New member here. I've recently acquired a nice 1971 with a very tired base engine (100K miles), four speed M20 project, and want to swap in a crate motor.
Going for lots of torque for street driving. No racing, clutch dumps, burnouts etc. Thinking of BluePrint's 383 or 396 stroker engines, but had a few questions, mostly regarding the higher than stock port heights and hood clearance.
1. First concern is that I want it to fit under the stock hood. I've read posts that said it won't fit..... some saying it should fit (but only w Performer intake and/or drop base air cleaner), but haven't been able to find one that says "I've installed one and it DEFINITELY will/will not fit under the stock hood, but only with these modifications.

If I can verify fittment, I'll start with my follow up questions.
Thanks in advance,........so grateful for the wealth of experience on this forum
Gary

 

Stock hood is about what intake manifold to use. The block itself is standard size. I have the Blueprint BBC 502 and used the Corvette LS6 manifold in order to fit.

The small block doesn't have raised ports.

I'm going to assume you will be using headers with the new crate. This tool from Summit makes getting to some of the plugs easy.
https://www.summitracing.com/parts/POW-POW301150

 

The exhaust ports on the Blueprint SBC heads are raised. Also the Blueprint SBC's use a Vortec style intake manifold. I have the Blueprint 350 341HP engine and I'm very happy with it.

 

Thanks for the reply. I'm happy to find someone who actually has sucessfully installed a BluePrint crate engine in an early C3.
Can I assume you got it to fit under the stock hood by only changing to the 71 LS6 4 barrel Intake manifold ? Can you tell me how much hood clearance you have now ?

In the Notes section of the Blueprint web page for the 396 SB it says "the heads on this engine feature a .500" raised port vs OEM"
In the same notes section for the 502 BB it says "the heads on this engine feature a .300" raised exhaust port vs OEM" The 502 says exhaust port..... the 396 just says port.
So it seems they both have a raised exhaust port.... the 502BB is raised .300" and the 396 SB is raised .500" over stock.

Did standard big block headers fit the 502 without modification ?

TIA..............Gary

 

Question for "Fly Skids up" : Did you have to do any mods to get the Blueprint 350 to fit under the stock hood ?

 

My 82 was originally a crossfire injection car but after removing the CFI duct work it fit under the hood with a dropped air cleaner with about 3/4 inch clearance. Because of the raised exhaust ports I needed to elongated some holes for the AC compressor brackets.You will need a different flywheel for that engine.

 

Thanks for all the good info. I've heard that the early C3 (like my 71) had less hood clearance than the later cars, but I'm encouraged that the Blueprint crate engines do fit these cars.

I'm assuming I'll have to go with the small (6 3/4") dia harmonic balancer?

Any problems getting standard small block headers to fit with the raised port heads ?

TIA............

 

The 8 inch blueprint harmonic damper fits without issue. My Doug's Headers P/N D350 also fits without issues.

 

Stock hood C3s have likely the lowest hood-line of any chevy ever built. It is what we pay for, to get the style.
The 70 Camaro is close, but it is as high as an LT-1 hood. Our std hood is lower.

Just measured a stone stock 70 LS5 with GM 2.0" drop base air cleaner. Had 1.25" of hood clearance. BB hood, iron intake, Q Jet, 3.0" filter etc. Intake is only 3.5" high carb height.


A small block is similar, but starts with a ~1.0" lower block rail, and the LT-1 can run a 1.0" taller intake than the BB, with the same air cleaner & hood.
Would love to get an exact LT-1 air cleaner to hood measurement!

The std hoods are lower, no one seems to know exactly how much.
But a Performer 2101 Intake, with it's 4.0" height, seems to fit well with the GM drop base air cleaner. Even tho it is 1/2" higher than an OEM intake.
I recently found the twin snorkel air cleaner winds up being 1/2" higher than the drop base.
So if you switch from the twin to the drop you save a 1/2".
And make up what you lost with the higher intake.
If you want to try another 1/2" higher intake, you could always use a 2.5" filter, vs the std 3.0" but you start to choke the airflow.
But the 2101 or a ZZ4 intake is probably your best bet.
IIRC one of the Performers is for the Vortec heads, maybe the 2104?

