My cam has very large lobes and I dont know if having 1.6:1 rockers will be too much for my springs. I bought it as a kit so I have springs meant for the cam (along with pushrods and lifters). With 1.5:1 rockers I get 0.495" lift on the intake and 0.502" on the exhaust. Obviously if 1.6:1 rockers are fine for my kit then I want to get them to give me as much HP as I can, I just dont wanna risk destroying the engine. Thanks guys.

Cam Kit:
http://www.compcams.com/Cam_Specs/Ca...?csid=187&sb=2

 

What heads are you putting the rockers on? Those can be the limiting factor too.
With that cam, 1.6 rockers will give you a .528 in., .536 ex. lift.

 

These are the heads:
http://performanceparts.com/part.php?partID=302400

Any idea?

 

Is this going to be a DD? What are you doing to strengthen the car (it is a convertible after all.) What are you doing about the transmission?

Bottom line, that's A LOT of cam for a 350. Adding the 1.6 ratio RR's will make it unstreetable IMO. The amount of lift is dependent on what the heads are machined for, as well as the springs and retainers (but it looks like you're buying the kit, so the springs and retainers aren't a big deal.)

The push rods will obviously be a weak point, those will need upgraded to a one piece chrome moly rod.

IMHO, that cam is pushing the limits of those heads. I'd say you would be fine with the stock ratio arms however.

This brings us back to the car: This cam is capable of producing at least 450hp with the right bottom end and supporting mods. What have you done to support this power?

 

You really think the engine is likely to push 450 HP? I plugged in some numbers in Desktop Dyno and it showed me peak performance at around 350, but I may have put in some of the data wrong since that was my first time trying to make an honest effort with the software. So far I havn't done anything to support the power, but I have been thinking about adding a roll-cage. I have heard I may need to re-enforce the frame with it being a convertible if the engine is too powerful, but I am not sure exactly what that entails (but I do have some friends that do work welding and what not on race cars, so I can always get help from them). The transmission is stock and thats one thing I have been thinking about upgrading some time in the near future unless you guys think its necessary for me to take care of it now.

And yes, this is going to be my DD, but as of right now I dont go too far for work and school, so I don't mind if it eats a bit more gas. Before the engine swap I was getting 10 mpg and I was okay with that, but I would prefer better.

 

I just did a quick simulation in Comp Cams Cam Quest. I'm not sure what induction you're running, so I did a very basic setup:

XR270HR cam
350
Pocket ported, standard size valve heads (1.94 intake, 1.5 exhaust.)
10.5:1 compression ratio (you'll need at least that to keep the motor happy with that cam.)
Dual plane intake
750cfm carb
Large tube headers, mufflers w/o cats

This netted 496 hp @ 5500 RPM and 506 ft. pounds of torque at 4500 RPM

Obviously, there are plenty of variables to take into account. As a result, this number is inflated about 10-15%, so realistically, you would see about 425-450hp at the crank from this setup.

You may see a bit less than that, as that cam may outflow those heads.

A stock T5 will grenade with anywhere near that much power. You will need to either swap to a T56 or an automatic.

I'm not familiar with how the convertibles frames are constructed, but I do know that you cannot use off the shelf sub frame connectors. It will need to be beefed up to handle that kind of power.

 

Is Shifty working on his 305, or is he building a 350 that I don't know about?

 

The engine that was originally in the car was a 305. The heads blew and I picked me up a 350 to rebuild.

As for what is going in the thing ... first I have that entire valve train kit and the heads I mentioned. The engine was .080 over, so I kept it the way it was (my mechanic told me that the cylinder walls are fine.) And I was planning on keeping it TBI since thats what it was before, so I have a rebuilt throttle body. Would that starve the engine too much? Also, should I upgrade my oil pump to a high volume oil pump?

 

A TBI system won't support that much power, and the ECU won't like that much cam. There isn't much you can do with a TBI setup either.

Either swap to a carb or find a complete TPI setup. The TPI will need a custom mapped ECU and larger injectors, so a carb will be the most simple. A Vortec intake, Holley carb, and an HEI distributor is all you will need.

I always recommend upgrading to a high volume oil pump. Some people say that with a stock volume pan, you may starve the engine for oil however I've never had any problems.

 

I was running a .512/.512 lift with 230 duration @ .050 cam with 165cc runner heads with 2.02/1.60 valves and I was having problems running into the high RPM band. I think those heads are going to have a small runner for that cam. A 180 runner would do great for low end and still leave the top end decent. If you have a good set of rear gears it will also cover up the duration.

My low end was great and streetable with no problem with around 14 - 15 vacuum at idle. I also run gapless piston rings which help with that.