1.5 or 1.65 roller rockers - Pontiac GTO Forum
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post #1 of 9 (permalink) Old 04-25-2018, 06:49 AM Thread Starter
 
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1.5 or 1.65 roller rockers

New to the forum and little experience building engines. I have a 64 GTO with a 67 400 out of some other Pontiac. I'm putting in a isky mega 280 hydraulic with .485 lift and edelbrock performer rpm heads and intake. It has a 750 carb and a 4 speed. I'll use it to have some fun at the local drag strip and to get groceries on the weekend. My question is do I go with 1.5 or 1.65 roller rockers when I put the heads together? I want it to be as mean as it can be with the parts I've already bought. Thanks in advance for your help
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post #2 of 9 (permalink) Old 04-25-2018, 07:59 AM
 
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I'd go with the 1.65 rockers. Thats not a lot of lift for the performer RPM heads. With 1.65 rockers it would bring your effective lift at the valve to .533. Just make sure you check ptv clearance and make sure your springs can handle that lift without coil bind.

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post #3 of 9 (permalink) Old 04-25-2018, 09:27 AM Thread Starter
 
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Or.... Would a bigger cam with 1.5 rockers be smarter. If so, any suggestions? Still need vacuum for power brakes.
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post #4 of 9 (permalink) Old 04-25-2018, 09:38 AM
 
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Yeah, your piston to valve clearance would be most important (ptv). Isky has a whole tech feature on this. See: Do you know your VOTC? - Isky Racing Cams

Also with the higher lift you may need longer vales. Ie: 5.11" vs 4.98" length vales. Someting to check out. Pontiac Engine Valves | Ferrea.com

Also check out post #9 on this thread written by BearGFR, good info for what you're doing. https://www.gtoforum.com/f170/rebuild...-heads-129282/

Best of Luck!
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post #5 of 9 (permalink) Old 04-25-2018, 12:37 PM
 
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"...Would a bigger cam with 1.5 rockers be smarter. If so, any suggestions? Still need vacuum for power brakes."


Cam choices always bring out lots of different opinions.

If you're going with a HFT cam, Paul Carter would recommend a Voodoo, probably a 268, or maybe even a 276. I don't think you really NEED 1.65 rockers. BUT, they will make more power, with the same cam.

Voodoo Hydraulic Flat Tappet Cam - Pontiac V8 268/276 - Lunati Power

http://www.lunatipower.com/Product.aspx?id=1777&gid=287

Some say that if you want more vac, you can have most any 110 LSA cam ground with a 112 LSA, or even up to 114.

Obviously, if you want more top end power, & don't care about low end torque that much, a bigger cam will usually provide that.

With a 4-speed, I wouldn't be afraid to go with an 041 clone, like the Melling SPC-8, but ONLY with Rhoads lifters.

https://www.ebay.com/itm/Engine-Cams...Ja21uu&vxp=mtr

https://www.summitracing.com/parts/r...w/make/pontiac

https://www.summitracing.com/parts/r...w/make/pontiac

Cliff Ruggles has posted that a Crower 60243 makes a good 400 cam, for 4-speed cars.

https://www.crower.com/camshafts/pon...m-284-hdp.html

KRE has the best price I've found, depending on shipping charges.

Kauffman Racing Equipment

https://www.summitracing.com/parts/c...xoCcccQAvD_BwE

If you don't like Rhoads lifters, but like the 041 cam specs, you might wanna consider the Howards 410051-14, with Hylift Johnson "R" lifters.

https://www.summitracing.com/parts/hrs-410051-14

Paul Knippen is one Pontiac guy who sells the Hylift Johnson lifters.

https://www.facebook.com/PaulKnippen...ors/?ref=br_rs

Again, these are some of my suggestions. I realize that many may disagree with my picks. No problem.

Last edited by bigD; 04-25-2018 at 01:13 PM.
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post #6 of 9 (permalink) Old 04-25-2018, 12:53 PM
 
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"...edelbrock performer rpm heads..."

Those RPM E-heads are said to be able to use up to .575 lift, out of the box.

https://www.summitracing.com/parts/e...xoCeC0QAvD_BwE

If you want something just a fuzz bigger than an 041 clone, this Crane may do.

https://www.summitracing.com/parts/crn-284281

Last edited by bigD; 04-25-2018 at 01:05 PM.
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post #7 of 9 (permalink) Old 04-25-2018, 02:25 PM
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Putting together a valve train is a lot more than just randomly assembling parts. "Everything" has to be carefully selected and matched to "everything else". (I just wrote about this on another thread a few days ago). Yes, 1.65's will provide a little more lift and a little more effective duration than will 1.5's. They'll also put more stress on your rocker studs and pushrods. Factory Pontiac bottleneck studs have been known to break at the bottleneck when put under higher than factory loads. Also when you start changing things, you change geometries and may be forced to run an adjustable rocker system (if you aren't already --- and if you're running a different cam then you really SHOULD be).

Personal experience: When I first built the engine for my '69, I went with 1.65's and what I thought were high quality parts all around. After being together for more than 5-years and having completed the 2013 HRPT "Long Haul", it ate a rocker arm going into Wichita KS on the 2016 HRPT, cut our tour short, and wound up coming home on/behind a rented UHaul rig. I'm just now getting close to having the car back together and running again. This time, I'm going with 1.5 rockers but with a cam that will actually be 'stronger' (both more lift and duration) than what I had previously.

You can do what you like, of course - it's your car and your bank account For me and from my experience, I believe it's better to run a cam profile that gives you the lift and duration specs you want while using 1.5:1 rockers as long as that's possible. The cam I'm using this time is (another) solid roller and will net 0.623" lift at the valves after allowing for lash settings. - with 1.5's. That's about the limit you can achieve without boring the cam bearing journals in the block larger and using larger matching cam bearings. Any bigger than that, and you can't install the cam because the lobes won't fit though the bearing journals. I've attached a shot of the card for my new cam.
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post #8 of 9 (permalink) Old 04-25-2018, 04:47 PM Thread Starter
 
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Thank you all for your time and advice. I will play it smart and go with the 1.5 for the time being until I learn a lot more.
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post #9 of 9 (permalink) Old 04-25-2018, 08:57 PM
 
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Originally Posted by nasty64 View Post
Thank you all for your time and advice. I will play it smart and go with the 1.5 for the time being until I learn a lot more.
Changing the rocker arm ratio will change the lift. Simply divide your cam lift (.485) by the rocker arm ratio (1.5) to get a good idea of the cam lobe lift which in this case is .323. To figure the lift using 1.65 on the same cam, simply multiply your .323 X 1.65 to get .533". The Edelbrock heads should be able to handle the 1.65's without issue & as bigD pointed out will handle up to .575" lift as is, but I have never used them and would confirm this with Edelbrock via email. Great way to increase lift if you choose to and see how it responds. Some will put a set on both valves, or try a set on the intakes, or just the exhausts to see what they do.

BUT, as has been pointed out, you want to make sure that you have the needed valve to piston clearance so your valve does not hit the top of the piston and check clearances between rocker arm & valve spring retainers. AND, you want to confirm valve train geometry and ensure you have the correct length pushrods.

You can buy a single 1.65 rocker and use this to set up your engine for 1.65's. Use the 1.5's for break-in and run it a while, and then if you decide to go 1.65's for more lift/power, you already know they will work.
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