GEARMAN69

Been thinking of down the road potential builds and the cost of the big stroke 425 crank 350 DX 450 ci neat but $$$ IMO

Assuming I run across any cheapo deals on a 350 DX i plan to grab one but thought why not just retain the cast big journal crank and do only a large overbore for say a simple flat top 377 ci .. ? Surely someone here as done this already.. Would only require the custom piston I suppose. Are those DX cranks ok up to 6500 rpm in say a 500 hp level ? Plus my 68 up style flywheel would work on the back right ?

70cutty

Why even waste your money on a DX block for 500HP?

GEARMAN69

Ok maybe re-phrase , what have been the rpm and HP levels stable with the cast big journal crank ?

If I ran across one at a Pick-Ur-Part or something for $100-200 I would just grab it and hold it for potential use down the road nothing written in stone.

Also the potential option of boost or NOS on said 500 hp NA engine

say a 250 shot on top, 750 hp at the crank ?

cutlassefi

I wouldn't do that with ANY cast crank.

GEARMAN69

True that is pushing the envelope a bit. Say a blow thru carb turbo build like under 6000 rpm , low PSI 10-15 with a 250 cfm intake port , the HP level would still be up there but not as high rpm. Lots of cast crank BB engines have held pretty nice numbers.

Anybody here actually run a DX crank in a Med High power level?

If I was to just do a 400-500 HP N/A SBO build with no plans to take it further one day I would just use my spare 68 std 350 block

joe_padavano

If you don't plan to change the stroke, why not just use a forged 330 crank with bearing spacers? Inexpensive, stronger, and lower bearing speeds.

GEARMAN69

I had wondered if there were bearing spacers actually. Just never looked.

Warhead

Stock Diesel crank that runs 9's:
https://www.youtube.com/watch?v=TF7n...ature=youtu.be

GEARMAN69

Thank you , that's exactly about what I was visioning.

GEARMAN69

keep it a 355 with W31 flat top forged , a 330 steel crank with main spacers (and studs) and set BBO heads w big valves or a decent flowing Pro Comp alum heads reducing octane sensitivity and a single 88 mm turbo blow thru 15 psi and wide 114 LSA mild cam like a OEM 286/286 .472 w 1.72 rockers to get it over .500 at valve or maybe a bit more cam whatever

captjim

That puts static CR at 9 to 1 +/- and you are going to add 15 pounds of boost? Good luck with that, IMHO. Even with aluminum heads (which I don't see happening since you are doing this on the cheap) you are going to detonate on pump gas. Like 70 Cutty suggested, if you are not going to do it right, just use a 350 and a 330 crank. But, you still need to keep the cylinder pressure lower, IMHO.

coppercutlass

I know that 67. That 9 sec pass was on nitrous. Its actually this car that made me stick with sbo's very early on as i got exposed to oldsmobiles. I have wanted to build a dx like that but we will see.

oldsmobiledave

If you are going to the trouble of building an Olds small block with a D or DX block do it right and stroke it along with a generous overbore. If you plan on one without the other just use a gas block and a 330 crank. Just my opinion.

GEARMAN69

Jim , I am not doing any of it just bench talk man.

I would target 8.0:1 if I was try to do a iron head turbo engine. A alum head turbo engine could tolerate 9:1 just fine. You can always run at least a point higher static CR with alum over iron at the same octane. Same reason I would build a street strip N/A 455 Olds at 11.0: if I sprung for the alum heads.

A buddy of mine ran 15 pounds on a 11:1 bowtie alum headed 4.3 V6 with E85 and drove it on the street. It made 630 rwhp thru a TH350 I was just shooting the **** and if I was doing a pump gas engine that was turbo charged that might make 800 fwhp on boost I would want the strongest block I could use that was the point. A DX is just as valueuable for a 355 boosted engine and does not have to be a 450 ci or a 377 ci build , I got a std bore 68 350 as a spare already. But if a picked a DX cheap along the way and DID decide to do a high HP build I would take the stronger of the two regardless of the nitty gritty on the build.

