Quote:
Originally Posted by Cliff R
"so far everytime i have tried spacers on a rpm the engine responded very very well (both 400 and 455), open spacers has worked great for me."
Some engines hate it when one side of a dual plane intake sees too much of the other. I've had to make dividers for my RPM intakes than I can count for that reason. Cutting them down will show a nice power increase upper mid-range and top end, but it may induce a "stumble" going from idle to full throttle that is difficult to tune out because lots of these engines woln't have superior power to weight or pretty tight converters in them.
I'd also add here that at the 500hp mark the RPM brings NOTHING to the table over a stock intake and just barely more power than an factory reproduction HO unit.
I did that testing a while back on a 440cid engine (428) we built here. KRE heads prepared here, Comp 236/242 HR (XFI lobes) cam, Ross pistons, Oliver rods, 10.6 to 1 compression. With my stock intake (sorry folks it's modified a little) it made 497hp/540tq. Installed the RPM with no other changes and it dropped to 491hp, Installed the HO intake and it dropped to 487hp.
When you read that think about how many folks run out and buy RPM intakes to replace stock ones on mild 350 and 400 engines. Then they have to put a drop base air cleaner in place to get the hood closed and loose another 20-30hp!.......FWIW......
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I have done tons of track testing with spacers on our 400 in our 73 Ventura, open spacers are worth a tenth (slightly more actually). Every car presents it's own issues, people need to test and modify as they see fit. Based on my experience (track and dyno) the rpm really likes spacers.