71OldscutlassS

Hello and happy new year to everyone!

Ive purchased a nearly-fresh rebuilt Olds 350 engine for my 71 Cutlass.

It has Speed-Pro flat top forged pistons 0.30 over with moly rings, sheet says 9.67:1 compression ratio with 64cc heads. (0.30 compressed gasket)

stock crank and rods, which were balanced/weight aligned with the pistons.

Crank Bolts, Head Bolts and rod bolts are from ARP.

the engine has #7a heads (which i think they have 64cc chambers?) With new valves, new comp valve springs, solid steel retainers and comp adjustable roller rockers with 1.6 ratio on ARP studs.

the engine will be driven with 3.23 gears and a TH350 with a transgo 1-2 shift kit (which i already have in the car). Ive already have a Hughes GM20 BPO converter lying around which i plan to use.

the current camshaft in the engine is a Comp 42-227-4. This is a RV Cam and seems very mild to me.

I will not race the car, but its a fun weekend/summer car and for sure like to have the best/most optimised bang which i can get from an off the shelf cam. Since its a street car, i would like to have good low end/mid range torque, but it would be great if it would pull over 5000 rpm.

i think with this setup i maybe can get a bit more cam?

i dont really care about the idle sound its making, im looking more on how the car runs

are there some recommendations of brands/grinds (lunati, comp, etc.) ?

Maybe someone has a similar setup 350 engine and have a good matching off the shelf cam and is satisfied with it.

thanks a lot!

Fun71

Those heads typically have 68-70 cc chambers unless they were milled.
And typical Fel-Pro head gaskets are .040-.045 compressed thickness.
Hopefully the CR is what's on your sheet; calculating with "typical" values gives over 10:1.

The current cam specs:
Lift .433"/.433"
Advertised Duration 252°/252°
Intake Duration @ .050" Lift: 206° / 206°

I'd say something similar to the cam in my engine would be a good choice.

71OldscutlassS

Thanks a lot for your fast answer

I just googled the chamber size of the 7a's and a few sites say 64 cc. So this have to be wrong information in google .

The sheet also says 8.9:1 with 72cc, so maybe the truth is somewhere in between. Since that i havent built the engine, i havent cc'd the heads out. But think that more than 9.5:1 would be a bit high, even because for sure i want to use pump gas (european 95 octane).

So, you think that this comp cam is a bit mild too?

What are your cam specs? Do you have an off the shelf or custom grind?

Fun71

The 64cc chamber thing is wrong; I think that is the NHRA minimum spec and not the real world production size.

What sheet are you referring to for compression ratios?
Using the calculator below gives way more than 8.9:1 with 72cc heads.
https://www.summitracing.com/newsand...ion-calculator


Your current camshaft would be good with a low compression engine but would result in high cylinder pressure and detonation with the compression ratio you likely have on this new engine.

My camshaft is an older UltraDyne grind that is currently available from Lunati:
https://www.lunatipower.com/street-m...8-272-276.html
.485/.485 lift
272/276 Advertised Duration
217/221 duration @ .050" lift

I think you really need to determine the actual compression ratio before trying to select a camshaft.

71OldscutlassS

this is the sheet of the Pistons. Sorry for the poor quality.

ok thank you a lot! So the current cam isnt just bad for performance, even for the 'health' of the engine?

71OldscutlassS

Yes, that would be the best for sure to find out the real compression ratio.

i just saw that these speed pro's aren't really flat tops, they have i slight, something like a 'dish'

Fun71

There are flat top pistons (L2320F) and 6cc dished pistons (L2321F). Big difference in compression ratio between the two.

I see that your sheet shows they are L2321F dished pistons. That is much better than the flat tops for a street engine; the calculator shows around 9.2:1 to 9.5:1 depending upon the combustion chamber volume and block deck clearance.

cutlassefi

Figure your compression is somewhere around 9.25-9.5:1.
And your 95 octane is about the same as our 89-90 so if it runs ok on that then you know your compression isn’t that high.

71OldscutlassS

yes, i already got some informations about the L2321F Pistons too and im pretty happy that theyre the 6 cc dished pistons.

I have to ask the previous owner if the block/deck was milled or maybe just flattened/grinded to calculate the CR right, but i think that the deck height is stock. BUT one question: if the deck height IS stock, how can i determine the deck clearence with these L2321F Pistons? I hope i dont have to pull a head

I even have a few hand written notices the previous owner/builder made while building the engine, but havent had the time yet to read them.

if the CR really is 9 - 9.5:1, i think about to get the Lunati Cam you recommended.

thanks a lot for your help!

71OldscutlassS

So, i think perfect for my goals.

Yeah, it would be great to use 95. We also have 98 and even 102 octane pump gas, but 95 is definitely the best for the wallet in europe .

joe_padavano

^^^THIS! The published numbers for Olds chamber sizes are the factory blueprint numbers for NHRA stock class minimum chamber volume. The production heads were typically 2cc-4cc larger than that. Actual chamber volume depends on factory machining tolerances, how the valve seats were cut (and how often), and how many times the heads have been milled. Don't take any published number as gospel.

71OldscutlassS

Thanks a lot!!

