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Big Cam x Low Compression Ratio #83875 07/04/08 08:14 AM 07/04/08 08:14 AM
Joined: Aug 2005 Posts: 637 Sao Paulo, Brazil dart_73_br OP mopar
dart_73_br OP mopar Joined: Aug 2005 Posts: 637 Sao Paulo, Brazil	Hi guys, I had a problem during the building of my 318 project so I had to finish the engine build up with the cast pistons and rings. The problem is that my engine is mounted with a big cam and low compression ratio. What should happen with this setup ? Cast heads with 2.02/1.6 valves EFI Megasquirted Single Plane Torker 2 modified for EFI 7.5 CR 240/246 @.050 .507 .510 cam lobe 110� overlap 70� So... how it�s going to work guys ? I�d like to achieve at least 9.5~10 CR but it will be done just in the next rebuild. Regards, Fernando 1973 Brasilian Dart E100, boosted 390"

Re: Big Cam x Low Compression Ratio [Re: dart_73_br] #83876 07/04/08 09:14 AM 07/04/08 09:14 AM
Joined: Jan 2003 Posts: 1,022 Andrews,In. U.S.of A. 6 67_Satellite super stock
67_Satellite super stock 6 Joined: Jan 2003 Posts: 1,022 Andrews,In. U.S.of A.	It's going to be "soggy" on the bottom end no matter what you do. The best you can do is advance the cam,and get all of your ignition timing in early. A loose convertor and low rear gears would help too.Look at the bright side,when you finally get the compression up to match the cam and intake,it will feel like you added a blower.

Re: Big Cam x Low Compression Ratio [Re: dart_73_br] #83877 07/04/08 09:18 AM 07/04/08 09:18 AM
Joined: Jan 2007 Posts: 7,664 IN A ahy master
ahy master A Joined: Jan 2007 Posts: 7,664 IN	Big cam + low CR + 318" + single plane intake = low & mid range very weak. It just won't have much cylinder pressure or torque. It may not wake up until 5000 or 6000 RPM and won't like to idle. Mileage won't be very good either. I'm no cam expert but I'd suggest with your short block a cam that is 210 or max 220 @ .050 would work much better. So would a dual plane intake but you've already got the EFI single plane. If time and budget don't permit increasing CR now suggest you at least change the cam so you can enjoy driving it. My

Re: Big Cam x Low Compression Ratio [Re: ahy] #83878 07/04/08 09:26 AM 07/04/08 09:26 AM
Joined: Jun 2008 Posts: 3,916 usa L lewtot184 master
lewtot184 master L Joined: Jun 2008 Posts: 3,916 usa	Quote: Big cam + low CR + 318" + single plane intake = low & mid range very weak. It just won't have much cylinder pressure or torque. It may not wake up until 5000 or 6000 RPM and won't like to idle. Mileage won't be very good either. I'm no cam expert but I'd suggest with your short block a cam that is 210 or max 220 @ .050 would work much better. So would a dual plane intake but you've already got the EFI single plane. If time and budget don't permit increasing CR now suggest you at least change the cam so you can enjoy driving it. My

Re: Big Cam x Low Compression Ratio [Re: dart_73_br] #83879 07/04/08 09:29 AM 07/04/08 09:29 AM
Joined: Jan 2003 Posts: 24,562 Brookeville, Md Mr.Yuck Not enough dumb comments...yet
Mr.Yuck Not enough dumb comments...yet Joined: Jan 2003 Posts: 24,562 Brookeville, Md	2 options, 1 - pull the cam and get a good grind for your combo. 2 - boost it

Re: Big Cam x Low Compression Ratio [Re: dart_73_br] #83880 07/04/08 09:35 AM 07/04/08 09:35 AM
Joined: Jan 2003 Posts: 25,200 Upper Midwest M MoparforLife Too Many Posts
MoparforLife Too Many Posts M Joined: Jan 2003 Posts: 25,200 Upper Midwest	Those big valve heads are more than likely going to hurt you more than help you.

Re: Big Cam x Low Compression Ratio [Re: MoparforLife] #83881 07/04/08 10:14 AM 07/04/08 10:14 AM
Joined: Feb 2003 Posts: 21,318 Manitoba, Canada DaytonaTurbo Too Many Posts
DaytonaTurbo Too Many Posts Joined: Feb 2003 Posts: 21,318 Manitoba, Canada	What you people are forgetting is that port EFI lets you get away with a lot of stuff that you can't get away with on a carb. IE single plane intakes don't kill bottom end, because there's signal to the carb to worry about anyway. Same with hi-flow heads, but to a lesser extent. But either way, that is a gigantic cam for a 318. Heck with that huge duration and 70* overlap, I wouldn't run that cam in a 440 with any less than 10:1 CR, and for that to run well in a small block, I would have to build a sky high CR. That's just way way too much cam my friend. Take it out and sell it. If you're low on cash, one of the cheapie summit cam/lifter kits will make more power throughout the entire RPM range than than monster you have in their now.

