Okay turbo people, chime in on this!

DNA DOA

DNA DOA

Member
Apr 3, 2005
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Scappoose
#1
Here is an example: t-70mm turbo w/ .82 a/r exh. I have seen .68 a/r exh. also. What does the .82 or .68 mean and which is better for a better than average built 306? Does it have anything to with how the turbo spools? Fast, slow?


Example: pt-70mm p-trim, gtq, and gts. What is the difference in the three?

Last one for now: Wastegate boost pressure-- .3, .4, .5, all the way up to 1.0 (which is one bar = 14.50 psi). What does the .3, .4 etc. mean? Is there a spring inside and what does it do? Why would you want a .5 vs a 1.0? More boost available and is it adjustable?

Thanks,
Ben SEMPER FI. :flag:
 
#2
AR is loosely the size of the turbine housing. the larger AR has more flow on the turbine side. a smaller AR will spool quicker but you MIGHT run out of flow (depending on boost) at the top end. how much boost are you planning on running?

here.....
www.stealth316.com/misc/grapeape-turbochargers.pdf

the wastegate... the .3, .4, and .5 are all in BAR settings. .5 BAR is a roughly 7 psi wastegate spring. .3 would be roughly 4 psi. that is the LOWEST boost you can run. with a higher base spring you can run more ultimate boost.

my car as an example....

i have 6 psi springs with my stock turbos so with my boost controller (blitz sbc-iD) im limited to about 25 psi at the most. with my other turbos i have 1 BAR springs so i can hit roughly 35 psi before i max out my boost controller.


if you have an OEM ford block id go with the .68 AR since you cant run too much boost anyways.
 
#3
For now, with my block and the 70mm turbo I plan on installing, 8-10 lbs of boost.

That is the second time I have heard someone recommend .68 for a stock block. I am thinking this is wise also.

Thanks VR4!
 
#4
Eventually I am going with a t-70 as well for my stock block and am getting the .68. T-70's are a little big for a stock block so the .68 will help it spool up faster but yours may be a little different since you have a 306 and looks like some hci stuff, you may want to go with the .82, that to me sounds about right. Go search turbomustangs.com, maybe ask but they can sometimes be... :mad:
 
#5
tsoccer3299 said:
Eventually I am going with a t-70 as well for my stock block and am getting the .68. T-70's are a little big for a stock block so the .68 will help it spool up faster but yours may be a little different since you have a 306 and looks like some hci stuff, you may want to go with the .82, that to me sounds about right. Go search turbomustangs.com, maybe ask but they can sometimes be... :mad:
Click to expand...



he will be better off with the .68 because with the stock block the block will crack before he maxs out the flow capabilities of the turbine.

with an aftermarket block id say go for the .82 and run 15+ psi.
 
#6
yeah but he can always just keep the boost down. I guess thats a good point, it would be pretty hard to choke a T70 with .68 a/r.

Kind of depends what you want
.68 - quicker spool maybe a little less on top end
.82 - slower spool, more up top, but have to keep the boost down unless you want to go boom!

vr4 is right though, .68 for stock block, .82 for aftermarket block and boost that thing!
 
#7
on my setup which isnt any thing crazy used a 62-1 turbo w/.96 a/r and car had no trouble building boost and did it around 2000 rpm. and built boost all the way to 6200 rpm. and i was only running 10lbs even the accedental time of 25psi spooled very quickly
 
#8
Okay there is an A/R (area ratio) for the hot side (turbine) and cold side (compressor). A/R is actually the distance between the turbine or compressor wheel and the housing and you can change housings to change this distance. So like what was already said the closer the a/r the quicker it will spool but at the cost of running out of steam on the top end.

Anyway I just happen to have a T70 on a stock block and have dynoed my car with both .68 and .96 housings. I didnt have any issue getting to 14 psi with the .68 just the same as I was running with the .96 but it did make less power. The reason for this is it just didnt flow enough. The housing actually turned into an exhaust restriction. Now you would think I would have made huge gains down low that might have made up for it but not so much.

It did make more torque through most of the curve (about 15 lbs ft) and it did peak about 400 rpm sooner but the actual peak number was still 20 lbs ft lower than with the .96. Hp peak was also down 31 rwhp. So I put the .96 housing on and called her good. Now one thing people dont talk too much about is P/R (pressure ratio). P/R is actually what pressure a turbo is efficient at. You can have a small turbo that is super efficient at a higher amount of boost and not as much at a lower pressure level and a big turbo that is efficient at a lower boost level and not quite as such at higher levels and vise versa.

