Rocker arm ratio

[killface]

Hey! I'm thinking of trying 1.6 ratio rockers on my Chevy C2500 350. It's got the stock TBI heads with new valve springs that can handle the lift. I have an Edelbrock can and they say to use only stock 1.5 ratio rockers. Any one tried this? And what was the outcome? Thanks!

[DOCBAWRENCHTURNER]

is it the Edelbrock fuel injection rated cam? If so they are probably just trying to keep the cam's lift within a range that can be handles by a stock TBI PCM

[killface]

Yeah, it's the 3702.

[jim_in_dorris]

One thing to consider is that with the increase in ratio, the geometry will change and your push rods may rub on the holes where they come through the head causing premature failure. It is common to enlarge those hole to make sure your push rods do not touch. The stock TBI PCM doesn't care about your lift, however it will run better with tuning. That cam even with the 1.6 ratio lifters will not be a problem. However if you have the stock 193 heads, some folks like a single pattern cam for better performance.

[steveo]

the difference between 1.5 and 1.6 on a smaller cam is really not much.

unless you're upgrading to full roller already or have them laying around, i wouldn't waste your money and time.

i went from 1.6 back to 1.5 on a mid-sized cam and ve barely even changed, the butt dyno didn't even feel it.

[killface]

I was just going to change the intake side so it would act more like a single pattern cam as far as lift is concerned. But if it really won't make a noticeable difference, then I might leave it alone. Probably not, I'll most likely mess with it, because as good as my truck runs, I cannot leave it alone, it's like a treasure hunt for horse power. Thanks!

[Fast355]

the difference between 1.5 and 1.6 on a smaller cam is really not much.

unless you're upgrading to full roller already or have them laying around, i wouldn't waste your money and time.

i went from 1.6 back to 1.5 on a mid-sized cam and ve barely even changed, the butt dyno didn't even feel it.

On the otherhand, I have put them on several different engines, noticed small changes in the VE, but have also seen gains of 10-20 HP depending on the setup. I will only use 1.6 or 1.7 full roller rockers on stuff I build. I put them on a TBI engine that was running a stock LT4 cam and stock heads and felt noticeable gains.

[Fast355]

I was just going to change the intake side so it would act more like a single pattern cam as far as lift is concerned. But if it really won't make a noticeable difference, then I might leave it alone. Probably not, I'll most likely mess with it, because as good as my truck runs, I cannot leave it alone, it's like a treasure hunt for horse power. Thanks!

If you have a roller cam compatible block that is drilled/tapped/machined and roller ready that would be the biggest difference you could make. I would run something in the 206/206 @ .050" range with the shortest seat to seat duration I could find on a 110* LSA with about .470" lift and advance it about 4*.

[killface]

Unfortunately, I would have to go retro-fit roller with the block I have. Not enough money to do it. Thanks for the good info, anyway! Now I know what cam specs to look for if I do another build that is roller.

[Fast355]

Unfortunately, I would have to go retro-fit roller with the block I have. Not enough money to do it. Thanks for the good info, anyway! Now I know what cam specs to look for if I do another build that is roller.

A really nice single pattern grind would work alot better than the slow ramp Edelbrock grind, IMO.

[killface]

Any recommendations for a single pattern grind?

[Fast355]

Any recommendations for a single pattern grind?

With a cam that small a 110* LSA will not be that hard to tune. Just about all the normal manufactures make a cam in the 252-260 range that specs 202-210* @ .050 and low-mid .400s in lift. The stock swirl port heads really do not need higher than .450" valve lift.

http://www.summitracing.com/parts/crn-10003/overview/make/chevrolet

http://www.summitracing.com/parts/cca-12-205-2/overview/make/chevrolet

http://www.summitracing.com/parts/lun-06105/overview/make/chevrolet

If you are decent at being able to tune the VE tables and the spark map, I would drop something like this cam in. I would install it 4* advanced. With the tight lsa and 4* advance it would close the intake valve quickly and capture alot of low-end cylinder pressure that would otherwise blow off.

http://www.summitracing.com/parts/isk-201262/overview/make/chevrolet

That being said I almost think their 256 Supercam would be better, but I really do not like the 112* LSA with a cam that small. Tighter LSA would bring the torque curve on earlier to match the heads, intake, exhaust, factory torque converter and gearing.

[killface]

I think I would prefer a tighter LSA after having this 112. It's ok, but, who wants just "ok"? I'm still a newborn in the world of tuning. I just figured out how to datalog! I'll check those cam grinds out! Thanks! Oh, and I do have a 2000 stall converter.