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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, 12:16 PM
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It seems like its a slug cause it is a slug. Just look at the factory rated torque output 326 ft/lbs. A 305ci motor makes more torque.

Its a very low cr motor with crappy smog heads that GM stuffed a L-82// L46 cam in it.
To make matters worse, the cam is factory installed 1deg retarded from "straight up"
114 LSA 115 installed in c/L
(this cam was designed and intended for the 11:1 cr 1969 corvette L-46 350-350HP motor with good fuelie heads, not a low cr smogger.
The cam is a mismatch for this low cr motor.
The actual measured cr is much lower than 8.5:1.

The cam needs to be degreed and advanced in this low cr motor by a full 7 degrees at least.
107 intake C/L (or just replace it)

It needs a serious dose of compression ratio and cylinder head flow fix.
A cam change is a good idea too.

Change the heads to high performance heads that flow and have small combustion chambers (53-58cc)

There are many ways to do this from low buck full home ported big valve #416 305HO heads, to home ported camel back/fuelie heads to vortec heads to entry level aftermarket heads with small chambers.
For best results install the new heads on this dished piston motor using thin .015" shim head gaskets.

A modern cam with around 218@.050" 108 to 110LSA
will help a lot too.

A 750 cfm carb is not too big. I'm not crazy about the 600cfm edelbrocks.

Much prefer the #1407 750 model.

I would modify the ignition timing advance curve. (more initial Up to 24deg at idle) , less (10-14) advance travel 34-36deg total mechanical advance.

10 or so deg of vacuum advance.

Last edited by F-BIRD'88; 11-29-2009 at 03:10 PM.
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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, 02:33 PM
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This motor would really wake up with a 144cid or 177cid supercharger.

Remove the cylinder heads and home port them as much as you dare. (more is better, you cannot over port these crappy stock heads too much) Drill and roll pin the rocker studs.
Get a machine shop to do a nice 3 angle valve job and a 30 back cut on the valves.
reinstall with new Z28 style valve springs
eg: these ones

Use a blower friendly Summit #K1105 hyd cam and lifter set

Or for max street supercharged perf use This Lunati street mechanical cam with solid lifters

bolt on this blower http://www.summitracing.com/parts/WN...1/?image=large

or for max perf this weiand 177ci bad boy

You'd want to blower prep a 750-850cfm 4bbl carb for it and upgrade the car's fuel system too feed it.

The stock crate motor cast pistons will be fine with 6 to 8psi boost on 92+ octane gas, correct jetting and moderate spark timing because of the low low cr. You can get it down to 7.5:1 with a .041" gasket by deshroudng the smogger combustion chambers to 80cc
The key is avoiding piston killing detonation.

With these changes and tweeks no one will believe its a 290hp crate motor.

Get a 3000 stall converter and a neck brace....

Last edited by F-BIRD'88; 11-29-2009 at 02:50 PM.
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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, 03:53 PM
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Quote:
Originally Posted by 40 grey
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.
The easy way to get around the starter labouring while hot starting issue is to install a simple SPST 15 Amp rated dash mount ignition/distributor 12v power interupt/kill toggle switch.
Kick it over with the kill switch off, 1-2-3 then throw the switch and it will fire up instantly without starter strain and pain.

Doubles as a stealthy anti theft ignition disableing device.

Be sure to install the required factory rear starter motor mounting support bracket/brace. this is a must do.
A fender mounted Ford style starter solenoid helps a lot too.
Also install a good ground strap system between the engine block, firewall/car body, car frame and battery -. The grounding is critical.

A starter heat shield and heat shield wrap is a very nice thing to add to block the radiant heat from your headers cooking your starter and solenoid.

Your GM starter motor will out live you with these upgrades. No more hot start problems even with full "locked out" timing. no more burn't out starters.

Last edited by F-BIRD'88; 11-29-2009 at 04:08 PM.
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Old 11-29-2009, 04:02 PM
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Quote:
Originally Posted by 40 grey
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.
While a flat top or D dish piston is more ideal with the vortec heads or any other good head, the vortecs wiht a dished piston will still be miles ahead of the head you got now.

The 350-330hp 350 HO crate motors comes with dished pistons and vortec heads.

For best results with the stock dished pistons, shave .040" off the vortecs (58-59cc finished chambers and install with .015" felpro 1094 gaskets.
Replacing the pistons with flat tops is also a good option.

Last edited by F-BIRD'88; 11-29-2009 at 04:39 PM.
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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.

Ed

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