I've seen a lot of conversation on the forums about the right cam, carbs, etc., for flatheads. I recently built a 49 Merc for my T-bucket, and dyno'd it before and after the build. It struck me that it could be useful to post the specs, dyno results, and overall impressions of the engine here. The car was built in the early '70s, and is pretty close to its original configuration. 49 Merc flathead, 64 Fairlane toploader 4-speed, and original Halibrand quick-change rear end. When I got it, the engine was stock under a set of Offenhauser 375 heads and an Offenhauser 3x2 setup with the end carbs blocked. Considerable blowby. On the ch***is dyno, it showed 175 ftlbs at 1600 rpm, and 80 hp at 3200. This translates to about 210 ftlbs and 97 hp at the flywheel (The measurements were taken in 3rd gear and through the quick-change. I figured 18% powertrain losses and used a factor of 1.2 to estimate flywheel figures). We bored the motor 1/8" for a 3 5/16" bore and a displacement of 276 ci. The final configuration: Literio L100 cam. Reground by Cam Techniques in Sarasota. .375 gross lift, 270 intake/260 exhaust. Isky 185G valve springs. Flathead Jack 1.5" undercut SS valves. Offenhauser 3x2 progressive setup with Holley 94 carbs rebuilt by Charlie Price of Vintage Speed. Bolted them on; no rejetting required. Did NOT port or relieve the block. Offenhauser 400 heads. I think the CR is about 8.8:1 but Joe Abbin's book disputes that. My number is based on cc'ing the heads. I run premium fuel. MSD distributor. 23 degrees total advance. Egge 3-ring pistons. On the same ch***is dyno some time later, we saw 235 ftlbs at 2600, and 144 hp at about 4000 on the ground. This translates to 282 ftlbs and 173 hp at the flywheel. The dyno sheet should be attached to this message. The interesting thing is that this a brute torque motor. I told the dyno operator to roll into full throttle, as I did not want to backfire through the Holleys, and he did around 1500 or so. The engine took full throttle nicely and actually has been a very tractable engine, with a lovely rolling idle. We took it close to 5000 on one run, just to see if it would, but there's not much point to it, as power is falling off above 4500. I would think full-performance shift points would be around 42-4400, but it's really not necessary. The T-bucket weighs around 1800 pounds, so it's pretty sporty on the street... Let me know if you have questions or need more information. Suffice to say that I am delighted with the end result. It is a pretty street flathead, runs like a scalded dog with the Holleys wailing away up front, and has none of the tractability or peakiness problems I was concerned about before I bult it.
Thank you for this post and the copy of the dyno sheet. It's so nice to see actual results. In case you missed it, here is a link to Blown 49's post that has a detailed compression ratio chart that may confirm your ratio: http://www.jalopyjournal.com/forum/showthread.php?t=482189
You're welcome. I thought some real data might be useful, as much of the information out there is either hearsay or opinion. Joe Abbin's new book is good, as he finally got a dyno and is getting some excellent horsepower out of the flatties. I appreciate the chart, but I have found that the quoted chamber volumes are incorrect, at least for Offenhause heads. Some of the posts I have read criticize Offenhauser heads for poor QC and varying chamber volumes. When I cc'd the Offy 400 heads on this engine, I found volumes varying from 62 to 66 ccs. The nominal value is 54 ccs, so these heads are more like Offy 425s with much more variation than I would like; the compression ratio is all over the place. If it was a compe***ion engine, it might be worth the while to machine the heads for a precise, consistent volume (also port and relieve it) for a bit more power, or see if I could find better heads. As it stands, it is a nice street engine and works well as it is.
I just found this thread Very cool! Thanks alot. I also found that a lot of the Chamber volumes are different from the charts. Michael
Yeah what Mickey said...I found my Offy 400 heads to be all over the place chamber cc wise as cast. Very interesting !! Ever run the car at the track? Rat
The flatty I built is nearly the same. I used Offy .425's, a copy of an Isky 400 Jr, and three 97's on progressive. It would start, idle, go like stink, stay cool, what more can you ask? the car was about 2200 pounds, I could open the throttle from the start all the way and the motor did not stumble, it ****ed air and went. Was it a high HP motor? No. Flatheads and high HP is an oxymron. Fun? Oh yeah!
Nice setup you got going there! Nothing like a strong running Flathead with a nice lopiness! Also thanks for sharing- especially from a perspective like my own as I am planning a Flatty build and researching on getting the right combo for what I'M really looking for! Thanks again! HC.
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