Why Destroke an Engine? - Ford Muscle Forums : Ford Muscle Cars Tech Forum
FordMuscleForums.com is the premier Ford Forum on the internet. Registered Users do not see the above ads.
Reply
 
LinkBack Thread Tools
Old 01-05-2005, 01:59 PM   #1 (permalink)
Subscriber
 
Join Date: Aug 2001
Posts: 2,908
Why Destroke an Engine?

I know why people stroke engines, and even why they choose not to. But why in the world does someone want to destroke an engine? I see this mentioned in articles about race cars quite a bit. Is it just to comply with cubic inches rules, or is there a mechanical benefit to it?
HankyJ is offline   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 01-05-2005, 02:17 PM   #2 (permalink)
Registered User
 
Join Date: Oct 2004
Location: Wichita, KS
Posts: 862
Why Destroke an Engine?

From what I understand it allows for higher revving capabilities.
gork1rogues is offline   Reply With Quote Quick reply to this message
Old 01-05-2005, 03:08 PM   #3 (permalink)
Registered User
 
Join Date: Jun 2002
Posts: 1,776
Why Destroke an Engine?

one reason is to meet class rules, another is to gain a better rod/stroke ratio, with attendant advantages and disadvantages. a third reason is to prevent and engine that is built right at class displacement allowances from growing to break the displacement rules. most engines will grow an inch to an inch and a half in displacement when they get hot, so you reduce the stroke a bit, usually a couple of tenths, so that when the engine grows, it meets class requirements.
__________________
64 falcon
66 mustang
82 fairmont
a mans fate is a mans fate
and life is but an illusion
rbohm is offline   Reply With Quote Quick reply to this message
Old 01-05-2005, 03:59 PM   #4 (permalink)
Subscriber
 
Join Date: Aug 2001
Posts: 2,908
Why Destroke an Engine?

Very interesting. Does the different rod ratio allow for higher revving as well?
HankyJ is offline   Reply With Quote Quick reply to this message
Old 01-05-2005, 04:21 PM   #5 (permalink)
Registered User
 
Join Date: Jun 2002
Posts: 4,520
Why Destroke an Engine?

What about valve size to piston surface area? given the same bore, but a shorter stroke; it seems logical that you would get better cylinder filling with a shorter stroked engine vs. one with the same bore and a longer stroke.

The concept goes a long way to explaine what an engine like the 289/302 is so very close to the same horsepower of much larger engines. Obviously the longer stoke engine will reach its horsepower and torque peak earlier. Butthat isn't the point. Strictly speaking of horsepower, a smaller engine, built right, should have a higher horsepower potential (cubic inch to cubic in) given the same valve sizes/restrictions.

Better breathing equals better volumetric efficency. This is a case were...given limits on head design, valve sizes. number of valves...smaller might not only be more efficent...it could actually be better.

Any one remeber the 350 Olds engines of the 60's and 70's? They were street terrors, more so than the larger 400-455.
__________________
" ... It is dangerous to be right in matters on which the established authorities are wrong. ..." - Voltaire
Beoweolf is offline   Reply With Quote Quick reply to this message
Old 01-05-2005, 04:31 PM   #6 (permalink)
Registered User
 
Join Date: Jan 2001
Posts: 739
Why Destroke an Engine?

I'm no expert, but I am under the impression that the circle track guys dealing with say 358ci limits might have different bore/stroke combos for different tracks. Shorter stroke/bigger bore is more of a top end combo with the opposite combo being better for a torque (shorter) track.
Also, talked with a machinist/engine builder who put together a de-stroked motor for a land speed record holder dealing with a ci limit. He did a long-rod combo and destroked the motor to make a peaky, top-end motor. I don't recall the displacement goal, but it was small for a domestic V8, so he destroked an sbc...
__________________

\'69 SCJMach 1,\'65 Fastback 422W project
R Code is offline   Reply With Quote Quick reply to this message
Old 01-05-2005, 04:41 PM   #7 (permalink)
Registered User
 
Join Date: Apr 2001
Location: Central West Virginia
Posts: 7,046
Why Destroke an Engine?

Especially back in the old days, the cylinder heads were the main restriction when it came to making horsepower.

Most stock heads did well to properly feed small engines... let alone larger ones. Larger engines would be 'wheezing out' by the time they hit very many rpms.

If you needed more top end than low end... which was the case for most with the crappy tires and suspensions of the day, you could de-stroke an engine and trade off some of that unneeded low end grunt for top end horsepower!

I top-end raced a 421ci small block Camaro on the interstate once (no bottle). We were close at first, but his big inch motor started to wheeze out of cylinder head around 130mph... and I was able to walk right past him. He was pissed and confused, and his friends made fun of him.

I don't do that stuff anymore.
__________________

66 Mustang, Toploader 4-speed
Pump Gas 306, 10.134@134.71
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220
n2omike is offline   Reply With Quote Quick reply to this message
Old 01-05-2005, 05:09 PM   #8 (permalink)
Subscriber
 
Join Date: Aug 2001
Posts: 2,908
Why Destroke an Engine?

