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Camshaft duration vs valve size question
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DRR Trophy
posted
I have a very limited budget to build my first engine and wondered if you can make up for smaller valves with a little longer duration. I want to run some small chambered heads on my 400 sbc, but they have 1.94 intake, 1.50 exhaust valves. Would like to build it to run e85 which is why I want the small chambers to up the compression. Let me know if I'm way off base, or if that is an ok plan for a not super powerful combo. Not looking for 800hp or anything.

Thanks! This is my first post and I'm an old dog that always loved drag racing, but never had the means until now.
 
Posts: 4 | Location: Temple, TX | Registered: August 02, 2014Reply With QuoteReport This Post
DRR Top Comp
Picture of wideopen231
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will run ok.But,there is always abut. The small valve size will be a big limit. I would think you could shop around and find some bigger valves and get heads done fairly cheap. Sanll chambers can help with compression and hurt if they shroud the valves.

Camshaft duration has to work with compression,induction flow,cars weight,gearing and transmission. Lots to take into account.If running a basically stock bottom end I would stay below 12:1 and that might be pushing it.11:1 night be even better.Keep rpm at 7000 max gear according.Go to Wallace calculator and it will help there.

If it was me. I think about selling heads if they are pure stock and especially if they are off 400. Take what you can get and put little to it and get set of after market iron heads with bigger valve and better ports.Nothing high dollar just dart iron eagle or something of that nature with say 2.02/1.60 valve.JMO but then sticking to a budget has never worked for me




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Posts: 4133 | Location: Greensboro NC | Registered: May 24, 2011Reply With QuoteReport This Post
DRR Pro
Picture of AlkyIROC
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You also need to consider air flow through the head. Bigger engines need more air flow. The OEM head is probably very restrictive. Even an inexpensive aftermarket head would be better right out of the box. Larger valves, better flow through the head, screw in studs ,thicker deck surface.

To use any aftermarket head on a 400 block, you just need to get some 400 head gaskets and drill the steam holes in the heads.

As mentioned above, small chamber may boost compression ratio but it also shrouds the valves. With the 400, they all came with dish pistons. Just switching to some flat tops will increase the compression ratio.

Unless you're building a stock replacement engine for a daily driver, there's no such thing as a budget build.


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Posts: 1347 | Location: Calgary | Registered: June 06, 2001Reply With QuoteReport This Post
DRR Trophy
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There is so much to think about and learn. I know I don't want to stay entirely stock bottom end. The small chambered heads will probably be an issue with trying to go with valves that will help it breath. I have an Edelbrock Performer EPS intake I'll be using, and looking for a 800cfm Holley, but might go wit have 750 do. I really want around an 11:1 or a hair over because I want to go E85 with it. Building it woth the idea that it can still be street driven, but not going to be often.already going to have to get the e85 conversion for the Holley, or find one that is already set up for it. Kind of thinking it may be better to start simple and rebuild it later for more power, but is that worth it? Looking at Linati VooDoo Hydraulic flat tappet, 489 intake, 504 exhaust lift, 227 intake 233 exhaust duration at 50. Might bump it up one more size if the larger engine would benefit and still be kinda streetable. Around 2,800 stall on a th400. Any suggestions which way to go on heads with that kind of setup? Also, maybe for now, max compression for 93 octane pump gas? Might hold off on the visions of grandeur E85 plans.
 
Posts: 4 | Location: Temple, TX | Registered: August 02, 2014Reply With QuoteReport This Post
DRR Sportsman
Picture of SST386
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To much duration will bleed cylinder pressure (compression). If using the small valve heads it will run better with the correct cam.
 
Posts: 361 | Location: KENTUCKY | Registered: May 15, 2006Reply With QuoteReport This Post
DRR Trophy
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What would be a correct cam for smaller valves, and I'm talking 1.94 intake 1.50 exhaust, on a 400 sbc?
 
Posts: 4 | Location: Temple, TX | Registered: August 02, 2014Reply With QuoteReport This Post
DRR Trophy
Picture of Dead On
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Randy your getting lots of great advice here, but asking people about what cam with what valves is a little vague. your best bet is to call the pros like bullet cams comp cams etc. Have all the info you can gather about your engine and build specs they will tell you the best cam for your engine specifics.
 
Posts: 73 | Location: Texas | Registered: March 18, 2015Reply With QuoteReport This Post



DRR Trophy
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I will try calling them. I don't have enough experience to know everything everyone is telling me about so I thought someone saying I need the right cam might mean they know what that is. I do understand that there is a bit of personally experience and preference for those decisions too. For example the Wallace Calculator page is very cool, but on spec'ing a cam out, it ask for CR as one of the fields. I don't know what it's wanting. I'll try asking the pros. Just looking for real world help, but I'll leave you guys alone until I learn better what I'm trying to do and will be able to contribute more than bug. Thanks everyone for all the help! I think I need to rethink my direction anyway. Maybe I should get the car ready to handle more power first thing (subframe connectors, etc.)
 
Posts: 4 | Location: Temple, TX | Registered: August 02, 2014Reply With QuoteReport This Post
DRR Top Comp
Picture of wideopen231
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CR compression ratio.Most cam manufacture will be asking same thing. Nothing wrong with asking its how you learn all this crap that some of here have been doing forever and that can be long time.LOL

You will need to know what kind of cam you want also. Hydraulic= zero maintenance. Not as consistent.Also cheaper.
Solid= will have to adjust valves every now and then.Little more cost.More consistent which is king in brackets.

Roller cam= True race cam.Lot more cost.More maintenance. Very consistent and allows changing cams latter w/o having to buy lifters

I would say hydraulic or solid for you deal' I would keep it around 235 degree at .050 lift or about 280 degrees advertised duration. Basically a stout street cam.

Biggest thing is it has to work with everything in car.Transmission(guessing 3 spd auto TH400) converters stall if not changing you might want to stay smaller than above numbers. Rear end gear ratio. 3.73 to 4.10 depending on which is main target track or street. Don't get stupid big tires a 9" or maybe 10" slick will be more than enough if you go slicks route.

Go to local track and see what others with similar ride are doing and if it works well. Lof cheaper to buy correct piece first time out than buy multiple pieces to see which will work. Bigger is not always better either.




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Posts: 4133 | Location: Greensboro NC | Registered: May 24, 2011Reply With QuoteReport This Post
DRR Sportsman
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Don't know what car you have or what your plans are. If just getting started keep it simple. My first braket car was a 1977 camaro all steel except hood. Was a street/strip car. Got it down to 11.8x on gas. Engine was a 400sbc with early 70s 186casting# heads. It used cast flat top pistons a hyd ft cam, lunati 00012, Victor jr intake 750 holley 1 3/4x3 in headders. 4.10 gears in the factory 10 volt 9x28 mt slicks with a th350 shift kit and 3500 converter. Was a lot of fun. Still have the car not the drive train. Need to fix it up again. Was way cheaper than current s/p s/st vega.
 
Posts: 479 | Location: Going to or returning from the chipmine. | Registered: July 01, 2011Reply With QuoteReport This Post
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