Joe, to our disappointment, we could not start any test pulls below 2500 RPM. WE tried at 1000 RPM and then 1500, but still the water brake would stall the engine at RPM's lower than 2500. Unfortunately, with engines that dont make that much power and torque down low, thats going to be difficult to test at lower engine speeds than that. Even though we peaked at 330 Ft.lbs. at 4500 RPM on some of our tests, the torque below 2500 RPM wasn't sufficient to prevent to brake from stalling the engine. Your small 6 engines might have the same issues as well. Im not sure what the threshold is for torque and power needed to sustain lower RPM pulls, maybe it is different with each dyno brand possibly, I think we used a DynoJet. As for torque, it was never below 300 ft.lbs. even at 2500 RPM, except for the very first test, which was a completely stock engine with a Offy intake and 4 bbl. carb and headers. We made just over 120 dyno pulls total in the 2-1/2 weeks we tested.Lazy JW":2z37ssv2 said:
HEAD PORTING & DYNO TESTING
- Thread starter waldo786
- Start date
Bummer.CNC-Dude":2w9fpw67 said:
Trouble is, most of us typically do not drive our vehicles in the same manner as the engines get tested on a dyno.
I still believe that mild pocket porting is beneficial on an otherwise stock daily driver, even though the results don't show up on WOT dyno pulls.
I have no real evidence to back up my statement, but my opinion is that it helps improve the QUALITY of air flow at part throttle operation with the end result being we can make the same cruise power at slightly lower throttle openings. Again, I have no proof, but that's my story and I'm stickin' to it! It is certainly no more harmful than running roller rockers on a daily driver
Joe
Yeah it was a bummer. We wanted to see how the Offy intake and Clifford intake compared in that RPM range. The Clifford yielded more peak HP than the Offy overall, but the Offy is best rated for the RPM below what we could test at, and thats what we wanted to see more than anything between the two,the off idle to about 2000 RPM comparison.
There could also be something to the lower RPM gain to bowl porting as well. But even in most magazines when they are dyno testing, they also usually start at an RPM above the normal cruise RPM range where we need to see those type of gains. We did however expect to see some sort of either gain or loss with that head swap we did on the stock engine, since it did have some many other bells and whistles compared to the stock head we had just tested. We were probably more shocked to see that it was the same as a stock head. I think the main drawback was the stock cam. It only opens the valves so much, and bowl porting and the lumps really dont increase the low lift flow #'s by any significant amount, especially using the same size valves on both heads, until you get to the .400 to .600 lift range. And since the valves don't open that far to begin with, the additional flow was never tapped into to be any benefit. I think what the engine saw was there was no real change made, and therefore no gain was seen. But when we changed to our first performance cam we instantly saw a big jump in both power and torque. Im sure if we had used larger valves in the lump ported head with the stock cam, we would have had a more dramatic change in the low lift flow #'s, and might have seen a gain moreso from that than the other things that were done to the head.
There could also be something to the lower RPM gain to bowl porting as well. But even in most magazines when they are dyno testing, they also usually start at an RPM above the normal cruise RPM range where we need to see those type of gains. We did however expect to see some sort of either gain or loss with that head swap we did on the stock engine, since it did have some many other bells and whistles compared to the stock head we had just tested. We were probably more shocked to see that it was the same as a stock head. I think the main drawback was the stock cam. It only opens the valves so much, and bowl porting and the lumps really dont increase the low lift flow #'s by any significant amount, especially using the same size valves on both heads, until you get to the .400 to .600 lift range. And since the valves don't open that far to begin with, the additional flow was never tapped into to be any benefit. I think what the engine saw was there was no real change made, and therefore no gain was seen. But when we changed to our first performance cam we instantly saw a big jump in both power and torque. Im sure if we had used larger valves in the lump ported head with the stock cam, we would have had a more dramatic change in the low lift flow #'s, and might have seen a gain moreso from that than the other things that were done to the head.
mugsy":1w93fkzo said:
8) mugsy, the amount of casting flash inside the ports and manifold will have an effect depending on how far into the airstream it extends. anything beyond .030" is going to affect airflow in a negative manner. also remember that the sharp turn at each port is going to affect both airflow and power. if those could be rounded off even a little to remove the sharp transition, it will be a help especially in keeping fuel in suspension, thus giving a more even fuel mixture cylinder to cylinder.
mike, you might want to test two different intake valve sizes over stock, a 1.75 and a 1.88. that assumes you have the time and money to do so.
CNC-Dude":1sesw5jx said:
Yup. That stock 292 probably makes peak torque at something like 1500 rpm and peak torque is where I "think" the benefit of mild porting will show up; by the time it gets to peak hp it has run plumb out of cam so the porting doesn't appear to benefit.
Sure do wish I'd been born a little richer instead of so good lookin"
Joe
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