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Hey everyone! I am a full on engine building newbie but it is time to start the planning stage of the engine rebuild for my Delta. I am keeping the 425 and plan on a rebuild that will include a Holley EFI system and a turbo. I'm decent a turning a wrench but as far as engine design goes I am starting from square one and there are no shops around that do it here. I am wanting to build a street car for road trips and cruising with the ability to go to the track occasionally with my dad and his 67 GTO. I am looking at the 500-600 hp range with the turbo. Again I am totally new to this so please let me know if I am looking at this wrong.
Currently I am looking at what to do with the bottom of the engine. I am currently looking at Moly piston rings with forged pistons and connecting rods. Opinions on domed vs flat or other options? Are the stock pistons viable for this build?
I was hoping to use the stock forged crankshaft. Is that a good idea or should I go a different route?
Opinions on using a girdle?
The most confusing part for me is the heads. I am planning on buying aluminum heads and have done some research into flow numbers and how they pertain to the cam. I know the cam will need a custom grind but any suggestions on where to start on the heads? Or suggestions on who to talk to? There is a machine shop that is highly rated here but they don't design builds and they are not very knowledgeable about Oldsmobile's. They will be machining the block and balancing the bottom end.
I am currently recovering form a knee surgery so I figured now is the time to do the research and start acquiring parts ahead of doing the machining.
Here is what I am starting with. Pictures from the ad that I bought it from. It did come with the front bumper and the engine does run but the transmission will need a rebuild that I plan on tackling myself.
Thanks in advance!
Sounds interesting! I'm likely doing a 330 turbo build in the future.
Just some thoughts:
I'm looking at using the factory crossover, make a custom downpipe to a T4 turbo under the passenger floorwell, output to either a FMIC or subaru-style top mount (w/ air vent on hood) on the passenger side. I'm still in planning stage but early thought is to run a pipe back across (nestled between engine / trans pans) through the space between the engine and brake master cylinder, to a matching vent on the other side for the intake.
I'm looking at going with a sniper efi 1250 or terminator (but ugh that sticker shock on that!). I think the 650 would be enough, but boost is addictive so maybe better to have the 8 injectors.
Anything over about 500 you'll need to convert to an EFI tank...
You'll want low-comp pistons, forged at least. 8-9 CR is what I'm looking at. 7.5-8:1 seems better for street gas, 9:1+ if ethanol.
Seen some machine the crank to run chevy pistons. If chevy pistons you can run alloy pistons, and there are a bazillion options. Stock pistons seems like a bad idea for anything more than about 5-7 psi.
I'm in a similar situation for machine shops. I trust the work of the one I met but he hasn't worked with Oldsmobiles at all. I'm going to keep looking a bit but I'm sure I'll need one for boring, decking, balancing, machining crank, etc.
With the 425 I would think the forged crank you've got is the best of all worlds. 1) you have it 2) forged *usually* as good or better than billet 3) there's not a ton of aftermarket options for Olds out there so otherwise you'd probably be stuck with a cast crank...
Might be worthwhile to get a set of cams. I haven't looked into the 425 cams but the 330 cam I have is... not ideal. With modern turbos you supposedly don't have to worry much about backpressure as long as you size it right, so if the current cam produces power in the band you want you're probably fine. CutlassEFI can (probably, don't want to speak for him) make a cam to spec for you, if not.
Please keep posting your progress and approach because I'd love to have a plan to crib off!
Last edited by InfinityOlds; December 30th, 2020 at 03:07 PM.
Sounds like you have a solid plan going! I've been very curious about the piston options and if the stock ones would work well for this application. They are forged and come in 2 options (9:1 and 10.25:1) and I am not sure which ones I have as of yet. I am also sure that There will have to be a little bit of boring done so it's probably a moot point anyway. The cam is one of my main points of concern because of that odd angle the 425 has going. I am, more than likely, going to go with an FMIC just so I don't have to cut a hole in the hood (I love the lines of the hood on this car especially with the huge trim piece that runs down it). Thanks a ton for your input and I am excited to see how yours comes along as well!
Sounds like you have a solid plan going! I've been very curious about the piston options and if the stock ones would work well for this application. They are forged and come in 2 options (9:1 and 10.25:1) and I am not sure which ones I have as of yet. I am also sure that There will have to be a little bit of boring done so it's probably a moot point anyway. The cam is one of my main points of concern because of that odd angle the 425 has going. I am, more than likely, going to go with an FMIC just so I don't have to cut a hole in the hood (I love the lines of the hood on this car especially with the huge trim piece that runs down it). Thanks a ton for your input and I am excited to see how yours comes along as well!
What i found with the 330 for pistons is I could *maybe* run mopar 318 stroker pistons & rods(didn't get any engine builder feedback), if I decked the block .030 or so. The other options are boring to 4" chevy pistons/rods & machine the crank, or 4.060 olds pistons & run the (supposedly soon to come) Scat or Molnar Olds rods.
Not sure of 425 piston options; tough for turbo builds because everyone's looking for high compression out of factory options & displacement, and you don't necessarily want to cut into the wall thickness to go to 4.125" bore if you're looking to run boost, where the heat dissipation and other properties of the thicker walls take precedence over a few extra cubes.
*edit* just looked it up and you already have the 4.126" bore. Whoops! Olds upped the stroke to hit 455.
Def agree aluminum heads is the way to go.
As far as cam, I'm in that same 39 degree boat. I think if you go alum heads you can bore the pushrod guide holes to fit a 45 degree cam bank angle cam & have it work. Could be wrong (somebody correct me! ). I'm still researching that. Mark (CutlassEFI) can cut a 39 degree cam for you/me, and I don't know that there's many people you could find that could do that, that you'd trust.
I'm leaning towards FMIC as well, with the A body I'm working with I can see that the radiator can be moved back about 2" without hitting the fan, which should make space. I'm pretty handy with composites so I may make a mold and new ~5lb hood with the vents, so I can keep the factory hood, which I love aesthetically, and simplify the piping & cool intake flow with little space to work with.
Last edited by InfinityOlds; December 30th, 2020 at 09:07 PM.
November 28th, 2020, 10:43 AM
