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Old 11-28-2009, 09:30 PM
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350/290hp G.M. crate engine thoughts

Hello all. Any thoughts or advice on my crate engine would be appreciated. Background: G.M. 350/290 hp crate bought new. Painted and installed without any modifications. Top dead center verified, and timing tab verified while on engine stand. Currently running 12* initial 25* Mechanical and 10* vacuum. Vacuum advance hooked to full time vacuum port at carb. Distributor is MSD E-curve. Carb is Edelbrock 1405 with stock jetting and rods. Intake: Edelbrock RPM. Plugs: Autolite 26(colored light tan on base of porcelain) Exhaust: 1 5/8'' x 26''fenderwell headers(Speedway) 2 1/2'' full length pipes w/ 40series flowmasters and 2'' H-pipe. Total mileage on engine: 1500. Now the problem, this things a slug. Overall runs well but is really down on power and not real crisp. Pulls a not real steady 11-12'' vacuum at idle. I know it only has 8.5:1 comp. ratio but it seems unresponsive. Have checked for vac leaks, have not found any. Its installed in a1940 chevy, 3100Lbs, 3.42:1 gears, th350, 2200 stall. Any ideas? Is this engine just a dog?

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Old 11-28-2009, 09:59 PM
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Hi,
With the vacuum gauge hooked up, advance the timing to the highest vacuum reading, take it for a ride, if it pings retard it 1or2* & try again.
Rich
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Old 11-29-2009, 12:53 PM
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yep, the 260 HP version is way better, the smaller cam works better with the low compression.. my dad's got 1 in his '72 C10 and while it's no power house, it's a strong runner.
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Old 11-29-2009, 03:30 PM
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Thanks for the imput guys. I have tried running as much as 22* of initial and 10* mechanical all in by 2500rpm in the past. Engine would labor to turn over at this setting, so I went back to less initial and more mechanical. I did notice that by increasing initial, idle quality was slightly improved and vac was stronger. However engine labored to turn over. Thats not the first time its been suggested to get a 177 weiand. I had the chance to buy one about two months ago still in the summit shipping box for $800 and had to pass. Wife wanted new bed room furniture. Story of my life. Thanks for the replies, they seem pretty spot on to my way of thinking as well.
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Old 11-29-2009, 03:47 PM
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Thanks again guys. One more thing. I have considered a vortec head swap in the past, but I have a few questions. I dont have a lot of experience with the vortecs in any performance situations. I have heard that vortecs wont work well with dished pistons, or really, any pistons that were'nt designed to work with vortecs chamber swirl and quench characteristics. Would they be O.K. with these dished pistons? Would aftermarket heads be a better choice with dished pistons? Also, I have used several Comp Cams shafts with specs similiar to those suggested in previous engines, with good results. I figured I'd be wasting time wit the comp ratio of this engine though. Thanks again.
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Old 11-29-2009, 04:06 PM
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I've always felt that the 350/290 is a little over-priced. It's the same engine as the basic Goodwrench "Universal" 350, the only difference I've ever noticed in all the specs I've seen is the cam, yet the engine sells for $450 or $460 more, which makes that a pretty expensive cam! For the price difference you could buy a Comp Cams "K" kit with cam, lifters, springs, etc, and an Edelbrock manifold to put on top, which would give a lot more flexibility in setting up the engine to be what you want. Although, I'm sure that once you've changed any internal parts (cams, etc) you've voided the warranty.

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Old 03-04-2016, 01:45 PM
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350/290hp

I have the same engine in my 33 chevy coupe 700r4 tranny 3:08 rear. quadrojet street master carb. I am curious as to your mpg on that engine ? 12 mpg is the best I can get at 60 mph expressway driving around town 9 mpg.
If you are doing better tell me the secret.

