Yes, definitely a good idea to mention pistons. I once worked on a 327 in which the owner had installed a set of 12:1 forged slugs from a 350. Actual compression ratio was far from expected. ;)
And you're right on with the numbers. The 327 and 307 share the same stroke, the difference in displacement is due to the 327's 4" bore. I believe the 307 went to '73 and the 305 began in '74, but the truck world may have lagged passenger cars.
According to David Vizard, author of "How to Rebuild a Small Block Chevy", there are some 283 blocks with cylinder walls thick enough to bore form 3.875" to 4.000" which makes the displacement 302 cubic inch.
One of the SBC engines I built was only 231 cubic inches, SBC 267 block (3.50" bore) with 3.00" stroke crank (from an original 1969 302). I used some pistons from an olds 260 V8 (3.50 bore), with olds 350 6.0" rods. I used heads from the 267.
dave w
Dave you are correct, I also need pistons. It was late and I forgot to include them in the list. The block currently has 882 smogger heads, which started me thinking about a head change. Then I DD's a 283 with a different cam, then started playing with displacement. The 283 by itself isn't a bad choice, We could probably just do that, but with 58 cc combustion chamber, and flat top pistons, the compression ratio would be pretty high. The Nova had 3.08 gears and a th350 with a STOCK torque converter. Needless to say, it wasn't very well parts matched. In third gear on the freeway, it didn't start running well until you were doing 80 mph. The guy who helped us build the engine and select the cam was a circle track racer, and the engine might have been okay for that. The rest of the valve train wasn't up to the rpm necessary to run right. At 52-5300 rpm the valves would start to float, limiting output (which peaked at 6500 for that cam). So I want to go to opposite direction for the 52, It doesn't have the original torque tube rear end under it, and I think we might go with 3.42 or 3.73 gears depending on tire size. I was worried about whether or not the 307 was a decent engine. Googling it didn't help me much. On the oil usage, the newer heads should solve that. GMPP has a new vortec design head that I may look at. The truck is a long term project, but I am thinking of dumping the 58 Jaguar project and co-building this with my son as it will be a lot cheaper build. (I can't afford to even start the Jag project anyways)Originally Posted by dave w
Square body stepsides forever!!!
Those blocks are very hard to find these days. An old stock car racer friend of mine passed away several years ago and there were a couple of them in his basement. I don't really have anywhere to store anything like that so I passed on the chance to get them. I did grab both of the original '67 forged steel 350 cranks, though. ;) In 80 or 81 you could get a 262 Chevy in a Camaro which had a stroke of 3.01". That crank in a 350 block makes a 302 but those engines are like hen's teeth. These days the easiest route to a 302 is a late model 350 block and pistons with L99 crank and rods. Gotta have it balanced though. The L99 rod/piston weight is lighter than the 302 weight so heavy metal must be added to the crank. Pluses include factory roller block, one piece rear main seal and four bolt main caps. What more could you want for a 302??According to David Vizard, author of "How to Rebuild a Small Block Chevy", there are some 283 blocks with cylinder walls thick enough to bore form 3.875" to 4.000" which makes the displacement 302 cubic inch.
Interesting. Why such a small engine? Displacement limit?One of the SBC engines I built was only 231 cubic inches, SBC 267 block (3.50" bore) with 3.00" stroke crank (from an original 1969 302). I used some pistons from an olds 260 V8 (3.50 bore), with olds 350 6.0" rods. I used heads from the 267.
The 307 suffered a bad rep with rodders for a few reasons. Guys tried stuffing in bigger cams that worked in the 350 but they turned the small engine soggy. It was never available in a 4 bolt main version and the low perf crank, rods, and 1.70 / 1.50 heads worked against running it up high like a 283. Finally, the big brothers 327 and 350 were much more common and therefore a cheaper upgrade route than a set of heads, intake, and cam swap for the small engine.I was worried about whether or not the 307 was a decent engine.
Last edited by 1project2many; 07-18-2013 at 07:34 AM.
Mechanical Engineering Challenge for a V8 Mileage Competition, had to use only factory parts. This was back in my college days during the 80's, dang to I feel old.
dave w
I've got a set of stock DZ302 pistons on my shelf somewhere,factory 13:1 from a 69 Z28 iirc.
