How much motor is too much motor?

[LateModel B23]

The basics: 2015 GRT running USMTS/USRA rules @ Devils Bowl in TX. This car is new and just assemble over the winter, it now has a total of 4 race nights on it. The setup is GRT by the book with exception of RR spring is 220# instead of 175#, RR upper bar is up one hole. These two differences are based on 20+ years of setting up cars @ the Bowl and being a very consistent top 5 - usually top 2 car. In modifieds and late models ( LMclass dropped in 2014 and sold out LM cars and all related items). The % numbers are 56.4% rear and 54% LS.

So here seems to be the issue, our motor is an "Open" motor, 3.875x4.155, roller cam, 14 degree Pro-Action aluminum heads. On a conservative dyno is was 752hp, I do not have the spec sheet with me and will post it later tomorrow when I am at the shop for more complete numbers. Prior to this season in our "older cars" which consistened of a2001 Smileys, 2005 Dirtworks (2 time champion car) a 2009 Shaw and recently a 2012 Skyrocket. Motorwise always had either basic 3.75 stroke x 4.04 383 w/ Motown heads, a couple of different 3.75x4.125 w/ similar heads and last seasn a USRA spec head 3.875x4.125. I could look up the dyno sheets but as I recall about 600 was the best of any of them.

So the problem we are having with these motor is it is a tire spinner, just no take off on starts or re-starts. Last night started 2nd row inside heat and car went nowhere, by the time it was too late the best was a 5th place finish. Started 5th row feature, went back to 9th then he got the momentum going and got to 4th and was closing on 3rd. A caution and re-start with 3 to go ruined that - went backwards and finshed 9th.

I will answer any more details or info I can, but like my title askes, is this maybe just too much motor for this class of car. We went to it because last season the Spec motor lacked a little on a typical Devils Bowl heavy track. Would lead heat races but at the end have one the open motor cars have just that little bit more.

Any thoughts, ideas or suggestions?

[powerslide]

Where did it peak and how many rpms are you turning it? That's a lot of motor for a 8in tire. It might take a couple dyno trips to get it smooth enough to drive.

[let-r-eat]

This could be a really good thread. I don't know Devil's Bowl other than what I've seen on the net. I could see your 600hp engines being a little weak on today's setups with good conditions. 750 real hp numbers is a nice engine if it has the power curve appropriate for the power level. Most don't. Light switches.

How hard are you turning it? What's the curve look like on the dyno?

[JustAddDirt]

Willy's carb shop makes a adjustable restrictor plate.
I would suggest it. get it set where it is drivable.

on a side note that kind of motor is common here in UMP country. most have no problems hooking them up. but we have a better tire for it, but we do not get any longevity out of them.

[HEAVY DUTY]

That is the reason that the 604 crates are winning so many IMCA races. I would say you are way over powered. I would say your car would be better with those old motors you had.

[mod88s]

WAY too much power for that tire. period

[LateModel B23]

Birdcage index is: 0.5* up in front on RR -- 0.5* down in front on LR.

[LateModel B23]

Here are the dyno numbers by the hundred starting at 4500rpm, first is Trq and next is HP:

4500= 634.6 557.7
5000= 665.8 646.5
5500= 663.1 705.8
6000= 644.9 751.3
6500= 604.2 756.4
7000= 558.7 750.7
7500= 513.9 732.7

[let-r-eat]

That's a horse 23 and it's going to be (not a nice word)(not a nice word)(not a nice word)(not a nice word) hard to hook that up. You could index the birdcages all you want and not hook that dude up in the slick. If you did, you'd be golden. LOL Do agree that taking it into the spring more is required.

HeavyDuty is spot on IMO. There is a reason these crates can run with open engines on certain tracks and it is directly related to the type of power they make. No tire can take that kind of power on a 1/4 mile bullring. You have to have momentum to use that type of power.

Get the restrictor plates and go that route and try it. You have to slow down the hit on those tires or you aren't going to go anywhere. I'd take .5 a point of gear out, maybe more. That thing would be idling come feature time. You'll have to free it to make it work but I'd bet you would do far better. That kind of power is going to pull your pants off no matter what gear you use.

[LateModel B23]

Already taken gear out, was 5.28 with spec head and down to a 5.11 now. Going to index the LR into the spring more. I will check into the plates.

[let-r-eat]

Big difference between a 23* spec head making 720 @ 8000+ and a 14* making 750 at 6000. That thing is a horse!

estimated 500 tq @ 5500 x 5.28 = 2640 lb/tq at the wheel. What you had before

663 tq @ 5500rpm x 5.11 = 3387 What you have now.

2640/663 = 3.98

Takes a 4.0 gear or so to hit the tire the same as a 500 tq spec engine @ 5500. That's right. Your 14* will pull the same with a 4.0 gear as a 500tq@5500 spec head engine will with the 5.28.

Think you are over hitting the tires LOL?

[oldtrackchamp4x]

Like when you do a comparative, Puts it in perspective. JMO

[powerslide]

Unless he is a cushion banger like a davenport style i think you are going to really struggle. Might be better off to put the spec in for a couple weeks and see if it helps.

[Confused?]

Are you running a pull bar or lift arm? May need to adjust for a stronger motor. As well as do some shock tuning

[LateModel B23]

It is a pull bar. Long Quik Car with all red bushings - NEW.