Okay, it's starting to make sense. It's why I only see destroked race engines and not street destrokers. Is that what they'd call it, "a destroker"? If not, they should.

Mike, I'm glad you embarassed that Camaro guy in front of his friends. It's our job.
HankyJ is offline   Reply With Quote Quick reply to this message
Old 01-05-2005, 07:40 PM   #9 (permalink)
Registered User
 
Join Date: Oct 2001
Location: Central Indiana
Posts: 1,745
Why Destroke an Engine?

A use to do a lot of dirt drag racing. It was 4x4s on a 300ft dirt track. Otherwise it was just like racing on asfalt. We did bracket racing and class racing. Many guys would have 2 engines. A big bracket motor and a small class motor. The classes were based on a weight per cubic inch ratio so the smaller engines had the advantage. Many guys ran 283, 302 and 327 chevies. The ford guys ran 289 and 302 fords. Some were more exotic "destrokers" like 351 Clevelands destroked to just over 300. Some Chevies were destrokers 350s and 400s with 283 and 302 cranks. It was and still is rare to see a big engine in a class being competitive.

In a weight/cubic inch race the smaller engines don't really make more power than big engines. The advantage is in the fact that they can carry less weight.
__________________
Grabber Green \'70 Mach I 351C 4V 12.32 at 111mph 1.63 60ft. time
Robin Egg Blue \'79 Fairmont 408C 4V 10.50 at 127mph 1.38 60ft. time
clevelandstyle is offline   Reply With Quote Quick reply to this message
Old 01-05-2005, 09:32 PM   #10 (permalink)
Registered User
 
Join Date: Jun 2001
Location: 35.753983 N, 91.634603 W
Posts: 5,551
Why Destroke an Engine?

Built a 353 SBC once with a 400 bore and 327 crank with main spacers. Been a while back and I don't remember all the details, but the guy that ran it loved it. Great little engine, too bad the GM cranks are total junk..even the "steel" cranks. I bet most don't know that a 429 Ford is basically a "destroker" 460. Same block, bore, rods...pistons are a bit different and the stroke is shorter. Same with several other makes of engines. 400 Mopar is basically a .020" over 440 with the short stroke of a 383. Weird how Chrysler thought that the 400 should have a larger bore than the 440?!

There was an article written in National Dragster a while back dealing with extreme RPM of the Pro Stock classes. 10,000 RPM is now the norm where it was once un-heard of not too many years ago. Advantage of higher RPM is that you can run more rear gear which gives you greater mechanical advantage, which gets the car moving quicker....not necessarily faster, but quicker. Quicker=better ET.

[ This Message was edited by: mavman on 1/6/05 9:34am ]

[ This Message was edited by: mavman on 1/6/05 9:35am ]
mavman is offline   Reply With Quote Quick reply to this message
Old 01-06-2005, 10:16 AM   #11 (permalink)
Registered User
 
Join Date: Jun 2002
Posts: 1,776
Why Destroke an Engine?

with its favorable rod/stroke ratio, the 289 breaths very well despite the restrictive ports in the head. it isnt so much the shorter stroke, but the better r/s ratio that helps the breathing. one good example of this is bob gliddens pro stock engines from the 70's. he used modified 351c 4v closed chamber heads that would feed much larger race engines very nicely. considering the fact that the ford competition in the same class also used similar heads, and head mods, why was glidden so successful with his combination? he overbored his blocks .080 over(yes they were highly modified to allow this), and destroked his engines to 3.25" giving him a much more favorable r/s ratio to his competitors. so even when you have heads that not just breath but hyperventilate, r/s ratios are important.
__________________
64 falcon
66 mustang
82 fairmont
a mans fate is a mans fate
and life is but an illusion
rbohm is offline   Reply With Quote Quick reply to this message
Old 01-06-2005, 01:58 PM   #12 (permalink)
Registered User
 
Join Date: Nov 2001
Posts: 1,470
Why Destroke an Engine?

Shorter stroke and larger bore is the reason Mopar has been so successful in drag racing. The larger bore allows the use of larger valves and better unshrouded chambers along with a good rod/stroke ratio. The vernerable 340 mopar is a good example of the benefits from over boring and destroking.
__________________
1966 Mustang Coupe, Glass hood, 331 stroker, solid roller, Twisted Wedge, Stealth, 750 DP, 3.50, 4spd. \"borderline 11\"
bluestreek is offline   Reply With Quote Quick reply to this message
Old 01-06-2005, 05:07 PM   #13 (permalink)
Registered User
 
Join Date: Jun 2002
Posts: 3,633
Why Destroke an Engine?

One point I didn't see mentioned was with a longer rod the piston dwells longer at tdc.
FoMoCo is offline   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Ford Muscle Forums : Ford Muscle Cars Tech Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -7. The time now is 09:21 AM.



Powered by vBulletin® Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Friendly URLs by vBSEO 3.6.0
 

Garage Plus vBulletin Plugins by Drive Thru Online, Inc.