Engine Rebuild Questions

[87944S]

Guys, new here and about to undertake a motor rebuild project on my 87 944S to correct for a worn thrust bearing. Figure I’ll follow through on my usual strategy that repairs are a good excuse to improve or clean up those “while you’re in there” things too. Car is in overall excellent shape except for the motor, so I figure it’s worth the time and effort.

Anyway, I’ve got a bunch of questions so I thought I’d throw some of them out there to see what you guys think. Since I track the car at DE events (90% of it’s future use) I’d like to try to get some more power out of it without going broke, but most everything I read tells me there is not much room for improvement on the 2.5L without spending $$$$$. I’d like to see if I could get 200-210HP with some carefully chosen improvements.

So here is what I was thinking I’d do, and I’d like to get some opinions as to the value of some of it.

Head – Stock rebuild with multi angle valve job, cam chain and tensioner. What is the performance gain by porting and polishing the intake and exhaust ports? Is there a benefit doing one but not the other? Is anybody making performance cams for these motors? Anyone have any experience with them? Any real value in what I think I saw as a “wide fire ring” head gasket vs. OEM?

Block – Clean up, lightly hone cylinders to get seating surface for new rings, replace all seals/bearings for balance shafts, oil cooler. Etc. Water pump all belts, etc. Anything I'm missing with the block?

Crankshaft – Repair whatever damage the thrust bearing wear has caused. Cross drill, micro polish, new bearings. I read about “knife-edging”. Can someone tell me what it is and what power gains can be had? Looks like it grinds the counterweights to reduce and reshape the mass, but I could not find any real info on it. Any power gain to be had? Assume it only makes sense with a lightened flywheel too? Anyone have any experience with crankshaft coatings (said to help shed oil and improve power)? Bearings – Glyco vs. OEM. Any recommendations?

Pistons and Rods – Plan to clean, check and reuse original, replace rings and pins, replace bolts. Anyone have experience with thermal coatings on the skirts? Any real power gain to be had? Balancing the piston/rod assembly add any real power gain?

Oil Pan – Install baffle and reinforce pickup. Anyone install a crank scraper? Any power gain to be had?

I’ve also seen a lot of discussion on removal of the AC using an AC delete bracket. Assume a decent weight loss helps performance. Any big issues with this? Looks easy enough.

Anyone install the light weight Odyssey (PC380? I think) battery? Looks like some decent weight reduction to be had, but I’m wondering about how well it will crank over in cold or hot weather those early season and mid summer track days.

Appreciate any recommendations or input form your own experiences. Thanks!

[porsche4life]

Not ever done a rebuild but you do want the wide fire HG. It withstands more pressure.

[flash968]

you can easily get silly on an engine - i regularly spend $15k building a track engine

but, you don't have to do everything

if it were me, and i absolutely had to stay with the same block, i'd bore it out, line the block and use normal pistons - going from a 2.5 to a 2.7 would give you about 12hp all by itself, and a bunch of torque

then, i'd bump up the compression to about 11:1

bigger throttle body for sure

then maybe some nice mid-range cams

always always always balance the engine

might need a header

a decent tune at the dyno

this should net you about 200hp - i know i've gotten that much out of one of these on a "streetable" engine

might be a lot cheaper though to grab an S2 3.0 or a 968 engine though, and give you a lot more power right out of the box - i think a guy here is selling one

weight reduction will give you improvements you can feel though - dump the seats for lightweight ones, and replace the rear hatch glass with lexan for the biggest changes

[HondaDustR]

Knife edging reduces rotating mass and reduces windage in the crankcase. A light flywheel will reduce rotating mass as well. Both combined may be difficult to drive around town, but should quicken the response a bit both accelerating and decelerating the motor for matching shifts. It doesn't create power so much as frees up a little to go to the wheels instead of being spent spinning up a few pounds of metal thousands of rpm. I've heard alot of lightenning makes it necessary to blip the throttle on upshifts to match revs since the motor spins down so quickly.

I would do a crank scraper since it also helps control oil mist in the crankcase and they're relatively cheap. I wish I saw how cheap they were before I rebuilt mine.

A good balancing job should make the bottom end last longer and free up a hp or two lost to vibrations. I''d say it would be especially important for a 16v since they like high revs more than the 8v.

Bumping the CR to 11:1 probably won't do much since the motor is already at 10.9:1, but you could probably do something to take it to 11.5 or 12:1 and gain some power. That combined with boring out would net a healthy increase.

