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Organized Drag Racing and AutocrossDrag racing and autocross discussions and questions. Techniques, tips, suggestions, and "what will I run?" questions.
I thought about posting in the "60' with suspension mods" thread because that really what my question is about. However, I am asking about specific modifications to my car/setup. If you don't mind sharing your opinions. I want to make it leave as good as possible at the track while KEEPING it street worthy. I will possibly give up a bit on the handling end but don't want to go full race either.
Current setup;
Stock 89 IROC springs and suspension. K-member, lower A arms (poly bushings) factory sway bars all stock.
KYB stock replacement struts/shocks
Boxed LCA's with urethane bushings
LCARB's
Custom adjustable tubular torque arm with poly bushing at the trans (stock setup)
Moser 9" with 3.50 gear
Bags in the rear springs.
Sub frame connectors
TKO 5 speed with McLeod RST twin disc
Clutch tamer pedal assist
Hoosier Quick Time Pro 26/9 16 on stock rims
Current 60' are 1.73-1.76's leaving at ~4000 and feathering the clutch via Clutch tamer.
7.35 best 1/8mi et @ 100mph
Power est at 500WHP shifting at 6200
Weight 3700# with driver race ready
I don't mind trimming some weight here and there but still plan on having all options (AC cruise stereo etc) and stock looking body.
Possible mods;
Lower rear end gearing (370-3.90?) 9" makes this easy to try and cost effective.
Front springs/struts- Are there any which will still preserve ride/handling and be worth changing?
Rears worth changing?
Front K-member/A arms- Is there a lot of weight to be saved here? Seems like a high $ to benefit.
Weight saving- Considering fiberglass hood, trimming front bumper support etc.
I don't mind "race day only" mods such as disconnecting front sway bar links if it will help.
Any suggestions or recommendations? What will be the best bang for the buck? I would like to get the 60's down to the 1.50's if possible and keep it a street friendly car as it is driven almost daily.
Last edited by antman89iroc; 08-20-2018 at 11:02 AM.
Remove the front swaybar and install a larger one in rear for the track.
Better rear gear. 3.90-4.10 would be my vote.
Ditch the poly bushings. They bind to much for me.
Remove the front swaybar and install a larger one in rear for the track.
Better rear gear. 3.90-4.10 would be my vote.
Ditch the poly bushings. They bind to much for me.
Thanks for the input. I didn't consider the poly bushing binding.
In regard to gearing, I currently cross the 1/8th mile in 3rd gear. A 3.90 would raise rpm at the line by 3-400 which would likely be OK. It would also still be appropriate for 1/4 mile tracks and more street friendly. However, if I gear to cross in 4th gear I could go to a 4.30 rear. I don't know if that would be too much for the starting line though.
Front springs & struts. Is there a combo that would be better for weight transfer and still be streetable and handle decently? The IROC is sprung pretty stiff and handles great. But possibly a stock V8 spring and a 70/30 adjustable strut would be a good compromise.
On the other hand traction isn't really a problem, (yet) at least not at the well prepped track I run. I don't know how much weight transfer would really benefit.
Moving to adjustable coil overs could net some benefit of both worlds. You could set it for track and then calm it down for the street. Jmo
It all depends on how far you want to take it. I daily drove mine with no sway bar in front at all, 90/10's and tricks springs in the front with 50/50 lakewoods in back. I wasn't going for corner carving and I just drove sanely and never had a problem.
Shocks/struts/A-arms/sway bar are all things that improve traction. They are not likely to gain you much until you run out of traction.
Weight reduction is almost always an effective way to reduce et, but it doesn't address an efficiency problem. Your efficiency could use some improvement.
You have the power for 100mph in the 1/8th, which basically means you have power for 125mph in the 1/4. Target efficiency would be around 6.70@100 / 10.55@125 with low 1.4 60's. To get close to that you would need to take max advantage of rollout, and geared to maximize power production. Basically geared for the stripe in 4th, which likely isn't going to be practical for the street.
