Rod length? Piston speed? - Page 2

04-17-2008, 02:19 PM

The longer the rod, doesn't the piston stay at TDC longer, therefore slowing piston speed down? Why do a lot engine builders say that long rods won't work for a short stroke engine? I've been curious about this for awhile. Thanks

Scott Tilley
IHRA
SS/PDA2

crazyponcho · 04-17-2008, 04:21 PM

I think that a lot of the short stroke engines run a low deck block thus negating some some of the benefits of a long rod since you can only run so short of a compression height. But I did freshen an engine not to long ago that had a three inch stroke and 6.2 in rods in a standard block that was at the top of its class, made for some real light pistons.But there is just as many opinions as there are engine builders.

NovaMan · 04-27-2008, 02:04 AM

You are both correct: a longer rod makes for a slightly lower piston speed.

Let's look at a 454BBC at 6500rpm. With the stock 6.135" rod, the peak piston speed is 7162.2 ft/min. If you go to a 6.385" rod, the piston slows slightly to 7135.4 ft/min. If you cram a 6.535" rod in there, you'll get the peak piston speed down to 7140.5 ft/min. That's less than a 1% difference.

04-17-2008, 02:19 PM	#1
Tilley2007 Guest Posts: n/a	Re: Rod length? Piston speed? The longer the rod, doesn't the piston stay at TDC longer, therefore slowing piston speed down? Why do a lot engine builders say that long rods won't work for a short stroke engine? I've been curious about this for awhile. Thanks Scott Tilley IHRA SS/PDA2

04-17-2008, 04:21 PM	#2
crazyponcho Junior Member Join Date: Mar 2008 Posts: 9 Likes: 0 Liked 0 Times in 0 Posts	Re: Rod length? Piston speed? I think that a lot of the short stroke engines run a low deck block thus negating some some of the benefits of a long rod since you can only run so short of a compression height. But I did freshen an engine not to long ago that had a three inch stroke and 6.2 in rods in a standard block that was at the top of its class, made for some real light pistons.But there is just as many opinions as there are engine builders.

04-27-2008, 02:04 AM	#3
NovaMan Member Join Date: Sep 2004 Location: Kalamazoo, MI Posts: 117 Likes: 0 Liked 0 Times in 0 Posts	Re: Rod length? Piston speed? You are both correct: a longer rod makes for a slightly lower piston speed. Let's look at a 454BBC at 6500rpm. With the stock 6.135" rod, the peak piston speed is 7162.2 ft/min. If you go to a 6.385" rod, the piston slows slightly to 7135.4 ft/min. If you cram a 6.535" rod in there, you'll get the peak piston speed down to 7140.5 ft/min. That's less than a 1% difference. __________________ ~Pete 1970 Nova