoRules

So besides the oil lubrication problem on #2 pistons connecting rod what other limitations are built into the 2.5 NA engine.
Obviously there are stronger 4 cylinder engines in production today but what really prevents this engine from being modded and turned into a real powerhouse????

What I gathered from the search is
1. #2 oiling problem

2. lack of a deck plate so at high rpms the cylinders can walk and tear up the headgasket.

3. the NA rods are weaker than the Turbo models?? (this I don't understand is the crank different??)..

4. Piston squirters are needed to cool the pistons from the bottom side if any real power is produced.

5. windage tray or crank scraper arrangement to keep the oil down in the pan so the sump can get to it.

6. Oil pump screen is a little two "rounded" and bennefits from a ring welded around it to keep it from sucking air around the edges...

7. Timing Belt is either way to long or is just poorly designed and doesn't tolerate high rpm well...

8. obviously depending on year the pistons are too high a compression to install any power adders to the NA.

Are any of these things "wrong"? What major drawbacks to the 2.5L design did I forget....
I see stories of Turbo models running up to 340 Rwhp...
As well I have read stories of Honda VTECH engines putting out 700 BHP..
Is the engine just too fragile?
4 Cyl ford turbo coup engines regularly put out 300+ hp with good survival rates...

Just a topic to consolidate all the flaws of the NA ......

9. AFM vs maf?

The tranny being made of gingerbread?

JC.

P.S. what does the engine actually weigh??

Cass944

you make a good point about some hondas making a LOT more power than a heavily modded 951... my guess is that those hondas only make it about 50 miles on each engine. you want a 951 to last a while so its just a safety and durability issue more than a engine strength issue. Im sure you could make a 951 have 700 hp as well but it wouldn't last very long and require a lot of work. but so do those little imports with lots of power out there. but those kids are all nuts and dont care about spending all theyre lifes savings on having a "sweet" ride.

xsboost90

cranks in turbo/n/a are same- high compression isnt a bad thing- if you could raise compression and still clear the large 8v valves, you would have a fast engine- which is why the faster n/a engines are 16v- more valve clearance w/ smaller valves- later blocks had a half deck to keep the pistons from walking- timing belt does fine at high rpms, but close tolerances make them dangerous if they stretch, esp. since they are so skinny.

Porschefile

Simply put, the 8v head. The 8v head sucks period. Efficient heads and combustion chambers are the main reason why you see such small displacement Hondas making tons of power. Take the F20c for example (s2k motor). At 2l it makes 240hp! True it makes a heck of alot less torque then a 968, but still that is impressive hp. I've seen built 2.2 and 2.3l s2k race motors making 300-340whp n/a! Look at the Honda K20 and K24 engines from RSX's and a few other Hondas. In stock form I've seen a K20 head flow ~290cfm on the intake! The only way you'll ever see significant hp with the 8v head is to convert to a 16v head or by using forced induction and beating the head to submission with lots of boost!

ljibis

[QUOTE=NeoRules]So besides the oil lubrication problem on #2 pistons connecting rod what other limitations are built into the 2.5 NA engine.
Obviously there are stronger 4 cylinder engines in production today but what really prevents this engine from being modded and turned into a real powerhouse????

What I gathered from the search is
1. #2 oiling problem

2. lack of a deck plate so at high rpms the cylinders can walk and tear up the headgasket.
The NA has a cast crank while the Turbo has a forged crank. Not sure about the rods, though. For a serious performance engine you'd surely replace the factory rods with a set of aftermarket ones. Pauter and Carillo both make excellent rods for the 944/951.

Doesn't the Turbo have this feature? There are people making big power in 951s without it if not. A lot can be done on the charge side to optimize combustion temps.

Yeah, lots of problems with the pump pick-up. It's also quite weak in certain spots and is prone to breaking in cars that are driven hard on the track. Some of my racing friends recommended having mine welded to strengthen it in several places when I was building my engine. Mine's not a track car, though, so I didn't bother.