Most T70s have a pretty ugly P/R and are more efficient at levels above 20 psi. Now when you start to get into where its really getting efficient CFM-wise (above 550 flywheel hp in most cases) this changes a bit. So basically the T70 is a good diesel turbo, which is what it was designed for. This could also have alot to do with me not getting the gains that I thought I would by going to a .68 housing.

The examples you were asking about are basically just different variants and pertain to compressor wheel design. P-trim is your old school design (what I have), Q is a slightly more updated wheel, and the GT design is the Garrett all new design and does not interchange with the older stuff at all.

Sounds like VR4 has your wastegate question covered.
 
#11
turbo's 101!!

When you run a smaller exhaust a/r, you will have high back preasure and tend to push out the bearing in the turbo, you want to run atleast a .81 exhaust a/r and I would personaly go with a .98 or 1.05, and try to run a 3.5- 4.0 inch down pipe. There should be know problem with it spooling, do you run a stock cam? They work great with turbos!!! Good luck
 
#16
Joey5.0 said:
Lol True.

Arent you on the stock block and internals E.J.?

My motor is out right now and i was gonna bore it .030 over, New rings and Bearings with Arp Rod Bolts and CHP Main Girdle......Good idea for a turbo or should i not bore it over?
Click to expand...

Yep, stock block down to the cam. The deal is, if you have a forged piston motor the weakest part of a stock short block is the block itself. So sticking all that money into a bunch of good parts is just a waste. Now if your engine has a ton of miles on it and is tired then obviously thats a different story.

You mentioned a girdle, well as far as I am concerned all a girdle is good for is protecting your pan. A main support does have its place, they do ad some mainline rigidity and reduce harmonics but thats generally only beneficial to high revving n/a motors. And trust me this isnt just opinion, I have seen my fair share of broken blocks with and without girdles.

Best thing to do is figure out how much power ($$$) you want and make a plan. If you wanted to stick an HP kit on your stock block it should be fine as long as you dont get too greedy, have plenty of fuel system, and you have a good tune.
 
#17
MyFordsFly said:
Yep, stock block down to the cam. The deal is, if you have a forged piston motor the weakest part of a stock short block is the block itself. So sticking all that money into a bunch of good parts is just a waste. Now if your engine has a ton of miles on it and is tired then obviously thats a different story.

You mentioned a girdle, well as far as I am concerned all a girdle is good for is protecting your pan. A main support does have its place, they do ad some mainline rigidity and reduce harmonics but thats generally only beneficial to high revving n/a motors. And trust me this isnt just opinion, I have seen my fair share of broken blocks with and without girdles.

Best thing to do is figure out how much power ($$$) you want and make a plan. If you wanted to stick an HP kit on your stock block it should be fine as long as you dont get too greedy, have plenty of fuel system, and you have a good tune.
Click to expand...


The Motor has 234K miles so its tired.......And it WILL be boosted. I want to make 400-500Rwhp. Just need to figure out what Kind of pistons i should get, or even get any at all. But if i bore it over then i will need new pistons correct? I just want to make sure 10Psi on a stock block bored .30 over is safe for awhile......
 
#18
Joey5.0 said:
The Motor has 234K miles so its tired.......And it WILL be boosted. I want to make 400-500Rwhp. Just need to figure out what Kind of pistons i should get, or even get any at all. But if i bore it over then i will need new pistons correct? I just want to make sure 10Psi on a stock block bored .30 over is safe for awhile......
Click to expand...

Boring the block .030 is fine and you do need to have new pistons that match the bore. At 234k miles the taper is probably so bad that you dont have much choice but to bore it and put in new pistons. As far as what to get, there are alot of choices, just make sure you get a decent forged piston that will yield under 9:1 with whatever chamber size your heads are.

Have you given any thought to trying to find a low mile forged stock block?
 
#20
MyFordsFly said:
Boring the block .030 is fine and you do need to have new pistons that match the bore. At 234k miles the taper is probably so bad that you dont have much choice but to bore it and put in new pistons. As far as what to get, there are alot of choices, just make sure you get a decent forged piston that will yield under 9:1 with whatever chamber size your heads are.

Have you given any thought to trying to find a low mile forged stock block?
Click to expand...


I believe if i go turbo route, then i am going to run the stock heads with new valves, comp Springs, and a good set of roller rockers so i am not sure what the CC is on the stock heads...

I have been looking over on corral a couple times, but its hard to trust people on the internet, especially on something so valuable.
 
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