high compression 7M

[Norbie]

Got any scientific sources for this? I certainly don't recall any street cars running upwards of 20psi on pump fuel in the 80's.

[jimmmayyy]

o_man the motor has an arp stud kit. thats why the bottom end has gone from detonation rather than the hed gasket. i don't believe that we have worse fuels today, unless someone would like to prove it. I know we have dodgy servos that mix fuels etc. thats the whole reason i'm in this mess now. if anyone in adelaide would like to know in PM which servo it is i'd be glad to let you know. after speaking to a few friends about it, they have had issues with the fuel from the same servo too.

Hibba, the car is an '89 MZ20, so what gen would the motor be?

[whatthe?]

Probably a Gen 2. Most of them seem to be.

Easy to tell, you can see the squirters and the crank will have a dirty big "6M" casting on it

[Jin~Jah]

this is my kind of thread


As Hibba said, we put a GE bottom end in mine after the rod-thru-block GTE setup. It's great to drive off boost, and certainly goes well on. Currently it's 9-10psi using a bleed valve on the stock wastegate. highest it's seen was 15-16psi, maybe more, i was watching the road not the guage.

It's hit that a few times, boost cut is a little bit after that, which i hit twice after getting it back on the road after finishing the BA/R33 brakes..... then i turned the bleed valve around the right way and it was all good.

I run 98 octane in it, and it seems fine. I can't hear if it's pinging over the spool and the exhaust, but the ecu has not retarded the timing due to knock sensors except for the first time we ran it with the vpc. It has been fine since then.

moral of the story = GE bottom end, as long as it's healthy, will cope pretty well with boost if my car is anything to go by

[jimmmayyy]

sounds good man.. have you ever gotten it on the dyno for a tune etc? i'm starting to lean back towards a GE bottom end because it's getting near impossible to source a motor here in SA.. but if i have to get it built then so be it i suppose. i'm currently trying to screw the fuel company to pay for it.. hopefully it comes through.

got one quote from a large adelaide supplier... 2000+ for a used 100k+ imported motor, lol. stick that up your arse!

[jeffro ra28]

Got any scientific sources for this? I certainly don't recall any street cars running upwards of 20psi on pump fuel in the 80's.

Just the fact that the chemicals such as Analine, Benzene, Dioxane and Toluene to name a few where the chemicals placed on the Government hit list to minimise polution. All these chemicals improved detonation resistance qualities of fuels and burn rates etc.

Ok so perhaps the fuels of today are good qaulity, but by no means are they more resistant to detonation as were the fuels years ago.

Engine and ECU technology has improved over the years to allow more boost and compression, but it certainly isnt the fuel that has allowed us to do so. Pump fuels btw.

[o_man_ra23]

Dunno why Toluene was placed on their hit list, its a fairly safe chemical on its own. Its the Benzene found in impure Toluene that is a problem.

Also EFI and Turbos were in their infancy in the 80s, and just werent up to the tuning standards to run those sorts of boost Norbs. So yeah, it wasnt the fuel keeping it back, it was the equipment... fortunately things have improved on that side of things since then. Unfortunately Flannel shirt mobiles can run on dirty sludge due to their low kW/L so quality fuels arent high on the local car market list of necessities.

[Norbie]

The point is, the 7M-GTE was designed to run on 91 RON fuel with 80's-tech engine managment. Today we can use up-to-date engine management and tune it for 98 RON fuel. Therefore, low compression ratios are no longer a necessity.

I'd also like to point out that the RON number is determined by physically testing the fuel's detonation resistance in a specially designed test engine, so it doesn't make any sense to claim detonation resistance has decreased when the numbers have increased.

[jimmmayyy]

have to agree with that. however it was premium fuel that the car detonated on.. have rung around and it looks like it's gonna cost more to get the fuel tested and motor inspected to screw the fuel company for a new motor. apparently $500+ just to get some fuel tested... weird.

-jimmy

[o_man_ra23]

Find a law firm who is willing to put up the fee and guarantee a win

Petrol companies use an emulsifier to blend in water in cheap fuels (beware of low cost servos, ive had an 18RG run like shit after a tank of cheap premium).

Also, the fuels dont get tested for their long term effects. The sulphur etc degrades engine components/sensors over time, and while not throwing an out of range error from the computer, it puts the readings out far enough to be dangerous.

[jeffro ra28]

Im not going to stress about this, because i am not certain. Perhaps the above mentioned chemicals further enhanced the MON rating then they did the RON. But by limiting the chemicals used in boosting octane i think they are downgrading its overall qaulity as a fuel.

[jimmmayyy]

Nah it was a big name chain servo, this one particular franchise is apparently notorious for bad quality fuel as i've found after all this bollocksing around.

-jimmy