Chevy Performance SP350/357

by 73sssb Wed Apr 25, 2018 8:46 am

Considering swapping my stock 350 for this one from Chevy Performance. There is a version that comes with all new accessories and pulley system for about $5,500, so I'm thinking it's a better idea than dumping money into my old block.

Thoughts? I'm looking to build a fun daily driver that has decent fuel efficiency. What would be a good cruising rpm for mpg with this setup? Or do I have the wrong idea here?

http://www.chevrolet.com/performance/crate-engines/sp350-357-deluxe

by bracketchev1221 Wed Apr 25, 2018 9:51 am

Unless you are looking for a race engine or maximum performance, a crate engine is by far the most economical way to put an engine together. By the time you have yours machined and new parts bought you will be more than a crate engine and these come with a warranty.

by 73sssb Wed Apr 25, 2018 10:00 am

I'm honestly just looking for performance noticeably better than my Crown Victoria - and it's not even an Interceptor! I want the Chevelle to put a smile on my face but still get over 15 mpg average if possible. I'll be running an overdrive so I'm assuming this is pretty doable.

I'd like to hear from people with similar setups as to the "fun factor" and efficiency.

I'm not familiar with cam profiles and what not - since this is a relatively budget model, I'm thinking it's not very aggressive? At what rpm will it cruise happily?

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by thatfnthing Wed Apr 25, 2018 10:33 am

My 0.02:

Assuming you're not going to deviate wildly from stock with the cam, and are going with an OD trans, your best choice for rear gear will be 3.42. It will keep the car at a relatively low RPM for highway cruising and fuel conservation, but still be in the low end of the power band. A 3.73 will get you better launches and response, but will run slightly higher RPMs, and therefore consume more fuel. Depends on how important mileage is to you versus fun.

by bigredlaguna Wed Apr 25, 2018 11:42 am

That engine would be a fun daily driver that will definitely get you the power you want. The engine in my daughter's car is essentially the same, except my camshaft has 206 degrees duration @ .050 on the intake and 212 @ .050 for the exhaust.

It should work well with the stock gearing, but I would recommend a slightly higher stall convertor. I went from 2.73 to 3.42 in the rear end. With the 2.73 gears, the engine felt really strong on the highway. With the 3.42 gears and a switch to positraction, it made it very fun to drive from a dig. At first it didn't have much power for the highway until I changed the jets in the carburetor. I also had to modify the governor to raise the shift points at both wide open and part throttle because the 3.42's made the trans shift much too quickly. The factory wot shift is usually at 4200 if you had 2.73 gears. A th350 with 2.73 gears cruises at around 2000 rpm at highway speeds. The engine you are looking at should be happy at that rpm. My car with 3.42 cruises at 2800-3000 on the highway with a 295/50 tire. If you do go with 3.xx gears, I recommend installing an overdrive also.

I had my engine built locally and while it didn't cost me as much, I did have to do some tuning to the carb. It was also a challenge to find a factory roller block that also accepted a mechanical fuel pump. It looks like the one you are looking at has that provision. Also had to verify the cam had a fuel pump eccentric, since most factory rollers were used in fuel injected apps the fuel pump lobe wasn't even there.

by 73sssb Wed Apr 25, 2018 11:56 am

I was quoted $2,500 minimum from my nearest shop for a rebuild. I think that's extremely optimistic and for $5,500 I can get this setup with new pulleys, intake, carb, alternator, starter, distributor, a/c pump, p/s pump, etc. And I know what the output would be. Hard bargain compared to the rebuild for my goals.

I don't think it comes with the mechanical fuel pump but I could reuse mine or buy a new one for cheap.

The plan right now is to do something similar to your daughters setup. I need to go through the rear anyway so I want to switch to positraction and maybe a 3.42 or 3.55 rear gear and will probably go with a 700r4. Trying to find a medium between performance and efficiency/reliability.

Thanks for the info so far everyone.

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by 73sssb Wed Apr 25, 2018 12:11 pm

bigredlaguna wrote:... th350 with 2.73 gears cruises at around 2000 rpm at highway speeds. The engine you are looking at should be happy at that rpm. My car with 3.42 cruises at 2800-3000 on the highway with a 295/50 tire. If you do go with 3.xx gears, I recommend installing an overdrive also.

I'm assuming in that range she is getting pretty poor fuel economy? I drove the Chevelle all the way home (about 150 miles) with stock engine and three speed and got 12 mpg. Main stretch I was going about 75 mph (if everything was accurate). I didn't think this was too bad.