GEARMAN69

If talking N/A I agree completely. Just what would a person say is the safe HP and RPM limit of a 68-70 reg 350 block versus a DX if they both had 330 steel cranks ? I do still like the look of a big over bore DX for a N/A combo too.

cutlassefi

I'm not really sure what everyone is thinking here but I've had three or four DX blocks sonic checked in the last couple of years. None of them would I take past 4.165. As compared to a gas 350 the only area of the cylinders that was thicker was the front and back, by about .060-.080. However the thrust sides weren't much different than a gas 350.
I had a 330 crank welded and Stroked to 3.750. Imo that's the way to go.

olds 307 and 403

With running that small cam, you could go with the 2321 6CC pistons with aftermarket 6" SBC rods, 330 crank, spacers and 4 bolt caps. I wouldn't run stock rods and a stock bore sbc 400 forged piston with a modern ring pack or ring adapters with a better ring or the D.S.S. Racing GSX series forged 350 3cc piston looks good. Is this the Probe replacement, did someone buy them out? I checked out their site, they have stroker kits for the Olds 400/455.

GEARMAN69

Thanks for the info, I imagine my 68 std bore 350 is what would get built if it comes to it but all this DX talk was mainly just a what if if I got one at a Pick n Pull yard for $150 or less is what I was thinking.

captjim

Apples and oranges, IMO. The cylinder head chamber design plays a huge role in the compression and cam that can be run, more so, IMO, than the material. I believe that the whole "aluminum heads let you run a point more compression" dealio has more to do with modern chamber design that it does with the aluminum dissipating the heat.

The issue with the DX is the cost of the crank. If you are shooting for over 500 HP, you can justify the cost of the upgrade. If not, boosted or otherwise, no reason not to use a gas block, as others have already stated.

Nitrous changes things. It adds cylinder pressure but lowers combustion temperatures. It also adds massive torque with means lower R's to achieve the same results.

wr1970

If you want a standard diesel crank i have one still in a D block. LMK

GEARMAN69

Thanks but I own no block that would fit it.

GEARMAN69

The reason it works does not matters to me , just that it does work.

wr1970

If you get a block and need one it is yours.

captjim

Obviously, you missed my point. What works on a Chevy may not work as well on an Olds. The aftermarket Bowtie chamber design is much different than the large open Olds chamber. There is a tad more quench area on the Olds aluminum heads, but not much. They are large, open, and slow-burning and the advantages are not as great as on Ford and Chevy heads where the chamber is much more efficient.

GEARMAN69

It works on others besides Chevrolet and the chambers vary greatly from brand to brand. If your trying to say an Olds wont run 11:1 on 93 with a aluminum head I imagine someone here may disagree. I did not miss your point at all, I was only giving a ridiculous high compression boosted example earlier. A N/A engine regardless of chamber design I fully believe you can run 11:1 static CR on 93 octane period with aluminum heads and street strip cam. There are guys running Pontiacs with alum heads on 87-89 octane at 10.5:1 let alone 93 for 11.0 that I was referring.

captjim

I do not disagree, but that was NOT what you stated earlier. I disagreed with your premise of running 9 to 1 Cr and 15 pounds of boost. Using either of these,
https://www.rbracing-rsr.com/compression.htm
http://goodvibesracing.com/Compression_Ratio.htm
You get an effective Cr of 18 to 1, that was my contention, 9 to 1 Cr is too high to add more than a couple pounds of boost.

GEARMAN69

Jim,

On this post I was "thinking " of a 83 cc chamber heads and un cut deck so the thought was at or under 8.5:1

The later post I said I would target 8.0:1 with a irons heads and the 15# boost ( so yeah it would probably need a 6cc dish piston instead of the flat top) I said you could likely tolerate 9.0:1 with alum heads at 15 # , I still believe you could actually. But if it came up at 8.5:1 actual instead with th parts used in a hypothetical build I would stay there.

The W31 piston advertises to be 8.75:1 w 80 cc chamber so 83 would be 8.5 ish , if the alum head is 77 cc then yeah it will be 9.0:1

captjim

9 to 1 and 15 pounds equates to over 18 to 1 Cr, you are NOT doing that with pump gas, aluminum heads or not.
Even at 8 to 1, with 15 pounds, you are at 16 to 1, no way you are doing that with iron heads. Altitude does play a part, not sure where you are, but not enough to really make a difference.

I am not a turbo guy, but the ones who are that I talked to like low compression and high boost. There is really no point in going to all the trouble and cost just to add 6 pounds, which is about the max on an 8.5 to 1 engine.

GEARMAN69

I dont want to just sit here and BS over opinions but 8.0:1 w irons head turbo 3.8 Buick GN can run 20# on 93 octane because they pull back timing in the chip and run like 20-24 degrees total , stock was close to 15# of boost at 8.0:1 in the 80's

cutlassefi

Really? How do you figure?

