Brodewok80

Hello. I'd really appreciate some conversation. I have a 1968 olds 98. Minutes after I traded a car for that car the cam broke in 3, A valve spring broke apart, that valve dropped into the piston, the piston/valve and top of the rod basically exploded and it all went into the oil pan. It was of course rainy on the side of that highway as I tried to get a tow 150 miles home. Afterwards I spoke with the man I traded with and he sent me 2000$ to make it right. I was grateful. I spent that money on the only 455 I could find on craigslist. It happens to be a fresh rebuild marine, e head, with a torker intake. It's sat around for a while without being used. The parts inside all appear new (besides the rockers). The valves seem new but the heads appear stock. I removed the torker intake to install a stock intake. I checked out the cam and it is a comp 280h. That's not at all what I want. I assume the compression ratio is 10+:1 just because of the cam and intake selection and it being built for a jet boat. Here's my question for you fine people..... What cam can I put in this thing to bring it to the closest to a stock runner as I can? I don't have means to replace the pistons. If it helps there's yellow marker paint on the springs. I see the melling MTO 1 cam. It's stage one. That sounds good but I don't really know. It also calls for vs720 springs. I don't know what springs I even have other than the yellow marker paint. Can someone please save the day for me????? It's killing me. I'm a decent backyard mechanic but performance isn't my thing. Im used to knowing what's in my cars and engines because the chassis service manual says so. Thank you for and potential time or assistance.
Brody​​​​

cutlassefi

You can buy stock cams from Supercars unlimited and a few other sites.

Brodewok80

Would a stock cam work best with a 10:1 compression?

66SportCoupe

The Comp 280H cam is not that aggressive of a cam.

cutlassefi

Are you sure you have 10.0:1 compression?

Brodewok80

No. I'm not sure it's 10:1. It was built for a jet boat and from what I've gathered about jet boat engines, it likely has higher compression. There's still assembly lube in all the spots and it has a higher rpm cam. Looking up at the bottom of the pistons and rods, they're all new. I assume performance. I can't tell what exactly they are tho. Also I don't know if the head has been milled down or anything.

Brodewok80

Isnt the rpm range 2000-6000? This car will be a daily driver that will never see 80 mph. Nor will it ever be floored to get up to speed. Obviously I'd like low and mid range ability for traffic situations. I also want zero lope.

cutlassefi

RPM ranges given for cams include the entire engine family. That cam will be more mild in a 455 vs a 350 for example. It also takes into account what manifolds will be used and a host of other variables as well.
BUT that cam will have a slight lope, even in a 455.
So, as i stated before, if you want a stock cam then SU and others will have what you want.

BillK

If you truthfully have 10 to 1 compression you need to be careful not going with too much less camshaft. You really need to be sure before you pick a cam. Can you borrow a bore scope and see if you can tell what pistons are in it ?

Brodewok80

I think I can peek down there if that's what has to happen. What are the signs I should look for to decipher the pistons?

Brodewok80

I really appreciate and respect you guys for helping strangers with your knowledge. I pray the world get more people like you one day.

Brodewok80

Stock 1968 Rochester and manifolds. Stock single exhaust with that manifold crossover thing. Blocked off heat passage in heads. Unsure of valve work other than they're new. Replacing points with hei only because I broke the points distributor trying to take it out. Stock th400. Unsure of rear gears but they're stock. a/c. Power brakes.

Would the lope in that 280h just sound kinda tough or will it be rumbling? Do you think from this new information the rpm range with the 280h get closer down to the idle or off idle range?

Brodewok80

Nevermind about the 280h. I just heard it on a video on you tube in a chevy 454. I don't want it to resemble that at all.

cutlassefi

There will most likely be a part number of some sort. In addition you can look to see how large the dish is in the piston. It would be helpful if you could take a pic of that as well.

BillK

The Melling MTO-1 is:
280/290 advertised 204/214 @.050 .448/.472 lift 112deg lobe seperation

That is very very close to an Erson cam I used in a 425 about 2 years ago and it is very smooth. The 425 I did is around 10 to 1.