Re: Big Cam x Low Compression Ratio [Re: DaytonaTurbo] #83882 07/04/08 01:19 PM 07/04/08 01:19 PM
Joined: Aug 2005 Posts: 637 Sao Paulo, Brazil dart_73_br OP mopar
dart_73_br OP mopar Joined: Aug 2005 Posts: 637 Sao Paulo, Brazil	With the EFI my engine idles @ 700 rpm with this wrong configuration... You can see it idling here... http://www.youtube.com/watch?v=JYn04t_URjU http://www.youtube.com/watch?v=FJ_lb9kaZBw Looks like I have a lot of homework to do.. I already have a set of JE forged pistons. These pistons look great and are lightweight. Problem is that they are 3.97" and I�m a little afraid of boring the block this much. They will give me 10.5:1 CR (aproximatly). Should I sell these pistons and go buying another ones ? I have the option of buying some Keith Black domes KB-399 that should give more than 11:1 CR. How much power these KB can handle ? I want to use some juice in the future. (100~150hp). Thanks for your attention guys, 1973 Brasilian Dart E100, boosted 390"

Re: Big Cam x Low Compression Ratio [Re: Mr.Yuck] #83883 07/04/08 02:42 PM 07/04/08 02:42 PM
Joined: Mar 2008 Posts: 571 Western NC 68Bullit mopar
68Bullit mopar Joined: Mar 2008 Posts: 571 Western NC	Quote: 2 options, 1 - pull the cam and get a good grind for your combo. 2 - boost it With your compression and fuel injection, BOOST IT!

Re: Big Cam x Low Compression Ratio [Re: dart_73_br] #83884 07/04/08 03:57 PM 07/04/08 03:57 PM
Joined: Feb 2008 Posts: 711 Montana P Posest super stock
Posest super stock P Joined: Feb 2008 Posts: 711 Montana	Advance your timing to 50 total and see how it runs. I have small valve 360 heads on my teen and a 292/501 cam in it. It ran like a raped ape with a 4 speed and 3:91 gears. My idle is at 900 to 1000 rpm now. I have it in a dakota with a 727 and a 3500 stall. With my poor gearing (3:55)I have now it is kinda doggy. I have not got WOT figured out yet and I should have my 4:10 in next week. That ought to wake it up quite a bet.

Re: Big Cam x Low Compression Ratio [Re: 68Bullit] #83885 07/04/08 07:04 PM 07/04/08 07:04 PM
A Anonymous Unregistered
Anonymous Unregistered A	Quote: Quote: 2 options, 1 - pull the cam and get a good grind for your combo. 2 - boost it With your compression and fuel injection, BOOST IT! Interesting concept here. http://www.ststurbo.com/

Re: Big Cam x Low Compression Ratio #83886 07/04/08 08:48 PM 07/04/08 08:48 PM
Joined: Feb 2003 Posts: 21,318 Manitoba, Canada DaytonaTurbo Too Many Posts
DaytonaTurbo Too Many Posts Joined: Feb 2003 Posts: 21,318 Manitoba, Canada	Quote: Interesting concept here. http://www.ststurbo.com/ Cool idea in theory, but all that extra piping makes me want to !

Re: Big Cam x Low Compression Ratio [Re: DaytonaTurbo] #83887 07/04/08 09:44 PM 07/04/08 09:44 PM
Joined: Aug 2005 Posts: 637 Sao Paulo, Brazil dart_73_br OP mopar
dart_73_br OP mopar Joined: Aug 2005 Posts: 637 Sao Paulo, Brazil	I just drove the car... for the frst time after finishing exhaust, installed O2 sensor... and surprise... it's a big Looks like the Adams Family car... I'll have to rebuild the engine... change pistons... how much CR should I look ? For street/strip ? 10 ? 10.5 ? I also want to use some juice after that... maybe 100~150hps.. What kind of pistons do you recomend me ? Hypereutetic handle nitrous ? BR guys and thanks,,, 1973 Brasilian Dart E100, boosted 390"

Re: Big Cam x Low Compression Ratio [Re: dart_73_br] #83888 07/04/08 11:24 PM 07/04/08 11:24 PM
Joined: Jan 2005 Posts: 12,423 Kalispell Mt. H HotRodDave I Live Here
HotRodDave I Live Here H Joined: Jan 2005 Posts: 12,423 Kalispell Mt.	I would shoot for at least 10 to one. That should wake it up quite a bit and run on 93 octane just fine. If you went to 11 to one you might be able to get away with 93 with a bunch of tuneing, low temp t-stat ect... Don't you have easy access to ethenol down there? If so you can run monstrous compression on it, with that cam you could get away with 14 to one easily. Nitrous and ethanol go together great I am not causing global warming, I am just trying to hold off a impending Ice Age!

