77 vette

I have this book that is a "GREAT READ" but it's for the 260 HP Chevy creat motor with stock cast pistons and crank. It has 6 chapters where they take a plan Jane 260 HP chevy long block and dino the "WEE" out of it, it comes out at 239 HP and 324 Torq. 6 chapters later they bolt on a Weiand blower and spin the WEE-WEE out of it, they came up with 471 HP and 452 ft lbs of torq all below 6000 RPM's, In between they do just about every thing you can with bolt on's to squeeze more HP out of it. I dig this book because they are obviusly trying to blow this sucker up with over a 100 full pull dino runs and it won't blow (even with the cast internals), it's insaine. Ref Small block chevy engine buildups, HP BOOKS, $20.00 bucks. Pease.

vetteguy75

I recently installed the GMPP 350/290 and I am totally pleased! It idles smoothly (800 in Park/600 in Drive); doesn't have that "burn your eyes out" smell when idling (Holley 670 SA); kicks *** when you floor it; AND has (and always has had) 12-13" of vacuum (12* initial timing and 36* at 3000). I'm using the silver vaccum advance spring in the carb;

But I'm always open for "better"

guitarcrazy02

I have the same motor, and experienced the exact same problem you are describing. I plugged every vacuum line, tried 4 different carbs, and 2 different intakes, with no real results to speak of.

I took the valve covers off and adjusted all of the rockers with the motor running. Loosened each rocker one by one until I heard a little chatter, and then tightened it until it stopped, then went a quarter turn past that. Did it for all of them, and it made it a LOT better. Got it to the point where it would at least idle on it's own, granted a little high, but it was drivable.

I have a little over 1,300 miles on the motor now, and it's infinately better. I think it was just really "tight" since it was new. I have a tool that I use to turn the motor over by hooking it into the teeth on the flywheel, and when I first had the engine in, I could barely get it to turn. I imagine now if I tried, it would move like butter.

Try adjusting your rockers. Mine were waaaay too tight. Once you do that, you just have to drive it, even if it drives like crap. Get your timing and fuel set about right, and then just go. It needs to "break in" and get some miles on it, and then I promise it'll be much better.

It's like a finely aged wine, really. It just needs time

guitarcrazy02

Also, the cam is not that big. It shouldn't idle bad because of that.

77 Vette Girl

Kev82vette, I see you have another thread on the same problem...keep after it. Guitarcrazy02 reminded me that I had a similar problem with the rockers when I was installing the 290 hp engine. I purchased full roller rockers and installed them while the new engine was still on the stand. Pulled the valve covers and started pulling factory rockers off and....low and behold , about 4 of them were so loose there is no way that engine would have run right, if at all!! I would not have checked them if not replacing the rockers. Sounds like you have the opposite (too tight rockers) problem, doesn't seem like a big stretch since this problem appears to be common. I thought these engines were run before delivery.....now I think not.

guitarcrazy02

I don't think that they are run before delivery. There's no way. There wasn't even a slight film of oil anywhere in my new engine. It was totally dry to the bone.

I was actually kind of disappointed with the whole quality of the engine. No break in directions. No spark plug and oil recommendations. Nothing. Just an engine in a crate.

I wondered, ironically, when I was putting the engine in, how they adjusted the rockers accurately without running it, since they're hydrolic lifters, and they need the little bubble of oil to adjust them to the proper height. Then I went to adjust them and realized, THEY DIDN'T! They must just torque them down to so many ft. lbs.

guitarcrazy02

I don't think that they are run before delivery. There's no way. There wasn't even a slight film of oil anywhere in my new engine. It was totally dry to the bone.

I was actually kind of disappointed with the whole quality of the engine. No break in directions. No spark plug and oil recommendations. Nothing. Just an engine in a crate.

I wondered, ironically, when I was putting the engine in, how they adjusted the rockers accurately without running it, since they're hydrolic lifters, and they need the little bubble of oil to adjust them to the proper height. Then I went to adjust them and realized, THEY DIDN'T! They must just torque them down to so many ft. lbs.

