Which FI engine is this?

[Paul P.]

All:

I am doing a feature article on the Corvette - Italy connection for my local vintage Corvette club. I am including the 1961 Chevrolet Corvette Vignale Coupe, see attached photos.

My question: is there any way to tell if the fuel injected engine is the 275 hp (code 353) or the 315 hp (code 354) from the attached photo? A minor point admittedly but I'd like to include that info if it is possible.

~paul

[Duke W.]

Re: Which FI engine is this?

Yes. First of all both the 275 and 315 HP 1961 engines were equipped with the new "big port" 461X heads that have the classic "double camel hump" casting pattern on the end faces, so you should check for that. This is how they got the name "fuel injection heads" because they were initially only installed on the two '61 FI engines, but usage spread to carbureted engines (300 and 340 HP) in 1962. Valve size is 1.94/1.50", and later follow on designs beginning with the 461 in '64 were built with both these "standard valve sizes" or "big valves" (2.02/1.60") on SHP/FI engines.

The 275 HP engine was equipped with the base engine camshaft, same as the 230 and 245 HP engines, and should idle very smooth at about 500 in neutral. The 315 HP engine was built with the Duntov cam, which will have a lopey idle in the 800-900 range. Also, I believe the 275 HP engine was equipped with reverse flow mufflers, but straight through, i.e. "glasspacks" with the 315 HP version. There's no mistaking the two.

On Covettes the 275 HP tach redline starts at 5300 and 6500 on the 315 HP version. Both were built with domed pistons, and the advertised CR was 11:1. The only fundamental difference is the camshaft.

Quite a stunning car... I assume it's a one-off, and the body is fitted to a standard '61 Corvette frame. Do you know how much it weighs?

Duke

[Mark S.]

Re: Which FI engine is this?

Just a couple of first observations: The plenum is not of the 275hp variety, nor is the gas filter. The 275hp did not have an air hose going to the front from the air filter. However, that does not rule out the internals.

[Richard M.]

Re: Which FI engine is this?

Paul,

If that photo is all you have for reference, the first indication to me that it is "configured as" a 315HP is that the generator is not a Tach drive type. The generator in the engine bay photo is the configuration used for the 315 HP engine.

The 275 HP used the generator to drive the tachometer via a cable drive mechanism and cable at the end frame of the generator. A extended armature with a splined shaft was used to drive the gear mechanism. As you can see in your photo there is no provision for a cable drive.

The 315 HP used a Distributor driven tachometer, which had the high rpm redline and was designed to run at 2X cable speed. The generator shown has the sealed end frame bearing with no tachometer drive end mechanism.

Rich

[Paul P.]

Re: Which FI engine is this?

I've only seen the car twice. First time was at the 2005 Pebble Beach Concours d'Elegance and the next at the Pasadena Art Center College of Design Car Classic in October 2013 where I got the engine photo. I don't recall the details of how it ran at idle so I can't help there. I do have a close up and (barely) readable photo of the FI ID tag which I've attached. I don't think my photo can answer the "double camel hump" casting pattern on the end faces question.

I agree, it is a stunning car. AFAIK it is a one-off and, to me, a great example of Italian coachwork at its best. I would like to know more about it, but there is not much out there that I've found, mostly a Jalopnik article at https://jalopnik.com/the-one-of-a-ki...y-w-1462400723

~paul

Yes. First of all both the 275 and 315 HP 1961 engines were equipped with the new "big port" 461X heads that have the classic "double camel hump" casting pattern on the end faces, so you should check for that. This is how they got the name "fuel injection heads" because they were initially only installed on the two '61 FI engines, but usage spread to carbureted engines (300 and 340 HP) in 1962. Valve size is 1.94/1.50", and later follow on designs beginning with the 461 in '64 were built with both these "standard valve sizes" or "big valves" (2.02/1.60") on SHP/FI engines.

The 275 HP engine was equipped with the base engine camshaft, same as the 230 and 245 HP engines, and should idle very smooth at about 500 in neutral. The 315 HP engine was built with the Duntov cam, which will have a lopey idle in the 800-900 range. Also, I believe the 275 HP engine was equipped with reverse flow mufflers, but straight through, i.e. "glasspacks" with the 315 HP version. There's no mistaking the two.

On Covettes the 275 HP tach redline starts at 5300 and 6500 on the 315 HP version. Both were built with domed pistons, and the advertised CR was 11:1. The only fundamental difference is the camshaft.

Quite a stunning car... I assume it's a one-off, and the body is fitted to a standard '61 Corvette frame. Do you know how much it weighs?

Duke

[Paul P.]

Re: Which FI engine is this?

Rich:

That's interesting about the tach drive differences, I did not know that.

FWIW, the Jalopnik article has a photo of the interior (https://i.kinja-img.com/gawker-media...w7t4jnejpg.jpg) which shows the instruments / dashboard as a combination of '61 Corvette and their own creation. Maybe they were put off by the bouncing of the mechanical tachometer and went with an electric unit? The photo shows a different tach.

