so, it's a given that you can't run a particularly long-duration camshaft with tbi. if you do, you won't have enough manifold vacuum at low rpm for the map sensor to read.

i was wondering if anyone had tried running a long duration camshaft with rhoades lifters? they make significantly more low end vacuum than traditional lifters.

 

I hear that most people who run those take them out because they dont like the way they perform. You can run a fair ammount of duration, but you have to know what your doing. The more cam you run, the more knowledgeable you have to be to get it to work right.

 

Ive noticed that youve got quite a stout exaust on your car. Bit more then what an L03 would need. What durations where you planning on running with your final setup?

 

at some point, i plan on replacing the 305 with a 383 or 400. i'm basically just thrashing on the l03 till it goes away. i won't put any money in the shortblock when it goes down the tubes. i did the exhaust with those engines in mind, knowing that it was more than was commonly done on an l03. suprisingly, i haven't seen the loss of torque people warn of when using 1 3/4" primaries on a 305.

anyway, since i plan on always running regular street tires on the car, i have to make sure the torque curve doesn't peak too low in the rpm band. while i won't know exactly what cam i want to run till i have the flow numbers on the heads i'm puting on the car, i imagine the duration i'll want will be somewhere in the 220-230 (@ 0.50) degree range.

 

With a large ci engine, the tbi is really going to struggle feeding the engine in its powerband when you go above around 214* of duration or so. Theres also the issue that itll be difficult if not almost impossible to tune with very high durations and low lsa's. Are you planning on keeping the tbi, going aftermarket efi, or carb?

 

i'm going to stay with the tbi till i can flog it no more! also, i'm planning that cam for the 305.

 

with the large cubes, the duration specs you mentioned, are not very radical at all.

good friend with a 383 runs a 230/238 cam on a 114 LSA, it runs fine with FI, Traxion runs a much larger cam than that, and has been able to tune it. it will take tuning, i hope you really like doing VE adjustments the real question is just picking the cam for your powerband, a 230* intake on a 383 is still pulling at 6500rpm, i won't have a actual power curve from the dyno on this engine until mid january, but i bet it is still making power to 7k. unless you plan on building a bottom end to see these kind of RPMs, you shoudl probably run a smaller than 230* cam.

 

Never said it couldnt be done with a modified SD or MAF tpi setup. What I was saying was in reference to his present tbi setup. With a 2 barrel 454/670 tbi the airflow and fuel capabilities will fall short for a large CI engine and itll cost power unless a 4 barrel is used but then theres the whole issue of getting it to properly fuel down low with the stock ecm. Thres also the issue of the lack of resolution that he'd run into with an unmolested tbi ecm with a low vacuum cam. If hes proficient with source code then he could easily implement a 4bbl system and rescale the tables to fully take advantage of them but there arnt too many of us who have reached that point yet.

 

yes, he would loose resolution if he was idleing in the 60kpa , or something like that.

but the engine will run, and probably run pretty good when properly tuned. the HP thing is another issue, and yes, a cam that size, in a 400ci engine, is probably going to make alot more power than a 2bbl TBI unit can support.

i was getting to point of being able to run long durraction camsafts. it has less to do with the durration, and more to do with the overlap. you can run alot of durration with very little overlap, and have it work well. but on the contrast a small duration cam, with tons of overlap, will cause problems with the computer.