The Nostalgic 265 Engine Build

[bfalfa55]

I know I could build my 350 more or anything bigger but I want to see what I can out of this little engine with a modern cam grind and better parts than an old school build. The engine is a 56 265, .060 over that has been balanced. It has cast dome pistons (still need to cc the pistons), 327 rods. It should be in the 10.5 to 11:1 comp range. It will be a street/strip engine. I am planning on using Comp Cams Extreme 4x4 Hydraulic Roller cam, .474 lift int & exh., duration 230 and 234 @ .050, 111 LSA. Being more limited to 1.94 intake valves due to bore size, I am planning on using a set of 1991 L98 Aluminum Corvette heads, 58cc chambers. WIth all this information put into Comp Cams CamQuest, it seems it should be a strong running engine. Reading one of your other posts here in the Engine Shop, I saw you say  many people port their heads too much for smaller cubic inch engines. I always thought that could be the case, glad I read that from somebody with more experience than myself. With stock flow showing 196 cfm @ .500 of lift, I only planned on porting them enough to clean them up and make them even. What ultimate flow numbers do you think would be good to shoot for based on the info. I have given ? Also, I am running a single plain manifold with a 650 dual feed, double pumper for a carb and roller tip rockers. I would appreciate any help from all of the rest of the FED groups expertise !

[George]

I found my 355 too light on power. Had to move up.

[wideopen231]

I have 2 283's sitting in building and have thought about building one for true Jr. Fuel car.Modern solid lifter cam,good set of heads and valvetrain,11:1 or so and 90% or so load.Run it high gear only with high rear gear. How long would it live? No idea ,but dang it would be a blast until the big blast of parts.

Right now I'll stick to getting car done and playing with little Hemi I have.

[Paul New]

A buddy of mine held the record in SS/P in his 55 Chev I think it was around an 11.60 with a 265 and an itty bitty carburetor. Pretty sure he keeps the RPM's below 9000

[bfalfa55]

I have been in contact with a 55 Chevy SS/O, SS/N driver who runs times similar to that. I figure with modern technology, a strong running street/strip engine can be built better than what you could make back in the good old days. I have tried to pick parts that would also work with a small blower in the future like m avatar pic shows.

[Van]

The top improvement needed is something around a 6.2 rod and a lot shorter compression height piston. On that 56 block, I cut a small groove in the #5 cam bore to connect the oil holes so it will oil the lifters without the cam having a flat. Do this before installing the bearing.

[bfalfa55]

Thanks Van. The oil groove issue I know.  Before finding this engine with domed pistons, I considered using after market domed 305 pistons and using GM 5.94 in rods. I figured this would be a more cost effective way to get after market pistons that wold be similar to the bore of a 265.Why is a longer rod setup a big improvement ?

[Roger]

A longer connecting rod will reduce the rod angle to the cylinder centerline. Less rod angle will reduce piston side loading so there will be less friction and less cylinder wear. The long connecting rod also allows the piston to stay at top dead center longer as the mixture ignites. That gives the combustion pressure more time to build before it starts to shove the piston down the cylinder. All this would result in additional power being produced along with a decrease in cylinder wall wear.

[bfalfa55]

Thanks Roger, that makes sense. Is there any formula or way to figure out the percentage of power increase you would get from one rod length to the next ? For example, if using 5.7 rods made 400HP, how much more power would 5.94 rods or 6.2 rods make as was suggested earlier ? Or is it something that would just have to be measured on the dyno ?

[Roger]

The conventional wisdom says that a rod-to-stroke ratio of 1.6 to 1.8 is a real good for a high performance engine. With a 5.7” rod and the 3” stroke in your 265 the rod-to-stroke ratio is 1.9; 5.7/3=1.9. With the 5.94” rod the ratio goes up to 1.98 and will probably do little good in producing more power as you are already over the sweet spot for rod length. The new engine I'm building for my altered has a 3.625” stroke with 6” rods resulting in a rod-to-stroke ratio of 1.65 and I’m very satisfied with it. Just my 2 cents.

[Van]

Roger's info is correct, but in your case the issue is the block is way to tall for that short stroke. The best fix is to run a long rod, this moves the pin up in the piston. The now shorter piston just lost a lot of weight and with the pin higher in the piston the side thrust is way better. Go to any piston Co. web site and look at MODERN racing pistons, they are very short & used with long rods. Compression heights around 1.0 to 1.2 are the norm in small blocks. 

[bfalfa55]

Thanks for all the engine info. I think I will just stick with what this engine is for my street/strip fun. I am thinking about building some nostalgia race car of some kind. I have more 265's to choose from in the garage !

[bfalfa55]

FINALLY a positive, forward update. My oldest daughter is now married, so I can spend some money !

I did a full cc job of my dome pistons in the bore. I will be right in the 10.5:1 compression ration depending on what head gasket I use. I have to use 350 style due to the mods the previous owner did to the top of the bores. So, my question is: what is the thinnest 4.03 bore diameter gasket I can use that will work with my L98 aluminum heads ? If I use a shim style gasket I will be around 10.68:1 if I use a .028 thick gasket I will be around 10.48:1.

I don't care if the gasket is pricey, as long as it won't cause me issues with the aluminum heads.
I also must add, piston is .015 down the bore, so I can't go too thin.

[jeff/21]

less than .030 between the pistons and the head with steel rods and normal piston clearance I run pistons on the loose side so i need a little more you can get shim gaskets .016-.018 thick and you can get gaskets that measure your bore size most of the gaskets I use are custom

[Roger]

Just put together a street machine engine with steel shim head gaskets. Used a 0.015 thick gasket and when visiting with a company rep, he told me the final compressed thickness of the gasket is between .022 and .024 inches in thickness. That is because it is embossed (stamped) round the holes. You can’t compress it back to original shape cause the stamping process stretched the metal. An option is to use a Multi Layer Stainless steel gasket (MLS). You can get one that has a 4.06 bore and is .027 thick, even when compress cause it isn’t embossed (they also come is various thicknesses). Shim gasket $45, MLS $150. Both work with aluminum heads, should work with your compression ratio, and both need smooth surfaces to seal correctly. Hope this helps.