bogor

Made my first dyno run today; 470 rwhp and 653 Nm. The cam is 224/234 at 114 LSA and should peak around 5500 rpms. The system is Blowerworks with a V2 S-trim with 3" pulley (overspinning the blower from 5800 rpms). gaseous injection from Blowerworks (9 GPH nozzle). I guess the figures are ok but peak hp at 5165 rpms seems a little low. I´m using a stock LT1 exhaust (from resonator and back) with EM headers and RT dual metal cats, maybe the resonator is holding me back. Peak boost is around 14 psi but it seems like anything above 11-12 is only heating the air.
Started with 19 degree maximum SA but reducing by 2 degrees on all load sites from low to high boost increased peak output with 20hp´s!

dizwiz24

Bogor,

Its tough to compare results

Any idea if that is a dynojet? Who makes the dyno? What about scaling? Sae (society of automotive engineers) or std scaling?

Is that cam you have the lloyd elliot custom grind? If so, we have the same cam, our specs are identical.

You mention reducing sa from low to high boost increased output 20hp.

How can you do that on a stock computer (w/ 1 bar map)? The best I can do is mod the last column (100 kpa) of the table. When my map maxes out at 1 bar, that's boost. Since the boost is linear vs. Rpm, I can scale back the spark advance as rpm (boost) goes up.

Do you have an aftermarket computer and a 2 bar map sensor?


Very cool you started your dyno run at low rpm and can see effect of boost!

Finally, do you think s trim is holding you back ? I think you would have made more power w/ bigger blower

bogor

The dyno is a custom build by the company Civinco (http://www.civinco.com/index_eng.html), dont know any specific details about it. The camshaft is a custom piece from Bret Bauer Racing made by compcams. Lift is around 0.550 on intake and exhaust. When looking at my logs, reducing SA by 2 degrees gave a 20 hp increase at around 5200 rpms (SA around 17.5 degrees at peak hp now). At 3000 and 4000rpms, reducing SA actually reduced power somewhat. The engine is a L98 so maybe different timing needs vs a LT1?

Yes, I´m using an Autronic SMC standalone engine management system so totally free to change things :-)

Don´t know about the blower; peak hp occoured at 45000rpms on the blower so its still inside its efficiency range (max impeller speed is 50000). Air temp out of the blower peaked at almost 250' F (then I was at 53000 rpms...) but dont know if this is (too) high or not. STill, my water might cool things down (the temp sensor is before the injection nozzle). I´m leaning towards my exhaust system to be the bottle neck.

mcm95403

You say it's an L-98 - which intake manifold are you using?

bogor

I´m using a Superram plenum with an Edelbrock HiFlow base, both very lightly ported.

mcm95403

Sounds like a great combo. Intercooler time?

dizwiz24

He says he has meth/water injection

bogor

Gregs (Blowerworks) water/meth system works really good and when he recommends this instead of intercoolers I have full faith in his advice.

LT1inaMGB

How can that hp/tq plot be? Torque and horsepower have to be the same at 5250 rpm.

SuperL98

The torque is in Newton Meters.

I'm guessing he is outside the USA

dizwiz24

Its interesting that you also wonder if your resonator is holding you back....

This was my same thought on my recent dyno pull. I expected just over 500 rwhp. (Perhaps I would have gotten there had I been willing to rev higher. )

I couldnt find anyone with a tubing bender big enough to bend 2 3/4" (stock lt1 size) exhaust tubing to make a resonator.

Commercial off-the-shelf x-pipes from summit or JEGS werent narrow enough to fit the trans tunnel of the c4. I tried both 3" and 2.5" x-pipes. Even the x-pipes specifically marketed as 'narrow'.

So I had to put my car back together without an x-pipe in order to get it driving.

I heard that stainless works makes a zr-1 x-pipe that might work on our lt-1 exhaust

bogor

dizwiz; you have almost the same heads and cam as me, maybe your engine respond the same way as mine regarding how much spark advance needed. I recall reading somewhere that these new AFR heads like less timing than older gen heads so maybe worth a try? If you like, I can send you my full fuel and timing map if you give me an email adress.

I have also tried a Magnaflow x-pipe (too wide). I am considering making a custom one (expensive) or buying the Magnaflow muffler with built in X-pipe (difficult getting one here).

I think there is some kind of "issue" happening after 5200 rpms. I extracted a log file from the best run and to me its no belt slip (boost climbes steadily). Maybe too much fuel (AFR about 10,5 at 12 psi)? The graph shows manifold pressure in kPa (maximum boost in "US units" is 14,2 psi).

dizwiz24

I start my spark advance high and then drop it back as boost comes on.

Boost curve hits like this:
(note: I had to drop down from 3" pullley to 2.75" diameter pulley to maintain the same boost curve (as before), after I swapped heads to AFR 195cc eliminator, comp ported. I also swapped from hotcam to the 224/236 114 LSA lloyd elliot cam at this time. )

3000 rpm = 5 psi
4000 rpm = 7.5 psi
5000 rpm = 10 psi
6000 rpm = 12.5 psi

Spark advance (at 100+ kpa) is like this:
2800 rpm = 31 deg
3200 rpm = 30 deg
3600 rpm = 27 deg
4000 rpm = 24 deg
4500 rpm = 22
5000 rpm = 22
5500 rpm = 21
6000 rpm+ = 21

<rev limiter set at 6000 rpm>

**Note I tried to run 23 degrees spark advance, from 4500 rpm and up, and instantly got 8 degrees knock retard. Though I will add the ambient air temp was 95F and the motor was thoroughly heat soaked - as it was my 2nd to last dyno pull.


