I bought a nice 96 A4 LT1 from a forum member and its an awesome car, but I would like to make it a little more street friendly as I spend a lot of time cruising in sub-45mph city traffic. Above half throttle, the car screams! But at lower RPMs, it has a bit of a surge in drive and OD at part throttle. Below are some quotes of the mods he made to it. I am planning on de-modding/re-modding it a little.


" I've done several mods to it including 226/230/595/595/111lsa Bullet cam, AFR 195 Street Eliminator heads, Edelbrock intake, Installed a Dana 44 3:45 rear end, MSD opti,LS7 lifters, hardened push rods. 1.7 roller rockers, TPIS 1-3/4" long tube headers. 2800 stall converter (Pete's) Lots of bolt ons also. Mileage is 101K..."

"A few more mods are: high volume fuel pump, adjustable fpr, MSD plug wires, Meziere electric water pump, new radiator and hoses, C- beam plates, double roller timing chain, TPIS long tube headers,58 mm Performance Products throttle body, Bosch III injectors (36's I think), DMH electric cutouts, X pipe, high flow cats..."

I'm thinking a more conservative cam and a set of 1.6 RRs along with a dyno tune by our local speed shop (Virginia Speed) would do the trick. What are y'all's thoughts? LT4 hot cam, maybe? What are your thoughts about reusing the opti and water pump since they are both working good?
What is the length of stock pushrods so I can order an adjustable pushrods tool to make sure I am measuring in the right range?

Any insight y'all can give is appreciated.

Chris

 

A good tune may be all you.need.

 

I'd certainly believe this would be where I'd start. You mention 101K but you don't mention the miles on the on the engine mods. It might be foolish to go after the engine mods if there's a lot of miles on the build already. Have the package "as it sits" evaluated by Virginia Speed.

Your intended changes would be completed by who? Yourself or a shop?

 

I will make this suggestion. Talk to Ed Hutchings. Ed is one of the greatest tuners ever and he is a supporting vender of this site. Here is a link to him. http://forums.corvetteforum.com/memb...edcmat-l1.html
Do a search on him and you will see he has many satisified customers on here.

 

I would definitely talk to Ed. I would also steer way clear of VA Speed. They tuned are car of mine and it was a crap half-assed tune that could have blown my motor up.

Ed is class act.

 

Cool. Sent Ed an email. Thanks

Chris

 

Understanding that Virginia Speed was the OP's "mentioned choice" I'd have never debated that and having no "first hand" experience with them I wouldn't/couldn't argue the decision. That's a "decision that" needs to be made by the OP.

I'd take the reference by "93 ragtop" as a "first class" referral and I believe a comment "Ed is class act" as a second might be great but I don't know that I would be so critical of a possible choice by the OP.

"crap half-assed" is maybe an assessment that is "personal"!

*** Looks like the OP is maybe wisely "shopping".

 

I'm not sure of the miles on the cam and RRs. The work would be done by me so I would only be looking at parts cost and tuning cost.

 

If these are the cam specs based on a 1.5 rocker, and you now have 1.7's that is your problem. Those cam specs with the rocker designed for these specs would be plenty. Increasing the rocker ratio not only adds more lift, but duration too. I once ran a comp 292 in a 327 that taught me a lot about drivability. Damn thing was like a 2 stroke dirt bike, and after 3000 rpm all hell broke loose. I ended up spinning this into a chain link fence that actually saved me from rolling over. Anymore, I want to be able to drive it, have it idle, and if my wife or daughter want to take it out I don't have to worry.
That cam is perfect if you use it with the right rocker. Change these out, and retune it and you should be good.

 

The first thing I would do is change the torque converter. Drop it down to a 2000 or so. 2800 is too high for it to be mild mannered. This alone should reduce the surge at low throttle.

 

I've thought about that too. The increased duration escaped me but I think the 1.7s are a bit much for typical street driving and accelerating wear on the valve train.

 

2000 converter may drag it down at idle Id think. Not a fan of 1.7s either. Sure it worked for him but boy can it be hell on springs/guides

Maybe some "cruise/part throttle" time on the tuning end could cure your ills.

 

I vote for 1.5 rockers too. Then, if the tune doesn't help, I'd consider advancing the mechanical timing on the cam. At least before pulling it.

Try it as much as 8-degrees advanced.

 

It appears to me that you may need a better tune. The rest of the combination seems OK to me. Do not change the converter to a 2000 RPM it will increase the problem by making the engine run where it does not want to run. My educated guess is you have too much part throttle timing at low load and rpm. Too much timing can cause the car to buck at light throttle. Have your tuner play with the low load timing to eliminate the bucking.

 

Well, I have an appointment with Ed on the 26th. I'll see what he can do with the car as it sits, but I may go back and swap the RRs to 1.5s if he can't eliminate the light throttle issues. I have no problems giving up some of the top end to improve the bottom end. It will be fun to watch... I'll keep y'all posted.

Chris

 

The main issue with the rockers is valve train longevity. Asking for more street drive-ability falls into that category IMO.

If the cam is really .595 with 1.5's, 1.7 RR is a ton of lift -- meaning you're well into the 600's for lift. That would be a very aggressive cam. It SEEMS more likely that you're hitting .595 with the 1.7's. If so, you're probably not going to gain much drive-ability (by lowering them). There are varied opinions on the degree of lift vs longevity. I had decided mid .500's was about the limit w/o swapping springs every couple of years. Engines with .600 lift are generally fairly aggressive and often require more periodic maintenance. Matching lift to the AFR195's is typically the goal for builders though...and having .600 lift -- with those heads -- is prime time. So, it can be a question of longevity versus performance.

The functional difference between 1.5 and 1.7 rockers is about 4 degrees of valve duration IIRC. It's doubtful that make/break the difference in performance. If the cam is retarded, advancing it would make more difference.

If the tune isn't right, that will make the most difference.

 

I really don't think the 1.7/higher lift have anything to do with your part-thtottle issues. I am running 605/622 lift with stock ported heads, and can lug my car around at 1100 rpms without issue. It's all in the tune.

Gregg' this sounds like "WeavsVets" car, and if I remember correctly the 595 lift was with 1.7 rockers.

 

Here, maybe this will help a little.

V/r,
Chris

 

Okay, a lobe lift of .3533 x 1.5 = .530, and .3533 x 1.7 = .600, but as I stated earlier it adds slightly to duration, so my guess at .050 is now closer to 234 / 238 and this may seem insignificant it does create a greater loss of vacuum signal at idle. This also requires a richer idle mixture and tuner can help by changing o2 setting to about 14.4 afr. My point is this added ratio takes what would be a street drivable cam, and makes it a difficult to tune, and smooth driving ability to a different level. It can be tuned, but will always be more performance oriented.

 

Yup...Just take the lobe lift x rocker ratio. If you have 1.7 rockers, your lift is .600 (essentially what was posted in your OP).

If the geometry is very good, you're fine. And, that's really the kind of lift you want to get the most out of the AFRs.

As mentioned in prior posts, check your springs every couple of years. Maybe more often if you put lots of miles on it.

So did you buy "WeavsVets" Corvette?