Dinsdale Piranha

How much boost will a 4.5 block take?

SeanR

Lots if you tune it right. Start with 28lb and let us know

Kidding, have no idea. What are you running right now? 6?

BC

If this is an honest question ( can never tell with you) then it depends on fuel management and the actual fuel used.

If you artificially limit yourself to 91 or 93 octane, it will be low. If you allow for other fuels (e85) then the boost limit is the physical strength limit of the structure of the block.

Ducman82

Boost=money

robot808

Well, I'm pretty sure Hacker-Pschorr was running 17psi on a 4.5 for a long time. I think at some other times he may have pushed the envelope well beyond that.
I'm pretty sure he ditched the stock fuel management.
Hopefully he will chime in with the specifics.

AO

Theoretically, 54.8 psi using e85. That's with stock cams, pistons, head, rods....

SeanR

So that is what blew up DR's old car....

Dinsdale Piranha

So far we have an 82 4.5 engine. Boosted with W/A IC . Stock engine management with rising rate FPR, 6 speed transmission. Been gathering all the goodies for Megasquirt COP. I was thinking about adding a rear mount turbo with additional air to air IC and pushing the envelope . If it blows up I have spare engines. Give me the good, the bad, the clinically insane advice. Aint skeered.

AO

no. What blew it up was about 6 psi, poor tuning, and a very crappy crankcase ventilation system.

AO

You'll want to back off the timing about 1 degree for each lb of boost.

Iwanna928

First time I took the 85 euro TS down the highway to Atlanta on 75 to a lesson it was a happy day. It was beautiful out and the car was stunning. On the way back from the lesson on the way home a car was next to me on the highway, light traffic etc. I downshifted and hit the gas, two seconds later I had to pull off the side of the highway as oil was all over the windshield! Put oil back in and cleaned her off and nevr ran right again. I got to enjoy a couple WOTpuills for a few seconds with that car and then the madness started.

For that brief moment that car was everything I had ever dreamed off since I was a kid. So on the bright side at least I was there once!

AO

It's unfortunate how that "oil control" system was installed. It just didn't work. I think that's what killed it. I still have not taken the old motor apart. Maybe next week I'll start the disassembly to find out what put the big gouge in the wall of cylinder #7.

BC

Except for with ethanol.

TexasDude74

Jeff, I don't think there is a forced induction setup out there that will fit under the 928 hood line and generate enough boost to split the block if the proper fuel ratio is maintained and engine oil is kept where it belongs. Six psi will take one out in a heart beat if it goes lean or is fed a 50/50 mix of fuel and oil.