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Old 08-08-2009, 10:21 AM
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1970 250 hp 350cid

I currently have a stock 250hp 350 in my 1970 Chevelle. Can I retain the original heads ( 72cc 1.94 I think )and upgrade the cam, intake, carb, change the manifolds to headers and beef up the ignition for a moderate improvement in power. The engine currently has 9:1 compression. I want to stick to pump gas.
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Old 08-08-2009, 10:51 AM
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Yes,you can
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Old 08-08-2009, 02:01 PM
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As said...yes you can....BUT you really need to know what you're starting out with. Pull a valve cover and see what the casting number on the cyl. head says, that will tell you if you have 1.94 or a 1.72 int. valve.

All the cam and induction in the world won't do a thing if the engine can't breath. You probably have around 8.25 to 1 comp (if the engine hasn't already been rebuilt). Depending on the age of your engine (ring seal) and your budget of course, while you have the engine torn down that far why not put a better set of heads on it? Like Vortecs which will take it's own specific bolt pattern intake manif. Lots of ways to make decent power, just don't overcam and carb it.....you will get plenty of advice here......good luck.
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Old 08-08-2009, 03:12 PM
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As 327NUT related, the actual static compression ratio is probably less than what you think it is. This will make it difficult to put any kind of performance cam in the motor. The more cam you put in the motor, the later the intake valve closes and you could find yourself with less power than you have now due to lower cylinder pressure.

In this age of reformulated oils and the reduction of extreme pressure ZDDP additives, I would resist using a cam such as a Lunati Voodoo, Comp Extreme Energy or any such grind from any other manufacturer which yanks the valves open quickly. We read of hydraulic flat tappet cams going flat every day on this forum and I see no reason to run right up against the ragged edge for a few more hp at the expense of turning the cam and lifters into mush. I would choose a cam that has gentler opening ramps in hopes that the cam and lifters would last longer.

The key to good performance is air-in and air-out, so you want to choose components at the intake and exhaust that will accomplish this.

Here's a low compression 350 combo that I had in my DynoSim file....
350 long block with 882 heads, 8.25:1 static compression ratio.
Edelbrock RPM or Weiand Stealth intake manifold.
650 CFM carb.
1 5/8" long-tube, equal-length headers, dyno'd through mufflers and pipes to the rear.
CompCams 265DEH (part #12-208-2) Dual Energy hydraulic flat tappet cam with CompCams #981 springs.
http://www.compcams.com/Cam_Specs/Ca...?csid=104&sb=0
I'm not saying you have to use a Comp cam. I'm just showing you the type of cam timing that would work best with this type of motor....
RPM HP TQ
2000 135 355
2500 171 358
3000 216 379
3500 269 404
4000 313 411
4500 345 403
5000 365 383
5500 345 329

While not a barn burner, this is a respectable street motor that will operate on pump gas.
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Old 08-08-2009, 06:19 PM
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i basically did everything you're asking about on my 70 monte.
started with ALL stock..2bbl 350
went to 4bbl edelbrock performer, performer eps intake, hyfire ignition with pertronix points replacement, headers, new moderate comp cam.
didnt cost much but was worth doing.
my 2.70 open rear end is though
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Old 08-08-2009, 10:36 PM
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Space....thats your next big project, 2.70 to a 3.50 or 3.73 will really make a BIG difference.
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Old 08-09-2009, 09:34 AM
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3.50 gear and 700r4

I have a set of 3.50 gears and a 700r4 in the shed. I currently have a 350th tranny with 2.56 gears in the car. Is it worth the effort to change the tranny to the OD or just swap gears? I was thinking of finding a set of 3.08s and retaining the 350th and meet half way (highway drive-ability)
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Old 08-09-2009, 12:46 PM
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I think the 70 350cid 250hp engines had 1.72" intake valves with 76cc chamber heads. The 70 300hp had 1.94 valve "Double Hump" heads with 64cc chambers.

Vince
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Old 08-30-2009, 11:46 AM
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3932441 heads

I finally looked under the valve cover and found the heads to be 3932441 76cc heads with 1.94/1.5 valves. Is there anything I can do at a reasonable cost to make more power ( milling? )
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Old 08-30-2009, 01:40 PM
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The 441 heads you can sometimes sell to a roundy rounder. These heads have decent ports but the chamber isn`t so good. You maybe able to shop around and find a set of better heads. Yes, you can mill the 441`s and install a .015 shim head gasket while it will slightly help compression it poor chamber design will still hold back the power gain. There is also the possibility the guides could be shot in your heads as well as they didn`t come with a hardened exhaust seat for use with unleaded fuels. If it were I, I would find a set of better heads and go from there. But if you want to keep the 441`s they will work. I can`t give a mill figure on them as I`ve never wasted my time on smogger heads. I`m sure somebody else on here can tell you what you need to know. Good Luck.
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Old 08-30-2009, 10:45 PM
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As a general rule of thumb and depending on chamber shape, 0.006" to 0.007" will reduce chamber volume by 1 cc on a SBC head.
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Old 08-31-2009, 02:27 PM
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Quote:
Originally Posted by shmiv
I have a set of 3.50 gears and a 700r4 in the shed. I currently have a 350th tranny with 2.56 gears in the car. Is it worth the effort to change the tranny to the OD or just swap gears? I was thinking of finding a set of 3.08s and retaining the 350th and meet half way (highway drive-ability)
In terms of drive-ability the 700R4 would be better even with your 2.73 rear axle. The 700R4 has a low gear of 3.06 against TH350 of 2.52 on the bottom and an overdrive of about .7 in 4th against the TH350's 1:1 in 3rd. This gives a lot punch out of the hole and decent gas mileage on the freeway.

Bogie
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Old 08-31-2009, 07:41 PM
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as many know im a huge fan of the 700r4 for a street car even on some racing applications, it has to be built to handle it but you have to love the low 1st and 2nd gears with a decent set of 3.42's or lower, then in OD you get on average 800-1000 less rpm at highway speeds, i would go with the 700, IMHO i would go with a better set of heads, you dont have to spend a ton of money on a set of redone camel humps or vortecs, and then you would have a much better base to start with, it will make a consideriable difference in average hp/tq and peak hp/tq #'s
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