Buckshot Motorsports Aftercooler problem, need to find a solution

[gorman]

Chris; are you still running secondaries ?

looks like the torque curve would move up low down, if you at least took out the brass blades.

Do you think the PSI would take longer to build if you took the secondaries out ? ... to get more boost low down, is that why you moved up to the next pulley upgrade ? .... G.

 

[Chris@CTA]

Here's something funny, the tachometer is so slow in first and second, that it only reaches around 6500rpm when the actual rev limiter kicks in at 7000rpm. I have my Interceptor displaying RPM to confirm that the shop set the rev limiter to 7000rpm. Now as far as the boost, I haven't had a chance to watch the boost gauge, but it should be around 9 to 10psi. full boost. I am running ST200 upper and lower intake manifolds, complete with secondaries. When the secondaries are held open, the low end takes a turd. If my SVT was turbocharged, I could see removing the secondaries, but because below 3500rpm, there is little boost, 2 to 3psi, the secondaries are needed to keep the low end torque (in this case). The slightly smaller pulley was installed to make up for boost lost to when the aftercooler was installed. The aftercooler is a restriction any way you see it, and I recall losing almost 1psi of boost after the install.

 

[gorman]

Chris; if you look at your torque curve on the vortec run...

the torque builds until 3k and then it starts to fall until the secondaries open ... can you lower the secondary opening point to allow the motor torque to keep rising ? ....G.

 

[gorman]

repost oops

 

[gorman]

re-post again sorry

 

[Beans]

You for sure will lose drive ability, but did you add timing when you had the secondaries held open? Otherwise it's useless.

First and second you are reaching 6500rpm? are you having spark issues?

 

[Chris@CTA]

Chris; if you look at your torque curve on the vortec run...

the torque builds until 3k and then it starts to fall until the secondaries open ... can you lower the secondary opening point to allow the motor torque to keep rising ? ....G.

From what I recall, 3500rpm was the optimal point to transition from primary runners to both runners, as to HP gains. (Best area under the curve)

 

[Chris@CTA]

You for sure will lose drive ability, but did you add timing when you had the secondaries held open? Otherwise it's useless.

First and second you are reaching 6500rpm? are you having spark issues?

I left the tuning up to the shop, but again, with such low boost at low rpms, the engine basically runs like a NA engine until the revs are over 4000rpm.

Just a recap, what I was saying is that the engine revs are hitting the 7000rpm cutout (revs as indicated by the interceptor gauge), no spark blow out. The tachometer needle is just plain slow and is not able to keep up under full throttle in first and second. I had to set up the interceptor to annunciate at 6900rpm to give me just enough time to shift before hitting the rev limiter.

 

[gorman]

From what I recall, 3500rpm was the optimal point to transition from primary runners to both runners, as to HP gains. (Best area under the curve)

Did your tuner try different opening points then ?

I'm interested to know if a tuner can change this with their tuning software; as every dyno graph I've seen, has that tell tale dip caused by the system.... wondering if this is one of the reasons Jaguar and Mazda used VVT.... never seen a dyno trace from those engines.

thanks ... G.

 

[Chris@CTA]

Did your tuner try different opening points then ?

I'm interested to know if a tuner can change this with their tuning software; as every dyno graph I've seen, has that tell tale dip caused by the system.... wondering if this is one of the reasons Jaguar and Mazda used VVT.... never seen a dyno trace from those engines.

thanks ... G.

I wasn't at the shop when they were tuning my car, but if you look at the older vortech dyno, you can see the bigger step in HP when the secondaries are opened at 3800rpm rather than at 3500rpm. All I can say is that the dip at 3500rpm still appears to be the best HP transition point between primary runner and both runners. It's been over a decade, but I might have a NA dyno run with the secondaries opening before 3500rpm. I'll see what I can dig up. The tuner should be able to move the point at which the secondaries open. Superchips were able to when they built the tune for the vortech kits.

UPDATE: Found an old dyno comparison with secondaries opening at around 3200rpm, Run 34. Compare it to Run 35, secondaries opening at stock 3500rpm, look at the HP curve and see how Run 34 drops a lot of HP, where as Run 35 only drops a little bit of HP during the transition. It's not just the torque curve to be aware of, have to consider the HP curve too.

 

[gorman]

Hi Chris; thank you for going to all that trouble to dig out the dyno sheet.

Looking at the results overall I think I might go down the route of getting a pulley size that starts to create more boost at a much lower RPM .... say 2500 and bleed off the excess at 8-9psi at the top. Beans has a 2.86" pulley, so it might be creating enough boost to cancel out that transistion dip

BTW I read HP is torque x RPM. so that would explain why the HP line only flattens out and not dip like the torque line. Since torque and gear ratios are creating the acceleration at low rev's it seems boosting at low RPM is the way to tune out the secondaries from choking off the power.Now that you've explained what happens when you hold the secondaries open, this approach seems to make sense to me.

Does all this makes sense to you or am I barking up the wrong tree ? .... .thanks ... G.

 

[Chris@CTA]

Hi Chris; thank you for going to all that trouble to dig out the dyno sheet.

Looking at the results overall I think I might go down the route of getting a pulley size that starts to create more boost at a much lower RPM .... say 2500 and bleed off the excess at 8-9psi at the top. Beans has a 2.86" pulley, so it might be creating enough boost to iron out that transistion dip

BTW I read HP is torque x RPM. so that would explain why the HP line only flattens out and not dip like the torque line. Since torque is creating the acceleration at low rev's it seems boosting at low RPM is the way to tune out the secondaries from choking off the power.Now that you've explained what happens when you hold the secondaries open, this approach seems to make sense to me.

This is my thinking ... feel free to shoot my thinking down if you feel I'm wrong thanks ... G.

Yes, totally agree, such as with running a turbo, get rid of the secondaries completely.

 

[gorman]

ultimately yes .... but i think with the V9 and belt slip issues from small pulleys, the best we might get is enough low end boost to raise the torque enough to eliminate the secondary transition dip.

..... maybe when you've got a buddy with you .... you could note the PSI reading versus the RPM so we can create some graphs showing the boost curve for different size pulleys ..... G.

 

[Chris@CTA]

ultimately yes .... but i think with the V9 and belt slip issues from small pulleys, the best we might get is enough low end boost to raise the torque enough to eliminate the secondary transition dip.

..... maybe when you've got a buddy with you .... you could note the PSI reading versus the RPM so we can create some graphs showing the boost curve for different size pulleys ..... G.

Yep, and yep.