Re: Big Cam x Low Compression Ratio [Re: HotRodDave] #83889 07/05/08 12:18 AM 07/05/08 12:18 AM
Joined: Feb 2003 Posts: 21,318 Manitoba, Canada DaytonaTurbo Too Many Posts
DaytonaTurbo Too Many Posts Joined: Feb 2003 Posts: 21,318 Manitoba, Canada	Shoot for 10.5:1 and quench - if running open chamber heads, use quench dome pistons. Scrap that cam either way. It WAY big. That's about as big of a cam as you can go on a streetable 10-11:1 440, nevermind a little 318. If you want to run nitrous or boost, go with forged pistons. Hypers will take it, but if you run into detonation with nitrous, hyper pistons will shatter, and stock cast pistons will melt down. Forged will survive a lot better.

Re: Big Cam x Low Compression Ratio [Re: DaytonaTurbo] #83890 07/05/08 09:04 AM 07/05/08 09:04 AM
Joined: Jan 2003 Posts: 24,562 Brookeville, Md Mr.Yuck Not enough dumb comments...yet
Mr.Yuck Not enough dumb comments...yet Joined: Jan 2003 Posts: 24,562 Brookeville, Md	Add up all you costs Pistons, machine work, rods, and so on. You can probably get a used S/C off a 5.0L for around $1500.

Re: Big Cam x Low Compression Ratio [Re: Mr.Yuck] #83891 07/06/08 09:55 PM 07/06/08 09:55 PM
Joined: Aug 2005 Posts: 637 Sao Paulo, Brazil dart_73_br OP mopar
dart_73_br OP mopar Joined: Aug 2005 Posts: 637 Sao Paulo, Brazil	I'm adding a pcture of the dataloging I've made. Note that when idling... the engine stays accelerating ... it comes up and down... look at the MAP curve... the pressure inside the intake manifold flutuates... it's the blue curve... This is because the low cylinder pressure ? What do you think guys? BR, Fernando 4535094-map.JPG (51 downloads) 1973 Brasilian Dart E100, boosted 390"

Re: Big Cam x Low Compression Ratio [Re: dart_73_br] #83892 07/06/08 10:02 PM 07/06/08 10:02 PM
Joined: Jan 2007 Posts: 7,664 IN A ahy master
ahy master A Joined: Jan 2007 Posts: 7,664 IN	Wide fluctuations in MAP are a characteristic of a long duration/high overlap cam. The settings in the engine control computer can exagerate or reduce this effect but its mostly the cam characteristic combined with the effect of engine displacement.

Re: Big Cam x Low Compression Ratio [Re: ahy] #83893 07/06/08 10:31 PM 07/06/08 10:31 PM
Joined: Aug 2005 Posts: 637 Sao Paulo, Brazil dart_73_br OP mopar
dart_73_br OP mopar Joined: Aug 2005 Posts: 637 Sao Paulo, Brazil	Found the right word guys... it surges... 1973 Brasilian Dart E100, boosted 390"

Re: Big Cam x Low Compression Ratio [Re: dart_73_br] #83894 07/07/08 11:44 AM 07/07/08 11:44 AM
Joined: Feb 2003 Posts: 21,318 Manitoba, Canada DaytonaTurbo Too Many Posts
DaytonaTurbo Too Many Posts Joined: Feb 2003 Posts: 21,318 Manitoba, Canada	Map readings all over the place are normal with a huge cam like that + small ci + low compression. In all honesty, you're not going to be able to get it to run right with that cam no matter what you do. Go stick a cam in that thing with specs no bigger than a stock 340 cam, then you will have something that is actually driveable.

Re: Big Cam x Low Compression Ratio [Re: DaytonaTurbo] #83895 07/07/08 05:51 PM 07/07/08 05:51 PM
Joined: Aug 2005 Posts: 637 Sao Paulo, Brazil dart_73_br OP mopar
dart_73_br OP mopar Joined: Aug 2005 Posts: 637 Sao Paulo, Brazil	Quote: Go stick a cam in that thing with specs no bigger than a stock 340 cam And.. how much is that ? How much the bigger cam for a good response in 1/8 mile ? 1973 Brasilian Dart E100, boosted 390"

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