"In 1978, GM began to market the 231 as the 3.8 liter as metric engine sizes became common in the United States. The RPO Code was LD5, though California-emissions versions were called LC6. Starting in 1979, the engine was used in the front-wheel drive Buick Riviera, though still with a longitudinal mounting. Larger valves and better intake and exhaust boosted the power output for 1979.
A turbocharged version was introduced as the pace car at the 1976 Indianapolis 500, and a production turbo arrived in 1978. The turbo 3.8 received sequential fuel injection and a distributorless wasted spark ignition system in 1984. In 1986 an air-to-air Garrett intercooler was added and the RPO Code became LC2. The LC2 engine has a bore of 3.80" and a stroke of 3.40". The respective horsepower ratings for 1986 & 1987 were 235 hp (175 kW) & 245 hp (183 kW). The limited production GNX benefitted from additional factory modifications such as a ceramic turbocharger, more efficient Garrett intercooler, low restriction exhaust system and revised programming which resulted in a 276 hp (206 kW) factory rating"

15# of boost would be worth about 20-25hp per #, or about 300-375hp conservatively. Even if you only made 150hp on motor alone, that's 450-525hp in stock form.
So with that, you're saying they were off by about half? Bullshyt. I don't believe that for one New York minute.

In consideration of others please get your facts straight before you post.
Thank you.

GEARMAN69

Sorry Mark, your wrong.

I did state facts. 15 psi was the stock max boost seen in a 86-87 GN typical around 12-13 bumping 14-15 peak

I had a 86 T type too but none of that changes the facts that I said.

Guys would tweak the stock turbo past 15 # and run up to 20-22 PSI , run a down pipe to dump it, a low timing chip and better fuel pump and get high 11's out of there otherwise stock car too , that is a lot of HP/TQ

stone stock made more rear wheel hp tq thru automatic trans that the factory rating was

250RWHP
350RWTQ

cutlassefi

Your rear wheel Hp vs math vs boost simply doesn't add up. Sorry.
What inj size and pressure did you run by chance? Thanks.

GEARMAN69

Not my dyno run nor from my Old car. , I rebuilt mine with Ford blue tops 36# I think it's been a long time and a walbro 255 pump , that motor went 114 mph 1/4 with next owner but it had a new bigger turbo. The max 15# stock is all over if you Google the question. The math was yours as is your hypothetical guess of hp that was never even something I brought up at all. Just max boost for a stock GN , not the hp .

cutlassefi

I'm sorry but your math continues to not jive. Based on an 85% duty cycle you'd need to have about a 47# inj. in order to make just 400 crankshaft hp. So with a 36# injectors, you would've had to up your pressure to about 75#, which will reduce the pump output noticeably. Were you running 75psi of pump pressure? Otherwise the math just doesn't jive. Sorry.

GEARMAN69

The 36# Ford blue top was the the common first upgrade for injector when starting upgrades on a GN as was the pump I mentioned . I don't have any special numbers to share these are just common parts combos that worked . The pump requires a hot wire kit to get full charging voltage 14 volt for proper performance of the Walbro 255 pump. Visit TurboBuick.com stock boost spikes at 14-15 common and settles down a pound or two at 12-13 typically on a stock GN or T type . The factory HP rating IS under rated . Not a shock since stone stock 86 T Type went 13.85@99 on stock tires

captjim

I'll make you a deal, you post up an example of an Oldsmobile engine with a carb, iron heads, and 8 to 1 cr that runs on pump gas (not a Buick with EFI and CCC, not a Chevy with better heads) with 15 lbs of boost whether it be turbo, centrifugal, etc, and did not beat the bearings out of it and I'll admit that you are correct. Until then, I stand by my position that it is waaaay too much cylinder pressure to run safely on pump gas.

cutlassefi

X2.

Gearman - your 12-13# of boost seems to be correct for a mid 80's GN. They peaked at 15 then rolled back to 12-13# so I stand corrected. But with that said you only need 425-450 crankshaft hp to run high 11's in a 3800# car, so they still didn't make big power in that form. Plus they had intercoolers and EFI, that helps a lot.

GEARMAN69

Fair enough Jim, I toy with the thought as future wagon combo after its returned to SBO power. Remember my original hypothetical combo with iron BBO heads on a 8:1 355 I suggested 10-15 psi. With locked out timing low 20's total with cool temps and proper fuel I would love to try

GEARMAN69

Here is our old T after I sold it and the new guy treated it right.

GEARMAN69

Here is back when I had it at home , that was like 12 years ago.