Another cam recommendation. Hyd roller - Page 2 - Chevelle Tech
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post #16 of 43 (permalink) Old Sep 19th, 19, 8:18 AM
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Gene
 
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Re: Another cam recommendation. Hyd roller

Ron, as the flutter happens right when the centrif advance weights/springs are nearing full extention, I 'm am wondering out loud if its a mechanical issue with timing variation , like maybe a weight is sticking, overcentering, or something. ?

Simple test would be to do away with it temporarily and run 36 "locked" .

I know they dont "race" all that well, but I do like my 4 gear, even after having rather a time with bellhousing centering.
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post #17 of 43 (permalink) Old Sep 19th, 19, 9:20 AM
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Re: Another cam recommendation. Hyd roller

There is no reason for the cam to cause any sort of surging. You have a timing fluctuation, vacuum fluctuation that's effecting timing or a fuel fluctuation. Sounds like you've eliminated the fuel as an issue. I'd say try another distributor, maybe with timing locked out. Eliminate the curve just as a test.
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post #18 of 43 (permalink) Old Sep 19th, 19, 12:26 PM
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Re: Another cam recommendation. Hyd roller

I agree that cam should not cause surge in that cubic inch. I am betting it is in your timing curve. What distributor? I run a 467 with a 228/[email protected]" Isky hyd roller. It would not run well at low rpm with that little of timing. It runs best with 36 locked out. Running 26 initial, 36 total all in by 2500 rpm with 10 degrees vacuum advance it ran similar, but did not start as well as with it locked out.
If you have a dist which you can't easily tune the curve, change it out to something that you can, like an MSD pro billet. Despite what some people feel are shortcomings about them, their tunability is one great point.
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post #19 of 43 (permalink) Old Sep 19th, 19, 5:00 PM
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Gene
 
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Re: Another cam recommendation. Hyd roller

Also, I had a pickup move, a reluctor on a Pertronix go loose and sort of wobble about at rpm, rotor loosen up....all sorts of mechanical anomolies in the distributor over the years. Most of which happened as I was buzzing the old mill well past 7, yet it sounds like a mechanical thing like that. Also had a partially clogged air bleed that did a nasty mid range flutter. Sounds likle carb is been eliminated a s variable tho.

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post #20 of 43 (permalink) Old Sep 19th, 19, 6:16 PM
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Re: Another cam recommendation. Hyd roller

What is the idle rpm and vacuum?

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post #21 of 43 (permalink) Old Sep 20th, 19, 12:31 PM
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Re: Another cam recommendation. Hyd roller

Quote:
Originally Posted by cstraub View Post
Your cam is a solid flat tappet. When comparing a flat tappet lobe to a roller lobe for area you need to subtract 18 degree if your comparing the lobes for area. 18 is not set in stone but a good starting point. So your Flat tappet that is 250/256 in roller area would be 232/238 @ .050"

Chris, this is very interesting. Does this 18 degree difference apply only when comparing a hydraulic flat tappet to a hydraulic roller, or would it also apply when comparing a solid flat tappet to a hydraulic roller? I have heard when comparing a solid to a hydraulic flat tappet there is about an 8 degree difference to account for valve lash, but haven't heard of this 18 degrees before. Thanks.

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post #22 of 43 (permalink) Old Sep 20th, 19, 1:03 PM
 
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Re: Another cam recommendation. Hyd roller

Quote:
Originally Posted by Jsavdog View Post
Chris, this is very interesting. Does this 18 degree difference apply only when comparing a hydraulic flat tappet to a hydraulic roller, or would it also apply when comparing a solid flat tappet to a hydraulic roller? I have heard when comparing a solid to a hydraulic flat tappet there is about an 8 degree difference to account for valve lash, but haven't heard of this 18 degrees before. Thanks.
Subtract the lash of the solid from a control number of 6. The difference will give you a close comparison of difference in area between the 2.
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post #23 of 43 (permalink) Old Sep 20th, 19, 1:27 PM
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Re: Another cam recommendation. Hyd roller

Quote:
Originally Posted by cstraub View Post
Subtract the lash of the solid from a control number of 6. The difference will give you a close comparison of difference in area between the 2.
Chris, thanks for the reply. Just to clarify, the 6 number you give is when comparing solid and hydraulic flat tappet cams, not when comparing either of them to a hydraulic roller, correct? That is why I was asking about the 18 degree number. So you are saying subtract 6 from the duration of the solid flat tappet so it is comparable to a hydraulic flat tappet, then subtract another 18 to get the equivalent duration for a hydraulic roller? Thanks.

