Hey guys, I’m looking to be in the 650-700 hp range with my 70mm On3 setup. I want to stay on 93 pump gas. Am I safe with CR at 9.4 or should I go lower. Also on the fence with cams. Currently have hot rods in and don’t like them. Should I go back to stock cams or search options.
Brenspeed makes a great boost cam (Detroit Rocker series) for the 3Vs. You will be safe on a 9.4 CR/93 pump gas for that hp range. As always, discuss your engine needs with your engine builder.
9.4 is plenty safe. Less than that, it will feel doggy until you are into the boost. As for cams, lots of people will say you need either turbo cams or stock cams but that is mostly BS. I have "turbo" cams and find the midrange torque to be weak until the boost comes on. If you don't like the hot rods, put something else in there but just remember that boost just amplifies what you already have.
Thanks, with the cams i love the idle but I feel like it takes a while to spool. I was thinking it was because of the overlap. Last Dyno was 512 @ 11 psi. It pulls decent once I get boost. That was with the stock long block. I’m building the forged short block now. Also jumping from the 42 lb injectors and a 340 pump to a twin return style 340s and 80lb injectors. Any thoughts?
Convention would say that with a turbo you will have higher exhaust back pressure on the engine than a NA engine would see and for that reason valve overlap should be avoided.
That is exactly what I was thinking. Should I put the stock cams back in? What kind of hp with stock cams is achievable
With a turbo you would be better off with the stock cams over the Hot Rods, they have way too much overlap for a turbo setup. Do some searching on here, there were several members that modified the On3 setup for better performance.
With a not so efficient On3 70mm turbo and a .96 exhaust housing, 3000 would be excellent spool characteristics. With my stock motor, it took to about 3200 rpms to reach full boost with a smaller 67mm turbo and a 0.81ar exhaust housing. With a borg s369sxe billet wheel 69mm turbo, 0.96 housing and "Turbo cams" , I am not fully spooled until 4300-4500 RPM in a 3rd gear pull. The Hot Rod cams have way too much exhaust duration but they are not killing your spool as much as you think.
Next order or business is replacing the on3 coldside. Its barely keeping up at 500rwhp. Seen bigger intercoolers on turbo 4 cylinders at 400whp. 4" thick bar and plate core and 3" piping through out. The better coldside will not only have better iat's and make more power but have better response and spool. The easier the compressor can get air at a lower pressure ratio into the motor the more exhaust mass you have to drive the turbine.
A little late to the party... just wanted to say I’ve been running the Brenspeed Detroit Rocker Blower Cam at 15+PSI boost with a Kooks longtube header off-road exhaust and I could not ask for better. It’s an awesome setup.
Why did the stock cams make peak horsepower at 4800rpms? Something seems really off with that dyno graph, all of the cams flatlined by 5000rpms.
I'm running comp cams 127350 stage II blower cams with my turbo setup (originally had a Saleen SC), they work good, I would probably see some gains with a custom grind, but not sure if it would be worth the $$$ already making 1081rwhp and 1241rwtq with my little 76mm turbo, when I move to a large turbo I might make the change then.
Here's my car on 6.5lbs with the Brenspeed turbo cams/70mm On3 turbo. Car starts to really pick up at about 3000 rpm.
