xxtremes33

so im looking for a setup to run on 89 octane at around 350rwhp minimum and no more than 400rwhp. so i know i will need to stay with lower compression. i know the lq4s are around 9.4:1 compression. will i be able to put down 350rwhp on 89 octane on a safe tune? are there any aluminium block alternatives without having to replace pistons? if i need more power i may just spray a wet 100-150 shot or so. i have searched and cant find much info on octane vs power.

this will be in my daily driven 3rd gen rx7. i dont generally drive my cars very hard. I want a reliable, good street mannered car. it puts down about 330rwhp right now, so i definitely dont wany any less. i own 5 cars and every single one requires premium gas 91-93 octane. i will never get rid of my 3rd gen rx7 and it will eventually need a new motor so im trying to piece everything thing together now. any help is appreciated!

Fry_

There are a lot of people here that are running 11.5+:1 on 91 octane. So as long as it's tuned for it you'd be pretty safe running 10-10.5:1. So your options for stock motor's would be LS1 10.25:1, LS6 10.5:1 this might be starting to push it but it could be tune to run on 89, 5.3HO L33 10:1, 6.0 HO LQ9 10:1, and all of the low compression truck motors.

xxtremes33

im curious to whether this could be done on 87 octane now. i forgot about the L33 and LM4. L33s arent readily available around here for a decent price. but theres a place about 30 minutes from me with a LM4 for 750 bucks.

redtan

iTrader: (5)

You can run an LS on 87 octane, but it will be severely limited in power output. You either have to detune it by running low timing, or you have to run low compression like the LQ4.

I always wonder tho why people go all out to try and stick to low octane and sacrifice so much power just to save a few cents a gallon. I mean the difference between 93 and 87 is what like 30 cents? That's 4 bux a tank?

If 4 bux a week means the difference between making and breaking your budget, then I would say you have bigger issues than trying to make an LS engine run on low octane.

Can it be done? Sure. Is it really worth it in the end? No really.

Grimes

iTrader: (3)

There are some things you can do to increase knock resistance, like increase quench area, thinner head gasket, cam with more overlap.

Honestly you'll save much more money by learning how to drive like grandma under normal circumstances. Google "hypermiling" for some good tips.

xxtremes33

not that i cant afford the gas cost. im more curious than anything. i own 5 cars currently. every single one uses premium gas. so i figured it would be nice to be able to run regular unleaded on at least one of them if it was feasible.

425+rwhp 2nd gen FC Convertible RX7
300+rwhp 3rd gen FD RX7
~400rwhp Twin turbo BMW 335i Sedan
Stock 01 Camaro Z28
Acura MDX

redtan

iTrader: (5)

Stick with a nice high compression motor (in the mid - high 10s) and just tune for the appropriate octane. Have a low timing tune for when you need 89 octane, and another tune for if you ever want to use higher octane. This way you have options. If you just build a low compression engine, you can't go between 89 and 93 octane since it won't make much of a difference.

My 10.9 compression LS2 can be made to run on 87-89 octane, just with lower timing. No need to hider yourself with 9.4 compression on an N/A car.

xxtremes33

yeah im just going to go with a stock bottom ls1. i picked one up last weekend for pretty cheap with only 78k miles on it

maf_diver

You should be ok with LS1 10.1:1 compression. I often use 94 RON E10 in my stock 2000 LS1 (~89 octane on your rating system) and only go to 98 RON (like your 93) in hot weather. I run ~21 degrees of timing at WOT on E10 vs. 25-26 on 98 and there's stuff all difference in power.