For a street/strip compromise-
If you have .64 overdrive, 3.90/4.10/4.30/4.56 gears would net you 2260/2375/2490/2640 rpm @ 70mph.
If you have .82 overdrive, I would stick with your current 3.50 gears (2600 @ 70mph) and lean on the clutch harder at the track.
At 125mph, rpm at the stripe for the above gearsets- 3.50=5650, 3.90=6300, 4.10=6625, 4.30=6950, 4.56=7370
At the track, I would raise launch rpm to around 6-6.5k (2-step & rev limiter would be nice).
If you have synchros, raise shift rpm as much as the synchros can stand with that dual disc. Also be sure to use a good oil to maximize synchro operation.
Shocks/struts/A-arms/sway bar are all things that improve traction. They are not likely to gain you much until you run out of traction.
Weight reduction is almost always an effective way to reduce et, but it doesn't address an efficiency problem. Your efficiency could use some improvement.
You have the power for 100mph in the 1/8th, which basically means you have power for 125mph in the 1/4. Target efficiency would be around 6.70@100 / 10.55@125 with low 1.4 60's. To get close to that you would need to take max advantage of rollout, and geared to maximize power production. Basically geared for the stripe in 4th, which likely isn't going to be practical for the street.
For a street/strip compromise-
If you have .64 overdrive, 3.90/4.10/4.30/4.56 gears would net you 2260/2375/2490/2640 rpm @ 70mph.
If you have .82 overdrive, I would stick with your current 3.50 gears (2600 @ 70mph) and lean on the clutch harder at the track.
At 125mph, rpm at the stripe for the above gearsets- 3.50=5650, 3.90=6300, 4.10=6625, 4.30=6950, 4.56=7370
At the track, I would raise launch rpm to around 6-6.5k (2-step & rev limiter would be nice).
If you have synchros, raise shift rpm as much as the synchros can stand with that dual disc. Also be sure to use a good oil to maximize synchro operation.
Grant
Thanks for the input and agreed, efficiency could be improved.
As stated, I do drive this car a lot and want to keep creature comforts, while making it as quick as possible. More of a street beast than a strip car.
My trans does have the .64OD and carbon lined synchros. I haven't had a problem with it shifting but haven't gone much over 62-300. Problem here is the cam is street friendly and tops out ~6k. I'm using a fair amount of nitrous too, 0.078" jet with a custom spray bar setup in the plenum.
Looks like the best compromise is the 3.90 gear set and leaning on the clutch. I do have rev limiter but not a 2-step. Only 1 test session with CT but 4000 launch seemed to do well. Traction isn't a big problem but it can blow the 8.5 wide Quick time bias tires without the Clutch tamer. Currently running 26 tall tires but will likely go 10.5/28's when these wear out. However on the street the diameter is ~26-27 max depending on tire selection.
BTW the clutch tamer did make launches much more consistent although it has only slightly improved to 1.720's-730's 60'. It was more inconsistent before only occasionally dipping in the 1.7's on a good launch. Although it's a bit portly it should 60 better. I am feeling the gear is the best next step and deal with traction issues as they arrive.
What do you mean by "take max advantage of rollout"?
Regardless of street use, what gearing would you use for 1/8 mile to maximize launch? Crossing in 3rd (1.28:1) and/or 4th (1:1)?
Last edited by antman89iroc; 08-22-2018 at 11:53 AM.
Do you have a way to graph rpm? Run it WOT out to 7k. The trace will tell you when the engine starts nosing over, that's when the cam/heads are actually done. Sneak up on that nose-over point until you run out of synchro ability to produce a quick shift. Regardless of synchro ability, you should still be able to raise launch rpm. The more you raise launch rpm, the higher recovery rpm will be in 1st gear.
With 1.7 60's and no spin I would add initial hit with the ClutchTamer, inner dial clockwise 1 turn per pass until the 60's start to drop off. Outer delay setting around 3 turns.