I'm hoping with this new engine and a 700r4 I'll be able to cruise at that speed between 1,900 and 2,200 rpm. Close to 20 mpg would really make me happy. Family lives far away and I'd like to be able to take the fun car.

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by brownbomber77 Wed Apr 25, 2018 12:35 pm

LS swap

by bigredlaguna Wed Apr 25, 2018 12:37 pm

I really don't know. My daughter just wanted something to cruise around town in and take to class/work once in a while. I suspect it does better than 12 mpg, though. We took it drag racing after I finally got the car tuned as well as I could, and it didn't use nearly as much fuel as I expected. I had topped it off in the morning, drove it 30 miles away, raced at least 15 1/8 mile passes, drove it back, and it maybe used 1/4 tank. Not accurate, I know, but I was expecting to use much more fuel. I will see if I can do a mileage run in the next few days for you.

by 73sssb Wed Apr 25, 2018 12:42 pm

It would definitely be interesting to know, especially based on the kind of driving you will do. I'm sure mid teens average is possible at least which isn't terrible.

To give you an idea I don't think the car had been driven more than 2,000 miles in the PO 10 years of ownership. Pretty bad fuel smell and oil leaking down both sides of the block. But it made it home! So I saved on towing costs at least.

by bigredlaguna Wed Apr 25, 2018 12:44 pm

My first Chevelle was also a 74 with a 2 bbl 350/th350 and 2.73 and I distinctly remember getting 19 mpg or so. Unless there is a problem with your engine, I firmly believe you can get better fuel mileage right now with a tune up of the ignition and getting the advance and curve set right for the car.

by JF74chevelle Wed Apr 25, 2018 1:41 pm

look into blueprint engines or ATK engines. they build good stuff.

by SSTOOLMAN Wed Apr 25, 2018 3:38 pm

I researched the GM Performance 300 hp 3 years ago this may have changed but you may want do your due diligence and check it out it. This motor does have a does have a warranty but there may be stipulations that involve buying it from a certified GM retailer and having it installed in a GM approved shop. The 300 hp only had a parts warranty (no labor) if you installed it your self.
I am pretty sure I talked to this guy at GM about warranty, cam lope and lower power brake vacuum also. He emailed me a engine installation guide and parts printout.
Gary A. Bell
GM Powertrain Technical Consultant
Chevrolet Performance Parts Technical Consultant
An Associate of Morley Company
Phone: 866-453-4123
Fax: 866-842-9480
Email - gary_bell@gmexpert.com

Jegs Tech support gave me the contact info.

by 73sssb Wed Apr 25, 2018 4:15 pm

Thanks for the info, much appreciated!

Did you end up going a different route? If so, what did you end up choosing?

Any bit of warranty is probably fine with me. I feel like local shops won't make any guarantees unless I pay them for install as well.

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by SSTOOLMAN Thu Apr 26, 2018 10:37 am

I went with the GM 260 hp long block. The only difference between the 260 hp and the 300 hp was the cam, all internals were identical. it was $600 cheaper for the 260 (I think around $1600) I bought the GM 300 hp cam (I cant remember the part # or specs) I put a MSD distributer, Edelbrock 600cfm a performer intake on that I had from a previous build. This bumped it up to 300hp. It has plenty of torque with the 3:42 rear end.
I can do effortless posi brake torques (B&M hole shot 2400 stall torque converter). Gas mileage sucks with my turbo 400 only about 13 HWY revs 3200 at 70 mph.

by bigredlaguna Sat Apr 28, 2018 1:53 am

I got the car on a mileage run today, and it sucks. 3000 rpm is 65 mph, and it only got 11.8 mpg at that pace. I might be able to lean the carburetor a little bit but I doubt it would be enough to break out of the 12's. I'm sure that getting an overdrive would improve it immensely, or if I put the old gear ratio in it would be good also.

by 73sssb Sat Apr 28, 2018 12:21 pm

bigredlaguna wrote:I got the car on a mileage run today, and it sucks. 3000 rpm is 65 mph, and it only got 11.8 mpg at that pace. I might be able to lean the carburetor a little bit but I doubt it would be enough to break out of the 12's. I'm sure that getting an overdrive would improve it immensely, or if I put the old gear ratio in it would be good also.

Good to know. Thank you for doing that. Let's me know where my revs should be to reach my goal.

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