Theres something new to learn every day in this great Forum!

olds 307 and 403

I believe those pistons will be similar to stock around .025" in the hole. Much like heads, it will depend on how much was removed when decking the block when it was machined, look at your paper work or talk to the machine shop. I used a 214/214 .472/.472 Erson custom on a 110 LSA that ran great in a 9 to 1 Olds 350. Erson has the TQ20 that is 214/214 .478/.478 on a 111 LSA that might work well. Again if you are closer to 9.5 to 1, you probably are, consider something in the 220 duration range.

71OldscutlassS

I just talked to the builder of the engine and he told me that the deck height ist stock and that he used the common Fel-pro head gaskets, so i calculatet with 0.025 in. Deck clearence and 0.040 in. Compressed gasket thickness:

Bore: 4.087 in.
Stroke: 3.385 in.
Chamber vol.: 68cc
Dome/Dish vol.: +5.8 cc
Deck clearence: 0.025 in.
Head Gasket compressed: 0.040 in.

= 9.3:1

i calculatet again with 70cc chamber volume:

=9.11:1

So i think this is fine.

Today i took a look at the Comp Cams XE268H camshaft, on the site of comp, they write that a 1800 + stall converter is recommendet for this cam. Since that i will use the Hughes GM20 converter, i think this cam would be a good choice for my goals?

Thanks a lot to all for your help!

70sgeek

I have similar build specs in my '72 350 and use this cam:
Howards Cams, Steet Force Hydraulic Flat Tappet Camshaft & Lifter Set, Oldsmobile 39 Deg. V8, 205/215 @ .050, .448/.475Oldsmobile 39 Deg. V8 260-455 1967-1990
Adv. Duration: 259/269
Duration @ .050": 205/215
Lift: .448/.475
Lobe Separation: 112 LC
Included Lifters: 91411 Hyd. Flat Tappet
800-4800. Street Force 1, Good idle, Mild Street Performance, strong low end torque.
It's a lively cam which still allows good vacuum and near-stock idle

My rear runs 3.08 posi and a 2300-2600 stall

71OldscutlassS

Or maybe the comp XE262h, the specs

262/274
218/224 @0.050

In. Lift 0.475, ex. Lift 0.48

are pretty similar to the Lunati 272/276 that Fun71 recommended. Or does this make a really huge difference?

71OldscutlassS

Thank you for your information! BUT, since that im no cam specialist its hard for me to understand if this cam would be a big difference to my current RV cam thats already installed?

Even, because its saying basic operation range under 5000 rpm? Does your engine pull good over 5000?

what im curious too is that my current cam has the same durations in. And exh.

can someone maybe explain me why its like this?
And i read that besser for a bit "more bang" is a longer exh. Duration. Maybe someone can explain this to me .

Even, is it true that the max. recommendet Lift with 7a Heads is 0.500 in.?

Is this Just with the non-adjustable stock rocker arms?

70sgeek

Keeping in mind I'm running a 3.08 gear it's my opinion that it pulls very well at least up to 5k , at least to the extent that I've ever pushed it that far. My car is street/highway driven, I don't race it and rarely push it over 80mph on road trips, thus I never really wind it past 3500-4k rpm.

I can't objectively state whether it will exceed your current RV cam's performance, but as SBO's go in general, mine checks all of my targeted boxes - good street idle, 18 lbs vacuum for the power brakes, strong power band from idle through at least 70mph cruise speed. The 3.08 also helps keep highway RPMs relatively livable up through about 80mph.

I initially installed a Hughes 2500 stall converter (the HD sprag model) but it turned out to be defective early on and I returned it, thereafter going with a 2300-2600 stall from a local builder. It's an ideal range for my overall drivetrain specs and so far no issues over the 10k miles I've driven it since build completion (approx 3 years ago)

Your ignition timing will also play a role in overall engine performance so keep that in mind as you contemplate your cam choice.

Fun71

The key parameters to note are lift and duration @ .050" lift as those can be compared directly. The advertised duration is not always a direct comparison since different companies use different methods to determine this spec.

Your current camshaft is more aggressive than the factory 350 auto camshaft but is still fairly mild.
.433"/.433" Lift
206° / 206° Duration @ .050" Lift
252° / 252° Advertised Duration

Factory 350 auto camshaft:
.400" / .400" lift
186º / 202º Duration @ .050" Lift
250° / 264° advertised duration

Generally, a 10º change in .050" duration moves the power band by 500 RPM.

This is a good explanation of things:
http://protwin.com/camfaq.aspx

71OldscutlassS

thanks a lot for your help, and thanks for the link for the explanations!


I think this is the Lunati 272/276 cam which was recommendet by you:

https://www.summitracing.com/parts/lun-10420312

I think this would be a good choice, operating range is listed to 5500rpm. If you think this too, i will get it with new lifters for sure and give it a try.

One last question: my current valve springs are the Comp # 73126 Single springs with damper. 1.100" coil bind, 103@1.800" seat load, 303@1.250" open load and a rate of 364 lbs/in.

Can i keep them for this cam, or do i need different springs?

Fun71

I don't really like to give camshaft recommendations as I am not an engine builder and have limited experience. I would suggest you contact cutlassefi from post #8 above and ask him for a cam recommendation, since he does this stuff for a living and has way more knowledge and experience than I ever will.

olds 307 and 403

X2 on Cutlassefi.

71OldscutlassS

Ok, great! I contacted him.