924Board.org

[Juho]

its not going to be cheaper than going turbo. but it could be done for "cheap" depends what internals u go for. And u have to add machinery costs aswell i overbore, crankbalancing, flatten surfaces.

I would personally go electronic ignition and bike carbs.

[TJC]

In my case the car I will be working with is my '80 924 Turbo as I have decided to keep it for now especially since my daughter and I have named it!
I'm presently taking steps to revive the existing engine so I may determine it's worthiness. Since this will be a long term project, (the car needs everything!), I have the time to decide what engine setup I prefer.

My thoughts concerning carburetion and a simple ignition system is factored on many things not the least of course is keeping it all fairly basic with no drama. Machining, etc. doesn't phase me as I managed a high performance/race engine machine shop back in the 80's and still have a good friend who I worked with then that is still in the business. Some nostalgia plays a role as well especially when it comes to the Webers. I first installed a pair on a brand new 2002 when I worked at a BMW dealership almost 50 years ago. I literally grew up working with those carbs, and although I've probably forgotten much I'd like to get back on that "bicycle" to see exactly how much I remember!
Oh, and I am quite fond of points and condensers too...so bloody easy to diagnose and fix!!! And cheap too!

Bottom line is that if the car sees 2K miles/year when I finish it that will be a lot!

Good luck with your project and quest to locate an engine!
_________________
'95 BMW 318i/5 ..."Pearl"
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"
'04 BMW X3..."Xander"
Still on the Prowl!

www.ttrs1.com

[MikeJinCO]

I'm starting to work out plans for a 931 head NA motor for my track car. I will try to make it a bit longer life motor rather than an all out motor. This engine will be in a track only car as it already has none of the street required amenities like lights etc(does have brake lights). General guidelines are : CR about 11or 11.5, pistons by JE from EBS, they remember doing the D prod motors. Ligntened connecting rods that I already have, lightened flywheel in stock, 45mm Weber carbs and exhaust headers.

First I'm working on finding a cam, want about 280 to 285 degrees as I don't really want to go to the all out race of 310+. From the cam we'll determine the valve springs and probably go with the light weight valve train that Gegge used of 6mm stems with Ford modular motor 5.4 seats, beehive springs and retainers with Parner lifters. That will require making valve guides and bottom spacers as the 931 heads are set up for rotators on all valves. The Weber manifold fits with some reworking due to the bolt spacing and I'll try to talk MSDS into making some headers to fit, pipes and centers of the NA header are fine again the bolt spacing is different, but I do have a .dxf file of the header flange.

I'll probably have to go to race fuel/Av gas. And it should give a motor of about 165-170hp with a redline of about 7k with a pretty long life ie 40-50 hours as a goal. I weighed the stock valve train at about 235 grams(less springs) and the lightweight one would be under 140 grams which should make a tremendous difference in performance.

That is the general plan at this time, nothing fixed in stone except the rods, flywheel, Parner buckets and carbs that are currently on my NA head in the car.
_________________
Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

[Fifty50Plus]

Just sticking turbo pistons in an NA engine will give you close to 11.5:1 compression. It then becomes an interference engine like the turbo but bends all the exhaust valves when the cam belt lets go.
_________________
1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car

[chuck21401]

Just sharing the link....wonder what the "call for price" number is

Mechanical fuel injection? Interesting.

https://www.mittelmotor.de/racing/en/4-1-motor/4-11-motorgehaeuse/68495/1-4-01005-neu-detail




_________________
1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

[gegge]

Turbopistons and NA head requires a zero overlap cam. No go for real.
_________________
Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

[MikeJinCO]

I have the 931S2 pistons in with a NA head in my race car now. There is a problem somewhere in that some of the pistons came out above the to top of the block and I had to buy a thicker head gasket to maintain .040" quench. I run a Elgin #66-15, 264 degree cam(vs stock 252). This cam has some overlap. I got it used but never installed so I have no data on it and Elgin doesn't publish much(they don't talk on the phone much either). I did have to mill valve pockets into the top of the pistons. I ran a clay on piston clearance check before milling the valve pockets and it was too close for comfort(hot valve growth) and again before final assembly and had quite adequate clearance. The valve pockets and thicker head gasket cost several tenths in CR and it calculated out to be about 10.2. It runs quite well, but has never been on a dyno, hope to get it there next month as I currently have some Weber manifold vacuum leak problems(not unusual with DCOE's).

I did not use Circle Seal rings on advice of several machinists whom had trouble with CS rings on pistons with worn lands so milled the pistons for standard NA rings. By the time I was done getting some JE pistons would have both been less expensive as well as much lighter.

As a side, this cobbled together motor was balanced and area costs for a 4 cyl locally are about $200. I looked at all the parts before assembly and there were remarkably few fresh balancing marks but that cost is almost trivial compared to the other costs. At the time I had no new rod bolts so I have a MSD ignition on it with a 6000rpm limit chip. At 6000 it is still pulling hard in 3rd gear. I'm running non-ethanol 91 octane gas. As a track only car it will sit for months at a time and the ethanol can really gum up carbs.
_________________
Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

[gegge]

Valvepockets does make sense when using the mentioned setup. My Mahle VW flattops and aftermarket BMW M5 rods accomplished the same thing and got similar CR. Also running regular gas.

My cam is hotter though. The rated duration is 276 but 251@0.05" equals an even hotter 286 combined with 14mm lift. Fair idle at 1000 rpm, not so below. The CIS is fully functional, legal and userfriendly as a DD, but I am aware of its powerlimitations.
_________________
Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

[Juho]

can u link those m5 rods? and u used 931 head?

[gegge]

Ordinary S14 and S38 rods are 144mm long, I ordered 142,5mm by mistake for my 931 enginge. Can´t remember if is was the 3,6 or 3,8 engine. Perfect match for NA and NA head though. You have to make guides for the rods inside the pistons because of the width.
_________________
Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

[Juho]

[Juho]

Good supplier for those vw flat tops in eu and do i have to buy cylinder kit?

[safe]

I got a set of flattop pistons from aapistons.com
1 x VW 87MM Type 1 Piston Set 1641cc for $67.96 each

Shipping was hefty to say the least, but overall its not that much money.
Subtotal $67,96 USD
Shipping and handling $55,40 USD
Total $123,36 USD

They will bump the compression a bit, might need to deck the block slightly to get it even better. Compression is the best bang for the buck on NA engines.
These pistons are lighter than the original:
Original 924NA: 512gram
AA: 440 gram
With our Frenchmen super light forged rods it would save kilos of reciprocating mass!! Could be a killer NA engine with proper fuel injection and timing.

[Juho]

https://www.maxpeedingrods.co.uk/product/high-performance-bmw-e30-m3-s14-4340-en24-chrome-moly-forged-h-beam-connecting-rods-conrod-with-arp-bolts-x4pcs.html?source=csslink&utm_source=shopello_fi&utm_medium=cpo&utm_campaign=google+shopping+ads&utm_term=autonosat+ja+autojen+lis%C3%A4varusteet-201&utm_content=CjwKCAjw_qb3BRAVEiwAvwq6VkvV0zF8HI3w-Ggbsfzgsme8iCr8Fndq4VIMwX_jpq31t7wr1CU-fhoCOc8QAvD_BwE%3B341%3B0


These doesent seem bad either, probaly going to get one set of these and one from frenchman

[safe]

Note that you need "spacers" to center the rods on the crank with those bmw rods.