I was searching the forums looking for a answer. This question has been asked but I didn’t seem to find a definite answer. So I have a high chance of need to rebuild my 1964 “98” engine and was think off maybe bettering the internals. To get a little more power of it. But I don’t know how much HP a “slimjim” can handle safely. Or should I just go stock rebuild?
currently the transmission runs fine with only 95k miles.

 

Slim Jim's were used behind Starfire engines and also behind 421 Pontiacs in Grand Prixs and Catalinas, so they'll take more power than they're given credit for. The key to a Slim Jim is that critical throttle valve rod adjustment so keep that in mind if you use any carb other than the 4GC.

 

They are troublesome with stock HP though I don't feel it's the HP fault but the general design of the transmission..... Tedd

 

I am very knew to the world of Oldsmobile and the car world in general I got a lot of decent know how and people around me to help but for something like this I just don’t know how to adjust it. I currently have a Edelbrock 650-700 CFM carb (I’ll have to check it. It was on the car when I got it.) but how would o go about adjusting the throttle valve rod? (Also sorry but can check still Sunday I’m on vacation)

 

The best way to adjust the throttle valve is to swap back to the 4GC carburetor and adjust it per the FSM. I had a 64 98 years ago and I was never able to get the Slim Jim to work with an Edelbrock carburetor I installed. IMHO, there is no way to handle more than stock HP with a Slim Jim. Your best bet is to leave everything OE if it currently shifts fine or swap it out for a different transmission if you see alot of HP in your future.

 

Liam, if you don't have it yet, invest in the 5 volume set of 1964 Olds factory service manuals. They're a must for you or for that matter any modern mechanic to be able to service your Ninety Eight.

Tell us where you are and we might be able to refer you to someone in your area who understands the adjustment. It can be done with an Edelbrock carb as that is basically a Carter AFB and Pontiacs used those with Slim Jims but Pontiac linkage is different.

Tell us about this big girl. 2 door, 4 door, buckets and console, options?

 

I have a copy of a pamphlet that came with the Hurst His/Her shifter they made for the Slim Jim (I dont have the shifter but I'd love too). Anyway this pamphlet shows different stages of internal modifications you can do to the transmission to "improve" the shifting and durability. I'm just not brave enough to do them yet.....

 

I do actually have the original service manuals 1-5. I’ll take a look into 5. The Beaty is a 4 door bench seat with no a/c. Though the plan is to get some buckets and a console or a Bench in between for comfort and safety. I live in Colorado about 24 minutes away from Denver.

 

is this pamphlet a piece a paper you have or is it a pdf? Because if you don’t mind for the future it might be worth to get a copy or if possible could you attach a photo.

 

It's the instruction sheet for the Hurst Dual gate and has been shared here before, here it is again.

 

Oldsmobile Club of America website and search chapters for Rocky Mountain Olds Club. There's a fellow who I think lives in Arvada who made up some of the SJ adjustment tools. Also jaswest.com has them but theirs have to come from Canada.

Four door- Town Sedan, Holiday Sedan or Luxury Sedan? If you have an LS you have a gem no matter what shape it's in. Custom Sports Coupes used the same drivetrain and bucket/console interior as the Starfire and them things would get up and boogie for a big car.

 

I will do that. I’ll email them about it and o just have an average town sedan

 

Has anyone tried any of these modifications to thier Slim Jim? #1 certainly seems worthwhile but #2 seems a little too extreme? Is that 85-90 mph shift under full throttle? I hate to assume. Automatics are like Voodoo magic to me lol.

 

I never did. Just my opinion but I was quite happy with the performance of my 63, although admittedly I was lucky to have a good transmission that shifted and downshifted properly. When the stock driveshaft is a two piece unit connected by a rubber cushion I always felt that car was never intended to be drag racer. If you want to hop up a giant car like these it will take a lot more than shift kit mods. That said it would be interesting to see someone else try it if they have a slim jim repair expert on retainer!