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Olds 350 piston weight, Stock vs Soeedpro vs Modern offerings?
Anyone know the stock 350 14cc piston weight? Of course the tell tale is the weight with stock pins and rings. How does it compare to the heavy Speedpro pistons? What is the weight difference vs the Mahle and CP pistons in a 4.065" oversize? I have the factory 14cc pistons and being the only option from 73 to 80 and 68 to 70 two barrel option, they are by far the most common.
I can tell you the balance bobweight, which is 2 big ends of the rods and bearings, the small end of the rod as well as one piston, rings and pin.
My stock rodded 350 with Speed pro L2321 pistons, rings and pins had a bobweight of 2248gr. That’s about the same as a typical BBC.
My mule with the Molnar rod and Mahle piston was 1835gr, or over 400gr lighter per rod throw than a stocker.
Just a word of note, my strokers are down around 1740gr or so. That’s one reason why they make such a huge difference, way stiffer crank, internally balanced yet a much lighter rotating assembly overall.
Hope this helps.
Last edited by cutlassefi; Dec 13, 2020 at 06:28 AM.
Thanks, I just have some decisions to make. The current 350 in my 70S needs some work. The cylinders are more than likely pretty good. It has 150 psi 1 through 6. Both 7 and 8 were 100 psi, probably from the badky sticking choke, which is now 100 percent. I used Kleenflo Combustion Chamber cleaner and gained back 15 psi and 25 psi filling the cylinders. I have done this multiple times and gained as much as 35 psi on other motors. I got bit and lost oil pressure. There is a bent rod from hydrolocking and it is toast, along with the shitty lightweight crank, probably badly scored. Oil pressure was very good before this. Also the 214/214 custom cam is losing a lobe, almost certain. I was looking for one rod and piston, a member is willing to sell a complete set. Not cheap but clean stock pistons on resized rods. Just not sure if $260 is worth it for stock parts. Maybe a dingle berry hone and new rings will still leave 7 and 8 low. I have a good used 204/214 cam to replace the current one but it is a step backwards. I have a 330 crank, ground .020" mains/.010" rods with good journals as is, balanced for heavy, discontinued 18cc dish Speedpro forged pistons and stock rods. The reason, I asked about factory piston weight is to determine if it is close enough to use. I also have everything but a quality timing set, roller cam, rod/main bearings, better pistons and rods to complete the 350. They would have to remove weight, not add expensive Mallory to balance it. I have#6 62 to 64cc heads with fairly fresh, valve job, positive seals and 2.07/1.56 valves with the bowls opened with a cutter. I would blend the bowls into the ports, tear drop the guide boxes and remove the air bumps. I also have a complete USED 403 stroker bottom end minus main bearings, Venolia custom 2618 pistons with unknown ring tension, Scat sbc 2" journal rods and an unbalanced offset ground 330 crank but only have a 1/2" 4 main Halo. It came from a class racer and I picked up the crank separate. It needs bored and honed .039" over, cam bearings which I have and it needs balanced and it will need 4 slugs minimum according to Mark to balance the bottom end. Either block will need an align hone on the mains. I would use either ARP main studs or the 4 main with longer ARP studs, I have both. The 350 could use either, the 403 needs the Halo and even it is questionable vs a 5 main. The current #6 will work great with the new Mahle pistons in the 350. They are small for a 403 stroker and I need 70cc chambers to keep 9.6 to 1, 10 to 1 is too much for iron heads. I also have 7/16", not 1/2" ARP head bolts for the 350. My rocker arms are 1.6 Comp roller tip and 1.72 full roller rocker arms. Both 3/8" stud and have the conversion studs to 5/16", need push rods either way and one guide plate. The 350 would be much stronger but make less power, especially if I go aluminum heads on the 403. The machine work and balancing would be cheaper on the 350, hone to 4.065" oversize and remove weight vs adding expensive slugs but about $1500 more in bottom end parts. The 403 stroker would be 5500 rpm max, the 350 could see 7000 rpm without issue. A beefed up 2004R with a 2200 to 2500 stall and 3.90 posi in the type O. At least 2.5" exhaust with some type of header as well. Thoughts or Suggestions?
The forged replacement pistons, SpeedPro, TRW, were designed to be near the weight of the stock piston so that they would balance up without major surgery. I have a 1967 CSM which provides the bare piston weight of those offered in 1967; unfortunately that doesn't help your question about the weight of a 350 piston. The more modern design pistons, Mahle, CP, etc. will be lighter than an OEM piston and thus make for a lighter reciprocating weight; easier on parts. My concern with a 350 would be the connecting rods; lighter pistons would help. About those rocker studs, if you are changing to a roller cam it will have more aggressive ramps than a flat tappet. It is so easy to have the stud holes drilled and tapped to 7/16" and use the stronger stud, 7/16" base 3/8" top. If you have access to a drill press you can easily do that yourself!
