0X-AutoProducts

what 's the difference between the 461 & the 461X heads? i'm told the 461X heads were specific to '63 FI cars, and had a longer inlet opening. also, were aluminum heads available in '63?

SWCDuke

Both the L-84 FI and the L-76 carbureted SHP 340 HP engines have the heads with the "X" suffix, but it's never been clear to me what the difference is between these and the plain jane 461 heads used on the 300 HP engine. Maybe someone else can explain. FI and SHP long blocks are identical. The only difference is the FI system versus a manifold and carburetor, plus minor machining changes in the exhaust manifold castings to accomodate the different choke clean air heater systems and the heat riser valve on SHP versus just a spacer on FI, which was a heat riser valve housing casting without the holes drilled for the shaft and spring.

Aluminum heads were not optional in '63. They were a planned option for '60, but it's not clear if any ever actually left St. Louis. There were problems with them and for that reason the Briggs Cunningham Corvette team that went to LeMans in 1960 used the iron version, the first year these "big port" heads with 1.94"/1.50" valves were available. I'm not sure if these early iron versions had the "X" suffix or not. These heads were only used on the FI engines with the Duntov cam in '60 and the power rating increased from 290 to 315 HP, In '61 they were installed on the FI engine with the base hydraulic lifter cam, increasing the horsepower rating from 250 to 275. Beginning in '64 461s destined for SHP/FI engines were cut for 2.02"/1.6" valves and had a circular relieve cut in the chamber on the axis of the inlet valve to reduce inlet valve shrouding.

I guess I can expand the question by asking if anyone knows the untilization of the 461X castings beyond the '63 SHP/FI engines.

Duke





[Modified by SWCDuke, 2:26 PM 1/24/2003]

66427-450

Duke said it all.....

I just remember: the "big" 327 heads had 1.94" intakes to 63, 2.02" 64 and later..... port sizes were the same.

63FI

The 461X heads were '61 only. The difference was the intake runners flowed better than the regular. I believe the stock flowed about 160cc and he X's did 172 or something close to that. The valve sizes were the same an 461's. Someone here will know the exact flow #'s for the X's.
Lou

0X-AutoProducts

no post from johnz???
:( :cry

JohnZ

Lou's got it - the 461X casting had a 175cc intake runner (vs. 160cc for the 461); most of the added capacity was in the bowl area under the valve, not in the main port cross-section. :thumbs:

SWCDuke

How to the 3890462 heads that were used on the '67 300 and 350 HP engines differ from the earlier 3782461 used on medium performance engines and 3782461X heads use on SHP/FI engines through '65.

Duke

0X-AutoProducts

duke, good question.

lou and john,
thanks for the info.

lou, were the X heads a '61-only option regardless of induction or required for a '61 FI car?
it seems they offered for later years as well. agree? the reason why i ask is because i've seen X heads offered for a '63. I've been thinking about buying a set of double hump heads and would like to get the correct casting/date code numbers for my jan '63 FI car. i know the heads are judged based on only external appearance/configuration, but i'm curious about the X heads. the heads i have are the non-X 461's, but the casting date is '67, and they have the bigger 2.02s and the 1.6 valves. are the non-X heads the correct # for a '63 fuelie?
i know, too many questions. i promise to stop after this
:flag




[Modified by bearvette, 5:43 PM 1/25/2003]

63FI

Bearvette,
I don't think the heads were an option, they were on the FI cars only.
I still say they were '61 only, so you can't get a set with the right date codes.
The 2.02 heads that you have on your car from a '67 will perform better than the CORRECT 461 NON-X's that came with your motor, because the 461's from '63 had the smaller 1.94/1.5 valves in them. So, to get the correct ones will cut performance a little. That is why the '63 FI was rated at 360HP , and the '64-5's were 375. Are you going NCRS?? If you are, forget what I am about to suggest. If you want a BIG performance increase, loose the stock iron heads and get a pair of either Trick Flow or Air Flow Research Aluminum heads. Remenber the big deal with the X heads were a 160 to 175 CC volume increase? Well, either head I mentioned has 190 CC's. I have a pair of the TF's and they are great! You loose 40 lbs, get angle plug entry, BETTER flow and they have removeable valve guides. That is one thing I HATE about the stock heads is you are at the mercy and tallent of some machine shop to work on your heads. They have no replaceable guides, so it is always a question of wprkmanship/ how they are going to do the job. I have my stock ones in the corner of my garage. I don't think I will ever use them again.
Lou

Solidlifters

63FI, I'm not positive, but I'm 99% sure that I've got some X heads with 63 date codes. I can also check my 62 fuelie which has the original heads and see if they're X's. If you're correct about this, you're enlightening me on something that I've been wrong about for a very long time.

Here's one statement that is incorrect: "That is why the '63 FI was rated at 360HP , and the '64-5's were 375. " The change to the 30 30 Duntov camshaft in 64 from the earlier camshaft that was a carryover from the 283's was more responsible for the increase in HP than the small difference (.008) in intake valve size.


[Modified by Solidlifters, 11:30 PM 1/25/2003]

SWCDuke

461X heads are correct for '63 SHP and FI engines. Not sure about 64-65, but I expect they are correct for those engines to. As stated, in the prior post, the increase in HP was primarily from the 30-30 cam used in '64 in place of the '63 Duntov, but it cost noticeable low end torque. The increase in valve size contributed, but not a great amount.

Since the head casting number and casting date is under the valve cover, NCRS cannot check them. They can only look for the external cues - double humps and no accessory bosses/holes on the front exterior surface of the head. I don't think you can disern the difference between 461, 461X, and 462 heads from their visible features when they are installed on the engine with the valve covers in place.

I think it was '68 when the heads got some pads and threaded holes on the front surface for accessory mounting, so at that point there is an external visual difference.

Duke

Solidlifters

One other thing that I can vaguely recall, without details of course, is that some of the double hump heads have one of the humps partially cut off on one end of the head. I've seen this on a significant number of heads, but can't recall the application pattern or years.