The N/A engine is pretty well optimized. You can tell that, interally, it is a very high-quality piece. The compression can be bumped up from stock on the earlier cars to gain a bit of power, but aside from increasing displacement or going to a 16-valve head there isn't much that can be done to an 8V that will get you big power gains.

You have to admit, though, that they did pretty well by going up to 3.0L with 16 valves in the S2, and then adding the variable intake on the 968. 8-valve cars breathe about as good as they can right from the box (which is not great)...all you can do is slightly optimize the compression, intake, and exhaust. You have to love an early N/A for what it is....it's a nimble car with great torque that loves to be driven hard, but it's no drag racer.

Lindsey Racing builds 951 engines that allegedly put out 400-500 hp very reliably. Having talked with them during my rebuild project I believe them. It will probably cost more than a Honda, but nothing good ever comes for free.

Legoland951

The turbo and n/a have identical cranks with same part number. I believe the turbo S is the only one with a different part number for all year all 944 2.5L engines. The bottom end of the engine is not the problem as the blocks are interchangeable for all 85.5+ 2.5L turbo or n/a. The stock bottom end is known to handle 500hp.

Early n/a rods are forged and I believe later cars (maybe even the turbo) have the inferior cast rods though the rods are the the part that fails.

The moving mass of the valve train, especially the lifters (more than twice heavier than a chevy 350CI engine) and weak valve springs will cause valve float at Honda RPMs.

Due to the small number of cars we have, there are not much performance parts since they won't sell much. Also, the budget of a typical 944 n/a owner is barely able to keep their car running in good condition.

Its alot cheaper to go faster for less money with a 944 turbo than a n/a so most people won't spend more money to go slower by starting with a n/a. A lot is determined by economical factors and its why I believe cost effectiveness is the main reason why there are not many high HP n/a 944s around. We all know with enough money, you can make anything fast. My friend who builds 2700 hp drag car once said, if you give me $100k, I can make your n/a put out more than 500hp though in the end, not many parts will remain Porsche in the engine.

bnewport

How big of a problem is the #2 piston oiling? I'm building a spec 944 (sp1) right now and am hoping for some low cost HPDE with that car. Am I about to be disappointed?

xsboost90

put the lindsey racing oil pan baffle in there- crossdrill the crank and keep it topped off on oil and youll be fine- really just keep it topped off and youll be fine but i think the LR baffle is well worth it.

Mongo

When I rebuilt my motor, I cross-drilled my crankshaft to help maintain lubrication in upper RPMs.

hacker-pschorr

It's funny how the 928 engine and 944 have the same limitations. Except with 928's the #2 & #6 bearing is the problem.

So far there has yet to be a documented 928 with a rod bearing failure while using an Accusump. Dry sumping will solve this as well.

Another old school trick to prevent rod bearing failure is rod side clearance. One particular 928 engine builder is experimenting with this as we speak.

PORobinSCHE

okay, now that we've discussed the limitations of building horsepower. what can be done to moderately increase the output of a n/a engine?
for me it's not cost-effective to try and buy a 944 turbo, so i'd like to get a lil more oomph!
nothing radical needed, merely, a bit stronger mid-range!

thanks

Robin

NeoRules

So you can put a 16V head on any 2.5 block? Hmmm...
Gets you about 30 hp or so?

Clint's 944

Have you checked on the prices for a complete 16v head?

NeoRules

yeah.. I can understand that... I just was so used to higher revving that when I first got my early 85 running I kept checking the tach just after it went off scale... I guess they don't have a rev limiter from the factory... I was shifting by sound alone (duh)...
I was so panicked that the timing belt would let go or a rod would shoot out the bottom.....
haven't driven it much since (trying to get the body ready for paint) But I will watch the tach from now on....
I promise...
Kinda...
most of the time...
I think....

NeoRules

Nope... haven't even thought about it.... why is it cheaper to buy the whole engine?