As far as porting and polishing, I'm thinking it will only make a noticable difference if you've got someone who really knows what they're doing to get it right. Polish is kind of misleading, as it has been found that shiny ports actually flow less. A good clean brushed finish (rough sandpaper or whatever) works the best is all I know. You can't just gouge them bigger, since you must preserve the correct shape to maintain port velocity, plus figuring out what variation of that shape would work best for those particular ports for good flow and scavanging as well. It would be much more important if you are looking to make more power spinning higher revs. I did some light porting work on my head involving smoothing out the casting lines and other mess left over from mass production, cut back a little bit of material from around the valve guide area in the intake ports, put a smooth brushed finish with 150 grit sandpaper, and port matched the intake to the head. Don't know just how much it helped other that the motor really hauls some butt compared to the somewhat tired 150K mi motor it replaced, especially considering it is still mostly bone stock.

[flash968]

my bad - i was looking at the US spec 944 which is 9.5 - the "S" is 10.9, so i agree about 11.5:1 - if you use the bump from 9.5 to 10.6 as a gauge, you gain 20hp there, so you would probably gain about 10 going from 10.9 to 11.5

[87944S]

HondaDustR, I been following your thread on your rebuild. Excellent write up, very helpful. Andy Flash, you definitely right in that I don't want to spend $15K on the rebuild! But it can get pretty crazy.

I did think about just upgrading to the 3.0L S2 or Vario Cam 968 motor, just for the additional power. I'd probably go with the 968 even through getting the electrical harness and controls for the cam timing worked out look to be the biggest challenges. Then again finding one that does not need some or most of the work I'll do to my own motor is another challenge, but at least your working with 245HP right up front. I've seen two 944/968 motor conversions, both ran very well.

Good input guys and it will definitely help me lay out a game plan.

One thing that surprised me as I started to look around at what's available was the lack of performance cams. This seems like it might be an easy way to gain some HP. Maybe old school thinking.

I'll probably wind up balancing the pistons, rods and crank, do a small amount of lightening, windage and scraper and start to look at a chip upgrade too.

More to come .

[Techno Duck]

The Glyco and OEM bearings are visually identical (same markings), the Glyco's being less than half the cost. If you look around on Rennlist you will see the comparison pictures.

I would go with a windage tray. I think any gains from a scraper or windage tray are minimal at best but you will probably increase the life of your rod bearings, especially on a car that sees track use. That paired with the pan baffle and i think short of a dry sump there is not much more improvement that can be done. Also consider crossdrilling the #2 and #3 oil ports on the crank.

I would do a lightened crank or flywheel, not both. The car will be a nightmare to drive.. my friend had a B16 EG hatch he ended up selling because the car was a nightmare to drive after his rebuild which included a knife edged crank, lightened flywheel and lightweight pressure plate. That sucker rev'ed to 10k all day long.. if you could get it rolling forward without stalling it!

A/C delete will drop a little more than 30lbs with the added benefit of removing the A/C condenser which will improve airflow to your radiator.

Ive had a Odyssey PC680 (i think thats what you meant) that is going on 3+ years now and have never had problems. Ive used it in both my 8v n/a and now my 951. The car saw routine use in north east winters running 15w50 oil when i needed to move the car or use it.. never had problems starting. Also has gone through many 100+ degree days at the track and auto-x starting up constantly. As long as your not running a crazy stereo in the car it will do fine. Forgot the exact amount of weight saved, but it was over 20lbs, high up on the car also.

[EBS_Don]

Your'e going in the right direction but you need to work with someone who knows these blocks and how to work with them. You cannot "hone" them in the traditional sense. You simply cannot use a ball or stone type hone in these types of cylinders. Also if you do decide to go with an aftermarket higher compression piston, such as a JE, they will need to have a proper coating applied to piston skirts to keep them from galling the cylinder walls. If you want to go larger on the bore size there are limitations based on the cylinder wall thickness especailly with an open deck design.

You should look at cams for a decent power gain as well as some intake tricks.

Don

[87944S]

Jon,

Yep, hearing the message loud and clear on over lightening the crank and plan to stay away from that. Reminds me a bit of the S2000 I drove a while back. Planning to cross-drill, polish and add a baffle, probably the windage tray as well.

Saw the pics of the OEM and Glyco bearings and they do look the same. Cost is a factor, but the OEM could be cheap insurance if they were known to last longer. I did see on a different site stepping up to a "performance" rebuild will add the OEM rod bearings, but use the Glyco mains. So maybe that will be my guide.

You got the Odyssey battery right. Glad to hear it worked well for you. I like the weight savings but didn't want to give up reliability. Sounds like the way to go.

Thanks.

[87944S]

Don,

I saw a some minimal info on the PCA Tech Forum about a special process needed in order to not remove the silicon and ensure ring life. HondaRDuster had an interesting process posted here on another thread that looked to be getting some good feedback. I'll have to look into it a little more before pulling the trigger.

I was thinking of staying with the stock pistons and rods and not getting too custom. I had read some interesting write ups on thermal coatings reducing friction and adding life to the pistons and it seemed pretty low cost by comparison to some other mods. I was thinking that cams could yield a reasonable performance gain without needing to beef up the rods. Problem is, I can't find anyone making them for the 16V motors, but I'm still hunting.

Thanks.