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Old 08-30-2003, 01:14 PM
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Guru Help on camshaft and carb choice

I am building a 400sbc .030 over, 5.7 rods, Trick flow 23 Degree Aluminum heads 195cc intake runners, 72cc CNCíd combustion chambers, 2.02 in. Intake, 1.60 in. Exhaust, Edelbrock air gap intake manifold.
The compression ratio will be about 9.7:1, the 400sbc is going into a 72 chevelle (about 3600Lbs) TH350 atuo. (with stall converter) Looking for a pos rear with around 3.55 gears for it.
It will be for street/strip racing (need street able idle). I have decided against a roller cam too much $$$. I have read so much information on camshaft and carbs the past week that my brain is turning to mush so I am looking to some Guru Hotrodders guidance on carb choices and cam choices (brand, lift, duration, lobe separation angle, overlap, duel pattern or not? etc).

As for the carb I was thinking a about a Speed Demon 750cc, but after reading members post on these carbs I wonder if it would be worth the trouble, if I do go with the Demon carb would the 750cc be to big????? (I read that the Demon Carbís have a under rated flow), My next choice would be an Edelbrock 750cc.

As for the cam, I need a street able idle and vacuum, I would like to keep my stall converter around 2500 or less, this motor is going to have a lot of torque so Iím thinking that I donít need a cam with peak low end torque for off the line, but maybe a cam with a flatter torque range.

Also I will be ordering the trick flow heads and Edelbrock manifold next week, so itís not to late to give your valued options on them to.

Sorry for the long desperate post, any guidance, opinions, or even criticism are greatly appreciated.

406chevelle

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Old 08-30-2003, 04:55 PM
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Your most streetable cam choice will have a duration@.050 of less than .224, this will ensure that you have manifold vac and a reasonable idle under varying weather conditions, as for lift, more is better especially with good heads, the 400 will love it, you can't go wrong with a 750 vac secondary carb on the street for driveability and gas mileage. I always advise my customers to use something like a Holley 3310, in one of its many variations, They work well, they have parts anywhere and I went to school for them way back when they were owned by Colt Industries.
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Old 08-31-2003, 11:51 AM
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cam choice narrowed down

Thanks for the guidance Bobcrman.

I was hoping to get close to .500 lift and maintain a street able duration, however it looks like the best I can do is with one of the two following Comp Cams:

Xtreme Energy XE268H Duration @ .050 IN 224 EX 230 Value Lift IN .477 EX .480

OR

Magnum 270H Duration @ .050 IN 224 EX 224 Value Lift IN .470 EX .470


I was hoping for a little higher lift to flow more air through those Trick Flow head, something like the following, but from what you have said the duration would be to high to maintain enough vacuum. I would go with a higher stall converter for this one:

Xtreme Energy XE274H Duration @ .050 IN 230 EX 236 Value Lift IN .490 EX .490

Anyone else have anything to add?????

406chevelle
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Old 08-31-2003, 12:46 PM
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you would be better off with the 268 if you want reliable streetability, the 274 is a bit lumpy and will need a mild convertor and you may have power brake and idle quality problems. The 274 is an excellent street cam tho, it makes a rather flat torque curve and generous horsepower, I've used it in several large cube engines with good luck.
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Old 08-31-2003, 04:37 PM
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Either cam will work well.The 268 being more lowend,streetable and better idle and vac.
The 274 would be more concerned with 1/4mi. ET,but also being as you have a 400 it will react slighly less to a larger cam than a 350.So maybe this one with a vac reserve can would be better for street/strip.
Actually the cam I would prolly pick for this combo is the Edelbrock Torker grind.With 232/234@050 .488 lift and a 108 split.I like this one cause of the tighter seperation on the 400sb.
As for carb I would put a 750cfm double pumper on it.
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Old 08-31-2003, 05:19 PM
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You could run the 268 with 1.6 rockers & be right at that .500 lift you want. Also I have a 750 Mighty Demon, and I love it. Talk to their tech, they may rec. a 650 for your app.? I did my homework & choose the 190 AFR's instead of the Trick Flow's, a little more money but hey it is just money ?

Later, Mark
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Old 08-31-2003, 10:12 PM
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I ran my motor through Desktop Dyno 2000 most of the day using several Head flow files and cam files, and reading everything I can get my hands on, it has shown that you guys are right on the money.

What I found on the cams is the 274 produces only 8 more HP and 7Lbs less torque and the HP is peaking at a higher RPM, I think the HP would be used better at the lower RPMs.

XE274H
RPM HP @ Fly Tork @ Fly
2000 159 418
2500 206 432
3000 252 440
3500 301 452
4000 346 *455
4500 384 448
5000 410 430
5500 *413 395
6000 399 349



XE268H
RPM HP @ Fly Tork @ Fly
2000 166 436
2500 214 449
3000 260 455
3500 308 *462
4000 350 459
4500 385 449
5000 *405 426
5500 401 383
6000 382 334
*The HP and Torque is higher from 2000 RPM through 4500 RPM then the bigger cam.

Being a 406 SBC Torker motor I donít think it will ever see 6000 RPMs probable more like 5000 RPMs, based on this information I am going with the XE268H Cam and then I can avoid any idle problems.

HotRod31 that is a great idea to use 1.6 rocker arms to get the higher lift I wanted, I will be researching it.
I also found the AFR heads to be much better then the Trick Flows, there is about a 30 HP gain and a slightly higher and flatter torque band, I am going with the 195 AFR heads they feed the 406 cubic inches a little better that the 190 AFR heads.

It is slowly looking like the Speed Demon Carb, and I will be calling a rep. To clue me in on a 650 or 750.

My motor is finally coming together, I canít wait to get the final parts and get it together.
Thanks for guidance Bobcrman, 78 monte, and HotRod31!!!!!!!

406chevelle
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Old 09-01-2003, 07:03 AM
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I just had a 406 built. It has a Scat crank, Sportsman 2 heads, 1.6 roller rockers, RPM intake and Edlebrock 750 carb, same comprression as your spec. The cam I am using is the Comp Cams 280H. It's 230/230 @ .050 and .512 lift with the 1.6 rollers. I had the engine dyno'd and it makes 425 hp at 5250 rpm and 470 lb ft at 4200 rpm. At 3000 rpm is makes 440 lb ft of torque. It idles at 750-800 rpm and pulls about 13-14" of vacuum. This is in a four speed 1965 Beaumont (Canadian only car based on the Chevelle platform). The engine is very mild, sounds like a slighltly cammed 350 as will pull 6500 rpm easy.
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