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After_Thought
Joined: 08 Oct 2019 Posts: 44 Location: Hudson ohio
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GregSC
Joined: 19 Jul 2008 Posts: 122 Location: Lovely, KY
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Posted: Mon Jul 27, 2020 11:08 pm Post subject: |
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Pm sent your way! _________________ 1981 931 |
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MikeJinCO
Joined: 08 Jun 2010 Posts: 1227 Location: Maysville, Colorado
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Posted: Mon Jul 27, 2020 11:52 pm Post subject: |
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Modifying these motors can get quite interesting, complicated and expensive, with not necessarily very cost effective results. If someone has a complete motor I'd seriously consider going that way.
The '77 motor is vastly different than later versions. It has 38mm intake valves that were changed to 40mm in the 77.5 version and stayed that way throughout. They also changed the cam and CR from 8.0 to 8.5 for the 77.5.
If you could get a complete newer motor then stick that Newman cam in it, it would make a real difference. I have a 264 degree Elgin cam in my track car and it helps quite a bit. The European cams are made with new blanks so are not undersize and you don't(shouldn't) have to fiddle too much with valve clearances.
I think the very poorly designed and made stock cast iron exhaust manifold contributes a lot to the motor breathing problems(ports in head awful also), grinding it out to match the exhaust and the head can help. A note on the exhaust manifold, check it for cracks as the later ones had more cooling fins. I have a '77 manifold that I improved, then found a small heat crack in it. _________________ Mike
'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild) |
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924RACR
Joined: 29 Jul 2001 Posts: 8794 Location: Royal Oak, MI, USA
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Posted: Tue Jul 28, 2020 12:35 am Post subject: |
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So first of all, no worries about milling the head affecting your compression. That doesn't happen on these motors; none of the combustion chamber is in the head, so it won't get smaller.
Decking the block will raise your compression ratio. It will also change your cam timing slightly.
Yes, the '77 has basically very low compression. The more you can add, the better, more power. Hard to overshoot and ruin it if you run good gas, keep reasonable timing, don't run it lean or overheat. Make sure your cooling system is pristine and up to snuff. 9:1 would be a happy place, or even 9.5:1, though you may need to be looking at premium gas at that point, 91 or 93 or so. Really depends on how much timing you run, and how hot you run.
Cam will be a big step-up too, those early cams are weak, even the late cams aren't amazing. _________________ Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype |
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anthonimartini
Joined: 17 Feb 2020 Posts: 240 Location: portland oregon
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Posted: Sat Aug 01, 2020 3:23 pm Post subject: |
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i build engines for a living. mostly vintage porsche stuff, 911's and whatnot. i gotta say this last 924 engine i built for myself was kinda a nightmare. pistons are not available unless you get custom ones made. so if your bores are good you can just hone/re ring them. if you need overbore you may get lucky and find a set scouring the world or if you have around 1500 bucks you can get custom ones made to whatever specs you need. i got lucky and found a good shortblock that didnt need oversize pistons. _________________ ive saved alot of 924's
current:
79 MochaSchwartz 931
83 944
87 924S
Instagram @anthoni.jpeg
formerly known as turbellion, lost password. |
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safe
Joined: 18 Mar 2017 Posts: 583 Location: Sweden
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Posted: Thu Aug 06, 2020 12:25 am Post subject: |
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anthonimartini wrote: | so if your bores are good you can just hone/re ring them. |
Assuming the ring grooves are in spec, which they probably aren't unless its a low mileage car.... which dosen't need a rebuild to begin with... |
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