72 Chevelle SS, 496, TH400, 3.73's, AFR 305's, [email protected], 1.48 60 ft. UD 288/286 sft cam. Still tuning.
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post #24 of 43 (permalink) Old Sep 20th, 19, 10:37 PM
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Re: Another cam recommendation. Hyd roller

Quote:
Originally Posted by ToocoolZ28 View Post
It surges anywhere from 2200 to 2800 rpm in 4th gear (od) at steady speeds

Really even the largest of cams should smooth out by 2000, so if your surging at that and above I think something is wrong.

What is your idle speed and vacuum do you know? Is it relatively steady? Wondering if you have a vac leak, weak cylinder etc. This almost sounds like an ignition issue, like a wire arcing on a header. I would go out when its dark, lift the hood and see if you can see any wires arcing, and whack the throttle a couple of times. May need the engine to get up to temp so the headers swell up a bit and get closer to the plugs. Perhaps the coil is going out, especially when it up to temp. Maybe change all the wires, plugs, etc. Actually you can put a timing light on each wire and check for consistent spark too.

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post #25 of 43 (permalink) Old Sep 21st, 19, 1:30 PM Thread Starter
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Re: Another cam recommendation. Hyd roller

OK guys, thanks. I'll get back on this next week. I will check everything mentioned here and may just replace my distributer because that's one of the thinks I've been planning to do anyway. Ill let you all know.
Im planning on buying these. Right now I am running an old Accel hei style distributer.

https://www.summitracing.com/parts/msd-8360 and this https://www.summitracing.com/parts/msd-8202

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post #26 of 43 (permalink) Old Sep 21st, 19, 7:35 PM
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Re: Another cam recommendation. Hyd roller

Quote:
Originally Posted by Jsavdog View Post
Chris, this is very interesting. Does this 18 degree difference apply only when comparing a hydraulic flat tappet to a hydraulic roller, or would it also apply when comparing a solid flat tappet to a hydraulic roller? I have heard when comparing a solid to a hydraulic flat tappet there is about an 8 degree difference to account for valve lash, but haven't heard of this 18 degrees before. Thanks.

Maybe this is what I was thinking of.
I might go with something in the low 220s duration for my next cam... Who knows LOL
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post #27 of 43 (permalink) Old Sep 23rd, 19, 6:46 PM
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Re: Another cam recommendation. Hyd roller

The OP said his timing is all in at 2800.
He then said it surges in 4th gear between 2200 and 2800.
Sure it will - the timing is moving in and out of full advance between those rpms. Iím sure there is no issue after it hits 2800 rpm.
Thereís nothing wrong with the distributer. Itís just set up wrong.
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post #28 of 43 (permalink) Old Sep 23rd, 19, 7:37 PM
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Re: Another cam recommendation. Hyd roller

Quote:
Originally Posted by cstraub View Post
A flat is physically limited to lift rate. Modern day heads flow air quick. You want to open a valve and shut it as quick as possible to make the biggest bang in the shortest amount of time. Delphi shut down the flat tappet lifter production line. Flat tappet lifters today are coming from China.
They are fools, if they made them with decent hardness they could sell a ton

Are the "Delco" lifters out there garbage? Are there any good ones left out there?

Personally I like them even if ones still leaving pwer on the table. Less weight, no needle bearings to go bad.

Quote:
This post is a duplicate of a post that you have posted in the last five minutes.

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post #29 of 43 (permalink) Old Sep 23rd, 19, 10:51 PM
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Re: Another cam recommendation. Hyd roller

Quote:
Originally Posted by bradley67 View Post
The OP said his timing is all in at 2800.
He then said it surges in 4th gear between 2200 and 2800.
Sure it will - the timing is moving in and out of full advance between those rpms. Iím sure there is no issue after it hits 2800 rpm.
Thereís nothing wrong with the distributer. Itís just set up wrong.
I experienced this exact thing!
I was using the lightest advance springs in order to bring my advance all in by 2500, which BTW is what I think the engine wanted (69 Z28 4.10 Muncie). I installed a heavier advance spring, all in at 3000, and bingo. No more surging.

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post #30 of 43 (permalink) Old Sep 24th, 19, 3:47 PM
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Re: Another cam recommendation. Hyd roller

Quote:
Originally Posted by ToocoolZ28 View Post
OK guys, thanks. I'll get back on this next week. I will check everything mentioned here and may just replace my distributer because that's one of the thinks I've been planning to do anyway. Ill let you all know.
Im planning on buying these. Right now I am running an old Accel hei style distributer.

https://www.summitracing.com/parts/msd-8360 and this https://www.summitracing.com/parts/msd-8202
If you do the MSD dist, order a set of these advance bushings also, so you can run more initial.

Performance Tuning MSD Distributors with the FBO Advance Limiter Bushing Kit. Cure Your Rich Idle Condition

Instead of the MSD Blaster coil, which are prone to failure, look at this one if you want a good cannister style
https://www.summitracing.com/int/par...0050/overview/
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