Also, I still read slightly lower vacuum readings, but not as much as before. Like I said, I think it has something to do with putting miles on it.

tgcattle

I purchased my engine from summit. It came with no timing suggestions or any engine specs. I called summit they said to set timing at 10 deg. And that the cam is 454/223. 9.5/1 compressin ratio. I have a performer intake, holly 600 cfm carb. Vac. is 17-20 in. Engine ran fine for about 3 months. Then the carb started shooting gas out the top. checked float level it was all of a sudden very high. I adjusted float level. Then i was unable to set the timing at 10 deg. with out the motor dying. Ok 600 holley I think is worn out. Solution, I installed an edelbrock 750, I know a little big so I'm told. I plan new alum. heads soon. The new carb helped some,still an exhaust popping on deceleration and timing would not go down to 10 deg. checked spark at least 3 cylinders seemed to not be firing. Solution order summit brand distributor and msd box. Timing now will set at 10 deg.. still popping upon deceleration. but has alot more get up and go. This problem happened overnight, ran fine one day the next day not so good. I spryed ether around intake to see if it was leaking, appears to be no leak. I suppose I may have a blown head gasket between 3 and 5 cyl?? Any ideas???
Thanks

corvettesilver78

I have this same crate motor in my 1978 Corvette and I had it installed professionally last sept and I found out yesterday from the Mechanic the the cam in this motor is the wrong one. They have to replace the cam in order for the engine to preform right. I had problems with low vacuum and no performance at all. Ran poorly for this long. I think GM needs to make this right. Now my Corvette will be out of commission. What do you Think?

mobird

jfurcht

I have the 350-300 GM crate from Pace Performance. Same base engine but a mild Lunati cam brings it up to 300hp. I have a Performer intake and originally had an Edelbrock 750 carb on it. Had low vacuum but it also fluctuated. I put on a Summit Racing 600cfm carb, which ran much better right out of the box. I also adjusted the timing per Lar's papers found here on the forum and elsewhere. Between that and just driving the car it has smoothed out and I am happy with it. Except for the 11mpg and 5 stops for gas going to Carlisle!

ESU

Had a low vacuum issue with mine also,,,, and I bought mine 9 or 10 years ago.

jb78L-82

You are alive?!!!! Call me dude

Buccaneer

Isn't that 290 hp crate a 8:1 CR motor?

theandies

That's what girlfriends are for...........

SI67

I have read that the cam GM puts in this engine was designed for use with higher compression and is actually a poor choice for this low-compression engine.

jb78L-82

Unfortunately, this crate motor is a disaster all the way around....

This motor often is picked as the replacement for the L-82 offered in the mid to late 70's..rated at 220-230 NET HP (78-80...basically all the same with minor tweaks to the motor..lets call it 225 NET HP). This crate motor rated at 290 GROSS HP, NOT NET, seems to be very optimistic with that gross rating. The net HP of this motor is probably around 190-200 NET HP pretty much equivalent to the base engine L-48 passenger car engine used in the C3's. . This engine is NOT equivalent to the L-82 ,as an example, which would be closer to the 71 LT-1 motor rated at 330 GROSS HP (very similar specs to the L-82). Here is why:

The 290 crate motor uses the L-82 camshaft (.450/.460, duration 222, LSA 114) but the compression ratio of this motor @ 8:1 is borderline incompatible with this cam. The L-82 had a compression ratio of 9:1 and even then this cam would have produced more power at 9.5-10:1. In addition, this motor uses the small valved base passenger car L-48 heads with the L-82 cam which would also hurt power. The L-82 heads were 2.02/1.60 verus this head @ 1.94/1.50.....

Your best bet if possible is to pull that motor and install a crate 383 with 400-425 Gross HP......

cv67

Unless you hate the whole enginer period just recam it and motor on
Something like a more modern 256 or 262 type cam should pick it up

could always sell off the heads/intake buy some summit prepped vortecs, used intake.it would raise compression and feel way way better.
Number of shops on ebay sell the improved vortecs upgraded for $400 or less

Kacyc3

Cam swap will be your cheapest correction, it will improve on whats there but it will still be an 8:1 engine with a cam. Changing the compression is what is really needed, you options are make it a 383 to resolve it or swap heads.

jb78L-82

New heads and pistons and you should be good to go...The L-82 cam is pretty decent with some compression. 9:1 compression with iron heads and 10:1 total compression with aluminum heads would wake that baby, up even with that cam.