I am also considering using my 3.5" stroke crank in the 350. I have the 6" Scat sbc rod with 2" journals. The 4.390" pistons have a .927" pin. The Icon forged 761-STD 2618 forged piston 4.125" with 1.561" compression height, it should be about the right compression height, modern 1.5 mm rings and the 15.2cc dish should give 9.5 to 1. Not cheap but cheaper than pistons and rods. I went through way too many overheating with the 403 in the G body, not sure I want to go that route, it sucked. I have brand new A body aluminum plastic rad which will cool the 350, the 403, probably not. A 375 ci SBO sounds better and may just go that way.
I think going with a 374 ci 350 stroker is the best with the parts I have. Cutlassefi is getting me prices on the roller cam and Icon 15.2cc dish piston and other odds and ends, I need. I will probably sell my extra 330 crank, polish my turd of a 88 CSC G body and sell it to focus on the 70S.
Last edited by olds 307 and 403; Dec 15, 2020 at 07:56 PM.
Youve been doing your 403 stroker as long as i can remember. No surprise nothing came out of it by the way you spout out whats your going to do and nothing ever comes out of it. Except lock-titing rockers stud nuts and wondering what went wrong.. Last time i checked you touted 1/1/1.5mm rings as modern rings, now the 1.5mm rings are modern. Next time i quess its a stock olds 260 build which is touted as modern, and as usually, nothing comes out of it, either.
Youve been doing your 403 stroker as long as i can remember. No surprise nothing came out of it by the way you spout out whats your going to do and nothing ever comes out of it. Except lock-titing rockers stud nuts and wondering what went wrong.. Last time i checked you touted 1/1/1.5mm rings as modern rings, now the 1.5mm rings are modern. Next time i quess its a stock olds 260 build which is touted as modern, and as usually, nothing comes out of it, either.
Maybe he's been saving money for the build, not every1 has thousands of dollars on hand, the cost of living is alot in the great white north, not to mention we get hosed in taxes, fuel prices, hydro and on and on again, probably pay the highest prices in the world..
Youve been doing your 403 stroker as long as i can remember. No surprise nothing came out of it by the way you spout out whats your going to do and nothing ever comes out of it. Except lock-titing rockers stud nuts and wondering what went wrong.. Last time i checked you touted 1/1/1.5mm rings as modern rings, now the 1.5mm rings are modern. Next time i quess its a stock olds 260 build which is touted as modern, and as usually, nothing comes out of it, either.
Go away, what is your problem? I have decided not to build it. I want something that can drive across Canada if I want, you know how big our Country is, HUGE. My 403 overheated way too many times, not going down that road. I figure 450/450 is enough. I contacted Cutlassefi, he is getting me prices on everything, I have the money, I stripping down my 88, it's drivetrain is going in the 70S while this motor is at the machine shop. Two hobby cars, is eating up my machine shop and parts money, one needs to go. I have 3 Daughters in University, the world doesn't revolve about what I want. 1.5mm is way better than 5/64 rings. Find a hobby, you need one, try fishing.
Last edited by olds 307 and 403; Dec 16, 2020 at 12:32 PM.
Oh, and if you didn't see it, my Mother just passed away. That alone is costing $3000 for my share and just put $2500 into running lines, I got trencher for free to install this.
Sorry, my mistake, add $300 for the Google Nest thermostat, best one I have ever used by far. I can turn on the heat in my garage from anywhere with the simple app. I am draining the coolant out as I write this. Pulling the top end of this week after work and this weekend. I plan on contacting Parkland Engine Builder's next week to see what their return times and costs are. The 350 block needs bored an honed .068" over, clean up mill on the deck, new cam bearings and an align hone on the main with the ARP studs and 1/2" 4 main halo installed. The 3.5" stroke was offset ground by Ohio crank to Smitty's clearance specs. It will need balanced along with the 403 pistons pressed off and new Icon pistons pressed on for the second round at the machine shop.
