Change rockers 1.5 to 1.6?

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fastoldman

fastoldman

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My 340 has 400 hp @ 5800 and 420 tq @ 4400. Cam is flat tappet 235,249 @ .050 and .497,.483 lift. Running 1.5 roller rockers. What would I gain with 1.6 rockers as opposed to a cam change?
 
About .030 lift, if your engine can use a bigger cam than the rocker should show a little more HP but I wouldn't expect more than 10hp with just the ratio change.
 
X-heads with mild porting and openings, air-gap also matched. 202 stainless valves.
 
I say even with the 1.6s, that cam is still small lift wise for those heads.
 
RustyRatRod said:
I say even with the 1.6s, that cam is still small lift wise for those heads.
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yeh I thought so too, but I let the tech at comp talk me into a smaller cam. Will be driven on the street and ocasional weekends on the 1/8. 727, 4.10, 26" tire. How big can I go and not loose tq and driveability? (manual brakes)
 
fastoldman said:
yeh I thought so too, but I let the tech at comp talk me into a smaller cam. Will be driven on the street and ocasional weekends on the 1/8. 727, 4.10, 26" tire. How big can I go and not loose tq and driveability? (manual brakes)
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More info? Compression and such? Intake? Exhaust? Shed some light. This shouldn't be like pullin teeth. lol
 
Sorry, I'm from ME. Please don't pull my tooth! lol Like I mentioned, airgap port matched to heads. Comp is 10.1:1. arias domed reverse deflector pistons. 1 5/8" headers 3" collectors, 2 1/2" exhaust with turbo's (for now. Our state's finest don't like loud exhaust) Oh dynoed with 600 shop carb. Now has holley 750hp. Did I forget anything?
 
Best way to tell is to do a cranking psi test. Your compression at 10 is not high. If your around 160 to 180 psi with this cam it's a good compromise between low end torque and hi rpm power , if your lower than 160 psi going with a bigger cam will start to cost you low end, you may pick up top end but it's a compromise. I don't think this cam is to small for a small motor with only 10 to 1. You could probably go bigger but not by much.
 
I can always up the comp. I used .060 cometic gaskets to lower my comp. Could go thinner. I have enough clearance. 93 octane is hard to find around here.
 
You can also install the bigger cam at a lower intake center line to get cylinder pressure back up and restore some bottom end torque. It will have a minimum effect on top end power. Starting with a compression test first would not be a bad idea though.
 
:d
 

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1.6 will gain a tad in duration too. Not much though. I did the same in a 451 and i didnt feel a difference power wise (no traction with either) but my idle was a little more noticeable and i lost 1 inch vacuum at idI. I did it as a trade sraght across so it didt cost me anythingy
 
Hey Idaho, that doesn't look like me at all! That's my twin brother, ayuh
 
what's wicked funny about that? I thought we were being serious! lol OK so I guess if I want to up the #s on that thrrrre fourrrrty I should go with a bigger cam and maybe more compression. Already have dual valve sprrrrings, can't remember pressures off the top of my head. Haven't checked cyl. pressure but everything is new. dyno time only. Just expected a little more. Stripping engine bay for paint before engine goes in. Now is the time to make changes if any. What are your opinions on the cam Rustyratrod sugested?
 
Rob's more of a guru on that than I am, I'm still trying to understand the performance aspects of engine building, I'm getting there though.

I didn't mean to muck up your thread, but when you stahted with the Maine talk, I couldn't help but say something.

I was born in Gahdnah, lol, not to fah from ya.
 
You will need the springs to match whatever cam you choose. Just having "dual valve springs" is not enough. They must be the correct springs for the cam. Regardless which cam you choose. That is imperative.
 
I understand. I just mentioned it cause I already cut my heads for duals. Hate to cut spring seats again. Maybe I could get lucky with diameters, shims. Any rough idea what I could gain with this swap? Theoretically?
 
Bad Sport said:
Rob's more of a guru on that than I am, I'm still trying to understand the performance aspects of engine building, I'm getting there though.

I didn't mean to muck up your thread, but when you stahted with the Maine talk, I couldn't help but say something.

I was born in Gahdnah, lol, not to fah from ya.
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No problem! Just havin fun. If you can't laugh at yourself, who can you laugh at?!
 
A cam change would make more difference and be cheaper than changing the rockers. I'm not as familiar with small blocks, but on big blocks a ratio change will sometimes require grinding on the heads for pushrod clearance. What converter do you have? Low stall speed +rad cam =sluggish.
 
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