James71Cutlass

I've got a '74 350 Rocket block with '71 heads(re seated seals and cleaned) a mild cam, headers. Basically the top end rebuilt. I had this done in the spring of 2021. Last year I had a rebuilt 200R4 with a shift kit along with a B & M ratchet shifter put in. I have 3:42 gears (no posi) and 2.5 inch duel exhaust. I find the car isn't fast or quick enough for my liking. I don't take it to the track or anything, but I do like to get on it once and a while. I want more power but not too sure what else I can do.

My mechanic has a few Olds big blocks and is willing to build one for me but the cost is 6k CAD. Not too sure I want to invest that much into the engine right now when I want to get the car painted or wrapped in the next year or so.

My questions are.
1. Would it be worth getting the bottom end of my current 350 done, bigger pistons bore out the block? How much HP/Torque would I gain?
2. If I didn't do the bottom end, how would I gain more HP/Torque?

Thanks.

joe_padavano

What are the specs on the "mild cam". How have the timing and carb been optimized for this combo? The reality is that your car should be plenty quick, assuming the engine is dialed in correctly. Simply bolting on parts isn't the right way to optimize performance. You need to ensure all the parts are matched for the application and are tuned for the combo.

OLDSter Ralph

How much power do you think you can get to the ground without limited slip ? Wouldn't a lower rear end gear ratio help with quickness ?

James71Cutlass

I have a Comp Cam high energy cam with lifters. Said to have duration 268/268, lift .456/.456. Edelbrock intake with a Edelbrock 1406 carb.

James71Cutlass

Not too sure. does limited slip make that much of a difference? I like the 3:42 set up I have in the car now. I do some good road trips in the car and would want to change those gears.

joe_padavano

Which Edelbrock intake? That 600 cfm carb is on the small side for that engine. And yeah, that's a pretty mild cam. The stock cam for a 1970 Olds 350 4bbl with manual trans was 286/286 with .472/.472 lift. The 3.42 gears are actually a good compromise. The 2.74 first gear in the 200-4R means that your effective ratio in first is equivalent to 3.73 gears with a TH350.

Tuffnut

I have a similar set up on 75 350.
342 gears with posi. 200-4R tranny, new torque Convertor, dual exhaust, Thornton manifolds, bored .030 over with shallow dish pistons, Edelbrock intake, rebuilt #5 heads, Rochester 4 bbl carb, new timing chain, mild cam
note : with all the mods I had to do a lot tinkering with the timing, and carb jetting/rods, runs real good. Happy with it. It will go when needed.
like previous posters said, make sure it is dialed in.

James71Cutlass

Thanks for that. Not too sure which intake, I'll have too look. Would a bigger carb like a 700 or 750 make a lot of difference?

James71Cutlass

Thanks. I'll do that. I have the stock ignition system in at as well. Posi might be something I should look at.

Fun71

I agree with that gearing it should launch extremely well assuming the torque converter has enough stall speed.
olds 307 and 403 has posted many times that changing the converter from 2400-ish to the stock 1200-ish made a HUGE difference in performance, as in went from unstoppable burnout to can't chirp the tire on launch.

olds 307 and 403

Joe, that Comp's duration at .050" is 218/218 vs 216/217 for the Supercars Unlimited manual trans cam, which is supposed to match the original. The basic D9 standard 2004R converter flashes around 1900 stall, better than the basic TH350 converter. Still consider something in the 2200 to 2500 range, it will help a lot on launch. You should be able to annihilate one tire as is, if not, you have issues. Look at tuning or better yet replace the 600 cfm with a 750 Holley, Street Demon or a custom tuned Qjet. You will need at least a 750, even for a stock smog 455 anyway.

cutlassefi

Your first issue is even with the 71 heads on a 74 short block, the less than 9:1 compression isn’t helping.
Secondly I’ll bet the carb was never jetted right etc.
My iron headed, 9.4:1, mildly cammed 350 Dyno mule makes 405hp/418tq. Your combination is off.

James71Cutlass

Thanks. I was told the 71 heads with the 74 block would improve the compression rate.

