Torn between swap and turbo

icetherice · Jan 18, 2019

My 2.5L has about 8k on it now and I want more power. I have a 289 block and heads in the shop right now but I'm starting to look lustfully at the Hahn 20g-TD05H sitting on my shelf. I'm not going to ask permission to run three atmospheres of boost on hypereutectics and stock 2.5 rods, just spitballing, pros/cons of a small 8 vs a low boost turbo.

I might even get serious and source a 2.3 crank, eagles, and forged if I decide to go that route.

On one hand, if I go the 8 route I'll be carbing and I'll have to deal with the pissed off computer, on the other, if I throw a turbo on this I'll probably be looking at megasquirt to manage it.

Opinions from experienced hands?

No replacement for displacement

But if I go that route that I'll be looking at finding a T5 and an 8.8 as well....

RonD · Jan 18, 2019

IMO, the choice is really only about MPG

If you want 4cyl MPG then go turbo

If MPG is not an issue then go with a V8 because as you said "there is no replacement for displacement"

Upside of 4cyl turbo is the MPG, downside is mechanical issues with engine not designed for the extra horsepower

Upside of V8 is stock power, downside is MPG sucks

icetherice · Jan 18, 2019

Thanks RonD. That was something I've been thinking about. I commute about 78 miles per day right now, but I'll be moving closer to work soon.

My plan for the 289 right now is:

SUM-K3600 mild towing cam w/ hydraulic flat tappet 280/289 .449/.473
Full roller rockers

Based on that cam profile the total valve lifts are:
With 1.6 rockers: .449/.473
With 1.7 rockers: .477/.502 I started to worry about crashing into a piston here

Basically a bone stock bottom end, just reuse the factory rods..do you have to reuse the wrist pins?
I have a set of C8OE heads (non HiPo) and that leaves my compression ratio around 9.3:1 with the 63cc combustion chamber. I'm planning on doing some port work during the build.

Holley 4bbl ~650cfm?
RPM intake probably since the stock cast intake is horribly rusted and is only 2bbl

I plan to keep the factory fuel pump since I don't really want to drop the tank, so I'll make a block off plate where the mech fuel pump would normally go.

I'll have to unplug the computer as well when I swap this.

Not trying to get E/Ts or make dyno pulls, just looking for a torquey daily that can tow when I need it (it'll probably go down the strip at some point anyway)

Any tips for a first V8 build?

RonD · Jan 18, 2019

I would use a Ford HEI distributor, HEI was one of Chevys better ideas, lol, literally 1 wire system, 2 wires if you want a tach

tomw · Jan 19, 2019

I have not gotten into building much, but roller rockers don't add a lot for the $$$'s spent. Unless geometry requires them, you would be better off spending the money on roller-tappets & cam. The flat tappets have a lot more shear friction than the tips of the rocker arms, and the rockers are sitting still more than the lifters which ride on the cam lobes 100% of the time.
tom

icetherice · Jan 23, 2019

I've done some reading and I honestly don't know if a roller cam is in my budget. I'm probably going to be in the machine shop for ~800-1000 by the time the heads are done. I still have to source:

Dual plane aluminum intake
6-650cfm carb Holley probably
Pulleys
Alternator
Radiator, electric fan
Exhaust manifolds
Dual sump pan
Fuel pressure regulator since I plan to keep the in-tank pump
HEI dizzy (thanks Ron)
Oil filter relocation
A 4.030 rebuild kit (looking at one for $500 that included forged pistons)
Whatever cam I choose (looking at an xe256h grind right now, but it's flat tappet)
Rockers, pushrods, etc...

It seems like there are way more grinds available in flat tappet.

That's a good point Tom, I may just stay with stock rockers or at least get roller tip rockers so the valves don't end up looking like they did the day I pulled the heads off.

This is my first engine conversion so I'm only assuming there are things I'll run into that I haven't considered.

I'll post up in the conversion forums after this.

Torn between swap and turbo

icetherice

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RonD

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icetherice

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RonD

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tomw

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icetherice

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