1.5/1.6 Rocker Arms

[Racer Roy]

Hello all:
My suspension questions have been addressed - Thanks balljoint !
I now have a rocker arm question for your consideration.
I just inherited a pair of bowtie heads with a set of comp roller rockers that I am really excited about. The rockers are a mix of 1.5's and 1.6's that were supplied in a baggie all mixed up. I'm not certain the guy I got them from even knew they were different.
The cam he ran was a Comp 12-515-5 listed at 259/266 @.050" .550/.570 lift.
With this cam, where should the 1.6's be installed?
I have seen lots of chatter supporting both intakes and exhaust.
Thanks again, forum faithful

RR

[let-r-eat]

1.6 on the intakes.

[LowTechRacing]

It debends on the duration of the cam, if you hang the exh open a little bit longer it will help pull in air fuel mix as the intake opens. I'm going to try mine on the exh first. But my camel humps I bought from scd have 2.05 intake valves in them.

[lovinlatemodels]

If your running a different cam you need to look at your cam card or call the cam company and see what they recomend there not all the same i had cams that were straight up 1.5, 1.6, and mixed on either int or exh. don't guess. Also you need to check valve to piston clearence if your changing rockers our pistons always have marks on them from the valves and we have plenty of clearence sitting in the garage cold but at 8200 rpm's is different.

[SLM98]

1.6 on the intake makes more power from the torque peak and up. 1.6 on the exhaust helps extend the rpm band, usually 6000 rpm and up is where it helps.

[Racer Roy]

Thanks for the help, guys. I am looking into what my current cam specs are - in was a "mystery cam" when I bought the engine a few years ago. I did so well with it, with stock 462's, I never cared what it was.
Now I'm going to be racing on 3/8 ovals as well as a 1/4 mile (both paved) and am considering swapping this Comp Cam in to go with the Bowties.
It does say it's for fast 3/8 miles and would likely make gains there, but I don't want to lose any performance on the 1/4 mile track.
Another note for you - the engine the heads and cam came from had big domed pistons and I'm running flat tops so there should not be any interference.
Thanks again

RR

[Racer Roy]

Hi again:
Am I understanding this intake VS exhaust correctly?
If I were to only turn this engine 6500-6800, would putting the 1.6 rockers on the intakes improve the mid range?
Is this generally true for any cam? (I can't get info on my current cam, will have to measure it)

[racing24]

you just need to double check your clearances for the valves cause they not only hold them open longer but open further... if your clearances are tight with 1.5s they might hit with 1.6 depending on lift of your cam

[perfconn]

Majority of the times an engine likes more rocker on the intakes.Exceptions is when you already have too big a cam(duration) on the intake.

[andy16]

i humbly disagree w most of these answers. first pick your heads. second pick your cam based off your head flow #s. third check your clearances. if it is possible to run the 1.6 ratio you need to think about 3 things. cam lift cam duration and port flow.. the bowtie head is a great casting and makes good power but has stock exhaust port location limiting ex port flow. most aftermarket heads have a raised .100-.200-.300 ex port these do not. there is a power combination that is agreeable among most pro engine builders that ex to intake flow needs to be around 75 to 80 % and i haven seen your heads so its hard to assume but most bowtie heads arent close to this unported. so with this info i would def. put them on the ex along w usually 10deg more duration on ex lobe. this 1.5 1.6 combo became popular bec back before they made dual profile cams you had the same lift same duration on int and ex. a way to minipulate this was to put 1.6 rockers on. most commonly on the ex in early production heads. now a days w cnc cam grinds you can find cams w more ex dur and lift so the split ratios aren as necessary. dont believe me lol ????? check out any performance parts catalog in cam section. i bet every single high end sbc cam has more lift and dur on ex than intake. got to get that air outta there.

[stockcar5]

nothing wrong with split ratios. just because you have a custom ground cam doesnt mean it wil be dead on correct. on 2bbl stuff ive found power with lots of intake ratio and very little on the ex with many different cams. most of my cams have less exhaust duration as well.

i'd be willing to best there are lots of high end engines out there with split ratios.

[lovinlatemodels]

nothing wrong with split ratios. just because you have a custom ground cam doesnt mean it wil be dead on correct. on 2bbl stuff ive found power with lots of intake ratio and very little on the ex with many different cams. most of my cams have less exhaust duration as well.

i'd be willing to best there are lots of high end engines out there with split ratios.

I agree nothing wrong with split rockers we still run them but thats what the cam calls for. We placed straight 1.5 on new motor one time by accident beinging in a hurry and not reading the cam card and motor was lazy. After 2 weeks we started checking and realized we needed 1.6 on the intake according to the cam card and what a difference it made but like i said it's what the card called for. My point is run what the cam card calls for there's a reason the cam was ground that way.

[andy16]

i never said dont run em lol. i said its hard to assume. if you have a cam card always follow its instructions as previous gentlemen stated. but i was under the impression you had little info about the whole combo and were asking where should you run em if we had to guess. previous knowlege of what worked MOST of the time points to exhaust. im sure there are exeptions. h3ll try it one way one week and the other the next? nothin wrong with the ol back to back test.

[Racer Roy]

To refresh:
The cam these heads were used with is a Comp 12-515-5 (have also seen 288TLS-6 for this cam) with 259/266 @.050" and .550"/.570" lift. (350CID, huge domed pistons)
I am going to install them on MY engine that has a "mystery" cam that I am going to have to measure to get spec's for. It is likely much less than the Comp listed above as the heads I am replacing are untouched 462's. (350CID, flat tops)
Funny thing is, the guy I got them from had six 1.6's on one head and the other two on an intake and exhaust on the other head. He told me that's how it was run, so I came right here for some opinions, which I thank you all for.

RR

[sj valley dave]

If he had (6) 1.6's on one head and (2) on the other head and the rest were 1.5's the guy let someone put that thing together who is clueless or was not paying attention..IMO...You would run (4) 1.6's on each head on the intakes, the other (4) would be 1.5's...Wow

[Racer Roy]

That's the case. The guy I got the heads from is very new to racing and the guy HE bought the car from had no idea what he was doing at all.
I'm a mechanic so I knew the rockers were all hinkey, and that the 1.6's should be on either the intakes, exhausts, all of them, or none of them.
It is nice to get opinions here to show the way, thanks once again.

RR