Engine rods/piston advice!

[j4cko56 1]

After some more engine tuning/strength advice!

 

Basically I have an AQP 24v engine and it's going to be turbo'd in a 4motion Mk1. The turbo is capable of easily pushing out over 500bhp and 500ft/lb, and it can do this as low as about 3200rpm, which is low! Standard internals i know are strong but at this low RPM I'm sure they would give up! So, if you were going to do rods or pistons, which would you do? Because some places say the rods are the weak link, some say the pistons are, and honestly I have no clue! I would like to have that power down low if possible, but if i am going to need to do both I will back it off and have less boost lower down. If i do the rods, what are thoughts on rifle drilling for my build? Needed? (I know about the 3/8 rods not fitting). 

 

As a side note, i very much doubt i will  be going above 500bhp and 500ft/lb.

 

Jack

[dave_424 48]

What turbo are you going to use? From what I've seen most vr6 turbo's spool between 3 and 4k. 

 

My build is using a GT35 with the .82 exhaust housing should spool around 3500rpm, aiming for 450bhp+ on 12-15psi of boost 

 

All I'm doing for engine internals are decompression plate, ARP head studs and ARP rod bolts. 

 

I'm expecting all my bits within the next few weeks and hope to be finished in about 5 weeks, I'll post up a build log sometime of my build experience

[j4cko56 1]

It's a modified Holset HY35, it will be on boost below 3000 and max boost at around 3000! The 2.5  L engine its tested on gives 500ft/lb at about 3200rpm, so the VR will be a little under this. The BHP isn't the worry for me, it's the torque! It will bent rods, but I'm not sure if the pistons will hold out as well as it won't be going much above 500 and i can't see it making any more heat that would muller the pistons!

[daveyboy 897]

I personally wouldn't worry too much about the pistons. I reckon the rods will be the weaker of the too so I'd consider swapping them for forged rods

[dave_424 48]

People say keep it under 500bhp/torque and you are okay on stock rods and pistons, but if thats where the limit is, I would want to be a bit below that. Can you not get a larger exhaust housing so that the turbo spools later. A turbo that reaches full boost at 3k could easily be restrictive at high RPM

[sleepymike 15]

What gearbox do you plan to run? I would imagine all that low down grunt will soon eat a standard box.

[j4cko56 1]

No, it will boost until the red line no problem at all! Trust me, Google the HY35! Thats my point is i want it spooling early, I don't want to have to rev to 4k just to get it to go on boost, its the low down grunt I'm after which is why i bought it!

 

No it's an 02M DRP box, strong and I have 2 spares for if i break them   I have a picture of your Caddy going up the strip at action last year!

[dave_424 48]

No, it will boost until the red line no problem at all! Trust me, Google the HY35! Thats my point is i want it spooling early, I don't want to have to rev to 4k just to get it to go on boost, its the low down grunt I'm after which is why i bought it!

 

No it's an 02M DRP box, strong and I have 2 spares for if i break them   I have a picture of your Caddy going up the strip at action last year!

Yes, but an exhaust housing that boosts below 3k on a 2.8 engine will be restrictive in the high RPM's. Yes it can hold boost up to red line but it can act as a flow restriction. It can also cause large turbo manifold exhaust pressure and high EGT's. 

 

It will probably be fine but a GT35 turbo with a .82 or 1.06 exhaust housing will have more high rpm power 

[RBPE 198]

Rule No: 1 - if you are going to add forged parts, make sure the engine is fully stripped down and all hones, alignments, cracks etc are checked, otherwise you are just wasting money on forged parts.

 

Gas can bypass the rings on older engines where the cylinder bores are not as perfect as they once were so if that is checked and okay, just get some new rings. Not sure on the oem spec of material for the pistons but 4032 actually holds up better at prolonged temps over the 2618 alloy also used - the 4032 also does not expand as much and so has less rattle (although you can get them coated nowadays) so bear that in mind if you do go forged.

 

If the bore/hone of the cyl is good, the pistons can last very high pressures (700+hp) but I would add forged rods with ARP hardware all around and a spacer plate if you cannot stretch to all those and forged pistons.