Phil
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Old 03-04-2016, 02:54 PM
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This thread is approx 6 yrs old.You may get better answers by starting a new thread.
FWIW, that milage sounds about rite for that engine & setup.The cam in that engine is too big for the low compression & doesn't even begin to get into it's powerband until approx 2500 rpm.At 60 mph & 3.08 gearing in a 700R4, I doubt you're even close to that, unless you have some really small tires.
A set of 64 cc modern heads like the L31 vortec, or similar. In iron , or, aluminum vs the large chamber smog heads on the engine now would help tremendously with milage & power.You will likely see 40 to 60 HP gain, from the head swap alone & much better milage & efficiency. If you're not interested in that route, dropping the cam size back some would work also & probably without much of any power loss.You will most likely see a gain in performance, especially in the lower rpm range.
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Old 03-04-2016, 03:18 PM
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X 2... the 195 - 260 - 290 HP crate engines are horrible early 1970's emissions technology still being sold today... most here would recommend against them... the actual compression ratio is even lower than claimed... about 7.6 - 7.8:1... gives about 9 MPG city and 11-13 MPG Hiway... if you can change pistons yourself, cheapest fix is some standard size mini-dome pistons re-using same rings in same cylinders giving about 350-390 HP, much more torque, and much higher MPG... next higher in price would be some Vortec or other 64cc or even 58cc chamber heads with .015" thick head gasket to replace the stock 76cc heads...
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Old 03-04-2016, 04:17 PM
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Quote:
Originally Posted by 40 grey View Post
Hello all. Any thoughts or advice on my crate engine would be appreciated. Background: G.M. 350/290 hp crate bought new. Painted and installed without any modifications. Top dead center verified, and timing tab verified while on engine stand. Currently running 12* initial 25* Mechanical and 10* vacuum. Vacuum advance hooked to full time vacuum port at carb. Distributor is MSD E-curve. Carb is Edelbrock 1405 with stock jetting and rods. Intake: Edelbrock RPM. Plugs: Autolite 26(colored light tan on base of porcelain) Exhaust: 1 5/8'' x 26''fenderwell headers(Speedway) 2 1/2'' full length pipes w/ 40series flowmasters and 2'' H-pipe. Total mileage on engine: 1500. Now the problem, this things a slug. Overall runs well but is really down on power and not real crisp. Pulls a not real steady 11-12'' vacuum at idle. I know it only has 8.5:1 comp. ratio but it seems unresponsive. Have checked for vac leaks, have not found any. Its installed in a1940 chevy, 3100Lbs, 3.42:1 gears, th350, 2200 stall. Any ideas? Is this engine just a dog?
This engine is a classic miss-match off too much cam for too little compression. Moreover, these heads are not only large chambered (76 cc with them the real SCR is more like 7.9 than the advertised 8.5) but they are also the slow burn SMOG heads used from the early 1970's to mid 1980's. What will wake this engine up at the minimum is milling a lot off the head and using the thinnest (.015?) gasket you can find. But the real solution is new heads in the vein of the L31 Vortec. You don't necessarily need to run out and buy the Chevy as many aftermarket heads with similar to better performance capability are out there and even GM makes an aluminum version called the Fast Burn. You need to develop a budget then we can fit a head to it if you want our help. Quite a few of the aftermarket heads also will bolt to standard intake bolt patterns (8 per side) as well as the unusual Vortec pattern (6 per side); so they would allow you to keep your current intake which can save a few dollars. These type heads with 74 cc chambers will get your SCR compression up to around 9.5 which is what is needed with the cam that comes in the 290 horse engine. The head change will move the power up around 40-60 foot pounds and 30-50 horsepower, if you get aluminum it's take 50 pounds off the front wheels. The higher compression will fatten the lower RPM range torque and power as well giving much improved bottom end performance. You'll probably see better gas mileage too if you can keep your foot out of the throttle and wipe the smile off you face every time you hit it.

Bogie
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Old 03-04-2016, 04:35 PM
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These type heads with 74 cc chambers
Bogie meant 64cc...
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Old 03-04-2016, 05:00 PM
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Bogie meant 64cc...
X2

Bogie
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Old 03-05-2016, 04:18 AM
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Quote:
Originally Posted by phil wilburn View Post
I have the same engine in my 33 chevy coupe 700r4 tranny 3:08 rear. quadrojet street master carb. I am curious as to your mpg on that engine ? 12 mpg is the best I can get at 60 mph expressway driving around town 9 mpg.
If you are doing better tell me the secret.

Phil

Ouch, that mpg is pathetic. If you drive this much, then you might actually be qble to save money by upgrading (at least you can tell your wife that).

What rpm range are cruising at? What size tires? Car weight?

I think you've got the worst of both worlds working against you, poor heads and compression in a vehicle with mismatched gearing. 3.08's with an overdrive transmission will need some tiny tires to get the rpm's into a reasonable range in OD.

X2 on a set of Vortecs.
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Old 03-05-2016, 06:49 AM
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In the mean time, you may actually get better milage by not using OD.It just depends on what your actual rpm is at cruising.
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