Rad drained and stored on top of my racing slicks, won't realistically need them till 2022. This was the factory 2/3 core rad recored at some point. They only used 2 cores, so cooling is marginal at best. I have a plastic/aluminum 1 core A body replacement that never went more than 10 degrees over thermostat temperature. It should cool the stroker just fine. Another reason to not go with the 403, the rad needed to cool it would cost around $500, nearly pays for the pistons. I am also shelving the 4 blade direct drive fan. It cools very well but has to be a power and mileage robber. I have Plymouth Breeze electric fans, they move a lot of air. I am going with the Davies Craig controller, all the rest I have used are junk. The most important part, I discussed taking my block to the machine shop with my Wife. I haven't been Married as long as I have without discussing this with my Wife. She didn't say no, so full speed ahead.
Oh and since I have to defend myself in my own thread, the reason I used Loctite on rocker studs is a bad valve tick. It ended up I was bending push rods and that is why they were loosening off. The tick has never went away, the cam is dying. I am parting out, probably basically getting the 88 towed away for $100. There is is some value in the 87-88 front end, otherwise none in the rest of the car. Nearly any Oldsmobile from 73 to 90 will never have much value, unfortunately and few reproduction parts. When no parts are made, it shows little following. I am really forward to a roller cam,Cutlassefi sold me slightly used roller lifters for 1/4 price. The forged 1.5 mm ring pack are the only pistons I can find in the proper compression height with a dish to run 9.5 to 1. I have an unbalanced 3.5" stroke 330 forged crank and 6" Scat sbc 2" journal rods. With the 1/2" 4 main Halo and ARP studs and head bolts should be very strong. I am letting Mark pick the roller cam, no input from me other than it has run with a reasonable timing curve on 91 non ethanol. So when it goes to the track and the majority of nearly any build on here, general running, he will get praise or scorn depending on the results. I will be using my great running custom tuned Everyday Performance Qjet, which Mark would not recommend, we disagree on that point I will be getting a wide band to tune it from him. With the adjustable APT and secondary rod design, it is super easy to adjust. It was set up for a 215 duration cam and the idle was a hair rich with that cam, so it should work. If not I have a 80 Pontiac and Cliff's HP rebuild kit, bushing rebuild kit and a new copy of his book. The 2004R will not live behind the easy 450/450 this motor will make, it will get it's own thread. Then again, who wants a TH350 in a car they drive any distance at 70 mph? The Type O will also get it's own thread as well. I have a bearing press, so rebuilding it will be easy. I will be keeping my eye on for deals on 3.90 gears and probably put a parts wanted request when the time comes. The 2.5" X pipe exhaust with Sanderson headers will move over from the 88 Cutlass. The Sanderson shorties are over 10 years old, so I will need a set. When Mark does dyno testing, I will buy a set at that point so these headers get a dyno run, either prove or disprove their value compared to manifolds and full length headers. Oh and the reason, I am building this motor after all these years, not because of shitty little comments, the pandemic. Believe it or not, things are only getting critical in Saskatchewan now. Life is too short, a lot of months, realizing the end could come at any time. Plan on getting the heads off this weekend and pulling valves, maybe start blending in the bowl hog cuts into ports, tear dropping guide bosses and blending the air bumps.
It is the siamese bore, no coolant flow between cylinders. I had endless issues cooling in my 88. I got so it was passable, still 195 to 215 is far from ideal. Towing, I still hit 230+ for temp. This was a Champion 3 core, Plymouth Breeze electric fans, over driven A/C pulleys and a Robert Shaw high flow thermostat. Issues like under drive pulleys, a bad but only at speed, Mr Gasket high thermostat did not help the issue. I tried 3 rads, no thermostat, two different high flow thermostats, a new clutch on the 5 blade, then 7 blade clutch fan and then Plymouth Breeze fans. I got to thinking, will a huge $500 radiator cool a .039" overbore 403, had to say, I'm not risking it.
It is the siamese bore, no coolant flow between cylinders. I had endless issues cooling in my 88. I got so it was passable, still 195 to 215 is far from ideal. Towing, I still hit 230+ for temp. This was a Champion 3 core, Plymouth Breeze electric fans, over driven A/C pulleys and a Robert Shaw high flow thermostat. Issues like under drive pulleys, a bad but only at speed, Mr Gasket high thermostat did not help the issue. I tried 3 rads, no thermostat, two different high flow thermostats, a new clutch on the 5 blade, then 7 blade clutch fan and then Plymouth Breeze fans. I got to thinking, will a huge $500 radiator cool a .039" overbore 403, had to say, I'm not risking it.
Gotcha, I didn't know that the 403 had Siamesed cylinders. Does the 400 cbc suffer from over heating also? Good luck with your build and Merry Christmas.
My wife has relatives in Melville, in fact her parent's were from there.
