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Torque / Power too low for this setup?

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Hi there we just finished our project and feels like its not making enough power for few first runs at spring pressure.

1786cc 20valve VW engine non VVT

G35-900 0.83ar 62mm turbo

Catcams 3658

8.5:1 cr and 145psi accross all cylinders when cold

Ran 200kpa @ 24 advance @ 0.80afr 384hp 385nm and power looks linear up to 7500rpm for now. Its not making peak torque early then stay flat, rather keeps making torque as rpm rises. Cams have been timed as per catcams spec sheet and everything has been checked. Whats funny is the engine almost hit MBT (24*) with 97-98ron fuel with zero knock. I been told to just increase boost as the setup wont work with low boost but something feels wrong. Its 100nm down off boost compared to similar setups with slightly higher CR. Whats weird is the ECU is also predicting the power same as the dyno and estimated airflow is 300g/s which matches the power output. That airflow is low for a G35-900 even at 1 bar.

Should I get to higher boost levels and then judge?

Attached Files

Others can better advise, but is that 200kpa absolute or boost?

It isn't really possible to make direct comparisons with other vehicles with "similar" engines, even with the same turbo-charger, as there are other factors that can have a big affect one way or the other, not least different dyno's may have different corrections and/or operator techiques, plumbing and charge cooler differences, etc. heck, a few degrees variation between the physical TDC and the "software" TDC can make a big difference, and may be worth checking if you think you're running more/less timing than expected.

I don't feel like you are that far off in terms or power, if the number you said are whp. I have to admit I'm not familiar with VW engines so I might be wrong.

G35-900 is a big turbo to spool on a 1.8 with low compression and no VVT, I also don't know these cams but they could make things worse in term of shifting the powerband to the right of the dyno graph.

How is the boost curve, does it creep? It will affect the torque curve as well if boost creep up with increasing RPM. Does your VE (or airflow) match the torque curve?

I would check to make sure my turbo inlet isn't restricted (air filter, piping collapsing) as this could affect the airflow. Then make sure there is no boost leak. Finally you can increase the boost and check if the power increase make sense (about 10-12 whp per psi I would say?).

Anyway, hope it helps!


Absolutely agree with what Frank just said- it's typical small displacement, low CR, non VVT, aggressive cams engine with large turbo situation. Usually it works only with high RPM and high boost combination as each component will be most efficient only under that conditions.

Hello guys thank for your responses. Frank boost does not creep and my VE mimics the torque curve and there is no leaks. We are running spring pressure only no MAC valve connected. Might gain a bit of response with MAC connected. I will update you guys when I have turned up the boost higher. What I might do to increase response as well is to advance the ignition timing a bit further currently at 25 degrees during spool which is low, I might get to 32 before hitting MBT and gain quite some torque down low. I was concerned because other similar setups with higher CR have almost 100nm torque more off-boost... same cams same turbo size same displacement.

Are you sure your cam timing is correct?

Do you know how much higher CR they use?

Catcams 3658 - 1.3mm lift @ tdc @ instake side / 0.95mm lift @ tdc @ exhaust side (as per specifications sheet by catcams) and it also matches OEM marking on Intake side. So I can't be wrong also its been done the same way my friend with S3 done it. I have checked this like 3-4 times before closing the valve cover it cannot be wrong, however I will re-open valve cover and re-measure just to make sure.

His setup is identical except for 9.25:1 CR. a more restrictive inlet manifold and slightly bigger Precision turbo, 6466, mine is a 6262 in terms of size. His engine makes 100nm more at same RPM off-boost on E85 and it spools relatively the same. My engine compression measurement shows 145psi accross when 5 degrees cold. I advanced the cam (mechanically with adjustable cam wheel) from -7 (hall sensor) on OEM marking, to -13 (hall sensor) so 5 degree advanced and gained almost 35nm more and a more realistical graph. However I cannot go past -15 because of non-VVT compatible setup and will lose top end power instead. I guess I can't say more without shooting for more boost and activating the MAC valve.

You should've said it from very beginning that appart from using higher cr he is also using e85. That can be the difference maker... Never mind making less torque with lowr compression ratio and pump gas.

As Shota said, even small differences can have a big overall affect when combined, which was my point in the earlier post.

E85, with the other differences on top of those not mentioned, can be a game-changer.

Yes, definitely the CR one of the reasons, but the main point is torque off-boost here, around 3500-5000rpm where we are not knock limited and where E85 wouldn't make a difference.

Few things I will be optimizing as I have not done:

- Lambda target before/during spool is currently too rich (0.83), I will lean it out and possibly gain some response.

- Ignition advance in non-knock limited area is still on base map (intended for 9.5:1 CR) so 25-26*, theoretically I will be able to gain torque in this area up to around 33* and hit MBT just about there, and it should theoretically give around 50nm of torque. I will test this all on our load controlled dyno in steady state.

- Also my power graph attached includes only 7500rpm run, the engine is built for 8500rpm. Will unlock the RPM for the next testing phase.

I will be filling up with Ethanol for the next few tests. Have no updates as of yet because I was working on a few other bits. Will update here on this post with next few results and dyno graphs with higher boost levels.

E85 is a power adder even off-boost, or in N/A engines because it gives higher effective cylinder pressures when tuned for it, it's not just used for detonation resistance.

Thanks, good info Gord. Tomorrow we will swap the run-in oil and filter for new one and put it on the dyno for some tuning and will see how the engine behaves with higher boost.

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