big block question
Thread Starter
Safety Car
Joined: May 2005
Posts: 4,176
Likes: 7
From: Jennings LA
big block question
I talked to the guy who built the motor in my car it was a 1971 454 365 horse motor. he said is was a tonowanda (sp) engine. he rebuilt it and used forged flat top pistons a comp 518 lift 272 duration cam, hedman headers. he sais the heads were the semi closed port heads.
I know nothing about big blocks.what do you think my comp ratio is and any idea on HP.
I know nothing about big blocks.what do you think my comp ratio is and any idea on HP.
Burning Brakes
Joined: Sep 2005
Posts: 769
Likes: 36
From: Goose Creek SC
you need to know how far the piston is below the deck when it is at top dead center, you need to know your head gasket thickness and the chamber volume. normally you would also need the volume of the dish or the dome in the piston but you say these are flat tops so that is not an issue. keep in mind if there has been some milling done on the heads or block this will change the numbers. i would think that the guy who rebuilt your engine knows what the cr is. i cant imagine rebuilding an engine and not knowing that.
Thread Starter
Safety Car
Joined: May 2005
Posts: 4,176
Likes: 7
From: Jennings LA
Originally Posted by Mr big block
71 454 ,compression is 8.5:1
I don't think 71's came with flat top pistons .
the builder said the compresion should be 10 to 1 and it should run on 93 pump gas. he also said he built many 454's like this one and they develop 500 to 525 hp. just sounded a little high to me. are the casting numbers under the valve cover?
Team Owner
Joined: Feb 1999
Posts: 34,454
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From: Republic of Texas
For what it's woth I'm running that same 272 came in my Small Block street rod. Plenty of vacuum and pretty smooth idle, but in a Big Block with that compression you are leaving mUCH horspower on the table. The smallest I personally would go in a 454 is a 280duration. Step up the came, compression and add headers and it will be a totally different engine. 
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Thread Starter
Safety Car
Joined: May 2005
Posts: 4,176
Likes: 7
From: Jennings LA
choppy idle
Originally Posted by pauvil
the 272 does not have a choppy idle, the 282 does, I'm using the 272 on my 454 with .100" domes and 119cc heads, the torque down bottom is insane, this is just under 9:1.
mine definitly has a choppy idle, the builder was going from his memory he built for the previous owner back in 2001. he said the po did not want to change the torque convertor so he put the biggest cam he could with stock convertor. it sounds pretty nasty at idle but it had not been on the road in 12 years so I did not even get into the four barrel ( but it sure was tempting) it may be a while before it gets back on the road I am starting a major restoration.
Racer
Joined: Jul 2005
Posts: 317
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From: PA
what kind of vac does it pull at idle?? With flatops on 110cc's you could go to the 282, it won't work great but it will work, you should change the converter with the 282. When you get around 224" and higher duration@ .050 and the centerline changes, you'll losse the cylinder pressure at idle. this gives you the choppy idle. Using a stock converter I've never seen a cam with those specs, unless he was trying to push it and save a few bucks, the 272 does not have a choppy idle. MY crane is a "272" ,that's advertised duration, the lift is.520" and duration is 218 @.050" on 110 cl. It's very very smooth and I can use a stock converter, I use 700 rpm above stock just to bring it up a little into the power range.
Last edited by pauvil; Nov 28, 2005 at 09:55 AM.
Race Director
Joined: Sep 1999
Posts: 11,361
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From: Plano TX
71 454/365 had flat tops stock. Heads were 113 cc and made 8.5:1 CR. With 100 cc heads it's about 9.4:1. Don't know about the "semi-closed" heads. Stock heads were open chamber. If he put another set of heads on it your CR could be anything between 7.5:1 and 10.0:1.
Racer
Joined: Jul 2005
Posts: 317
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From: PA
I'm pretty sure the "semi closed" is 110cc. Opens would be 119cc and closed would be the 100cc. He can run the 282 cam but it will run like crap with no cylinder pressure at idle. Stick with the 272 unless your putting in domed pistons. You can do the 282 but I would definatly use a converter with this setup.