2 Quick Engine Questions

[1986Warthog]

#1: I have a 305 under the hood of my Parisenne and my caprice. Do they use the same engine mounts.

#2: How far can I over-bore a 305, and what pistons would I need?

[silicon212]

Originally Posted by 1986Warthog

#1: I have a 305 under the hood of my Parisenne and my caprice. Do they use the same engine mounts.

#2: How far can I over-bore a 305, and what pistons would I need?

The Caprice and Parisienne are the same car, just with different front and back cosmetics. A 305 is a 305 (SB V8, that is ... ) - they all have the same mounts.

The furthest safe overbore is .030-.040 depending on the block. As for pistons, that depends on how you want your engine to perform.

I'm using Silvolite hypers in my engine - 277k miles (some of them were hard driven, too) later and they're still going strong.

[PeteA216]

How far can I over-bore a 305, and what pistons would I need?

I know you've probably already heard this, and people preached the same thing to me when I wanted to build my 305... but my advice is to get a 350 and build that instead. Internal parts such as pistons, rings, etc are in much greater abundance and selection for a 350 over a 305 and in some cases cheaper for the 350. Plus, the same amount of money put into a 305 and 350will result in the 350 way out performing.

If building the 305 however, I'd strongly recommend replacing the heads simpy due to the small size of the valves in a 305's stock heads. Also I personally wouldn't bore more than .020 over for a couple of reasons: 1) It leaves room for another punch of .030 or even .040 if another rebuild will come in the future. and 2) Although very rare, it brings to possibility of cracking the block under extreme conditions due to less material between the cylinder wall and water ports. I've seen it only once and that was on a 327 bored .040 during a drag race down the Lester NYIRP 1/4 mile strip. But like I said... extreme conditions.

[1986Warthog]

Originally Posted by PeteA216

I'd strongly recommend replacing the heads simpy due to the small size of the valves in a 305's stock heads.

Could I just machine thr heads and put oversize valves in?

[PeteA216]

I think Silicon would know more about this, but you can lightly mill the heads for a little higher compression and port the valve ducts to be larger, but as far as I know the size of the valve itself can't be changed. I could be wrong though.

[silicon212]

Originally Posted by PeteA216

I think Silicon would know more about this, but you can lightly mill the heads for a little higher compression and port the valve ducts to be larger, but as far as I know the size of the valve itself can't be changed. I could be wrong though.

There are heads that can accept a machine to a 1.94 intake/1.5 exhaust relatively safely (for the engine). The heads used on almost all 305s are of the lightweight, thin casting variety, so there isn't much area for machining - whether it's to unshroud a large valve or mill the heads. The most you can really safely mill from the head is perhaps .005" or so - just enough to true it. Don't look to milling to increase C/R - look to a good set of aftermarket heads.

Most 305s have 1.84/1.5 size valves as this is the largest valve the engine can safely take due to bore size (again, excepting the one head which puts the valves closer together). The problem is valve-to-piston and valve-to-cylinder block interference. Most factory 305 engines have pistons that do not have valve reliefs in them (they're not 'fly cut'). It is for these reasons that in the overwhelming majority of cases, you cannot use larger than 1.84 intakes on a 305 - and this in turn is why the 305 is anemic and cannot breathe at higher RPMs.

Personally, I'd recommend a good set of aftermarket heads such as World Products S/R Torquer 305 heads. These do use 1.94 intakes.

[1986Warthog]

Thanks Guys...
Here's another question. One of my Co-Workers gave me a 305 out of a late 70's Firebird. I was looking at possibly getting an Edelbrock top end kit for it and working my way up from there. any suggestions?

[silicon212]

Originally Posted by 1986Warthog

Thanks Guys...
Here's another question. One of my Co-Workers gave me a 305 out of a late 70's Firebird. I was looking at possibly getting an Edelbrock top end kit for it and working my way up from there. any suggestions?

What is it going in?

[PeteA216]

Edelbrock comes with what they call a "total power package" which comes with a full roller cam, aluminum heads, performer intake, and carb.

[1986Warthog]

Originally Posted by silicon212

What is it going in?

