Melling 1.65 Rockers on Exhaust

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Phil400
Two Feathers
Posts: 25
Joined: July 10th, 2020, 8:14 am

Melling 1.65 Rockers on Exhaust

Post by Phil400 »

The previous owner installed the single pattern 268H cam in my car years before I got it. Would it be worth the effort to look i to 1.65s on the exhaust? I've read it can help with the single pattern.

I would be using the stamped style rocker by melling which I've also resd measure out closer to 1.6.
78 T/A 4 Speed, mine since '99, Third and final owner as long as I'm alive.

JayS.
Yellow Horse
Posts: 82
Joined: June 23rd, 2020, 2:44 pm

Re: Melling 1.65 Rockers on Exhaust

Post by JayS. »

Just a guess, at best maybe 5-8 hp gain on a lower 8 ish scr compression engine. As the compression is raised it might pull that to the lower end of the range. On the street I doubt you would be able to really notice it much.

If your someone that likes to rev the engine out it might be worth considering. It would tend to broaden the power or hold on to the power a little longer past the power peak. Even though the engine may not show any hp gains the effect of the larger profile on the exhaust makes the cam feel like it is bigger. Best results are likely running the bigger rocker arms ratio on the intake also.

That 268h cam would be close having enough push rod clearance to working with 1.65 (1.60 ish) mellings. You would have to check it throughly, some heads would clear. A comp or prw 1.65 roller tip would hit for sure, a melling might work. The mellings 1.65s have more distance between the pushrod and the fulcrum that the 1.65 aftermarkets.

Phil400
Two Feathers
Posts: 25
Joined: July 10th, 2020, 8:14 am

Re: Melling 1.65 Rockers on Exhaust

Post by Phil400 »

Alright thanks, I do like to get on it and like the idea of spreading out the power, but guess it's not really worth it.
Probably would need different length push rods too ? And figure lift would jump to 480sh with a 1.6sh rocker so then clearances would all have to be checked too?
78 T/A 4 Speed, mine since '99, Third and final owner as long as I'm alive.

JayS.
Yellow Horse
Posts: 82
Joined: June 23rd, 2020, 2:44 pm

Re: Melling 1.65 Rockers on Exhaust

Post by JayS. »

The push rod length is the same. Or close enough. If it has comps 988 springs the extra lift would be ok. You would want to check coil bind to make sure if they are not 988s or your unsure what they are.

A 068 cam with a compcams roller tip 1.65 just barely clears on the intake push rod. Some heads will hit, it is close. A 041 cam with the stock melling 1.65 (1.6ish) rockers will hit, but just barely. You might be able to able to run the melling 1.65s with a 268 H on intake valves without having to do any grinding.

Phil400
Two Feathers
Posts: 25
Joined: July 10th, 2020, 8:14 am

Re: Melling 1.65 Rockers on Exhaust

Post by Phil400 »

Oh I could use my pushrods hmm, that makes it alittle easier, I don't know who did the cam swap but I recently replaced the valve stems seals, think they are stock springs, I noted a .060" shim under them. So my guess is they couldn't handle the extra lift.

Thanks
78 T/A 4 Speed, mine since '99, Third and final owner as long as I'm alive.

JayS.
Yellow Horse
Posts: 82
Joined: June 23rd, 2020, 2:44 pm

Re: Melling 1.65 Rockers on Exhaust

Post by JayS. »

They may have shimmed the stock springs after a valve job. Do the heads still have the splash guards on the springs? A .080” spacer sounds like the machinist made a adjustment for a valve job and did not run the splash guards.

I think the bigger melling 1.65s would have a valve lift of .487 with a 268 h. About all a stock spring will handle is .46-47” depending on the install height.

Phil400
Two Feathers
Posts: 25
Joined: July 10th, 2020, 8:14 am

Re: Melling 1.65 Rockers on Exhaust

Post by Phil400 »

Yes they still have the shields. Its .060" shims, not .080" my guess is they just shimmed the stock springs as you say. In any case doesn't seem worth the effort. Thanks again for your help.
78 T/A 4 Speed, mine since '99, Third and final owner as long as I'm alive.

JayS.
Yellow Horse
Posts: 82
Joined: June 23rd, 2020, 2:44 pm

Re: Melling 1.65 Rockers on Exhaust

Post by JayS. »

Not sure how I got .080 and .060 shims confused. Lol :roll:

With the stock springs you are right not changing anything.

I have a 218/218 .050” cam on the shelf, not a comp version. But we have contemplated using it in a 400 and trying the big rockers.

I like to look at this type of stuff. As much for imagination as learning or experience. I ran some quick computer sims on a sim5pro. Look at trends versus the numbers, not just the number.

Here are some dyno sims for a 400 stock compression, 268H with stock 6x-4s and a decent exhaust. I think the gains would be higher than this, peak power would be a couple hundred rpm higher. Plus the stock 1.5s generally run less than 1.5, more like 1.47-1.48.

1.5s baseline
438 ft lbs@3000
431 ft lbs@3500

316 hp @ 4000
328 hp @ 4500
306hp @ 5000


1.61 on exhaust
-2 ft lbs @ 3000
Even @ 3500
+1 hp @ 4000
+2 hp @ 4500
+13 hp @ 5000

1.61 on intake and exhuast
-2 ft lbs tq @ 3000
+3 ft lbs @ 3500
+2 hp @ 4000
+4 hp @ 4500
+ 16 hp @ 5000

You can see how the bigger exhaust rocker holds on to the power past the power peak. A 13 hp jump is a lot. On the street you may not even notice that though. If you were doing some road courses and had a awkward part of the course were you needed more rpms without a gear change, or at a drag strip and needed a few more rpms to get through the traps with out shifting. IMHO Those are the types places were little changes like this show up.

We liked the single patterns cams better than the dual pattern cams in the 462 engine we had in this dirt track car. On a dry track that was fast it would run out of power at the end of the track though. A perfect time for a bigger ratio exhaust rocker swap. :idea:
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tjs44
Posts: 1
Joined: June 23rd, 2020, 3:36 pm

Re: Melling 1.65 Rockers on Exhaust

Post by tjs44 »

What heads?Has the pushrod holes been opened up to allow 1.65s without binding?Tom

Phil400
Two Feathers
Posts: 25
Joined: July 10th, 2020, 8:14 am

Re: Melling 1.65 Rockers on Exhaust

Post by Phil400 »

6x-4 heads, 98% sure the pushrod holes have not been opened up.
I would do the swap in heartbeat if the springs and holes were set up for it.
78 T/A 4 Speed, mine since '99, Third and final owner as long as I'm alive.

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