higher RPMS?

blockhead said:

what add on would make my RPM's higher? chip, cams, heads, tune? I’m assuming that’s its cams because my friend just got a 99 Cobra and the only difference is that he is 32v and im 16v.. oh and his intake right? He’s RPM's are around the 6,000+ mark and mine is at 5,500+. the reason why i ask is to help me make my dam mind up on gears.. i plan to go s/c but want more than the 3.73 that everybody goes with.. i want a little more bite so I’m debating on 3.90 or 4.10.. to much gears perhaps since i drive allot in the highways . but thats why i want to find out how to get a higher rpm. if i cant realy do anything about it ill go with the 3.90. just dont like that they are not from FRPP. but if i can WOW 4.10 here i come

Click to expand...

Theres alot of cobras running blowers and 4.10's, not the best for traction, but great for a fun street ride.. Highway will suck no matter how high your max rpm's is...If you got your heads worked on and swapped out the cams you could set ureself up to rev to 8k..depending on how radical you are going of course, but once you start messing with that then your internals need to be forged or you will start blowing things up! oh and i heard its a big pain to go the 3.90 route, may be other parts needing to be replaced... either 4.10's or 3.73's just base it on your highway travel good luck

for higher RPM's you need P&P heads, cams, and new springs. you probably can get 7,000rpm out of the stock block. but i wouldn't push it too much. get a built shortblock and you can push 8,000rpms. but you may not make any power up that high with 2V heads n/a.

With a stock 4.6 ...the stock springs are going to allow valve float to begin around estimated 6500 rpm. As the valves are no longer seating fully you notice that you cant seem to rev it any further. Since the valves are starting to hang open you can no longer make any more power ...rpms no longer climb. Kinda like a mechanical rev limiter. The real problem is if you have some valves hanging open and bump into a piston...thats not good.

Maybe someone can comment on a stock setup, with ECU rev limter turned off, exactly how high can you rev before the valve float starts. It will first show up as though the engine is no longer making any more power or reving any higher.

In MM&FF (sept 2003)they did a test on Cobra motor with aftermarket springs and roller rockers and solid lifters and ran it up to 7000 many times and considered it stable at 7000 rpm

The key things the Second Street Speed indentified was that stock springs are too weak above 6000 rpms and that the stock hydraulic lifters go solid at extreme rpm 8000+ causing valve float.

So lifters and spring would have to replaced to build at 8000 rpm monster. And remember this was a Cobra motor with forged internals?? So you maybe some can comment on if a GT's rotating mass is as balanced as a Cobra's?? are the Cobra's internals balanced to a tighter tolerance??

So I guess to answer your question for sure you can take your GT to 6500-7000 with the right spring and cam and rocker and lifter choice. But who knows beyond that. (the Second Street Speed roller rockers and solids are gonna set you back $1800 and that doesnt include your cams).

Second Street Article