[C1] Changing out from 283 to 350
05-23-2018, 01:59 PM
#21
Race Director
For all intents and purposes the 350/290 is the same as a seventies vintage L-82, and the 350/260 is a L-48. The 290 has a more top end power, but the 260 has more low end torque and uses what is essentially the '67-up 300 HP cam, but with slightly refined lobes and a different part number.
the 290 cam IS the exact same as the L-46/82 cam from that era... same part number.
Duke
the 290 cam IS the exact same as the L-46/82 cam from that era... same part number.
Duke
It's interesting though that I used the cam I took and and installed it in my '62 when I broke the camshaft in the LT-1 short block. That engine has Dart Iron Eagle heads, 72 cc to lower compression a little, headers Weiand manifold and 670 Holley Avenger. The cam with that combo makes it extremely responsive and strong.
If you are going to buy a crate engine and not want to make any changes get the 260hp one, with the 290 hp one you are going to want to change at least the heads and while you're at it change the cam too.
05-24-2018, 07:41 AM
#22
Team Owner
Member Since: Mar 2003
Location: Greenville, Indiana
Posts: 26,118
Received 1,843 Likes
on
1,398 Posts
FWIW. I bought a new '71 Cheyenne pickup truck. 350 ci. Standard transmission. Low compression. I think it was 8-1 or maybe a little more.
The truck was a total dog. As delivered, it would run 72 mph in the quarter. Over about 5000 miles I changed:
195* to 180* thermostat
Quadra-Jet to a 780 Holley
Vac advance distributor replaced by dual point Delco
Single exhaust replaced with duals
Removed the fan blade
Stock cam replaced with L 79 cam
With these simple changes, the truck now runs 93 mph in the quarter and I picked up 3.5 mpg highway. I checked fuel mileage on on every tank of gas and documented 1/4 mile trap speed after every change. By far, the biggest improvement in power came with the camshaft change (on the low compression heads).
100 thousand miles later, I took the opportunity to change the 76cc heads for (stock) 64cc heads and boosted the compression. I don't remember what improvement I recorded but SOTP's, it felt as big as the cam change, thousands of miles before.
My only point here is, don't think the L-79 cam won't work with low compression. It will.
The truck was a total dog. As delivered, it would run 72 mph in the quarter. Over about 5000 miles I changed:
195* to 180* thermostat
Quadra-Jet to a 780 Holley
Vac advance distributor replaced by dual point Delco
Single exhaust replaced with duals
Removed the fan blade
Stock cam replaced with L 79 cam
With these simple changes, the truck now runs 93 mph in the quarter and I picked up 3.5 mpg highway. I checked fuel mileage on on every tank of gas and documented 1/4 mile trap speed after every change. By far, the biggest improvement in power came with the camshaft change (on the low compression heads).
100 thousand miles later, I took the opportunity to change the 76cc heads for (stock) 64cc heads and boosted the compression. I don't remember what improvement I recorded but SOTP's, it felt as big as the cam change, thousands of miles before.
My only point here is, don't think the L-79 cam won't work with low compression. It will.
05-24-2018, 11:02 AM
#23
Race Director
Member Since: May 2000
Location: Redondo Beach USA
Posts: 12,487
Received 1,974 Likes
on
1,188 Posts
It's not the same. The 290 hp version is about 8 1/2 to 1 compression and with 76cc smog heads. With the L-46-/82 cam it makes it a real slug. It was a real dog when I put it in my '68 Impala wagon. I changed the cam to a Lunati 101 and put on a set of old World Product heads, 64 cc and 2.02 intake. It made all the difference in the world.
It's interesting though that I used the cam I took and and installed it in my '62 when I broke the camshaft in the LT-1 short block. That engine has Dart Iron Eagle heads, 72 cc to lower compression a little, headers Weiand manifold and 670 Holley Avenger. The cam with that combo makes it extremely responsive and strong.
If you are going to buy a crate engine and not want to make any changes get the 260hp one, with the 290 hp one you are going to want to change at least the heads and while you're at it change the cam too.
It's interesting though that I used the cam I took and and installed it in my '62 when I broke the camshaft in the LT-1 short block. That engine has Dart Iron Eagle heads, 72 cc to lower compression a little, headers Weiand manifold and 670 Holley Avenger. The cam with that combo makes it extremely responsive and strong.
If you are going to buy a crate engine and not want to make any changes get the 260hp one, with the 290 hp one you are going to want to change at least the heads and while you're at it change the cam too.
Likewise, the L-48 is 8.5:1, 76cc heads with 1.94/1.6 in valves and the ...929 cam, which is why I drew the comparison between the L-48 and 350/260, which uses what is essentially the same cam with some minor refinements to the lobe dynamics.
Since the 350/290 trades low end torque for top end power, it would not be a good choice for a heavy car with an automatic and tall axle ratio.
Duke
05-25-2018, 01:17 AM
#24
Drifting
I'm looking at the GM 290 hp 350 crate engine from Summit. My period correct 283 just can't do the long tours reliably anymore. I could get it rebuilt but think it's cheaper to get the crate engine. I want a workhorse engine that will allow my wife and I to tour longer distances. The replacement engine doesn't come with an harmonic balancer or water pump. My 283 has low mileage balancer and pump...will they fit on the new engine? Also, has anyone does this swap? Thanks again for your suggestions.
There are several possible solutions to this problem, but they each require some time and attention. Other threads on this forum have discussed this topic and offered various solutions.
If you want an engine that has the rear crankcase vent, you will have to use a pre-1968 327 block or one of the GM replacement 3959512 blocks that were made in the 1970's. Any of these blocks can be fitted with a modified 350 crank to give you 350 CID.
So, you can either get your replacement 350 by purchasing a crate motor or by having an earlier block built as a 350. The difference is that the older block will not require any effort to sort out the crankcase ventilation.
Aside from the crankcase ventilation issue, I agree that the GM crate motors are very attractive in terms of cost. However, I think you should select a crate motor that you do not need to modify. Once you get into changing the heads and cam, the cost benefits of the crate motor start to evaporate.