 

So:

Full strip and check of engine:

New bearings, preferably coated

Forged rods (4340 steel)

ARP rod bolts

ARP Head studs (better clamping than bolts)

with a spacer plate

or a set of forged pistons, I would personally go with 4032's unless doing a drag build rather than the 2618 alloy's

 

And 0.82ar on the turbine will get you a bar at about 3500rpms cam/boost/tune depending and is probably best for 500hp or so

Edited June 15, 2015 by RBPE

[FishWick 21]

If I was to do it all over again, I would get Mahle 142S pistons with 23mm wrist pins and find a machine shop that can replicate the factory honing - with a torque plate.  

 

That will give you a nicely sealed and very strong bottom end.

[j4cko56 1]

I have already bought the turbo, it has a 3.75 inch outlet, it's designed for use between 2.2 and 2.8L, which is exactly what I want. I don't want power up high, this is my point, the car is being designed and build as a motorway mile muncher, i want it to have instant response in any gear at any speed, and I know this turbo will do this, it has been proven on many engines, in fact I actually have one that is modified to improve its performance based on bad points of the original HY35. It won't be spending its life high in the rev range anyway!

 

This is the original HY35: http://www.ebay.co.uk/itm/NEW-HOLSET-HY35-Turbo-500bhp-turbocharger-Mega-fast-spool-1JZ-SR20-RB25-HX35-/261745950670?nma=true&si=o60F1tYAViZiAaOxMqU5lbwDNPM%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

 

This is the refined version that I have: http://www.ebay.co.uk/itm/261887656828?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

Yes I'm planning to use ARP bolts anywhere i possibly can, con rod, mean bearing caps, head studs etc. The rods I have looked at have also been 4340. I have heard that the stock pistons can take some power, which is fine, but its the torque I'm more worried about then coping with! I know a guy currently who is building an engine up and may sell it if i can persuade him, its been rebuild from the ground up with PEC rods and Wossner pistons, and in terms of block work, you name it, its been done! Including re cutting the valve seats and guides, and chains, pumps etc. But he would be looking for £2800, which seems a lot but the list of work is huge!

 

Thanks for the help guys! 

[RBPE 198]

It's flame propagation problems and so on that usually bend rods!

 

3.75" outlet is MASSIVE - bigger than 750+hp turbo's I sell (Garrett/EFR). In terms of gas dynamics it will certainly lose bottom end being that big, it's probably designed for the high revving engines the ad advertises and the turbines are always massive on those turbo's as they are designed for high boosting diesel engines! Couldn't see the AR ratio on the add either which would give you an idea as to spool.

 

So, you'll now have to go from 3.75" down to;

2.5-2.75" (300-450hp)

3"-3.25" (450-625hp)

3.5" (650+hp)

and so on from the outlet->downpipe->exhaust route

Edited June 15, 2015 by RBPE

[RBPE 198]

https://en.wikipedia.org/wiki/Compressible_flow

[j4cko56 1]

So you think if its well sealed and it's tuned properly it should be ok?

 

I'll be having a 3" exhaust, or there abouts, did you look at the power chart for the HY35? 

[RBPE 198]

So you think if its well sealed and it's tuned properly it should be ok?

 

I'll be having a 3" exhaust, or there abouts, did you look at the power chart for the HY35? 

 

Just had a look at the comp chart for the HY35 and have plotted a graph to show you;

95% VE, 6800rpm rev limit, 100degF temp etc - about right for a stock VR:

 

 

As you can see you are going to be pretty much out of efficiency at every level even on a relatively stock engine with that turbo - the one in the ad could have a slightly larger chart but not by much I would think! It's also why the ad said it's for high boost as they are diesel based turbo's so good for small 4 cylinder engines with high revs, high boost as the chart shows from 1.5bar to 2bar. (2.5 to 3 on the graph for about 450hp).

 

The 3.75" turbine must be for diesels or perhaps rotaries or something as that is the size you choose for a 750hp VRT set-up. Saying that, he has made some mods on the turbo and a 2.5ltr engine had some good results at low boost but I would bet they used the 2.75" option for the turbine!