I would love to have one of them 262 [4.4] v8s in my truck, highway driving I think it would be very impressive and smooth operating. along time ago we hot-rodded vws, had to shave a little off the top of the piston to get the compression ratio we wanted, now anything past 9-1 better look at what you will fuel it with,maybe e85?
im sitting here wondering how on earth i hadnt heard of or found this site before I absolutly love delco ecu's and everything petrolhead related LOL
It's about time you came across the pond mate!
1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
-= =-
Late to the small displacement party, but here is my two cents. A small displacement engine has to work harder than a larger displacement one to move the same load. Any 'mileage" gain you think you will get goes away in the form of higher rev's, and more fuel to move whatever it is in...
actually, the proportionally higher load is what will cause the higher fuel efficiency.... the lower your throttle, the higher the vacuum, which results in throttling losses.
with a smaller engine, you'll need a higher throttle angle to produce the same amount of power/torque, so it will have less throttling loss.
it's a very similar situation to going to a numerically lower final gear. you'll require more throttle to achieve the same power output. that also has the benefit of dropping RPMs and engine friction is most definitely related to engine speed.
1995 Chevrolet Monte Carlo LS 3100 + 4T60E
If I remember correctly, the Buick 231 V6 did slightly better in MPG than the 231 V8 I built. The Buick 231 V6 had more torque, less HP than the 231 V8 I built. The Buick 231 V6 was not allowed to compete in the V8 competition for obvious reasons. With a 6" connecting rod and 3" stroke, the rod length ratio was 2:1, which is an excellent ratio for high RPM's. I feel 8 cylinders @ 231 cubic inches is better than 6 cylinders @ 231 cubic inches. If I was to do this engine build again, I would want 4 valves per cylinder! The limiting factor of the 231 V8 was VE, not enough cylinder diameter for larger valves in the 267 head!
dave w
And yet, smaller diameter pistons tend to be better for economy and emissions. After combustion there are high concentrations of unburned fuel remaining above the top compression ring. Additionally, combustion tends to be incomplete wherever the mixture contacts cooling parts such as heads and cylinder walls. Xeeping the ring pack near the top and keeping bore diameter small reduces the areas where incomplete combustion tends to happen.
It's all about the tradeoffs. Each engine has weaknesses and strengths. Is the engine rpm high enough to take advantage of intake and exhaust harmonics? Are the combustion chambers promoting best burn? Is the engine oil viscosity causing too much hp loss? Is there too much leakage past the rings?A small displacement engine has to work harder than a larger displacement one to move the same load.
Generally it seems this is true, but it's not due to engine displacement. You can find very classic examples by looking at Honda and GM published fuel economy data. When they use the same size engine in cars with similar aerodynamics you'll see that GM (favors low rpm cruising) gets a slight edge over Honda (loves to keep the revs up). An even better comparison is to be found when GM introduced an automatic overdrive transmission into the Cavalier, where the fuel economy of the 2.2 rose by a very small amount.Any 'mileage" gain you think you will get goes away in the form of higher rev's, and more fuel to move whatever it is in...
In addition to throttling losses, most frictional losses increase with engine rpm as well. After the valvetrain, friction at the piston skirts and rings is a major player. Keeping piston speed down helps keep these numbers low.actually, the proportionally higher load is what will cause the higher fuel efficiency.... the lower your throttle, the higher the vacuum, which results in throttling losses.
Buick built some very nice V8's over the years. Nailheads were ahead of their time in many ways and are still popular with rodders today. The next generation 350 could usually be set up to achieve better mileage than the Chevrolet counterpart in a similar vehicle. And 455's usually got better mileage than Chevy 454's. I think their downfall was the sheer size of the engine. It's tough to build a small car with the top of the engine measuring 27" from valve cover to valve cover.If I remember correctly, the Buick 231 V6 did slightly better in MPG than the 231 V8 I built. The Buick 231 V6 had more torque, less HP than the 231 V8 I built. The Buick 231 V6 was not allowed to compete in the V8 competition for obvious reasons. With a 6" connecting rod and 3" stroke, the rod length ratio was 2:1, which is an excellent ratio for high RPM's.
Leaving for Portland OR again tomorrow morning for wifes surgery... may be gone a month? May stay first week and return?
Dave W was very gracious and gave me his guest room, also has some EFI projects to keep me entertained during all the wait and worry time, this will help a lot!
1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
-= =-
Should I hold off sending that ECM or will someone be there to receive?
I hate hospitals,the hurry up and wait game is exhausting.
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