The Caprice... I hope

[PeteA216]

I do know for a fact that the early 305's had a soft cam lobe issue (70's up 'till '83). So if it has the stock camshaft, I'd relace it before putting the engine in as preventive maintanace.

[1986Warthog]

Turns out the engine is from an '84 Firebird.
I am going to start the tear-down next week. The guy said it ran good, he just bought the car for the Transmission. If it's not bad, I think I'll just hone the cylinders and replace the rings. But, what type of headers should I get? (Full Length or Shorties)

[silicon212]

Originally Posted by 1986Warthog

Turns out the engine is from an '84 Firebird.
I am going to start the tear-down next week. The guy said it ran good, he just bought the car for the Transmission. If it's not bad, I think I'll just hone the cylinders and replace the rings. But, what type of headers should I get? (Full Length or Shorties)

If you're going for just street stuff (which, good God man, it's a 305 - you'd look ridiculous at a racetrack), then stick with 1-5/8" primary tube headers with collectors that are 3", and at least 6-8" long.

PeteA216's cam suggestion is some sage advice. I'd suggest a decent cam for it such as a COMP 270 Magnum, or one of the Extreme Energy grinds in the 260-270 range with lift in the ~4.5" range. Make sure you use new lifters and new valve springs, and Shell Rotella-T 15w40 motor oil! Also, replace that sh*tcan plastic coated timing sprocket, timing chain and crank sprocket with a decent new timing set. Chances are, the chain is stretched, and those nylon teeth will eventually wind up in the oil pan, and in your oil pump pickup. It doesn't *have* to be a high dollar roller set, a decent aftermarket OEM-style one will work good as well. It's a little more money to spend on the engine, but you can get all of this stuff for around $300. The cam will add low-end (which a 305 desperately needs), and a nice rumpity idle as well.

[PeteA216]

Headers... I've only used headers twice personally, but most of the guys I hang out with use headers. Three things I recommend based on what I've seen, done, researched, and read in magazines (big fan of Car Craft... lots of great hints, tips and specs)... Coatings: A chrome coating looks nice in the short run, but I see them discolor very quickly from heat. I'm not sure how long they last in terms of the chrom staying intact. I'm sure if maintained properly, it can last for quite a while, but heat is it's biggest killer. Ceramic coatings do a lot for headers. They come in a variatey of mixtures including tungsten and titanium. The function ceramic coatings serve that I like the most is that they act as a heat barrier. The ceramic helps to keep the heat inside of the header as opposed to letting it out into the engine compartment. They also help to protect the metal against corrosion and corrosive materials like salt. Corrosion isn't an issue with good stainless steel headers though, which brings me to my next subject... Materials: There's basically only two materials I see headers made of steel and stainless steel. With a ceramic coating, it's usually overkill to get stainless steel headers, but for chromed or painted headers stainless steel is a good idea becasue hot metal likes to rust much faster and easier than cold metal due to the fact that rust is a chemical reaction and all chemical reactions take energy to react. Heat = Energy = Nice energy supply for rust. The third thing I like to look at is the Header Collector: Long tube headers are nice, if you have the room. If space is an issue short tube headers will work just fine. The collector of the header makes the biggest difference however (The area where all 4 pipes come together into 1 and reduced). A collector acts sort of like a cam or an intake does in the way it affects what RPM range will have the most power. Shorter, large diameter collectors have more peak power. Longer, smaller diameter collectors have more power in the midrange.

There's more information that varies the powerband and how you want it to perform such as sequential piping length vs non-sequential piping. You cand find out much more in greater detail and spec here

[PeteA216]

Oh and Silicon reminded me about the cam thing.... something I regret is not installing a roller cam in my engine project. After looking at power charts and spec comparasons a roller cam will out perform a flat tappet cam in power, longevity, and efficiency. I personally chose a cam that was just above stock, to give it a little bit more get up and go, while still keeping the nice spooth idle a Caprice should have (it turned out it's still a little rougher than I thought, but I'm still happy with it.)... unless it's like Silicon's in which case I'd be afraid to line up with him for 2 reasons... he could be a cop, and I'd probably get spanked. I guess it depends what your looking for... you can do a lot with a Caprice.