Hey guys. I have a built 408 with fully forged bottom end and arp hard wear. I have a TVS 2300 on top of it and was wondering how much boost can i safely run on 91 pump gas and meth. I was thinking 15-17 psi. My compression is 9.1:1. if you guys need more info just ask.

thanks

 

I think you can do it on 91 pump gas with meth. I'm running 13psi now with 91 and it doesn't like it. I've added an alky control kit and it is about ready to roll.

 

I wouldn't run much more than 12psi and that's with some very carefull tuning. With meth you could probably get away with 14psi hosing it pretty heavily. You built your setup with some pretty low compression which is ok if you plan for high boost, but for a street truck you're just losing power from that.

 

Don't mind me reviving a long dead thread, if we build for a 10.5:1 or so compression on the 408, but followed with aTVS2300 would this be a more comfortable area to be sitting in? I don't really want to go meth with it, but just keep an aggressive street truck on 91.

 

what's your elevation? that plays a big factor in octane effectiveness/requirement (compared to sea level, each 2500ft of altitude needs a point less octane).

also, SCR don't mean much without knowing your cam specs because what actually matters is your cylinder pressure & DCR. case-in-point: when i rebuilt my LS1's top end, i bumped from 10:1 to 10.6:1 but still ended up with slightly lower DCR than stock because i threw a huge cam in it.

another consideration is that unless you already have the 2300 & the 408 in-hand, smaller cubes or a 2650 would be better options unless you're only planning for moderate boost. asking for > 2.0 pressure ratio on a 400+ci engine out of a 2300 requires spinning it awful fast... which equates to a lot more heat than you'd want (read as costing a lot extra to combat that heat... or just accepting less-than-impressive output numbers). not trying to dissuade you - simply relaying what i've seen & experienced over the last decade.




PS: also consider that basing requirements & power discussions around a boost figure is very relative. a target CFM and/or horsepower number are better for discussion because "boost" only tells you how much air the engine ain't using. my previous setup (stock long block, headers, stock balancer, 3.3 front/1:1 rear pulleys) made ~12psi and my current setup (heads/cam, ported blower manifold, OD balancer, 3.8 front/OD cog rear pulleys) still makes ~12psi... but it now lays down almost 150whp more than before.

 

back to your question, though: depends on how you plan to drive it. for street use where you ain't burying the skinny pedal all the time - i'd go for higher compression (roughly where you're at) because it'll be much more responsive & efficient in part-throttle application. that does narrow your tuning window & boost limits to keep the engine happy, but i'd say it's worth it.

if you're building this as a weekend warrior that plans to go roll racing on Saturday nights or always hitting the drag strip, then i'd opt for something closer to 9:1 and spin the blower harder because boost doesn't generate as much heat as cylinder compression... which means that hitting the same cylinder pressure via blower CFM means there's more O2 molecules per stroke & therefore greater power potential.

 

PS: my LS1 vette is laying down over 650h/630t through my 2300 on 93 with no meth. i do have a KillerChiller to help IATs, though.

 

~2000', up to 4k when back in MT on occasion.

I don't have either yet, tentative plan is build my Lq9 into a 408 and upgrade my side mount Whipple. Figured a Whipple 2.9 or TVS2300would be enough but still researching. Not going for crazy boost or horsepower, itis a street toy for show and the occasional go but want it reliable. No dissuasion, i truly appreciate the input as this is my first build so still learning alot.

Yup, weekend warrior to the local hardware store and carshow, occasional road trip long distance to special events like Cool Deadwood nights or something, maybe a drag pass on special occasion but its more show with enough go to FAFO

Downside to my current set up, non intercooled whipple. That and the engine needs a rebuild regardless hence the start off the whole project.

 

ahh, gotcha.

i would've suggested you just keep the 2.9 until i got to the non-intercooled part. i personally think a 2300's a little small for those cubes, but would work fine - especially if only pullied for 8-10psi on a mild top end. guys have pushed 2300s hard on much bigger engines (~20psi on 408 / 427 / upper teens on a 454)... they just get a lot more expensive to cool down & keep from slipping the belts.

another consideration is that PD blowers come on pretty early with the torque, so you don't really need a stroker & could build something like a 376 or 388 instead.

start digging around for compressor maps, which will help you determine how efficient each supercharger option will be at whatever airflow requirements you end up needing for your power goals (based on pulley setup, cubes, boost level, etc). if i remember right, targeting high 8.x for dynamic compression is a happy balance for power, responsiveness, efficiency, and tuning safety - wallace racing makes some good calculators that'll help you determine that & how displacement / head / cam changes affect it.

i think it might've been Atomic on here who created an excel sheet that estimates your blower airflow/boost/temps based on your engine & pulley specs. dig around - it's worth saving a copy.

unless you're shooting for 700hp, a 90mm TB is plenty & won't require selling a child to obtain a 102 + a 4" intake.

 

Yea, while 700 would be alot of fun, i really don't need it and would be happy with 600 (ii say that now).

I've gotten a few quotes and all the 408s are ~9K built no install or tuning. Wondering if a turn key crate in the ~12k range (all these without SC included) would be a better option for me. Could likely sell my current SC and the Lq9 and recoup some cost.