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Old 04-03-2008, 04:43 PM
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mild sbc build help, cam help

I've been researching my sbc 350 rebuild for over a year now. My head is pretty full. Thought I'd run my situation past you guys. Any help, advice is much appreciated.

I have a 1980 Chevy Malibu wagon with:
rebuilt TH350 trans with stage II shift kit,
stock torque converter,
2.73 : 1 rear gear,
stock ignition.

I am rebuilding a 350 crate motor with the goal of having a daily driver that can get decent gas milage (ideally) on 87 octane fuel and also tow 5000# over mountain passes several times each year. Fun performance has taken third place priority. This will be my 1st motor build.

The 350 is second hand but looks very clean with cross-hatching still visible in most cylinders. Some moisture sat in one cylinder and there is some shallow rust pitting. I want to have the block
cleaned,
bored,
decked.

I'll buy new
flat top pistons,
cam,
lifters,
pushrods?? (if deck height changes),
oil pump.

I'll use the stock
crank,
connecting rods,
heads (casting 3998993),
rocker arms,
rocker studs,
valve springs??.

I also have a
flexplate (from 1980 lg4 305),
Edelbrock 1404 carb (500 cfm),
Edelbrock Performer intake manifold,
headers to 3 inch dual exhaust to Flowmaster 50s to 2.5 inch tailpipes.

This is a long post. Thanks for reading. Anybody see any oversights on my part. All my knowledge is from books, this and other forums, and magazines.

Any thoughts on a good cam for this application?

thanks,
j

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Old 04-03-2008, 05:24 PM
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Just my opinion but before you do any engine work get rid of those 2.73 gears. They might be great for gas mileage IF you weren't towing anything but putting that kind of a load on your engine will kill mileage. Your engine will never be in any kind of power band unless you tow in second gear.
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Old 04-03-2008, 05:50 PM
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Thanks for the input.
I need to build the engine now in order to get the car moving. and won't be towing until September.

any suggestions on a rear gear ratio given my goals for the car. It has a 7.5 inch 10 bolt.

Will a different rear gear affect my other decisions about the engine? like cam selection?

j
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Old 04-03-2008, 07:46 PM
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September is not that far in the future considering the time it often takes to bring a project engine to the point of usefullness. You only want to build this once, correct? Engines should be built for what they do most of the time. Things they rarely do should be of much less concern. A mid sized G-body wagon with a mild 350 already has a pretty good power to weight ratio. If you must drag 5k#,s up over a mountain, your TH350 should handle it in second without issue. I strongly recommed a tranny cooler though. Cam selection is all about power bands. Rear gear choice is all about making use of that power band. Good gas mileage usually requires peak torque to be at lower RPMs'. Towing mileage is usually best in midrange RPM's. Your 7.5 will live if not seriously abused, but if you are going to bump up your ratio, you might find a beefier Rear that bolts right in with a friendlier ratio and bigger brakes for cheap out of a junk yard. And while your there mabey you coud find a post 85 TH700r4 for cheep too. The extra low first gear sure will come in handy trying to take off with a heavy load and the over drive with lock up converter will work miracles for non-towing milage. Sounds like the block is in good shape, Avoid boring if a hone will do. Check chamber volumes, as flat top pistons and block decking could leave compression ratio to high for 87 octane gas. As for the cam, choose a moderate cam that will work with other modification you are doing. If you can afford it, go with a mild retrofit roller cam. If you are going to use the 500cfm carb, don't install parts that have far more flow capability than it. Install parts like a gasket matched intake manifold, cc'd & matched lightly ported heads, agood freeflowing exaust, and you will do just fine! You will still most likely use second gear up mountains while towing but who cares, you'll get there and back trouble free.
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Old 04-03-2008, 07:53 PM
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If you could be more specific about horsepower needs, MPG desires and budget limits, it would help us help you. Tell us more about your project plans. We love to help!
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Old 04-03-2008, 08:16 PM
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Thanks for the replys.

As specific as I can be:
My budget is low, (maybe $1500 after everything inc. surprises) so I need to use most of what I have. That includes the heads without any work other than what is necessary (valves guides etc). I don't want to port the heads at this point. So this alone dictates in large part my goals for the project.

I am willing to put money into a new cam and lifters as I understand this is where I'll see the most benefit. Since I'll be towing (infrequently) and most all my driving is in the city, I want to build for low rpm torque over high revving hp. Gas milage is important but I don't want the car to be a dog when I load it down.

j
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Old 04-03-2008, 09:04 PM
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My budget is $1500.
but I already have the
block,
crank,
heads,
valves,
rockers,
intake manifold,
carb,
air cleaner assembly,
headers,
oil pan,
water pump,
connecting rods.

