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#41
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As an auto tech in the industry working at a shop that worked on all makes in the 1980 era, my experience mirrors what Brad stated. We were doing major engine repairs on 1-2 year old domestic cars and the sales of Hondas and Toyotas and Datsuns was really starting to take off. For good reason. All those cars seemed to need were brake jobs and oil changes. The domestics? Cranks, cams, heads, you name it. On top of all the electrical problems. 1980-1990 was indeed the nadir of American auto manufacturing.
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Jeff |
#42
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“It takes considerable knowledge just to realize the extent of your own ignorance.” Dr. Thomas Sowell |
#43
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I didn't know that my question would stir up so many emotions! I appreciate the responses and advice, especially since it comes from long standing SME's in the field. My plan for now is to do a basic re-ring and deck the heads to 90cc then run it. The car is a 455 factory car so I will patiently be on the hunt for a 455 while I drive the 400 and keep working on the rest of the car. I'd love to daily drive a 12 second T/A but that's not realistic in my opinion, and I don't mean just cruise a few miles but as the only car, all weather every day driving.
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#44
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FWIW: in 1971 The YS 400 engine found in the GTO was rated at 250 or 300hp with 96cc heads and the 067 cam.
It does have the larger exhaust valve; not sure how much that matters at this level. I had one for 20 years. It burned rubber on demand with 3.08 posi; and ran great. So if you could mill your heads to 96 cc or less, you'd give your engine a pretty respectable bump in power, and stay very budget friendly. |
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#45
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That sounds like a solid solution to what I am trying to get done. I need a new cam anyway and from what I can find the torque is around 400 on the '71 GTO so I could live with 375 with my smaller valves.
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#46
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I dont think the smaller exhaust valve is going to make a bit of difference at this level, but i'm not an expert.
I've got a 464 with 041 clone cam, and 6X-4's with the smaller, 1.66 exhaust valve. Runs great. I dont race it so I cant say when it runs out of breath, but it will burn tires all the way down the street. As Brad or someone has mentioned, the '64, '65, (and maybe '66?) GTO's all had smaller valves, and 300+ HP. I dont disagree with Steve; the bigger valve would be nice; but if you're hoping to someday upgrade the heads; i'd just do the minimum. Agree with the others who said build the best bottom end that fits the budget. I've only owned one pair of 4x heads. Mine weren't cracked but the other members have seen more heads than me. Last edited by F ROCK; 03-22-2022 at 07:11 PM. |
#47
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I have somewhat compressed the OP's initial post;
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There is a member here who constantly makes great post that seem to go against the flow - for good reason; Quote:
BINGO - NAILED IT!! Quote:
Again, nailed it. honestly, these engines make great torque, even in the low hp configurations. Back to the OP; I have found that searching for cylinder head cc ratings can be confusing - because they are often wrong. It has seemed to me that PMD when in two year cycles - that is they essentially made the same drive trains for two years; Generally 1971-1972 motors are rated at 8.4:1 compression Whereas 1973-1974 are rated at 8.2:1 compression I say this because you are considering 1973 vs 1972 heads; Those 7k3 heads will probably make a smidge more compression than the 4X heads, and as pointed out they do have large valves. According to the Wallace racing head page, the 4x-4 (350/400) heads are 99cc, while the 7K3 are 96cc. I have run like a couple others here have, small valve heads on my car's motor, and was surprised with how little difference it made; My take away was that engine compression and camshaft play much bigger roles than valve size. If I was you (eodcoduto), I'd run the 4x heads, because those are the correct castings for your Trans Am. I'd be sure to at the very least clean them up well with what ever tools you have available, and inspect for cracking - not because you have any reason for concern, but because you have the engine apart, and this is a good time to find if you have any potential issue. That engine picture to me looked like factory cast slugs, and even though some (more or less) scoffed at them, they are great parts and were used in nearly all the pre-smog engines including the RAIII - so I'd take any scoffing at the idea of using cast slugs with a grain of salt. If you decide to get new slugs, stay away from the ones with more valve reliefs - only because those will lower your compression. If you decide to clean up the engine, and leave the short block alone, I wouldn't fault you - it is after all only a 55k mile engine that ran fine (I understood that correctly - right?) You can play with deck height (if the block will see any machining); You can play with cylinder head milling (if the heads will be resurfaced); You can play with head gasket thickness. All three of those will help you bump compression - if you want to do that. If you will humour it, I'd suggest leaving pretty much everything as-is, and replacing that '255 cam with something slightly bigger like a 066 or a 067 - but don't go too big. It reads as though same year 066 cammed 400/4bbl motors were rated at 200hp (+20), while 067 cammed 400/4bbl motors were rated at 230hp (+50hp). Please let us know what you do, and the results.
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1970 Formula 400 Carousel Red paint on Black standard interior A no-engine, no-transmission, no-wheel option car. Quite likely one of few '70 Muncie three speed Formula 400's left. 1991 Grand Am: 14.4 @ 93.7mph (DA corrected) (retired DD, stock appearing) 2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs) |
#48
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Dennis |
#49
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if the engine didn't seem to have any short block issues, I"d just clean up the gasket surfaces, and swap top ends. I've never had a problem from doing that; If you take you're time, and don't rush things, it's pretty straight forward.
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1970 Formula 400 Carousel Red paint on Black standard interior A no-engine, no-transmission, no-wheel option car. Quite likely one of few '70 Muncie three speed Formula 400's left. 1991 Grand Am: 14.4 @ 93.7mph (DA corrected) (retired DD, stock appearing) 2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs) |
#50
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I’ve done that a few times as well, and have a Chevy 366 I’m doing the same to now for my C/60. As long as the tolerances can be kept it a great way to keep an engine going. Buying all new top of the line everything sound cool, but isn’t realistic for the majority of rebuilds.
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#51
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Dennis |
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