OldCarBum

It all depends on the work he wants done to the heads.
Cleaning up the ports, surfacing, and a good valve job is much less money than buying a bare set of aluminum heads.
If he wants something special done, then it’s the cost of labor to do the work.
If your machine shop is any good, they will want to do all the same work to a new set of heads anyway.
If they just install the components and slap on the heads, I would find a new machine shop and a new engine builder.

ctmccloskey

I too would seriously consider rebuilding the original engine. You already have the big parts and you could build a pretty nice engine out of your original parts. When I rebuilt my engine I made a deal with a buddy who owned a speed shop. I bought the parts from him (at a fixed %) and we assembled the engine at his shop where the customers could see it being built slowly. We took months to build the engine and spread the cost over almost a year which made the project much more affordable. This made the cost of the "new" engine much easier to absorb into our family budget without a lot of hassle.

Numbers matching means nothing with all the fake re-stamped engines out there. Your block should be checked out and then start rebuilding the engine. When it came time to rebuild my engine a buddy offered me two LS3's provided I haul them away. The LS3 is a nice engine but it doesn't look like the engine that came in the car. I took a mild 427 and built a L88 out of it with a few extra parts.

In my case this experience was great as I had never really been inside of a Chevy BB. My buddy had lots of experience with BB's and he taught me a lot while we did the work together. Building the engine in his speed shop made it get lots of attention and many people wanted to buy my engine, my buddy sold a lot of engine builds from that project of mine. It was a Win-Win for both of us.

drspencer

I never mentioned using aftermarket heads.

Thanks

augiedoggy

He's pointed out it's just a street cruiser so performance isn't really a huge factor.
Just my opinion but I suggest that the OP not get talked into something he's never going to utilize.. a mild freshened up 350 will be fine and if the stock exhaust manifolds are being used there really is no point is spending $$ on performance that will be limited by those other choices anyway. He will get the best bang for yhe buck out of flat top pistons and some modern budget heads along with a mild cam.

carriljc

drspencer
I would not spend money rebuilding that SBC. If I was going to rebuild I'd get an LS to rebuild.
As far as EFI. I would get the engine you want first .............and ponder EFI later.....but if I was starting now I would probably be leaning to the Holley EFI system.
It seems to have the most positive feedback.

BUT the truth is that if I starting now and was going to EFI then I'd spend the money on an LS engine and that EFI.
I say having had the following systems:
1. Holley Pro-Jection analog efi on my old 327.
2. Ramjet 350 on GM MEFI ECU
3. Ramjet 350 on GM 730 ECM
4. Ramjet 350 on FAST EZ-EFI 2.0.

HOWEVER - since you have that itch, and you cannot find a cheap LS, then I suspect your original plan to get the 350/357 Crate Engine and one of those low profile Vortec Intake manifolds would make you quite happy. I say just do that, slap your sbc components on there and go....... you can play with EFI later.

drspencer

If the net HP on my stock 350/270 is only 210HP, is the net HP on the GM 350/357HP crate engine actually 357HP?

If so, that's quite a big bump in power, no?

Thanks

BKbroiler

Crate engine HP ratings are gross not net.

drspencer

Any idea what the net HP would be from a GM Performance 350/357 HP crate engine?

Thanks

Newbomb2469

Some interpretation from the data is needed, but generally it seemed the difference between gross and net HP figures was app 60-70 HP.

drspencer

GM 350/357 Crate Engine Specs:

• Part Number: 19367080
• Engine Type: Chevy Small-Block V-8
• Displacement (cu. in.): 350
• Bore x Stroke (in.): 4.000 x 3.480
• Block (P/N 10105123): Cast iron with 4-bolt main caps
• Crankshaft (P/N 10243070): Nodular Iron
• Connecting Rods (P/N 10108688): Powdered metal
• Pistons (P/N 88894280): Cast aluminum
• Camshaft Type (P/N 12677151): Hydraulic roller
• Camshaft Lift (in.): 0.473” intake / 0.473” exhaust
• Camshaft Duration (@.050 in.): 215° intake / 223° exhaust
• Cylinder Heads: Cast iron; as cast with 64-cc chambers
• Valve Size (in): 1.940 intake / 1.500 exhaust
• Compression Ratio: 9.0:1 nominal
• Required Fuel: Premium pump
• Maximum Recommended rpm: 5600

Regrettably, I'm not familiar with cam specs. Given the above data, can anyone comment on what type of street manners this engine will give (slight lope, smooth as glass, etc.)?

Thanks

ddawson

Thoughts, https://www.summitracing.com/parts/mll-bp3505ct

C3Cliff

If you dig around a bit, you'll find the cam in that engine has a 108* lobe separation angle (LSA). That's borderline approaching the LSA of the Thumpr and other such mall crawler cams that typically have LSA around 106-107 degrees. Most street cams designed with good idle in mind have an LSA in the 112 to 114 degree range. So, to answer your question, its very unlikely that this engine would have the good idle manners you're looking for.

drspencer

Thank you, Cliff. That's the exact type of info I was looking for.