For my rollout comment, shallow staging is generally a couple tenths quicker than a deep stage. Rolling in 6" after the stage lite can easily add an extra tenth to your 60'. Some even go as far as offsetting the front tires to maximize rollout, as it basically gives you more of a running start on the clocks.
Gearing I would choose for the track depends on what rpm the engine actually starts giving up.
Do you have a way to graph rpm? Run it WOT out to 7k. The trace will tell you when the engine starts nosing over, that's when the cam/heads are actually done.
And by nose over, you're not talking about the downhill side of the power curve... you're talking about the cliff where the engine falls on its face, right?
Seems rare to find somebody that understands this. So many people focus on engine dyno curves and forget that the torque to ground is what moves the car. A gear shift results in a massive loss of torque at tire. People can stay in gear longer than they think.
Do you have a way to graph rpm? Run it WOT out to 7k. The trace will tell you when the engine starts nosing over, that's when the cam/heads are actually done. Sneak up on that nose-over point until you run out of synchro ability to produce a quick shift. Regardless of synchro ability, you should still be able to raise launch rpm. The more you raise launch rpm, the higher recovery rpm will be in 1st gear.
With 1.7 60's and no spin I would add initial hit with the ClutchTamer, inner dial clockwise 1 turn per pass until the 60's start to drop off. Outer delay setting around 3 turns.
For my rollout comment, shallow staging is generally a couple tenths quicker than a deep stage. Rolling in 6" after the stage lite can easily add an extra tenth to your 60'. Some even go as far as offsetting the front tires to maximize rollout, as it basically gives you more of a running start on the clocks.
Gearing I would choose for the track depends on what rpm the engine actually starts giving up.
Grant
Yep, here's a screen shot from a recent run with Clutch tamer. It's not the quickest run since the data log cut off in the middle of that run but it's close by a few hundredths. Actual data from time slip for this run was;
1.735 60'
4.884 330'
7.403 1/8mi
99.32 MPH
Not the greatest resolution but you should be able to see what happened. Please comment.
And QwkTrip I hear you regarding the RPM and power curve. I have had some valve train issues in the past so I have kept it conservative. However, I have had good service since changing valve springs so I could push it a little higher now. ECM rev limit is set at 6300 and MSD is set at 6500. Shift light is set for 5900 and generally results in an actual shift at 6100ish.
Last edited by antman89iroc; 08-22-2018 at 08:26 PM.
If you place a straight edge along either the Erpm or mph curve, you can see that it was still pulling hard when the engine hit the limiter. I would raise the limiter to 7k and make a 1st or 2nd gear rolling pull to the limiter, just to see where mph climb rate begins to nose over as it's nice to know when making gearing decisions. Another thing to remember is that hitting the limiter under power will cost you et, you can see it in the mph trace just before the 1/2 shift.
Data shows the clutch was slow to hit, and when it did it pulled the engine down to around 3k. I would start by raising launch rpm to around 6k, which should elevate the low point of the bog to around 4500. I would set the ClutchTamer's outer delay **** to 3 turns, then turn the inner hit dial 1 turn clockwise per pass until the 60' stops improving. Also raise the shift lite rpm 200 per pass until either you find the limit of the synchros or et stops improving.
If you place a straight edge along either the Erpm or mph curve, you can see that it was still pulling hard when the engine hit the limiter. I would raise the limiter to 7k and make a 1st or 2nd gear rolling pull to the limiter, just to see where mph climb rate begins to nose over as it's nice to know when making gearing decisions. Another thing to remember is that hitting the limiter under power will cost you et, you can see it in the mph trace just before the 1/2 shift.
Data shows the clutch was slow to hit, and when it did it pulled the engine down to around 3k. I would start by raising launch rpm to around 6k, which should elevate the low point of the bog to around 4500. I would set the ClutchTamer's outer delay **** to 3 turns, then turn the inner hit dial 1 turn clockwise per pass until the 60' stops improving. Also raise the shift lite rpm 200 per pass until either you find the limit of the synchros or et stops improving.