The rust pitting in visible and can be felt, so I think it's past honing.

thanks
j
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Old 04-04-2008, 09:19 AM
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Gasket matching and mild porting can be easily done at home with a cheap die grinder. This is virtually free horsepower and helps increase fuel economy. Personally, I would not miss the opportunity to do this while the engine is apart. At the very least gasket match the intake to the heads. If you have to bore, obviously you already know that pistons will be part of the budget. I like hypereutectic pistons so as to run tighter cylinder wall clearances, but any cheap cast piston will do just fine for a low rpm build. Lighter is better. Thermal barrier coated tops and anti friction coated skirts can also add to HP and mileage. These too can be applied relatively easily at home for cheap, but many piston manufacturers are now offering these at very affordable prices. Thermal coating the combustion chambers will also compliment the package. Heat=Power, If you keep it in the chamber, it won't be wasted through the radiator. To keep the powerband fairly low in the RPM range, avoid going too radical with your cam choice, especially with that small carb. All cam manufacturers will be happy to give you solid advice on which off the shelf grind is right for your needs. Hydraulic rollers offer huge advantages when looking for more lift with the short duration your going to need, but they are quite expensive. Keep the lift under .5" and the duration very mild if you want to keep those low RPM torque numbers up. A cheap stock oil pump is fine. High volume pumps just rob power and are inappropriate for your needs. If you feel you need a little more pressure just shim the spring, I just use a thin washer or two. I think $1500 is a tight budget, but you should be able to put together a good strong engine for that. Just remember, keep the friction and restriction to a minimum!
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Old 04-06-2008, 12:14 PM
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anybody have any specific cam suggestions?

thanks

j
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Old 04-06-2008, 01:34 PM
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K12-210-2 Competition cam kit
Take the 2.73 out an slip in something in the 3.40-3.55 range as for as gears.
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Old 04-06-2008, 01:44 PM
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Quote:
Originally Posted by 327NUT
Just my opinion but before you do any engine work get rid of those 2.73 gears. They might be great for gas mileage IF you weren't towing anything but putting that kind of a load on your engine will kill mileage. Your engine will never be in any kind of power band unless you tow in second gear.

fo sho' bro'.

getta stock truck cam. i used a cheapo erson E 923 P with 204 / 214 @ 50. use only stock 1.5 ratio rockers. top o' the page cam broski. maybe even less duration. i dont know. can't you getta cheapo GM engine for not much more money than 15oo? those gears will blow yer arse up on top of the mountain so i hope you're towin a travel trailer so you have somewhere to sleep.

as for gears (this is an edit obviously) no taller than 3.50's

Last edited by bullheimer; 04-06-2008 at 03:21 PM.
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Old 04-06-2008, 02:00 PM
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alright thanks.
any suggestions on how I figure out which rear gear ratio will put my engine in the power range with a cam like that while towing???
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Old 04-10-2008, 02:05 PM
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any thoughts on these cams for my motor and application?

Summit K1102
204/214 duration, .420/.442 lift
operating rpm: 1500 - 4000

Edelbrock Performer-Plus 2102
204/214 duration, .420/.442 lift
operating rpm: idle - 5500

Crane Z-Series 113502
206/218 duration, .432/.459 lift
operating rpm: 1200 - 5200

and why to do Summit and Edelbrock rate what seems like the same grind for different rpm ranges??

thanks.
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Old 04-10-2008, 03:37 PM
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I pull a trailer around with a 3.08 gears and 28 inch tall tires. 80 mph is 3000 rpm which is right in the meaty part of my engine power band. If my gear was lower, I would need to slow down to keep the rpms under 3000. I don't like revving my engine over 3000 for long periods because it seems to not like it much.

A 2.73 gear will tow OK. When you are going up a steep hill, put the transmission in 2nd gear to make a 4.15 gear. (2.73 x 1.52 = 4.15). Other wise a 2.73 gear with 26 inch tires will put fine on a level road at 75 mph with 2700 rpms (if you build a torque engine).

I would use 8.75:1 to 9:1 cr. Do the math! use the right pistons, gaskets, to make this cr with your head volume.

Then use a cam with 202 to 206 on the intake and 208 to 212 on the exhaust. Then use 108 to 110 lobe separation angle (LSA). check crane cam's website.

I would also use 2-1/4 to 2-1/2 pipe from the headers to the mufflers and install a cross over pipe. 3 inch off the headers kills low speed torque and make noise.

I don't like your carb but it's paid for. one day get a Q-jet rebuilt by a good carb shop. will cost 400 to 500 for a q-jet but it will be worth it.

Bore your engine with torque plates because it is worth the extra money to have straight piston walls. Also have the machine shop set the main and rod bearings at 0.002" and the rear main at 0.003.

get the head disassembled and cleaned. then pick up the bare heads and smooth the area between the valve seat and cylinder head. There is always a ridge there and your engine will make 20 extra hp with a few hours of work. This is the low hanging fruit in the head porting world (bowl smoothing). I wouldn't mess with gasket matching, doesn't do much.

you can use the stock valve springs and rockers.

when you get it running. Make sure to check the total advance. 80's hei don't have much advance. set total mechanical advance to 38 degree and let the initial fall where it may. Vacuum advance should add another 12 degrees. crane makes a nice adjustable one. You may need to disconnected the vacuum advance when towing with 87 octane.

Last edited by 454C10; 04-11-2008 at 11:54 AM.
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Old 04-10-2008, 04:57 PM
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get yourself some vortec heads
*this cam Summit K1102 204/214 duration, .420/.442 lift operating rpm: 1500 - 4000
*Roller rockers 1.50 ratio
*A good double roller chain
*8.5:1 cr or 9:1 max
on gears Id run some 3.42's and swap to a th700-r4 later on that would help alot
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