Can you recommend a good crate engine that might be more suited to my needs?

Should I just pony up the $8K to have the matching #'s engine rebuilt to stock?

Thanks

Eric P

Blueprint rates their engines conservative , Red Line in Illinois install/dynoed a 408 Ford Windsor and a LA 408 Mopar both the 450 hp option, the Ford matched claimed power at the rear wheel and the Mopar was super close

augiedoggy

What about the elephant in the room here that keeps getting overlooked...Quiet stock exhaust and exhaust manifolds? The engine is an airpump and this setup will limit any gains from other mods. It doesnt have to be loud but it does have to be able to flow substantially better.


All these higher hp builds (im pretty sure Torque is what The OP is really looking for here as he may not understand that without expensive mods like gear changes the higher hp will typically make the car less peppy around town) I would stick with a smaller cam myself around 215-220 duration if you want that throw you back feeling at the stop lights it comes from torque (or high rpm hp + torque with 4.11+ gears). Car and driver rated the l48 more fun to drive in the city over the L82 for this reason.

drspencer

Can someone please tell me what cam/specs came stock in my '71 350/270?

What currently available cam would be most close to the original?

Thanks

Roadster71

A little lumpier but not a lot. Definitely made a difference in street manners. More hp and Torque.

leigh1322

Your 270 HP L48 can be refreshed inexpensively, and a little more HP added without changing the characteristics of the way it runs.
That is what I am hearing you say.
Your engine has very low compression of 8.5, and may actually test lower.
It was an early attempt at emissions. They don't do that anymore.
You should change the pistons and raise it.
You have dished pistons, go for the 4 eyebrow flattops. You'll probably get 9-9.5+ and it will feel a lot more crisp.
Inexpensive cast pistons will be fine for this build.
The Q-Jet is a terrific carb, keep it. Have Lars go thru it.
An aluminum intake may help a little, if you like, no biggie with stock exhaust.
The cam is the heart of the engine's characteristics.
Most people tend to go one or two steps too big in search of more HP.
If that is not your intent, based on what you said you want, stay with a very mild cam.
I will bet you duplicate the 300HP engine or even get 320HP.
The increased compression will help the most.

These are from Comp Cams. The top one is like your stock cam, the lower one like the much rowdier L46 350HP cam. For you I would go 260H or similar. pay close attention to the lower recommended rpm that increases from 600 to 1200 with this cam. You will barely notice it. But it will pull better. Larger cams lose more TQ at bottom end and you do not sound like you want that.

Here is that cam compared to true L48 and L46 cam specs: It's 212 duration at .050"


There is a lot of concern over Comps cams lately.
Here is a very similar cam from Howards, you offers a garauntee against lifter failure with their "certified" sets:

The 2nd & the 3rd cam are both good choices for you. The 2nd will cruise better, smoother and have more MPG.
I would not worry about changing the heads at this power level. The HP difference is very little. Just base it on $ vs rebuilding yours.

drspencer

Wow, thanks for the detailed response.

I was strongly leaning towards the new GM 350/357 Crate, right until I was told that the cam that comes with it has a 108* LSA, which apparently gives a lumpy idle, by nature. Others have claimed that because it is a roller cam, the rowdy idle of a 108* LSA will be lessened. Of course, vacuum is also an issue, as well.

Regrettably, I haven't found any videos or testimony from people who are actually using the GM 350/357 to hear their opinions.

When I inquire with Jeggs, Scoggin, etc., every agent I speak with just tells me what I want to hear. If I ask if it has a smooth idle, they say yes. If I ask a different vendor if it has a lumpy idle, they say yes. If I ask if it cures lower back pain, they say yes.

Thanks

leigh1322

My first car was an L48. 1968 SS350 Camaro. 10:1 CR 350-300 HP. QJet.
I loved that engine! It was great smooth idle. Great TQ from idle. Almost a dead flat TQ curve. Rev'd great til 5000-5500 or so. Just "went" in any gear or rpm.
Even got 18MPG on a trip. With mild 336 gears. Kept it for years.
It did everything but like 6000rpm with 160k miles on it. OOPS!
I have driven the later 8:1 CR ones and they just don't have the crispness, they feel very soft off idle, not a lot of go unless you rev it up, then they are closer.
The same engine even ran great in our family's 4500lb Impala.

I also loved my 70 LT-1 that I owned for a couple decades after that one. That one would shut down most big blocks!.
But from a dead stop, from Idle, the L48 would smoke it, until the tach climbed past 3000rpm!