Most aftermarket air cleaners are not as low as the GM drop base open one.


LT-1 and ZZ4 intakes can be made to fit, but Performer RPMs, probably not. Just a 1/4" too far.

Someone on here had a Performer on a 650HP SB, with a stock hood, and it fit, flowed and made HP just fine!

 

Good info....thanks.

Since the Blueprint engine has vortec style heads, I guess I need to source the shortest dual plane that fits vortec heads. Edelbrock has a performer 7116 that fits vortec, but there is a big disclaimer saying it will not fit under stock corvette hood. I can't seem to find a carb pad height for the zz4 manifold. Anyone know off hand ?

 

The only help I can offer my engine came with This intake manifold which has a carburetor pad height of 4.595 inches. You going to have to find out if the engine you're considering uses the same or a intake manifold with increased carburetor pad height. Food for thought, the Blueprint 350 341 HP engine will run circles around the base L-48 engine.

 

Thanks "fly skids up". I think thats exactly the same manifold that comes on my 396. If it fit in your 82, thats a good start for me.
The only difference that I can think of that might bite me is the lower hood on the early cars.
Anyone know how much lower the hood is on the 68-73 cars, compared to the later c3's ?

TIA..........

 

Both are in my chart.

Jebby has built a lot of engines, and he very strongly recommends the 2701 for C3s.

 

A bit spendy but the GM Performance ZZ6 EFI fits under 1971 base model hood. Turn key. The EFI intake is an inch lower than the carb version.

cheers,
Richard

 

Go for the 396.

 

Thanks leigh1322. I guess I didn't fully read your chart.
I also discovered (from one source at least - I need to confirm with Blueprint) that the Blueprint heads are drilled for BOTH vortec and traditional intakes.
If this is true, then my choice of manifolds just got exponentially greater, along with my chances of getting this under my hood.

 

The 80-82 hoods look very low. I would say they look similar in height to a 68-72 std hood.
The 68-72 LT-1/BB hood has a little more clearance, and so does the std scooped hood on 73-79.
Somewhere around an inch, maybe? In both cases?

 

Yeah...... A taller hood would be my last ditch option. I'm trying desparately to get everything under the stock hood, but an LT-1 or L88 hood would get me some more breathing room.
I don'tmind the look of the LT-1 hood but don't really like the looks of the L88 hood. I read somewhere on this forum that the LT-1 hood only had 1/2" more under hood room than the stock hood tho.

 

LT-1 hood - yeah 1/2" could be in the right ballpark. Not too much more.

So your factory twin snorkel fits well. With "X" clearance. Lets guess ~1"
A GM drop base (2.0') with 3" filter is 1/2" lower than that one.
Your stock intake has a 3.5" carb pad ht.
A 2701 Performer is 4.21"or 3/4" taller. So 1/4" taller in total than a stock setup. Still ~3/4" clearance.

That is likely your best combo. And Jebby loves it and says it fits well on C3s.
Takes a square bore holley or EFI tho.
I'd suggest a vac sec Holley, it fits that air cleaner much better.
The rear air tube vent pipe interferes with double pumpers. It would on your twin snorkel also. Same tube, same position.

Here is a recent thread on the drop base air cleaners.
https://www.corvetteforum.com/forums...-cleaners.html

This guy runs 650HP under a stock hood. And looks like a 3.0" or even a 4.0" air filter!

That looks to be a 7530 Weiand single plane, with a 4.1" carb ht, just like a ZZ4.

 

I did the crumpled up aluminum foil trick to measure my existing hood clearance and got right at 3/4" clearance, at the tightest point.
Thats with the twin snorkle and cast iron manifold w/ Q-Jet.
My Blueprint will come with Holley's sniper 2 FI, but the height is exactly the same as the Q-Jet, so no savings there.
It might give me trouble with the dropped base air cleaner tho.. I've read that the fuel inlet fittings sometime hit the dropped base.