Neil, thank you for sharing the data but it is difficult for me to tell how relevant that 2.7 flow data is for my current build because I don't know the specs of what was tested and the comparative size of the manifolds. On my engine the magnesium stocks and TBs were significantly modified by Eurometrix for more flow. Specifically, they opened a set of the older 70-71 magnesium stacks to 46mm at the top which is about 4mm greater than a stock 73rs. Then the manifolds were tapered to the 38mm intake port.
The difference in a manifold between a stock MFI, CIS, or carbs for an S, E, T, or RS sub model can be significant. What might be interesting is what would the manifold on a 46 ITB or a 46 Weber Carb flow? Maybe that would be a closer comparison, but I agree that testing mine at some point would be ideal or maybe Eurometrix or Aaron might know the incremental flow value from these modifications above a stock RS since they have done this work quite frequently over many years.
However, to illustrate a situation where a stock manifold can yield close to 300HP, my previous stock 73RS engine that was modified 20 years ago did make such power. It had a few important modifications that made a big difference. While the manifold and the heads were not opened up, the second dyno chart on this thread shows that it was already generating 277 BHP even while running quite rough with poor AFRs.
Where did the other 67 HP come from above a stock RS? It had Elgin RSR sprint cams (instead of an S cam), it was twin plugged, and had high compression 2.8 Mahle RSR pistons/cylinders (about 11 to 1 instead of the lower 8.5 to 1 stock rs compression), aluminum flywheel, rsr injection pump, etc. Although my first engine was originally running quite rough it did seem to rev up much further and faster at the high rpms than my current engine and did generate about 17 more HP than this build (i.e., 277HP) in a similar untuned state. After the injection pump was fixed though, my old engine made 300hp and got better gas mileage, too.
As many know, a stock 73 RS engine was rated at 210 BHP from the factory and ran on normal 87 pump gas, but many say that HP was understated, so a stock 73 rs probably makes the power you indicate above. But then if one adds twin plug, more aggressive cams, head work, higher compression, a modified injection pump, the engine can generate a lot more power. If the power isn't coming from flow due to high valve lift, could the power be coming from higher flow velocity and longer cam duration? My previous engine also had a smaller SSI exhaust than what I'm using now (European headers that are about 1/8" wider). I don't know the answer to why the previous engine generated such high power with less performance modifications, but it did.
For this current engine, the stacks were opened to 46mm which is between what a 73 RS had (I think 42mm) and what a 73RSR had (50mm). It doesn’t seem that engine is reaching it's full potential yet based on my past experience and I don't think it's related to the ports being too small but perhaps I'm losing flow somewhere else along the line in the engine. The combination of everything just does not seem to be working together yet to generate the expected power.
Similar to the last build, this engine's AFR readings are also rich at the lower end and lean at the higher end. The oil also has strong smell of gas and it has been difficult to start when cold. When I pulled the plugs they don't look black, which surprised me due to the rich AFRs at part throttle and lower rpms. Here's are pictures of one of the plugs. What do you think? I did check that my throttle bodies are opening all the way, so I do have WOT. Thanks for your help. Keep it coming!!
