boost limit with single nozzle alky and stock heads?

[HouTX87]

Is it safe for me to run lets say 26-30 psi with 93 and alky or should I add race fuel at that boost level to be safe? Should I consider upgrading to a double pumper or a fmic? I'm sure there are a lot of variables that make this safe for some combos and not others. I haven't gone above 25psi with my current setup. My signature is current.

 

[Razor]

If you don't see any knock.. there is no issue. Typically the single nozzle should get you into the 10's if the setup is capable. Rule of thumb is 124-126 mph.
Now managing back pressure, air fuel, etc come to play a role. If the boost goes up and the mph does not follow.. step it down or else. once motors get tired, more blowby, valve sealing, etc.. Your knock gauge will tell you the limits.
Also helps to have a good fuel pump(fresh) and good alcohol pump(fresh). The rest is play/work

 

[HouTX87]

Thanks Julio.

 

[we4Mateo]

Agree w/ Julio, mph is more an indicator than boost pressure itself. SloGN is going 130+mph on a single nozzle and a stock throttle body and I'm sure he runs "all the boost" but what that is is just a number.

 

[HouTX87]

Okay. I've had a few tips to add some race fuel to the tank next time I take it to the track. Want to make sure I'm playing it safe.

 

[we4Mateo]

Okay. I've had a few tips to add some race fuel to the tank next time I take it to the track. Want to make sure I'm playing it safe.

It won't hurt; safety first right? I run my times below at 27-30psi on 91/alky only. KevinS stated he ran 35psi on 87/alky, but no times to back it up.

I crept up on my tune though. Low timing, which I still run, and I got it running right at 18psi and went up from there. When I got tired of 20, I went to 22psi. When that got old, I went to 25psi; and that's where it really started to come alive. At the nats I ran "all the boost" and netted my two best runs below. I figured out how to launch on vacuum footbrake too at the same time and JD and Patrick helped me with my tire pressures, so it all just came together at that right time. Last run of the last day for me at the '12 Nats. My car is 3760lb with me in it.

 

[HouTX87]

It won't hurt; safety first right? I run my times below at 27-30psi on 91/alky only. KevinS stated he ran 35psi on 87/alky, but no times to back it up.

I crept up on my tune though. Low timing, which I still run, and I got it running right at 18psi and went up from there. When I got tired of 20, I went to 22psi. When that got old, I went to 25psi; and that's where it really started to come alive. At the nats I ran "all the boost" and netted my two best runs below. I figured out how to launch on vacuum footbrake too at the same time and JD and Patrick helped me with my tire pressures, so it all just came together at that right time. Last run of the last day for me at the '12 Nats. My car is 3760lb with me in it.

Right, safety first. I've also been told mixing in race gas will richen the tune a bit. You're weight is close to mine. I think I weighed 3740 with me and half tank. "all the boost" meaning wiring the wastegate shut?

 

[we4Mateo]

Right, safety first. I've also been told mixing in race gas will richen the tune a bit. You're weight is close to mine. I think I weighed 3740 with me and half tank. "all the boost" meaning wiring the wastegate shut?

Yep, almost 30psi is all I could make. I guess my cam and intake port matching makes those crappy irons flow ok.

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[Eric Stage I]

Right, safety first. I've also been told mixing in race gas will richen the tune a bit.

It all depends on what fuel it is. You could also go leaner. The differences are usually very small though.
Eric

 

[HouTX87]

Yep, almost 30psi is all I could make. I guess my cam and intake port matching makes those crappy irons flow ok.

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You've got me thinking about port matching mine to help maximize the stock setup. I don't want to change the cam unless I go roller and at that point I'd be buying champion irons as well.

It all depends on what fuel it is. You could also go leaner. The differences are usually very small though.
Eric

Good to know. Thanks Eric.

 

[we4Mateo]

You've got me thinking about port matching mine to help maximize the stock setup. I don't want to change the cam unless I go roller and at that point I'd be buying champion irons as well...

It helps a lot and is easy to do. Open the heads up a bit more than the intake so there is no step for the air to jump up against. I picked up 40rwhp with the cam swap and this mod and it couldn't have been all cam, imho, all else equal.

 

[HouTX87]

Actually I'd be tempted to just upgrade to a champion intake since they say all cores must be unaltered. Then again I'm bad about hoarding original parts instead of exchanging them as cores but $250 is an expensive core charge.