My 6 bolt engine need a rebuild. My plan is a 95% street car, I want to push my td05h-20g to the max like 24-25psi on 91 octane (that's premium fuel here in Quebec) looking for ±400 crank hp. I was thinking of rebuild it with NPR 7.8:1 and stock 6 bolt rods but I'm curious to know what kind of fuel economy can I make if I rise my compression ratio to 8.5:1? Does it worth the extra money spend?

In fact, I have 3 options in mind :

-stock rebuild with NPR 7.8:1 and stock 6bolt rods

-stock 6 bolt rods with forged pistons 8.5:1

-eagle rods with 22mm pin and NPR 8.5:1

What do you guys suggest me?

With a street car, I've always found a higher CR better, since a decent portion of driving will be done off boost, and better mpgs(l/km). As far as fuel economy goes, a 20g at 25psi will not likely fair well unless you're highly skilled in the art of hypermiling.

And as far as rebuild options go, 6 bolt rods should hold 400bhp, but I wouldn't trust it for too long. Although I've heard of a lot of people taking that setup far beyond 400hp, I would build beyond my desired power goals. Your weak link will lay with your transmission, any plans for it?

I'll put a 4 spiders center diff in my tranny. and what do mean by : As far as fuel economy goes, a 20g at 25psi will not likely fair well unless you're highly skilled in the art of hypermiling.

And so you suggest what 8.5:1 or even 9.0:1 with better rod and forged pistons??

I was just saying that if you're looking to push 400bhp, that you probably shouldn't worry too much about fuel economy.

I just want to be able to drive it normally on the street without empty my pocket and be able to beat it at the drag strip with 400hp of pure fun.

9:1 Compression and E-85

I have your set up in a way. I went with better pistons though.

I can detune it for 93 octain and it still runs ok.

manifestmessiah said:

With a street car, I've always found a higher CR better, since a decent portion of driving will be done off boost, and better mpgs(l/km). As far as fuel economy goes, a 20g at 25psi will not likely fair well unless you're highly skilled in the art of hypermiling.

And as far as rebuild options go, 6 bolt rods should hold 400bhp, but I wouldn't trust it for too long. Although I've heard of a lot of people taking that setup far beyond 400hp, I would build beyond my desired power goals. Your weak link will lay with your transmission, any plans for it?

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Turbo size has very little to do with gas mileage. In fact, larger turbos will usually allow for better mileage since you can stay out of boost longer. 6-bolt rods are also way more than enough for 400hp daily.

OP- Higher compression ratio can yield more power across the RPM range, so of course it's possible to gain mileage from the increase.

Plan ahead. Go with a forged piston(Wiseco HD, Ross, Mahle are IMO the better choices) and rod setup(any H beam) if you can afford it. You can find good deal on either in the classifieds.

If you're ballin on a budget, you can't go wrong with 1G rods and 2G pistons.