Im not too sure if the carb was jetted. Looks like I should get a bigger carb or put in bigger jets.

joe_padavano

They will. The original #8 heads had 80-ish CC chambers. The #7 heads had 64-ish CC chambers.

olds 307 and 403

Unless they were milled, expect more like a 68cc chamber. With .042" compressed Felpro head gaskets and pistons at least .025" below deck, you will be right around 8.5 to 1. What torque converter is in the car? I would start there, along with a carb tune or different carb and check your total timing as well with the vacuum advance disconnected.

joe_padavano

Stock 1974 pistons had an 11.86cc dish, unlike the 22.6 cc dish used on the 1971 low compression 350 motors. Assuming the factory spec 0.002 deck clearance, 0.042 gasket, and 68 cc chambers, that's just over 9.0:1. With 0.020 deck clearance that drops to 8.7:1. Steel shim gaskets get 9.5:1.

James71Cutlass

Not too sure what converter is in the car but I'll ask. Someone earlier said that a convertor with more "stall speed" would make it feel like there was more power. My mechanic is a transmission guy. I'll ask him and see what convertor he put into it.

olds 307 and 403

Sounds good. I ran a 2200 to 2500 rpm converter, flashes at 2350 with a 9 to 1 Olds 350 with a 214/214 cam .472/.472 on a 110 LSA and 2.78 gears. It was a dog with the 1600 stall TH350 stock converter. With the 2200 to 2500 stall converter, easy 1/4 block, one wheel peels.

cutlassefi

Advertised dish is 14cc but let’s go with 12 instead.
Typically the piston is about .020 in the hole, not .002. At BEST he’s at 8.7:1, but I’ll bet it’s lower than that. I’ve seen the pistons be every bit of .025 and lower in the hole.
Still and all his combo needs help.
OP- don’t just throw jets at it. Buy a wideband and tune it correctly.

olds 307 and 403

Yeah, my 76 350 had pistons .025" below deck, as does my current 403. I agree, 9 to 1 or better is highly unlikely with standard Felpro head gaskets. It could be worse, some older Dodge V8's had pistons .100" below deck! Even the newer Magnum like my 5.9 have pistons .040" below deck.

James71Cutlass

Thanks for the info. I'll look into that.

FStanley

I am no expert but what I see in general is people just throw parts at this builds and hope it works...

All needs to work togther Compressoin ratio, cam, timing , carb and intake and most of all tuning....

In general a lot fo aftermarket partd are for full race conidtions.. Ma throttle, etc that doesn't worl so well on the street.. or one doesn't see a lot of difference or makes it worse but changing components out..

I have a bone stock 455 W30 spec engine that was running hot. Learned a lot and had the benefit of being able to reference stock timing specs, etc etc Found my vacuum advance was not working. common as 50 yo distributior advance rubber diaphrms crap out. Needed a carb restore, Cliff Ruggles rebuilt and we sent to a 44 carb primary rod due to ethanol gas in my state. Runs great and normal temps now..

Moral of the story, it all has to work together.

keep in mind when you bump the compression ratio, you will probably need to put higher ocatne gas in it... I have to use some 100 race gas in my 455 W30 spec engine, as 91 octane doesn't cut it..

A good chassis dyno guy might give you some ideas of what to change..

I have a 350 in other olds, runs great, even with a stock rebuild, good enough for me, reliable...

Fred

68post

Lets hope your cam is set at the correct timing also. In the past alot of Olds timing sets were very retarded when set dot to dot.
When you look at Comp's dyno charts for this cam it doesn't out pace the smaller 260HE cam (next size smaller) until past 4,000 rpm and without a stall that is higher than stock
you're playing catch-up from the get go.

James71Cutlass

Thanks for that.

James71Cutlass

Talked to my mechanic yesterday and I do have stock convertor in it. Going to look at a 2200. I can get the tires to peel out, but over all its a dog off the line.

OLDSter Ralph

You get ONE tire to peel out with no limited slip. TWO tires peel out with limited slip differential. Notice the difference in the pic below.

James71Cutlass

Yes, I meant to say tire. I only have a one wheel peel machine.