BillK

If they used the 995 spring that Comp calls for that cam it will be pushing the open pressure a lot. The Melling VS720 will be around 80 closed and 210 open. The Comp 995 will be 115 closed and 305 open. Probably too much.

Its a tough call on the springs. You really need to pull a couple and measure the installed hgt and the pressures to be certain.

67OAI

You could try camcraftcams.com; they supply both performance and stock camshafts for most engines.

BangScreech4-4-2

Why?

bccan

Too small cam = potentially high cylinder pressure = potential preignition, detonation. Been there and done that, once. Once!

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Fun71

Yep. The intake closing event on a "smaller" camshaft occurs earlier so it traps the air as the piston moves towards TDC, which results in higher cylinder pressure. A later closing event allows the piston to push some of the air out before the intake valve closes and therefore creates less cylinder pressure. At high RPM the velocity of the incoming air "rams" into the cylinder due to the later intake closing event, which then creates higher cylinder pressure than what occurs at lower RPM.

Brodewok80

Brodewok80

Brodewok80

What octane were you using? I would have ordered this cam already (half blindly) if it wasn't for my vs720 spring confusion

Brodewok80

Are there cams that account for this while keeping the cam non-lopey? Basically a small cam with a later intake closing? Pardon my newness!

Brodewok80

400165 stock 442 cam? Might that be a option?

matt69olds

I would agree. The first cam I bought for my car was a 280H. While there was no question it wasn’t a stock cam, it definitely wasn’t a “shake the fender off the car” kind of idle.

Brodewok80

TAke into account it's going into a luxury car that I don't plan on pretending is a muscle car. I want smooth idle and don't plan on fast take offs or going faster than 80 mph. Would you still recommend? Also has A/C, power steering, power brakes.

68post

I have a stock GM cam that's NIB, and that # sounds familiar (I can double check to confirm - if needed), but you have to be sure the compression isn't too high (as mentioned).
I'd bought it thinking it was the mild '68 400 auto cam and it wasn't correct. It's milder !

Edit; GM Restoration #400117 or #562303, 1973 & 1974 all 455
The 400165 is the Hurst or '70 W30 auto cam.

BillK

I am sure he is using 93 octane Shell. Your pistons look like the shallow dish so it probably is 10 to 1. I think the Melling cam would probably run fine. I have used a fair number of their "torque and pulling" cams over the years in various engines and they are very mild.

Can you get a couple of close up pictures of the valve springs from a couple of angles ?

Brodewok80

Brodewok80

Isn't the 400165 for a high compression engine?

BangScreech4-4-2

So how did Olds keep detonation at bay on mildly-cammed engines like the 10.25:1 CR Turnpike Cruiser and the other HC 2 BBLs they built throughout the '60s?

Brodewok80

I Can order this 400165 for about 200$. I'm fine with that if it'll work for my needs. Even tho it's a muscle car cam I don't imagine GM putting in something too crazy from the factory. Maybe I'm wrong. I wasn't around in 68. And wasn't the 442 high compression in those years? What I'm gathering is this is the high compression cam

Brodewok80

The answer to this question might be the answer to my questions.

Brodewok80

Again. So grateful for you guys.

cutlassefi

it’s called Sunoco 260, and even their 220 and 230. Way better gas back then than what we have today.
And, the carbs were jetted to at least be close. Something too many don’t ever address these days.

Fun71

Dual springs with dampeners looks like higher spring pressure to me.

Brodewok80

So I'll probably need to change em to use a non aggressive cam?

68post

Yes ! Those were Hi Comp engines, but it isn't a cam I'd necessarily want in a 98. Their hi comp likely was only about 9.8 or so,if I have to guess , not a true 10.25 or 10.5.
Have Mark R. spec a custom cam for you.

matt69olds

In that case, probably not the best choice for a cruiser. Get with Mark (cutlassefi) he can help pick a cam that will do what you want and be compatible with the rest of the combination.