Carpokes Porsche Forum

Perhaps if MM is feeling generous he can provide some details for Henk's motor that he built. Was pretty trick and had more power than this one iirc.

For those not familiar with the Accusump, here is a video from Jessie Prather, an SCCA racer with years of experience and championships in MGA and now Miata engines.
I would agree that once your engine gulps some air, its too late for the bearings, but the video is interesting regarding the usage of an Accusump.

Motosport wrote: Fri May 05, 2023 3:10 pm Fantastic thread and a very interesting topic..

Seeing how a 2.5 944 engine can make 318 HP with an increase in capacity and some careful engine work, I would be very curious to know what Michael's approach would be with a 968 engine? What would be some beneficial upgrades and engine work (within reason) to get a 968 engine up to the same power figure in NA form, if possible?

I would imagine that many of the experiences from a 944 engine upgrade could also apply to the 3 liter engines, and perhaps Michael has some ideas of the most worthwhile upgrades for trackday/fast street purpose?

Thanks, Alex

Here's one example. There are others with fewer mods and fewer HP. If there's interest I can probably come up with links, or answer specific questions.
https://rennlist.com/forums/924-931-944 ... ngine.html#

Here's more, and perhaps more directly answers the question about most worthwhile...
Interesting question. I had to think a bit. No dramatic changes, just some simpler and cheaper ways to get there:

I'd have Mile High Cranks or Marine Crankshaft Inc. offset grind for an even larger stroke. (Note: There may be other specialists that can do a good job with this.) 95mm is possible depending on the condition of the crank and skill of the machinist. A little shorter stroke is fine, but the bigger is usually better. Compromise: Use a stock 3L stroke.

I'd use Molnar Mitsubishi 4G63 rods. His rods are very attractively priced and his quality is excellent. I often used a longer rod, but never did any back to back tests. Some of the Honda rods are longer, but I haven't looked at their other dimensions. Talk to Molnar about the B18 or K24 rods which are longer. Compromise: Use a 951 rod with stock stroke (with Rod Mod).

I'd use a custom JE piston. I can help with specs to accommodate any stroke, valve size and compression. Compromise: Stock pistons will work, but ring seal will be marginal because the pistons are worn out.

The valve sizes I used are great. Compromise: The 968 39mm intake valves and the standard Porsche 33mm exhaust valve may be a reasonable cost saving without giving up a lot of power.

PROPER head porting is very helpful. (Few can do it, though, and you can hurt power easily.) Compromise: Leave the head alone, but a GOOD valve job is needed. Go to a race oriented machine shop.

1.875" (1 7/8") header from Karl at Racer's Edge. Compromise: Stock headers. The cheap 944 headers will hurt power.

I'd use ITB's if someone were to make a nice setup. I made some years ago, but the interest wasn't there. The injection would require a capable ECU and a capable tuner, and the latter is the biggest challenge. Compromise: The stock intake will do in a pinch, particularly with an enlarged throttle (maxbore.com) or a Ford TB. I wouldn't necessarily avoid carbs since they work well and don't require an ECU. Weber DCO-55's get maxed out with airflow but make good power (365fwhp on a stock stroke 3.1L.)

I wouldn't worry about oiling as long as a race type H bearing is used from Clevite or ACL. 7500rpm now and then would be okay with proper valve springs and cylinder head setup. Compromise: H bearing "Rod Mod" on Porsche rods.

333pg333 wrote: Fri May 05, 2023 8:37 pm Perhaps if MM is feeling generous he can provide some details for Henk's motor that he built. Was pretty trick and had more power than this one iirc.

More reaching into the 'wayback machine', but most of the info is in this thread. Also happy to answer any questions that may come up:
https://rennlist.com/forums/924-931-944 ... 400hp.html

https://shaftech.com/

You also mentioned Shaftech in past conversations for crank work.

I assume it’s still another good option????

gruhsy wrote: Mon May 08, 2023 6:38 am https://shaftech.com/

You also mentioned Shaftech in past conversations for crank work.

I assume it’s still another good option????

Oh yes! Shaftech in Ohio is great for any crankshaft service or modification. I should have included them.

Michael:

I have a spare 968 motor, a head that you rebuilt and put some special touches on (ported, larger valves etc), and your split cams (though I may just go with Cat Cams to keep things simple). I plan on having MaxBore enlarge the TB and buying the headers from Karl at RE. I live in Massachusetts but am willing to drive down to Behe to have him tune the stock DME.

My goal is to for a reliable, peppy, free revving street motor that can do a few track days.

Any suggestions would be appreciated!

cp99 wrote: Fri May 19, 2023 9:55 am Michael:

I have a spare 968 motor, a head that you rebuilt and put some special touches on (ported, larger valves etc), and your split cams (though I may just go with Cat Cams to keep things simple). I plan on having MaxBore enlarge the TB and buying the headers from Karl at RE. I live in Massachusetts but am willing to drive down to Behe to have him tune the stock DME.

My goal is to for a reliable, peppy, free revving street motor that can do a few track days.

Any suggestions would be appreciated!

You don't mention the condition of the lower end. Have you rebuilt it? Have you installed the ACL Race rod bearings (4B2475H)? A sound lower end is surely important for longevity and performance. Yes, the tune is critical, and your camshaft choice will allow the cylinder head mods to provide max benefit. Have fun!

michaelmount123 wrote: Fri May 19, 2023 10:42 am

cp99 wrote: Fri May 19, 2023 9:55 am Michael:

I have a spare 968 motor, a head that you rebuilt and put some special touches on (ported, larger valves etc), and your split cams (though I may just go with Cat Cams to keep things simple). I plan on having MaxBore enlarge the TB and buying the headers from Karl at RE. I live in Massachusetts but am willing to drive down to Behe to have him tune the stock DME.

My goal is to for a reliable, peppy, free revving street motor that can do a few track days.

Any suggestions would be appreciated!

You don't mention the condition of the lower end. Have you rebuilt it? Have you installed the ACL Race rod bearings (4B2475H)? A sound lower end is surely important for longevity and performance. Yes, the tune is critical, and your camshaft choice will allow the cylinder head mods to provide max benefit. Have fun!

Good point - the motor has 140k miles and I plan to change out the rod bearings for ACL units, at the very least. The bores look fine with no scoring.

OTOH, I can go all out and get the crank offset ground, new rods and pistons, etc per your posts above…. but what do you estimate the cost to be and do you feel the benefit is worth it? The good thing is I have the original motor in the car right now and get to enjoy driving the car while making these decisions.

I won't get into cost estimates since it may be parts only, or may need to include labor. Your 140K mile 968 engine is tired, and even with good looking bores piston/ring wear is compromising good seal. Can (should) you move ahead with it? Ideally, no. Can (should) you freshen the bores and install new pistons? Ideally, yes. If it were mine and I had adequate funds, I'd at a minimum have Millennium Nikasil the bores and install a fresh set of pistons and rings. Now you're looking at 300fwhp with the proper cam. That's a significant increase in power. You'll also be confident to have created a long-lived engine. I can help with piston specs if you like.