7m build question

[Timmie_g]

Sorry to bug you guys but im in the process of discussing my rebuild with my rebuild shop here in the city and we came across the question of which pistons i wanted to go with.

Now i have a good idea of what i want to accomplish with this build and would be pretty upset if i couldnt do it.

The man rebuilding my motor told me today that i should decide which turbo i am using and that will help determine the static comp ratio we should shoot for.

Baically in short i am looking to build a ROUGHLY 400whp street car that WILL see track time, both strip at street legals and road course.

So as far as i know i should not need a huge rebuild. A fairly mild bottom end rebuild combined with some good head work and proper supporting mods should easily create 400 horse.

So my turbo question is

Upgraded CT26 or Garret GT35R

a 35Ris way more turbo than ill use (for now, i say this cause i never know what i may do in the future) but is also well built has fast spool due to the ball bearings but is also not on the cheap end

still not bad in the driftmotion kit

The ct26 however is MUCH cheaper as well as already having the proper manifold lines exhaust and so on. But i do not know the capapbilities or reliability of a ct26 producing that much power and i do not want to run the turbo right at its limit constantly.

(yes all supporting mods are being completed with the build, intercooler, new cooling system new fuel system and so on.)

Does anyone have any input on my situation, if so i would be very excited to hear it, and if any of you want to tell me im nuts or i have got the wrong information i would appreciate the correction.

Thanks

Tim

[Keros]

Look into BOSS/greddy turbos, specifically those built on the TD06 chassis. It shouldn't be hard to find info on them.

There's also a turbo shop in town, see Jim's build thread about that.

There's alot of options to go ball bearing if you want to get good spool. A CT26 upgrade would do 400hp, but it will be more like a blunt hammer than a precision laser while doing it: be prepared to wait a bit for your power, even moreso than you did on your stock CT26. A 57 or a 60 trim should be sufficient for those goals... it's covered plenty of times on SM.

[annoyingrob]

I would recommend NOT going for an upgraded CT26. It's a band-aid approach IMO. Mismatched compressor/turbine combos are not usually a good idea. A 57 trim CT26 might make 400whp in Calgary's air, but it's going to be pushing hard. A 60 trim will likely do it, but they call it the shaft snapper for a reason.

A GT35R is a lot of turbo for what you're looking for. If you WERE going to build a motor around it, why not build a motor for 500whp, instead of 400whp. When you start talking 7Ms, there's going to be work required for both power levels, so it may make sense to spend a few hundred more now to make the motor ready for the future.

I would suggest you look at a GT40-82 if you're only looking at 400whp, maybe even a GT30-76. Despite what you may think, a GT40-82 is actually a slightly smaller turbo than the GT35-82R you're considering.

[Keros]

Well, come to think of it... isn't it sort of putting the cart before the horse to build the engine around the turbo?

Consider for a moment that 650CFM of air is 650CFM of air, no matter what is moving the air. The CR required to make 400hp will not change regardless of the turbo used to make it.

I think a more optimal question for what pistons you should get is "what CR do I need to attain my power goals"... then ask what turbo you'll need to attain that power goal.

I have all the notes to do the math somewhere... but I'm afraid I don't recall where somewhere is.

However, stock CR or lower will suffice for a meager 400hp. People run 400hp on completely stock 7M's regularly.

[Timmie_g]

yea i knew the stock motor could make 400whp, so i figure with some good bearings a set of similar CR pistons rings and arp rod bolts should be capable of creating and handling that power number quite well.

and the motor should flow much better due to the head work being done so getting the air should not be a problem.

My original plan was a 35R but the ct26 only came up as a way to save money and for ease of build, but cutting corners for sake of saving some cash now will probably cost me in the future.

I thought it was odd as well trying to decide turbo first because i thought you build the motor then complete the supporting mods but this is just what i was asked.

i would be using edmontons air as well so it would be slightly less stress on the turbo as the air is more dense here but i dont think it is much of a difference

thanks for your input thus far guys

[Funkycheeze]

the biggest issue is going to be how you do the headgasket, and making sure the engine is cooled properly. 400 can be done on stock cast pistons, or forgies at stock CR

[Timmie_g]

headgasket will be replaced with a metal gasket of some brand which is yet to be decided and will all be assembled by the engine rebuilder with arp bolts for everything(rod bolts, headstuds, flywheel bolts), as far as cooling i will be upgrading to an aluminum rad and new hoses, as well as a new inctercooler and piping to keep the charged air temps down. Everything should be fairly mild.

As far as pistons go I THINK I will be going with the .020 over Probe pistons

another small question is this:

The motor must be decked with the front timing cover attached correct?? But why is that??

[annoyingrob]

Because if you just remove material from the head alone, the timing cover will stick down past the surface that little bit, preventing the head from sitting flat.

[Supra_devil]

thats so that the cover isn't 'taller' than the head and that can cause leaks.

[Funkycheeze]

It is the front lower timing cover that needs to be attached to the BLOCK when it is decked

what about the crank and rods? micro polishing? shot peening, rebushing and beam polishing? are there any cracks in the head? what about the valves?

[Supra_devil]

i'm not sure about the 7m, but on the 5m for sure the upper cover needs to be on the head when its resurfaced as well, especially if using a MHG, BTDT

[Timmie_g]

thanks for the clarification on the front cover thing.

The crank will be micropolished as well as any other work my engine builder tells me i should complete.

Rods will be shotpeened and also whatever else i am told should be done.

The entire rotating assembly will be balanced.

There are no cracks in the head, i will be replacing valve springs, retainers, stem seals as well as a port and polish and a 3/5 angle valve grind up to the rebuilder. I may yet go with oversized valves.

The builder is a friend of mine and i trust what he says and if he tells me what i should do i will do it, if its not needed he wont tell me to do it. I am not familiar with all the intricacies(sp?) of building a motor which is why im getting it done profesionally. I do not know what im looking at with clearances and tolerances and so on. He is doing research and most of the question i ask are on his behalf.

[Funkycheeze]

Well, make sure he uses toyota bearings of the correct sizes for the bottom end, and chooses the correct headgasket based on the amount he needs to shave from the head and block. And make sure you get a good surface finish on the block deck and head surfaces.

Also, a good torque number for the head studs is 80 ft-lb

[Timmie_g]

is there a trick to choosing the proper head gasket size??

NVM I found it on supramania

[Keros]

There's no such thing as 'too smooth' for the head and block finish for the headgasket surface if you're doing a MHG. You should have the mating surfaces finished to the best possible finish provided by the available equipment; not to what anyone "thinks" is required.

I've also read that the HKS stopper MHG is the best you can get. The titan MHG is a relabelled Greddy gasket.