Hi all,
I'm planning an N/A M20 stroker and would really value advice from the M20 gurus here. I have quite a bit of engine building experience, but I'm new to the M20 and its quirks, so I'd rather learn from people who know these engines well.
The build so far:
• 85 mm bore (unless you'd recommend otherwise)
• M54B30 crank, 89.6 mm stroke
• OEM BMW 135 mm rods
• Custom forged pistons (4032 preferably)
• 885 head, to be ported.
• 325i intake manifold (port matched to the head)
The car: E28 that already runs a SETA 2.7 with 885 head built by Bimmerheads and their 274 cam, all other 325i parts, Motronic 1.3. Getrag 260 + Z3 3.46 torsen diff. And it's not a daily driver - 1000 miles a year at best.
The goal: I want the engine to keep pulling all the way to the limiter, and I'm fine giving up some low end to get there.
Questions:
1. Block. I'm buying a core engine tomorrow and have two options: a 1987 ETA with 885 head(manual), or a 325i(auto) engine of unknown year. From what I've found, the 325i block deck height is 206.7 mm, and the ETA is either 206.2 or 206.7 mm. Which block would you choose for this build? My thoughts are - a low-revving ETA engine could have a head in better shape, but 325i with auto could be less abused and more parts can be used from it.
2. CR. BimmerHeads advised against going over 10:1, but I see plenty of builds at 10.5 or even 11:1. I'll most likely run 91 octane (California). What would you target?
3. Pistons. How much better is a OEM domed/dished crown shaped to the chamber than a flat top? From my research, JE offers the shaped crown and CP and MM(Wiseco) does flat tops. Please correct me if that's wrong. Also, when ordering custom pistons, where should they sit relative to the deck at TDC: slightly below, slightly above, or flush?
4. Head. I've talked to BimmerHeads about porting. 600$ sounds reasonable. Who else should I consider? 5150 cnc porting costs 1500$ plus shipping which is a bit too much for me but if this is essential I might do it.
5. Camshaft. This is where I get lost. Which cam would you pick for a top-end bias with a smooth, linear power curve? I understand static CR is one thing and dynamic CR depends heavily on the cam, so the cam and the CR have to be chosen together. I'm fine with a slightly lumpy idle, but I don't want a full blown hot rod cam. Any combos you've had good results with?
6. Valves. Do I need oversized valves, or is a good multi-angle valve job enough at this level?
7. Valve springs. Are the stock 325i dual springs good enough, or should I go to single springs as Metric Mechanic recommends - their explanation looks very reasonable.
8. Exhaust. Are headers worth it, or do the stock manifolds flow enough? Right now I have 325i manifolds into a dual pipe with a resonator and a muffler.
9. Engine management. Can stock Motronic 1.3 with a tuned chip handle this setup, or do I need a standalone? I've seen plug-and-play options that use the factory harness and add a wideband, knock sensor and maf. What are people using, and is it worth it?
10. Power. Can I touch 200whp with it or what's your estimate?
One more note: ITBs are a bit outside my budget for now. As I understand it, they add roughly $2,500–3,000 to the build.
To thank you for your help, I'll document the whole build here with photos and post dyno results when it's done.
Thanks in advance!
I'm planning an N/A M20 stroker and would really value advice from the M20 gurus here. I have quite a bit of engine building experience, but I'm new to the M20 and its quirks, so I'd rather learn from people who know these engines well.
The build so far:
• 85 mm bore (unless you'd recommend otherwise)
• M54B30 crank, 89.6 mm stroke
• OEM BMW 135 mm rods
• Custom forged pistons (4032 preferably)
• 885 head, to be ported.
• 325i intake manifold (port matched to the head)
The car: E28 that already runs a SETA 2.7 with 885 head built by Bimmerheads and their 274 cam, all other 325i parts, Motronic 1.3. Getrag 260 + Z3 3.46 torsen diff. And it's not a daily driver - 1000 miles a year at best.
The goal: I want the engine to keep pulling all the way to the limiter, and I'm fine giving up some low end to get there.
Questions:
1. Block. I'm buying a core engine tomorrow and have two options: a 1987 ETA with 885 head(manual), or a 325i(auto) engine of unknown year. From what I've found, the 325i block deck height is 206.7 mm, and the ETA is either 206.2 or 206.7 mm. Which block would you choose for this build? My thoughts are - a low-revving ETA engine could have a head in better shape, but 325i with auto could be less abused and more parts can be used from it.
2. CR. BimmerHeads advised against going over 10:1, but I see plenty of builds at 10.5 or even 11:1. I'll most likely run 91 octane (California). What would you target?
3. Pistons. How much better is a OEM domed/dished crown shaped to the chamber than a flat top? From my research, JE offers the shaped crown and CP and MM(Wiseco) does flat tops. Please correct me if that's wrong. Also, when ordering custom pistons, where should they sit relative to the deck at TDC: slightly below, slightly above, or flush?
4. Head. I've talked to BimmerHeads about porting. 600$ sounds reasonable. Who else should I consider? 5150 cnc porting costs 1500$ plus shipping which is a bit too much for me but if this is essential I might do it.
5. Camshaft. This is where I get lost. Which cam would you pick for a top-end bias with a smooth, linear power curve? I understand static CR is one thing and dynamic CR depends heavily on the cam, so the cam and the CR have to be chosen together. I'm fine with a slightly lumpy idle, but I don't want a full blown hot rod cam. Any combos you've had good results with?
6. Valves. Do I need oversized valves, or is a good multi-angle valve job enough at this level?
7. Valve springs. Are the stock 325i dual springs good enough, or should I go to single springs as Metric Mechanic recommends - their explanation looks very reasonable.
8. Exhaust. Are headers worth it, or do the stock manifolds flow enough? Right now I have 325i manifolds into a dual pipe with a resonator and a muffler.
9. Engine management. Can stock Motronic 1.3 with a tuned chip handle this setup, or do I need a standalone? I've seen plug-and-play options that use the factory harness and add a wideband, knock sensor and maf. What are people using, and is it worth it?
10. Power. Can I touch 200whp with it or what's your estimate?
One more note: ITBs are a bit outside my budget for now. As I understand it, they add roughly $2,500–3,000 to the build.
To thank you for your help, I'll document the whole build here with photos and post dyno results when it's done.
Thanks in advance!