Ive heard some guys (C5 forced induction site) say one trick is to drop spark advance back 1 or 2 degrees just before your TQ peak (my TQ peak is around 4800 rpm). Then you can add what you took out, back in once beyond your TQ peak (prob as long as you arent going too crazy with the boost). I may try this.

HighMileage

Bogor,

It could be the resonator holding back some power. Geoff Scoruppa who writes for Vette had a supercharger shop here in Chicago and specialized in c4s back in the day and told me the resonator was bigger restriction on c4 exhaust. Stock mufflers were ok.

Having said that, in my opinion your intake manifold is holding you back. The superam will start losing torque at 5000ish when normally aspirated. For NA this is still a great manifold, especially with gear split ratio of a 700r4/4l60.

A centrifugal blower makes more boost as it spins higher. Problem is while blower is spooling up boost, the manifold is rolling off torque curve. A TPIs mini-ram would keep torque flat above 5000 and the boost increase above this would net more power because peak boost is lining up with peak torque instead of rolled off torque caused by super ram. You may be leaving over 50 hp on the table.

Other thing to consider, the AFR heads would match better to a mini ram/LT1 manifold. Those are high rpm breathing heads, you need a high rpm style manifold.

bogor

Thanks HighMileage, very interesting info! I actually have a friend that has got a Lingenfelter ported TPIS Miniram for sale...
However, since I´m running on fumes dollarwise replacing the resonater with something less restrictive seems like a good start.

Dizwiz, thanks for sharing your settings. Here are mine (to be able easily compare I put your numbers in bracket):
2800 rpm-20 (31)
3200 rpm-19,5 (30)
3600 rpm-19 (27)
4000 rpm-18,5 (24)
4500 rpm-18 (22)
5000 rpm-17,5 (22)
5500 rpm-17 (21)
6000 rpm-17 (21)

Boost:
3000 rpm-3,6 psi (5)
4000 rpm-6,5 psi (7,5)
5000 rpm-10,2 psi (10)
6000 rpm-13,2 psi (12,5)

bogor

It seems like The exhaust system is a bottleneck. I put a pressure gauge just ahead of the right muffler. Pressure at 5500 rpms reached approx 11psi and according to "john lingenfelter, how to modify smallblock chevy engines" pressure above 5 psi indicate restriction in the system. How this trnslates into lost horsepower, i dont have a clue about... Iwill now try to tap in the gauge before the resonator to find out if it is the same pressure or even higher.

Edit: Tested backpressure at the right header collector today. I tapped into the exhaust via the lambda sensor bung (ahead of the cat and the resonator).

Result: 15 psi at 5600 rpms

I don´t think the cat create alot of backpressure (Random Tech 3" metal matrix bullit cat) so it looks like the resonator is even more restricte than the muffler and I am now quite convinced this is causing a significant power loss.

QuickGlass

If there is 15 psi before the cat and 11 psi before the muffler, then it seems like the biggest restriction is the mufflers.
The cat and resonator only added 4 psi of back pressure.

I've been following your thread because I think I have the same problem, but don't want the exhaust too loud.

bogor

Agree, this sounds very logical.

After some detailed studies (I videotaped the gauge during the runs) it looks like I peaked at 14 psi.
I now plan to replace the stock mufflers with Dynomax Ultraflows as well as take out the resonator (replace it with a Flowmonster X pipe-mostly for reducing sound level).hopefully, I will be able to make another back pressure test before snow starts to pile up....

dizwiz24

bogor,

you inspired me!

During my dyno run thursday, I put a bung in place of my wideband and measured exhaust backpressure. This bung is just behind the header collector.

My exhaust is the stock lt1 2 3/4" tubing with a 2 3/4" xpipe in place of resonator and dynomax superturbo lt1 mufflers. No cats. While I do have an x-pipe (2 3/4" diameter tubing), Im not sure it is a super-great design. I mention it in a post I made in c4 tech.

Anyways, during the dyno run,,, I measured 7 psi at 5500 rpm.

Whats interesting is there is virtually no back pressure until I get to about 4500 rpm, then there is 2 or so psi.

Then backpressure climbs rapidly to 7 psi by the time I am ready to let off the gas at 5500 rpm. I also videotaped the gauge.

bogor

[QUOTE=dizwiz24;

Anyways, during the dyno run,,, I measured 7 psi at 5500 rpm.

Whats interesting is there is virtually no back pressure until I get to about 4500 rpm, then there is 2 or so psi.

Then backpressure climbs rapidly to 7 psi by the time I am ready to let off the gas at 5500 rpm. I also videotaped the gauge.[/QUOTE]

FWIW I found info from someone that reduced backpressure and measured power before and
after. I recall his conclusion was like each psi reduced backpressure increased power with approx
8 hp (I think he was at around 600 rwhp level).

Dizwiz: same for me, the backpressure starts to climb rapidly whenI reach +4000rpms.
7 psi alot better than my 14psi but probably still room for improvement. I'm in the process of building a better flowing exhaust and i will use a knock-off version of Utraflow/magnaflow. Hopefully I can add some more info and measurments pretty soon.

If everything works out, I also test if injecting meth pre-compressor will give any benefits.