 

If you are on a budget, HX40 would be better, or a T3 60-1 turbo (slightly higher flow levels than the HY35 but at a much lower boost level akin to a VRT set-up) or one of those hybrid 60-1, this one looks like it has the GT35 esque turbine side with a GT30 esque compressor;

 

http://www.ebay.co.uk/itm/Kinugawa-Turbo-3-Anti-Surge-TD06H-Garrett-60-1-Wheel-T3-10-cm-V-Band-External-/121183392739?pt=LH_DefaultDomain_3&hash=item1c3717d3e3

 

 

A 3" exhaust is still a  touch too big unless you want over 500hp, best for 500-600hp really but evidently the HY35 will not be able to do that with the VR without it being highly inefficient! It also slows the gas speed down - you want a balance on the width of piping.......

 

So, if you have to stick with it - see if the guy will change the turbine section for the 2.75" one and do a 2.75" system straight through for 400-450hp. Might not be too efficient for the turbo but they are supposed to be able to take a battering and it will give you a nice flowing, responsive set up over what you are doing so far. If you are looking at more power later on, I would still change the turbine side to 2.75" and then step it up to a 3" exhaust for when you change the turbo!

Edited June 16, 2015 by RBPE

[RBPE 198]

Sorry, forgot to mention - if you have to stick with the turbo you have, have the 3.75" taper down to 2.75" or 3" fairly quickly, don't make it too much of a change at the outlet though in case you introduce turbulent flow, but the longer it is a larger hole, the slower the gas speeds will be and the worse the low end response will be if that is what you are aiming for!

 

https://en.wikipedia.org/wiki/Moody_chart

 

https://en.wikipedia.org/wiki/Laminar_flow

[j4cko56 1]

I'm going on the performance figures from data they have collected from it. They tested it on a 2.8 Saab V6 and the results were really good according to them! The HY35 stock outlet is 2.5 inch, and my one is 3.75, I think so it gives the option for huge power if it's desired more than anything. Originally I was planning to purchase the HY35, I only bought this because it came up and i knew how rare they were and thit was basically a tuned version of the HY35!

 

So you think the exhaust side is too small? surely that is better for low end? The HY at 1.5bar puts out 500 of each at a low rpm! I'm wanting around the 450-500bhp mark, and equal in torque. So a quickish cut down to 2.75 inch should work ok?

Edited June 16, 2015 by j4cko56

[RBPE 198]

I'm going on the performance figures from data they have collected from it. They tested it on a 2.8 Saab V6 and the results were really good according to them! The HY35 stock outlet is 2.5 inch, and my one is 3.75, I think so it gives the option for huge power if it's desired more than anything. Originally I was planning to purchase the HY35, I only bought this because it came up and i knew how rare they were and thit was basically a tuned version of the HY35!

 

So you think the exhaust side is too small? surely that is better for low end? The HY at 1.5bar puts out 500 of each at a low rpm! I'm wanting around the 450-500bhp mark, and equal in torque. So a quickish cut down to 2.75 inch should work ok?

 

 

I am not sure of the mods but the data I saw about the oem unit said a 56mm inducer - the ad for this one also says that but I do not know if the 78mm compressor exducer is larger than the one on the graph I plotted. It is, however, 2mm bigger than a GT30 so should be good for 52-54lbs/min (or about 550hp) at a guess.

Looking at the ad it has a turbine side of 66mm which is 2mm smaller than the 67lbs/min GT35 turbo so lag would be similar to that but the GT is DBB etc which means the turbine side is good for 600+hp if it wasn't restricted by the smaller compressor side.

 

So who knows - this modded unit may be good, it's hard to actually say but I know VRT owners in the states said they were too small a turbo - the kind you want to use on a  low-boost, 400-450hp set-up with a 2.5" straight through system really!

 

No idea why there is a frankly ludicrous 3.75" outlet they sell on that turbo, must be for the rotary engines, but you can make that smaller with piping, shame there is no turbine AR ratio info on the add for that housing though!

 

You've got the turbo mate so give it a go but it is not designed to be pushed past 500hp based on the oem compressor graph and as stock, is not very good for anything over 2 litres looking at it.

[Rocketrunner 0]

Hey what’s up guys I’m on my second 2.8 24v vr6 Jetta and was wondering what rotating assembly to run if I’m looking for 750 crank hp without coming undone on the first pull? Any advice will be greatly appreciated