Grant
Thanks for the input and advice. During this run the delay setting was at 3 1/2 turns and the "hit" had been increased from previous runs. I understood the goal was to keep the RPM from dropping too low off the line so I was letting it slip more. However, raising the launch RPM makes sense. Up to now I have taken a conservative approach (to everything really) to keep from breaking parts. I'm ready to "step it up" but still will give up a tenth or two to maintain reliability and road worthiness.
You suggestions are steps I can easily implement and try during a test and tune session.
Also to note, this run is with nitrous and I'd probably need to check power curve NA too just to understand the difference.
Ok, here's a screen shot of another run after making some changes. +1 turn on the "hit" dial. Rev limit increased and shift light raised to 6100. Not shown in the screen shot is the 5000RPM stage prior to launch. 60' did improve slightly and tire spin increased. Shifts did seem more difficult to get a quick shift. ET was about the same as before.
1.644 60'
4.779 330'
7.368 1/8mi
94.98 MPH
It was cooler and N2O pressure slightly lower so that may account for the lower MPH. Previous runs did net 98MPH speeds and this was the last run of the night. Maybe a bottle heater is in order.
Regardless, the gear change may be the only way to really make a noticeable improvement. That and weight reduction or more power!
Oh and one note about my data log. It captures only 17 data points per second and the MPH is speedo cable driven and the sensor in in the speedometer gauge. I think this accounts for some of the fluctuations. I may use the sensor in the trans and a speedometer interface rather than the on in the gauge. This would be actually counting the output shaft rotation rather than the gear drive/cable/speedometer combination.
Last edited by antman89iroc; 08-25-2018 at 01:22 PM.
TPS shows about 0.2sec added to the 1/2 shift, you might have been getting about all you could get out of the synchros with the 5900 shift lite.
How is the nitrous being controlled? The afr looks really fat even for e85, might be a good idea to pull some timing and work on that first. Going from 10.5 to 12.5-13.0 can make a big difference in torque and clutch tune, a bottle heater might be able to fix it but I suspect you will likely have to take out some fuel.
TPS shows about 0.2sec added to the 1/2 shift, you might have been getting about all you could get out of the synchros with the 5900 shift lite.
How is the nitrous being controlled? The afr looks really fat even for e85, might be a good idea to pull some timing and work on that first. Going from 10.5 to 12.5-13.0 can make a big difference in torque and clutch tune, a bottle heater might be able to fix it but I suspect you will likely have to take out some fuel.
Grant
Agreed on the shift, I'm gonna work on that but you may be right. Shifts seemed more sluggish at higher revs.
The nitrous is controlled by the ECM. RPM window, MPH, TPS and spark timing reduction parameters all in play. It also has a progressive feature set at 60% initial and 1/2 sec to 100%. The intake is a front mount plenum with a custom spray bar system at the top of the intake runners. The nitrous solenoid is pretty much maxed out but the fuel has a little more flow available. I have tried leaner AFR but it likes it fat. I can lower fuel jet and see how it performs. Running a single 84 nitrous jet for all 8 outlets and premium 93 pump gas. Pulling 6* timing for 30* total right now.
One of the odd characteristics of my nitrous system is a tendency to lean on initial hit. Progressive control tones this down a lot but you can see it's still there. Lower start % seem better in this regard. Lift on shift also starts timer over so it's progressive after shifts. Also, on the 2nd graph run, the night was cooler and NA run a little leaner so I may have needed to raise NA AFR.
There are a lot of variables going on here so I'm trying not to change too many parameters between runs. Generally, I get 4 or 5 runs per session so it's difficult to get it nailed down for a particular session. However, 60' are definitely getting better with CT. Last test and tune netted 4 runs of 1.69 60' or better with 2 at 1.64 & 65. Before I was lucky to get mid 1.7's.
Hoosier quick time pro tires 26/8-16 been running 20PSI until last session. Tried dropping pressure to 18 then 16 and may try lower. I tried to keep pressure as high as possible to reduce rolling resistance on the big end.
Last edited by antman89iroc; 08-26-2018 at 04:29 PM.
08-20-2018, 10:58 AM