~paul

Paul,

If that photo is all you have for reference, the first indication to me that it is "configured as" a 315HP is that the generator is not a Tach drive type. The generator in the engine bay photo is the configuration used for the 315 HP engine.

The 275 HP used the generator to drive the tachometer via a cable drive mechanism and cable at the end frame of the generator. A extended armature with a splined shaft was used to drive the gear mechanism. As you can see in your photo there is no provision for a cable drive.

The 315 HP used a Distributor driven tachometer, which had the high rpm redline and was designed to run at 2X cable speed. The generator shown has the sealed end frame bearing with no tachometer drive end mechanism.

Rich

[Paul P.]

Re: Which FI engine is this?

Mark:

Interesting, thanks for the reply. I am tending to go with it being a 315 hp code 354 type. The production numbers seem to push it in that direction as 1,462 of the 315 hp were sold vs. 118 of the 275 hp variety, according to the Black Book. The cost was the same ($484.20) so it would follow that most buyers would opt for the extra horsepower?

~paul

Just a couple of first observations: The plenum is not of the 275hp variety, nor is the gas filter. The 275hp did not have an air hose going to the front from the air filter. However, that does not rule out the internals.

[Loren L.]

Re: Which FI engine is this?

I think you 'll find that the 275 HP is a continuation of what was the 250 HP and used flat-top pistons.

[Duke W.]

Re: Which FI engine is this?

The advertised compression ratio of both the 275 and 315 HP engines is 11:1, and since they both have the same 461X heads that implies the same piston, which I recall is domed, but I think it was cast, not forged. The antecedent 250 HP FI engine advertised CR is 9.5 and 10.5 for the 283/290 HP versions with the Duntov cam.

Since the 275 HP FI engine has the same cam as the base 220/230 HP engines, which has a much earlier closing inlet valve, I would think it would be more prone to detonation.

One question I've never gotten a definitive answer to: Do the 275 and 315 HP FI inlet manifolds have larger cross section runners to match the larger 461X head ports or are they the same as earlier manifolds that had "283 port size" runners.

Duke

[Loren L.]

Re: Which FI engine is this?

"...implies the same piston..." is not what your parts man wants to hear. The piston chart in Gr. 0.629 dtd July 1, 1961 has 3 entries for 1961 Corvettes:
"57-61 ALL, CORVETTE (283) (exc F.I. w/H.L. Cam) 3739886"

followed by:
"61 CORVETTE w/F.I. (L.H.) 3769731
61 CORVETTE w/F.I. (R.H.) 3769732"

In short, the heads mean nothing if the pistons aren't domed.

I think you'll find that ALL of the pistons were cast, not forged. The intake adapter carries the same part #.

[Duke W.]

Re: Which FI engine is this?

The parts book data supports what I said. The LH and RH pistons apply to "w/F.I." so they must be the same for both 275 and 315 HP engines, which is why the advertised CR is the same for both with the same 461X heads.

The next question is why different part numbers for RH and LH pistons.

A little background information is required . Back in that era small block pistons had .060" offset toward the major thrust side of the cylinder. The theory behind this was that the offset reduced piston slap noise. And this is why the flattop pistons have four valve notches. Otherwise "mirror image" pistons with different part numbers would be required for each bank.

The fact that LH and RH pistons are required to the two '61 engines says they have the pin offset, ut only two valve notches.

Beginning with the '62 SHP/FI forged pistons, the pin offset was eliminated, so the same piston can be used on both sides, but it continued for the four-notch cast pistons for some time.

Duke

[Loren L.]

Re: Which FI engine is this?

So there is NO MEANING for the 3rd 1961 engine entry where it reads "(exc. F.I. w/H.L. cam)"? I don't think "(L.H.)" and "(R.H.)" refer to a "TV Tommy Ivo" side-by-side setup, it refers to cylinder banks......and you'd better not get them installed wrong.
I'd also like to hear your source for the 275 HP having 11 to 1 compression.

[Duke W.]

Re: Which FI engine is this?

My '77 vintage P & A catalog shows, std. size, "57-60 F. I. w/H. L. cam (R. H.)3746290." No listing for LH.

Same as what you quoted for '61.

The spec CR of 11:1 for both 275 and 315 HP engines is from the NCRS Spec. Guide, 1997.

Duke

[Loren L.]

Re: Which FI engine is this?

"Same as what you quoted for 61." I quoted 3739886 for 57-61 "(exc. F.I. w/H.L. cam)" and 3769731 LH and 3769732 for RH 61 FI w/H.L cam. How is that "the same"?

[Duke W.]

Re: Which FI engine is this?

"The same" refers to the fact that my '77 P&A catalog shows the same std. size piston part numbers, both RH and LH for "61 CORVETTE w/F.I." as your earlier vintage catalog.

Duke